Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

9 files changed, 5570 insertions, 0 deletions

diff --git a/third_party/rust/url/src/form_urlencoded.rs b/third_party/rust/url/src/form_urlencoded.rs
new file mode 100644
index 0000000000..b97f35d25a
--- /dev/null
+++ b/third_party/rust/url/src/form_urlencoded.rs
@@ -0,0 +1,347 @@
+// Copyright 2013-2016 The rust-url developers.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Parser and serializer for the [`application/x-www-form-urlencoded` syntax](
+//! http://url.spec.whatwg.org/#application/x-www-form-urlencoded),
+//! as used by HTML forms.
+//!
+//! Converts between a string (such as an URL’s query string)
+//! and a sequence of (name, value) pairs.
+
+use percent_encoding::{percent_decode, percent_encode_byte};
+use query_encoding::{self, decode_utf8_lossy, EncodingOverride};
+use std::borrow::{Borrow, Cow};
+use std::str;
+
+/// Convert a byte string in the `application/x-www-form-urlencoded` syntax
+/// into a iterator of (name, value) pairs.
+///
+/// Use `parse(input.as_bytes())` to parse a `&str` string.
+///
+/// The names and values are percent-decoded. For instance, `%23first=%25try%25` will be
+/// converted to `[("#first", "%try%")]`.
+#[inline]
+pub fn parse(input: &[u8]) -> Parse {
+    Parse { input }
+}
+/// The return type of `parse()`.
+#[derive(Copy, Clone)]
+pub struct Parse<'a> {
+    input: &'a [u8],
+}
+
+impl<'a> Iterator for Parse<'a> {
+    type Item = (Cow<'a, str>, Cow<'a, str>);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        loop {
+            if self.input.is_empty() {
+                return None;
+            }
+            let mut split2 = self.input.splitn(2, |&b| b == b'&');
+            let sequence = split2.next().unwrap();
+            self.input = split2.next().unwrap_or(&[][..]);
+            if sequence.is_empty() {
+                continue;
+            }
+            let mut split2 = sequence.splitn(2, |&b| b == b'=');
+            let name = split2.next().unwrap();
+            let value = split2.next().unwrap_or(&[][..]);
+            return Some((decode(name), decode(value)));
+        }
+    }
+}
+
+fn decode(input: &[u8]) -> Cow<str> {
+    let replaced = replace_plus(input);
+    decode_utf8_lossy(match percent_decode(&replaced).into() {
+        Cow::Owned(vec) => Cow::Owned(vec),
+        Cow::Borrowed(_) => replaced,
+    })
+}
+
+/// Replace b'+' with b' '
+fn replace_plus(input: &[u8]) -> Cow<[u8]> {
+    match input.iter().position(|&b| b == b'+') {
+        None => Cow::Borrowed(input),
+        Some(first_position) => {
+            let mut replaced = input.to_owned();
+            replaced[first_position] = b' ';
+            for byte in &mut replaced[first_position + 1..] {
+                if *byte == b'+' {
+                    *byte = b' ';
+                }
+            }
+            Cow::Owned(replaced)
+        }
+    }
+}
+
+impl<'a> Parse<'a> {
+    /// Return a new iterator that yields pairs of `String` instead of pairs of `Cow<str>`.
+    pub fn into_owned(self) -> ParseIntoOwned<'a> {
+        ParseIntoOwned { inner: self }
+    }
+}
+
+/// Like `Parse`, but yields pairs of `String` instead of pairs of `Cow<str>`.
+pub struct ParseIntoOwned<'a> {
+    inner: Parse<'a>,
+}
+
+impl<'a> Iterator for ParseIntoOwned<'a> {
+    type Item = (String, String);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner
+            .next()
+            .map(|(k, v)| (k.into_owned(), v.into_owned()))
+    }
+}
+
+/// The [`application/x-www-form-urlencoded` byte serializer](
+/// https://url.spec.whatwg.org/#concept-urlencoded-byte-serializer).
+///
+/// Return an iterator of `&str` slices.
+pub fn byte_serialize(input: &[u8]) -> ByteSerialize {
+    ByteSerialize { bytes: input }
+}
+
+/// Return value of `byte_serialize()`.
+#[derive(Debug)]
+pub struct ByteSerialize<'a> {
+    bytes: &'a [u8],
+}
+
+fn byte_serialized_unchanged(byte: u8) -> bool {
+    matches!(byte, b'*' | b'-' | b'.' | b'0' ..= b'9' | b'A' ..= b'Z' | b'_' | b'a' ..= b'z')
+}
+
+impl<'a> Iterator for ByteSerialize<'a> {
+    type Item = &'a str;
+
+    fn next(&mut self) -> Option<&'a str> {
+        if let Some((&first, tail)) = self.bytes.split_first() {
+            if !byte_serialized_unchanged(first) {
+                self.bytes = tail;
+                return Some(if first == b' ' {
+                    "+"
+                } else {
+                    percent_encode_byte(first)
+                });
+            }
+            let position = tail.iter().position(|&b| !byte_serialized_unchanged(b));
+            let (unchanged_slice, remaining) = match position {
+                // 1 for first_byte + i unchanged in tail
+                Some(i) => self.bytes.split_at(1 + i),
+                None => (self.bytes, &[][..]),
+            };
+            self.bytes = remaining;
+            Some(unsafe { str::from_utf8_unchecked(unchanged_slice) })
+        } else {
+            None
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.bytes.is_empty() {
+            (0, Some(0))
+        } else {
+            (1, Some(self.bytes.len()))
+        }
+    }
+}
+
+/// The [`application/x-www-form-urlencoded` serializer](
+/// https://url.spec.whatwg.org/#concept-urlencoded-serializer).
+pub struct Serializer<'a, T: Target> {
+    target: Option<T>,
+    start_position: usize,
+    encoding: EncodingOverride<'a>,
+}
+
+pub trait Target {
+    fn as_mut_string(&mut self) -> &mut String;
+    fn finish(self) -> Self::Finished;
+    type Finished;
+}
+
+impl Target for String {
+    fn as_mut_string(&mut self) -> &mut String {
+        self
+    }
+    fn finish(self) -> Self {
+        self
+    }
+    type Finished = Self;
+}
+
+impl<'a> Target for &'a mut String {
+    fn as_mut_string(&mut self) -> &mut String {
+        &mut **self
+    }
+    fn finish(self) -> Self {
+        self
+    }
+    type Finished = Self;
+}
+
+// `as_mut_string` string here exposes the internal serialization of an `Url`,
+// which should not be exposed to users.
+// We achieve that by not giving users direct access to `UrlQuery`:
+// * Its fields are private
+//   (and so can not be constructed with struct literal syntax outside of this crate),
+// * It has no constructor
+// * It is only visible (on the type level) to users in the return type of
+//   `Url::query_pairs_mut` which is `Serializer<UrlQuery>`
+// * `Serializer` keeps its target in a private field
+// * Unlike in other `Target` impls, `UrlQuery::finished` does not return `Self`.
+impl<'a> Target for ::UrlQuery<'a> {
+    fn as_mut_string(&mut self) -> &mut String {
+        &mut self.url.as_mut().unwrap().serialization
+    }
+
+    fn finish(mut self) -> &'a mut ::Url {
+        let url = self.url.take().unwrap();
+        url.restore_already_parsed_fragment(self.fragment.take());
+        url
+    }
+
+    type Finished = &'a mut ::Url;
+}
+
+impl<'a, T: Target> Serializer<'a, T> {
+    /// Create a new `application/x-www-form-urlencoded` serializer for the given target.
+    ///
+    /// If the target is non-empty,
+    /// its content is assumed to already be in `application/x-www-form-urlencoded` syntax.
+    pub fn new(target: T) -> Self {
+        Self::for_suffix(target, 0)
+    }
+
+    /// Create a new `application/x-www-form-urlencoded` serializer
+    /// for a suffix of the given target.
+    ///
+    /// If that suffix is non-empty,
+    /// its content is assumed to already be in `application/x-www-form-urlencoded` syntax.
+    pub fn for_suffix(mut target: T, start_position: usize) -> Self {
+        &target.as_mut_string()[start_position..]; // Panic if out of bounds
+        Serializer {
+            target: Some(target),
+            start_position,
+            encoding: None,
+        }
+    }
+
+    /// Remove any existing name/value pair.
+    ///
+    /// Panics if called after `.finish()`.
+    pub fn clear(&mut self) -> &mut Self {
+        string(&mut self.target).truncate(self.start_position);
+        self
+    }
+
+    /// Set the character encoding to be used for names and values before percent-encoding.
+    pub fn encoding_override(&mut self, new: EncodingOverride<'a>) -> &mut Self {
+        self.encoding = new;
+        self
+    }
+
+    /// Serialize and append a name/value pair.
+    ///
+    /// Panics if called after `.finish()`.
+    pub fn append_pair(&mut self, name: &str, value: &str) -> &mut Self {
+        append_pair(
+            string(&mut self.target),
+            self.start_position,
+            self.encoding,
+            name,
+            value,
+        );
+        self
+    }
+
+    /// Serialize and append a number of name/value pairs.
+    ///
+    /// This simply calls `append_pair` repeatedly.
+    /// This can be more convenient, so the user doesn’t need to introduce a block
+    /// to limit the scope of `Serializer`’s borrow of its string.
+    ///
+    /// Panics if called after `.finish()`.
+    pub fn extend_pairs<I, K, V>(&mut self, iter: I) -> &mut Self
+    where
+        I: IntoIterator,
+        I::Item: Borrow<(K, V)>,
+        K: AsRef<str>,
+        V: AsRef<str>,
+    {
+        {
+            let string = string(&mut self.target);
+            for pair in iter {
+                let &(ref k, ref v) = pair.borrow();
+                append_pair(
+                    string,
+                    self.start_position,
+                    self.encoding,
+                    k.as_ref(),
+                    v.as_ref(),
+                );
+            }
+        }
+        self
+    }
+
+    /// If this serializer was constructed with a string, take and return that string.
+    ///
+    /// ```rust
+    /// use url::form_urlencoded;
+    /// let encoded: String = form_urlencoded::Serializer::new(String::new())
+    ///     .append_pair("foo", "bar & baz")
+    ///     .append_pair("saison", "Été+hiver")
+    ///     .finish();
+    /// assert_eq!(encoded, "foo=bar+%26+baz&saison=%C3%89t%C3%A9%2Bhiver");
+    /// ```
+    ///
+    /// Panics if called more than once.
+    pub fn finish(&mut self) -> T::Finished {
+        self.target
+            .take()
+            .expect("url::form_urlencoded::Serializer double finish")
+            .finish()
+    }
+}
+
+fn append_separator_if_needed(string: &mut String, start_position: usize) {
+    if string.len() > start_position {
+        string.push('&')
+    }
+}
+
+fn string<T: Target>(target: &mut Option<T>) -> &mut String {
+    target
+        .as_mut()
+        .expect("url::form_urlencoded::Serializer finished")
+        .as_mut_string()
+}
+
+fn append_pair(
+    string: &mut String,
+    start_position: usize,
+    encoding: EncodingOverride,
+    name: &str,
+    value: &str,
+) {
+    append_separator_if_needed(string, start_position);
+    append_encoded(name, string, encoding);
+    string.push('=');
+    append_encoded(value, string, encoding);
+}
+
+fn append_encoded(s: &str, string: &mut String, encoding: EncodingOverride) {
+    string.extend(byte_serialize(&query_encoding::encode(encoding, s.into())))
+}
diff --git a/third_party/rust/url/src/host.rs b/third_party/rust/url/src/host.rs
new file mode 100644
index 0000000000..9afc6d8e74
--- /dev/null
+++ b/third_party/rust/url/src/host.rs
@@ -0,0 +1,454 @@
+// Copyright 2013-2016 The rust-url developers.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use idna;
+use parser::{ParseError, ParseResult};
+use percent_encoding::{percent_decode, utf8_percent_encode, CONTROLS};
+#[cfg(feature = "serde")]
+use serde::{Deserialize, Serialize};
+use std::cmp;
+use std::fmt::{self, Formatter};
+use std::net::{Ipv4Addr, Ipv6Addr};
+
+#[cfg_attr(feature = "serde", derive(Deserialize, Serialize))]
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+pub(crate) enum HostInternal {
+    None,
+    Domain,
+    Ipv4(Ipv4Addr),
+    Ipv6(Ipv6Addr),
+}
+
+impl<S> From<Host<S>> for HostInternal {
+    fn from(host: Host<S>) -> HostInternal {
+        match host {
+            Host::Domain(_) => HostInternal::Domain,
+            Host::Ipv4(address) => HostInternal::Ipv4(address),
+            Host::Ipv6(address) => HostInternal::Ipv6(address),
+        }
+    }
+}
+
+/// The host name of an URL.
+#[cfg_attr(feature = "serde", derive(Deserialize, Serialize))]
+#[derive(Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
+pub enum Host<S = String> {
+    /// A DNS domain name, as '.' dot-separated labels.
+    /// Non-ASCII labels are encoded in punycode per IDNA if this is the host of
+    /// a special URL, or percent encoded for non-special URLs. Hosts for
+    /// non-special URLs are also called opaque hosts.
+    Domain(S),
+
+    /// An IPv4 address.
+    /// `Url::host_str` returns the serialization of this address,
+    /// as four decimal integers separated by `.` dots.
+    Ipv4(Ipv4Addr),
+
+    /// An IPv6 address.
+    /// `Url::host_str` returns the serialization of that address between `[` and `]` brackets,
+    /// in the format per [RFC 5952 *A Recommendation
+    /// for IPv6 Address Text Representation*](https://tools.ietf.org/html/rfc5952):
+    /// lowercase hexadecimal with maximal `::` compression.
+    Ipv6(Ipv6Addr),
+}
+
+impl<'a> Host<&'a str> {
+    /// Return a copy of `self` that owns an allocated `String` but does not borrow an `&Url`.
+    pub fn to_owned(&self) -> Host<String> {
+        match *self {
+            Host::Domain(domain) => Host::Domain(domain.to_owned()),
+            Host::Ipv4(address) => Host::Ipv4(address),
+            Host::Ipv6(address) => Host::Ipv6(address),
+        }
+    }
+}
+
+impl Host<String> {
+    /// Parse a host: either an IPv6 address in [] square brackets, or a domain.
+    ///
+    /// <https://url.spec.whatwg.org/#host-parsing>
+    pub fn parse(input: &str) -> Result<Self, ParseError> {
+        if input.starts_with('[') {
+            if !input.ends_with(']') {
+                return Err(ParseError::InvalidIpv6Address);
+            }
+            return parse_ipv6addr(&input[1..input.len() - 1]).map(Host::Ipv6);
+        }
+        let domain = percent_decode(input.as_bytes()).decode_utf8_lossy();
+        let domain = idna::domain_to_ascii(&domain)?;
+        if domain
+            .find(|c| {
+                matches!(
+                    c,
+                    '\0' | '\t'
+                        | '\n'
+                        | '\r'
+                        | ' '
+                        | '#'
+                        | '%'
+                        | '/'
+                        | ':'
+                        | '?'
+                        | '@'
+                        | '['
+                        | '\\'
+                        | ']'
+                )
+            })
+            .is_some()
+        {
+            return Err(ParseError::InvalidDomainCharacter);
+        }
+        if let Some(address) = parse_ipv4addr(&domain)? {
+            Ok(Host::Ipv4(address))
+        } else {
+            Ok(Host::Domain(domain.into()))
+        }
+    }
+
+    // <https://url.spec.whatwg.org/#concept-opaque-host-parser>
+    pub fn parse_opaque(input: &str) -> Result<Self, ParseError> {
+        if input.starts_with('[') {
+            if !input.ends_with(']') {
+                return Err(ParseError::InvalidIpv6Address);
+            }
+            return parse_ipv6addr(&input[1..input.len() - 1]).map(Host::Ipv6);
+        }
+        if input
+            .find(|c| {
+                matches!(
+                    c,
+                    '\0' | '\t'
+                        | '\n'
+                        | '\r'
+                        | ' '
+                        | '#'
+                        | '/'
+                        | ':'
+                        | '?'
+                        | '@'
+                        | '['
+                        | '\\'
+                        | ']'
+                )
+            })
+            .is_some()
+        {
+            return Err(ParseError::InvalidDomainCharacter);
+        }
+        let s = utf8_percent_encode(input, CONTROLS).to_string();
+        Ok(Host::Domain(s))
+    }
+}
+
+impl<S: AsRef<str>> fmt::Display for Host<S> {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        match *self {
+            Host::Domain(ref domain) => domain.as_ref().fmt(f),
+            Host::Ipv4(ref addr) => addr.fmt(f),
+            Host::Ipv6(ref addr) => {
+                f.write_str("[")?;
+                write_ipv6(addr, f)?;
+                f.write_str("]")
+            }
+        }
+    }
+}
+
+fn write_ipv6(addr: &Ipv6Addr, f: &mut Formatter) -> fmt::Result {
+    let segments = addr.segments();
+    let (compress_start, compress_end) = longest_zero_sequence(&segments);
+    let mut i = 0;
+    while i < 8 {
+        if i == compress_start {
+            f.write_str(":")?;
+            if i == 0 {
+                f.write_str(":")?;
+            }
+            if compress_end < 8 {
+                i = compress_end;
+            } else {
+                break;
+            }
+        }
+        write!(f, "{:x}", segments[i as usize])?;
+        if i < 7 {
+            f.write_str(":")?;
+        }
+        i += 1;
+    }
+    Ok(())
+}
+
+// https://url.spec.whatwg.org/#concept-ipv6-serializer step 2 and 3
+fn longest_zero_sequence(pieces: &[u16; 8]) -> (isize, isize) {
+    let mut longest = -1;
+    let mut longest_length = -1;
+    let mut start = -1;
+    macro_rules! finish_sequence(
+        ($end: expr) => {
+            if start >= 0 {
+                let length = $end - start;
+                if length > longest_length {
+                    longest = start;
+                    longest_length = length;
+                }
+            }
+        };
+    );
+    for i in 0..8 {
+        if pieces[i as usize] == 0 {
+            if start < 0 {
+                start = i;
+            }
+        } else {
+            finish_sequence!(i);
+            start = -1;
+        }
+    }
+    finish_sequence!(8);
+    // https://url.spec.whatwg.org/#concept-ipv6-serializer
+    // step 3: ignore lone zeroes
+    if longest_length < 2 {
+        (-1, -2)
+    } else {
+        (longest, longest + longest_length)
+    }
+}
+
+/// <https://url.spec.whatwg.org/#ipv4-number-parser>
+fn parse_ipv4number(mut input: &str) -> Result<Option<u32>, ()> {
+    let mut r = 10;
+    if input.starts_with("0x") || input.starts_with("0X") {
+        input = &input[2..];
+        r = 16;
+    } else if input.len() >= 2 && input.starts_with('0') {
+        input = &input[1..];
+        r = 8;
+    }
+
+    // At the moment we can't know the reason why from_str_radix fails
+    // https://github.com/rust-lang/rust/issues/22639
+    // So instead we check if the input looks like a real number and only return
+    // an error when it's an overflow.
+    let valid_number = match r {
+        8 => input.chars().all(|c| c >= '0' && c <= '7'),
+        10 => input.chars().all(|c| c >= '0' && c <= '9'),
+        16 => input
+            .chars()
+            .all(|c| (c >= '0' && c <= '9') || (c >= 'a' && c <= 'f') || (c >= 'A' && c <= 'F')),
+        _ => false,
+    };
+
+    if !valid_number {
+        return Ok(None);
+    }
+
+    if input.is_empty() {
+        return Ok(Some(0));
+    }
+    if input.starts_with('+') {
+        return Ok(None);
+    }
+    match u32::from_str_radix(input, r) {
+        Ok(number) => Ok(Some(number)),
+        Err(_) => Err(()),
+    }
+}
+
+/// <https://url.spec.whatwg.org/#concept-ipv4-parser>
+fn parse_ipv4addr(input: &str) -> ParseResult<Option<Ipv4Addr>> {
+    if input.is_empty() {
+        return Ok(None);
+    }
+    let mut parts: Vec<&str> = input.split('.').collect();
+    if parts.last() == Some(&"") {
+        parts.pop();
+    }
+    if parts.len() > 4 {
+        return Ok(None);
+    }
+    let mut numbers: Vec<u32> = Vec::new();
+    let mut overflow = false;
+    for part in parts {
+        if part == "" {
+            return Ok(None);
+        }
+        match parse_ipv4number(part) {
+            Ok(Some(n)) => numbers.push(n),
+            Ok(None) => return Ok(None),
+            Err(()) => overflow = true,
+        };
+    }
+    if overflow {
+        return Err(ParseError::InvalidIpv4Address);
+    }
+    let mut ipv4 = numbers.pop().expect("a non-empty list of numbers");
+    // Equivalent to: ipv4 >= 256 ** (4 − numbers.len())
+    if ipv4 > u32::max_value() >> (8 * numbers.len() as u32) {
+        return Err(ParseError::InvalidIpv4Address);
+    }
+    if numbers.iter().any(|x| *x > 255) {
+        return Err(ParseError::InvalidIpv4Address);
+    }
+    for (counter, n) in numbers.iter().enumerate() {
+        ipv4 += n << (8 * (3 - counter as u32))
+    }
+    Ok(Some(Ipv4Addr::from(ipv4)))
+}
+
+/// <https://url.spec.whatwg.org/#concept-ipv6-parser>
+fn parse_ipv6addr(input: &str) -> ParseResult<Ipv6Addr> {
+    let input = input.as_bytes();
+    let len = input.len();
+    let mut is_ip_v4 = false;
+    let mut pieces = [0, 0, 0, 0, 0, 0, 0, 0];
+    let mut piece_pointer = 0;
+    let mut compress_pointer = None;
+    let mut i = 0;
+
+    if len < 2 {
+        return Err(ParseError::InvalidIpv6Address);
+    }
+
+    if input[0] == b':' {
+        if input[1] != b':' {
+            return Err(ParseError::InvalidIpv6Address);
+        }
+        i = 2;
+        piece_pointer = 1;
+        compress_pointer = Some(1);
+    }
+
+    while i < len {
+        if piece_pointer == 8 {
+            return Err(ParseError::InvalidIpv6Address);
+        }
+        if input[i] == b':' {
+            if compress_pointer.is_some() {
+                return Err(ParseError::InvalidIpv6Address);
+            }
+            i += 1;
+            piece_pointer += 1;
+            compress_pointer = Some(piece_pointer);
+            continue;
+        }
+        let start = i;
+        let end = cmp::min(len, start + 4);
+        let mut value = 0u16;
+        while i < end {
+            match (input[i] as char).to_digit(16) {
+                Some(digit) => {
+                    value = value * 0x10 + digit as u16;
+                    i += 1;
+                }
+                None => break,
+            }
+        }
+        if i < len {
+            match input[i] {
+                b'.' => {
+                    if i == start {
+                        return Err(ParseError::InvalidIpv6Address);
+                    }
+                    i = start;
+                    if piece_pointer > 6 {
+                        return Err(ParseError::InvalidIpv6Address);
+                    }
+                    is_ip_v4 = true;
+                }
+                b':' => {
+                    i += 1;
+                    if i == len {
+                        return Err(ParseError::InvalidIpv6Address);
+                    }
+                }
+                _ => return Err(ParseError::InvalidIpv6Address),
+            }
+        }
+        if is_ip_v4 {
+            break;
+        }
+        pieces[piece_pointer] = value;
+        piece_pointer += 1;
+    }
+
+    if is_ip_v4 {
+        if piece_pointer > 6 {
+            return Err(ParseError::InvalidIpv6Address);
+        }
+        let mut numbers_seen = 0;
+        while i < len {
+            if numbers_seen > 0 {
+                if numbers_seen < 4 && (i < len && input[i] == b'.') {
+                    i += 1
+                } else {
+                    return Err(ParseError::InvalidIpv6Address);
+                }
+            }
+
+            let mut ipv4_piece = None;
+            while i < len {
+                let digit = match input[i] {
+                    c @ b'0'..=b'9' => c - b'0',
+                    _ => break,
+                };
+                match ipv4_piece {
+                    None => ipv4_piece = Some(digit as u16),
+                    Some(0) => return Err(ParseError::InvalidIpv6Address), // No leading zero
+                    Some(ref mut v) => {
+                        *v = *v * 10 + digit as u16;
+                        if *v > 255 {
+                            return Err(ParseError::InvalidIpv6Address);
+                        }
+                    }
+                }
+                i += 1;
+            }
+
+            pieces[piece_pointer] = if let Some(v) = ipv4_piece {
+                pieces[piece_pointer] * 0x100 + v
+            } else {
+                return Err(ParseError::InvalidIpv6Address);
+            };
+            numbers_seen += 1;
+
+            if numbers_seen == 2 || numbers_seen == 4 {
+                piece_pointer += 1;
+            }
+        }
+
+        if numbers_seen != 4 {
+            return Err(ParseError::InvalidIpv6Address);
+        }
+    }
+
+    if i < len {
+        return Err(ParseError::InvalidIpv6Address);
+    }
+
+    match compress_pointer {
+        Some(compress_pointer) => {
+            let mut swaps = piece_pointer - compress_pointer;
+            piece_pointer = 7;
+            while swaps > 0 {
+                pieces.swap(piece_pointer, compress_pointer + swaps - 1);
+                swaps -= 1;
+                piece_pointer -= 1;
+            }
+        }
+        _ => {
+            if piece_pointer != 8 {
+                return Err(ParseError::InvalidIpv6Address);
+            }
+        }
+    }
+    Ok(Ipv6Addr::new(
+        pieces[0], pieces[1], pieces[2], pieces[3], pieces[4], pieces[5], pieces[6], pieces[7],
+    ))
+}
diff --git a/third_party/rust/url/src/lib.rs b/third_party/rust/url/src/lib.rs
new file mode 100644
index 0000000000..d60935c29d
--- /dev/null
+++ b/third_party/rust/url/src/lib.rs
@@ -0,0 +1,2553 @@
+// Copyright 2013-2015 The rust-url developers.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+/*!
+
+rust-url is an implementation of the [URL Standard](http://url.spec.whatwg.org/)
+for the [Rust](http://rust-lang.org/) programming language.
+
+
+# URL parsing and data structures
+
+First, URL parsing may fail for various reasons and therefore returns a `Result`.
+
+```
+use url::{Url, ParseError};
+
+assert!(Url::parse("http://[:::1]") == Err(ParseError::InvalidIpv6Address))
+```
+
+Let’s parse a valid URL and look at its components.
+
+```
+use url::{Url, Host, Position};
+# use url::ParseError;
+# fn run() -> Result<(), ParseError> {
+let issue_list_url = Url::parse(
+    "https://github.com/rust-lang/rust/issues?labels=E-easy&state=open"
+)?;
+
+
+assert!(issue_list_url.scheme() == "https");
+assert!(issue_list_url.username() == "");
+assert!(issue_list_url.password() == None);
+assert!(issue_list_url.host_str() == Some("github.com"));
+assert!(issue_list_url.host() == Some(Host::Domain("github.com")));
+assert!(issue_list_url.port() == None);
+assert!(issue_list_url.path() == "/rust-lang/rust/issues");
+assert!(issue_list_url.path_segments().map(|c| c.collect::<Vec<_>>()) ==
+        Some(vec!["rust-lang", "rust", "issues"]));
+assert!(issue_list_url.query() == Some("labels=E-easy&state=open"));
+assert!(&issue_list_url[Position::BeforePath..] == "/rust-lang/rust/issues?labels=E-easy&state=open");
+assert!(issue_list_url.fragment() == None);
+assert!(!issue_list_url.cannot_be_a_base());
+# Ok(())
+# }
+# run().unwrap();
+```
+
+Some URLs are said to be *cannot-be-a-base*:
+they don’t have a username, password, host, or port,
+and their "path" is an arbitrary string rather than slash-separated segments:
+
+```
+use url::Url;
+# use url::ParseError;
+
+# fn run() -> Result<(), ParseError> {
+let data_url = Url::parse("data:text/plain,Hello?World#")?;
+
+assert!(data_url.cannot_be_a_base());
+assert!(data_url.scheme() == "data");
+assert!(data_url.path() == "text/plain,Hello");
+assert!(data_url.path_segments().is_none());
+assert!(data_url.query() == Some("World"));
+assert!(data_url.fragment() == Some(""));
+# Ok(())
+# }
+# run().unwrap();
+```
+
+
+# Base URL
+
+Many contexts allow URL *references* that can be relative to a *base URL*:
+
+```html
+<link rel="stylesheet" href="../main.css">
+```
+
+Since parsed URLs are absolute, giving a base is required for parsing relative URLs:
+
+```
+use url::{Url, ParseError};
+
+assert!(Url::parse("../main.css") == Err(ParseError::RelativeUrlWithoutBase))
+```
+
+Use the `join` method on an `Url` to use it as a base URL:
+
+```
+use url::Url;
+# use url::ParseError;
+
+# fn run() -> Result<(), ParseError> {
+let this_document = Url::parse("http://servo.github.io/rust-url/url/index.html")?;
+let css_url = this_document.join("../main.css")?;
+assert_eq!(css_url.as_str(), "http://servo.github.io/rust-url/main.css");
+# Ok(())
+# }
+# run().unwrap();
+*/
+
+#![doc(html_root_url = "https://docs.rs/url/2.0.0")]
+
+#[macro_use]
+extern crate matches;
+extern crate idna;
+extern crate percent_encoding;
+#[cfg(feature = "serde")]
+extern crate serde;
+
+use host::HostInternal;
+use parser::{to_u32, Context, Parser, SchemeType, PATH_SEGMENT, USERINFO};
+use percent_encoding::{percent_decode, percent_encode, utf8_percent_encode};
+use std::borrow::Borrow;
+use std::cmp;
+#[cfg(feature = "serde")]
+use std::error::Error;
+use std::fmt::{self, Write};
+use std::hash;
+use std::io;
+use std::mem;
+use std::net::{IpAddr, SocketAddr, ToSocketAddrs};
+use std::ops::{Range, RangeFrom, RangeTo};
+use std::path::{Path, PathBuf};
+use std::str;
+
+pub use host::Host;
+pub use origin::{OpaqueOrigin, Origin};
+pub use parser::{ParseError, SyntaxViolation};
+pub use path_segments::PathSegmentsMut;
+pub use query_encoding::EncodingOverride;
+pub use slicing::Position;
+
+mod host;
+mod origin;
+mod parser;
+mod path_segments;
+mod query_encoding;
+mod slicing;
+
+pub mod form_urlencoded;
+#[doc(hidden)]
+pub mod quirks;
+
+/// A parsed URL record.
+#[derive(Clone)]
+pub struct Url {
+    /// Syntax in pseudo-BNF:
+    ///
+    ///   url = scheme ":" [ hierarchical | non-hierarchical ] [ "?" query ]? [ "#" fragment ]?
+    ///   non-hierarchical = non-hierarchical-path
+    ///   non-hierarchical-path = /* Does not start with "/" */
+    ///   hierarchical = authority? hierarchical-path
+    ///   authority = "//" userinfo? host [ ":" port ]?
+    ///   userinfo = username [ ":" password ]? "@"
+    ///   hierarchical-path = [ "/" path-segment ]+
+    serialization: String,
+
+    // Components
+    scheme_end: u32,   // Before ':'
+    username_end: u32, // Before ':' (if a password is given) or '@' (if not)
+    host_start: u32,
+    host_end: u32,
+    host: HostInternal,
+    port: Option<u16>,
+    path_start: u32,             // Before initial '/', if any
+    query_start: Option<u32>,    // Before '?', unlike Position::QueryStart
+    fragment_start: Option<u32>, // Before '#', unlike Position::FragmentStart
+}
+
+/// Full configuration for the URL parser.
+#[derive(Copy, Clone)]
+pub struct ParseOptions<'a> {
+    base_url: Option<&'a Url>,
+    encoding_override: EncodingOverride<'a>,
+    violation_fn: Option<&'a dyn Fn(SyntaxViolation)>,
+}
+
+impl<'a> ParseOptions<'a> {
+    /// Change the base URL
+    pub fn base_url(mut self, new: Option<&'a Url>) -> Self {
+        self.base_url = new;
+        self
+    }
+
+    /// Override the character encoding of query strings.
+    /// This is a legacy concept only relevant for HTML.
+    pub fn encoding_override(mut self, new: EncodingOverride<'a>) -> Self {
+        self.encoding_override = new;
+        self
+    }
+
+    /// Call the provided function or closure for a non-fatal `SyntaxViolation`
+    /// when it occurs during parsing. Note that since the provided function is
+    /// `Fn`, the caller might need to utilize _interior mutability_, such as with
+    /// a `RefCell`, to collect the violations.
+    ///
+    /// ## Example
+    /// ```
+    /// use std::cell::RefCell;
+    /// use url::{Url, SyntaxViolation};
+    /// # use url::ParseError;
+    /// # fn run() -> Result<(), url::ParseError> {
+    /// let violations = RefCell::new(Vec::new());
+    /// let url = Url::options()
+    ///     .syntax_violation_callback(Some(&|v| violations.borrow_mut().push(v)))
+    ///     .parse("https:////example.com")?;
+    /// assert_eq!(url.as_str(), "https://example.com/");
+    /// assert_eq!(violations.into_inner(),
+    ///            vec!(SyntaxViolation::ExpectedDoubleSlash));
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    pub fn syntax_violation_callback(mut self, new: Option<&'a dyn Fn(SyntaxViolation)>) -> Self {
+        self.violation_fn = new;
+        self
+    }
+
+    /// Parse an URL string with the configuration so far.
+    pub fn parse(self, input: &str) -> Result<Url, ::ParseError> {
+        Parser {
+            serialization: String::with_capacity(input.len()),
+            base_url: self.base_url,
+            query_encoding_override: self.encoding_override,
+            violation_fn: self.violation_fn,
+            context: Context::UrlParser,
+        }
+        .parse_url(input)
+    }
+}
+
+impl Url {
+    /// Parse an absolute URL from a string.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let url = Url::parse("https://example.net")?;
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    ///
+    /// # Errors
+    ///
+    /// If the function can not parse an absolute URL from the given string,
+    /// a [`ParseError`] variant will be returned.
+    ///
+    /// [`ParseError`]: enum.ParseError.html
+    #[inline]
+    pub fn parse(input: &str) -> Result<Url, ::ParseError> {
+        Url::options().parse(input)
+    }
+
+    /// Parse an absolute URL from a string and add params to its query string.
+    ///
+    /// Existing params are not removed.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let url = Url::parse_with_params("https://example.net?dont=clobberme",
+    ///                                  &[("lang", "rust"), ("browser", "servo")])?;
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    ///
+    /// # Errors
+    ///
+    /// If the function can not parse an absolute URL from the given string,
+    /// a [`ParseError`] variant will be returned.
+    ///
+    /// [`ParseError`]: enum.ParseError.html
+    #[inline]
+    pub fn parse_with_params<I, K, V>(input: &str, iter: I) -> Result<Url, ::ParseError>
+    where
+        I: IntoIterator,
+        I::Item: Borrow<(K, V)>,
+        K: AsRef<str>,
+        V: AsRef<str>,
+    {
+        let mut url = Url::options().parse(input);
+
+        if let Ok(ref mut url) = url {
+            url.query_pairs_mut().extend_pairs(iter);
+        }
+
+        url
+    }
+
+    /// Parse a string as an URL, with this URL as the base URL.
+    ///
+    /// Note: a trailing slash is significant.
+    /// Without it, the last path component is considered to be a “file” name
+    /// to be removed to get at the “directory” that is used as the base:
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let base = Url::parse("https://example.net/a/b.html")?;
+    /// let url = base.join("c.png")?;
+    /// assert_eq!(url.as_str(), "https://example.net/a/c.png");  // Not /a/b.html/c.png
+    ///
+    /// let base = Url::parse("https://example.net/a/b/")?;
+    /// let url = base.join("c.png")?;
+    /// assert_eq!(url.as_str(), "https://example.net/a/b/c.png");
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    ///
+    /// # Errors
+    ///
+    /// If the function can not parse an URL from the given string
+    /// with this URL as the base URL, a [`ParseError`] variant will be returned.
+    ///
+    /// [`ParseError`]: enum.ParseError.html
+    #[inline]
+    pub fn join(&self, input: &str) -> Result<Url, ::ParseError> {
+        Url::options().base_url(Some(self)).parse(input)
+    }
+
+    /// Return a default `ParseOptions` that can fully configure the URL parser.
+    ///
+    /// # Examples
+    ///
+    /// Get default `ParseOptions`, then change base url
+    ///
+    /// ```rust
+    /// use url::Url;
+    /// # use url::ParseError;
+    /// # fn run() -> Result<(), ParseError> {
+    /// let options = Url::options();
+    /// let api = Url::parse("https://api.example.com")?;
+    /// let base_url = options.base_url(Some(&api));
+    /// let version_url = base_url.parse("version.json")?;
+    /// assert_eq!(version_url.as_str(), "https://api.example.com/version.json");
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    pub fn options<'a>() -> ParseOptions<'a> {
+        ParseOptions {
+            base_url: None,
+            encoding_override: None,
+            violation_fn: None,
+        }
+    }
+
+    /// Return the serialization of this URL.
+    ///
+    /// This is fast since that serialization is already stored in the `Url` struct.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let url_str = "https://example.net/";
+    /// let url = Url::parse(url_str)?;
+    /// assert_eq!(url.as_str(), url_str);
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    #[inline]
+    pub fn as_str(&self) -> &str {
+        &self.serialization
+    }
+
+    /// Return the serialization of this URL.
+    ///
+    /// This consumes the `Url` and takes ownership of the `String` stored in it.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let url_str = "https://example.net/";
+    /// let url = Url::parse(url_str)?;
+    /// assert_eq!(url.into_string(), url_str);
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    #[inline]
+    pub fn into_string(self) -> String {
+        self.serialization
+    }
+
+    /// For internal testing, not part of the public API.
+    ///
+    /// Methods of the `Url` struct assume a number of invariants.
+    /// This checks each of these invariants and panic if one is not met.
+    /// This is for testing rust-url itself.
+    #[doc(hidden)]
+    pub fn check_invariants(&self) -> Result<(), String> {
+        macro_rules! assert {
+            ($x: expr) => {
+                if !$x {
+                    return Err(format!(
+                        "!( {} ) for URL {:?}",
+                        stringify!($x),
+                        self.serialization
+                    ));
+                }
+            };
+        }
+
+        macro_rules! assert_eq {
+            ($a: expr, $b: expr) => {
+                {
+                    let a = $a;
+                    let b = $b;
+                    if a != b {
+                        return Err(format!("{:?} != {:?} ({} != {}) for URL {:?}",
+                                           a, b, stringify!($a), stringify!($b),
+                                           self.serialization))
+                    }
+                }
+            }
+        }
+
+        assert!(self.scheme_end >= 1);
+        assert!(matches!(self.byte_at(0), b'a'..=b'z' | b'A'..=b'Z'));
+        assert!(self
+            .slice(1..self.scheme_end)
+            .chars()
+            .all(|c| matches!(c, 'a'..='z' | 'A'..='Z' | '0'..='9' | '+' | '-' | '.')));
+        assert_eq!(self.byte_at(self.scheme_end), b':');
+
+        if self.slice(self.scheme_end + 1..).starts_with("//") {
+            // URL with authority
+            match self.byte_at(self.username_end) {
+                b':' => {
+                    assert!(self.host_start >= self.username_end + 2);
+                    assert_eq!(self.byte_at(self.host_start - 1), b'@');
+                }
+                b'@' => assert!(self.host_start == self.username_end + 1),
+                _ => assert_eq!(self.username_end, self.scheme_end + 3),
+            }
+            assert!(self.host_start >= self.username_end);
+            assert!(self.host_end >= self.host_start);
+            let host_str = self.slice(self.host_start..self.host_end);
+            match self.host {
+                HostInternal::None => assert_eq!(host_str, ""),
+                HostInternal::Ipv4(address) => assert_eq!(host_str, address.to_string()),
+                HostInternal::Ipv6(address) => {
+                    let h: Host<String> = Host::Ipv6(address);
+                    assert_eq!(host_str, h.to_string())
+                }
+                HostInternal::Domain => {
+                    if SchemeType::from(self.scheme()).is_special() {
+                        assert!(!host_str.is_empty())
+                    }
+                }
+            }
+            if self.path_start == self.host_end {
+                assert_eq!(self.port, None);
+            } else {
+                assert_eq!(self.byte_at(self.host_end), b':');
+                let port_str = self.slice(self.host_end + 1..self.path_start);
+                assert_eq!(
+                    self.port,
+                    Some(port_str.parse::<u16>().expect("Couldn't parse port?"))
+                );
+            }
+            assert_eq!(self.byte_at(self.path_start), b'/');
+        } else {
+            // Anarchist URL (no authority)
+            assert_eq!(self.username_end, self.scheme_end + 1);
+            assert_eq!(self.host_start, self.scheme_end + 1);
+            assert_eq!(self.host_end, self.scheme_end + 1);
+            assert_eq!(self.host, HostInternal::None);
+            assert_eq!(self.port, None);
+            assert_eq!(self.path_start, self.scheme_end + 1);
+        }
+        if let Some(start) = self.query_start {
+            assert!(start > self.path_start);
+            assert_eq!(self.byte_at(start), b'?');
+        }
+        if let Some(start) = self.fragment_start {
+            assert!(start > self.path_start);
+            assert_eq!(self.byte_at(start), b'#');
+        }
+        if let (Some(query_start), Some(fragment_start)) = (self.query_start, self.fragment_start) {
+            assert!(fragment_start > query_start);
+        }
+
+        let other = Url::parse(self.as_str()).expect("Failed to parse myself?");
+        assert_eq!(&self.serialization, &other.serialization);
+        assert_eq!(self.scheme_end, other.scheme_end);
+        assert_eq!(self.username_end, other.username_end);
+        assert_eq!(self.host_start, other.host_start);
+        assert_eq!(self.host_end, other.host_end);
+        assert!(
+            self.host == other.host ||
+                // XXX No host round-trips to empty host.
+                // See https://github.com/whatwg/url/issues/79
+                (self.host_str(), other.host_str()) == (None, Some(""))
+        );
+        assert_eq!(self.port, other.port);
+        assert_eq!(self.path_start, other.path_start);
+        assert_eq!(self.query_start, other.query_start);
+        assert_eq!(self.fragment_start, other.fragment_start);
+        Ok(())
+    }
+
+    /// Return the origin of this URL (<https://url.spec.whatwg.org/#origin>)
+    ///
+    /// Note: this returns an opaque origin for `file:` URLs, which causes
+    /// `url.origin() != url.origin()`.
+    ///
+    /// # Examples
+    ///
+    /// URL with `ftp` scheme:
+    ///
+    /// ```rust
+    /// use url::{Host, Origin, Url};
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let url = Url::parse("ftp://example.com/foo")?;
+    /// assert_eq!(url.origin(),
+    ///            Origin::Tuple("ftp".into(),
+    ///                          Host::Domain("example.com".into()),
+    ///                          21));
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    ///
+    /// URL with `blob` scheme:
+    ///
+    /// ```rust
+    /// use url::{Host, Origin, Url};
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let url = Url::parse("blob:https://example.com/foo")?;
+    /// assert_eq!(url.origin(),
+    ///            Origin::Tuple("https".into(),
+    ///                          Host::Domain("example.com".into()),
+    ///                          443));
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    ///
+    /// URL with `file` scheme:
+    ///
+    /// ```rust
+    /// use url::{Host, Origin, Url};
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let url = Url::parse("file:///tmp/foo")?;
+    /// assert!(!url.origin().is_tuple());
+    ///
+    /// let other_url = Url::parse("file:///tmp/foo")?;
+    /// assert!(url.origin() != other_url.origin());
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    ///
+    /// URL with other scheme:
+    ///
+    /// ```rust
+    /// use url::{Host, Origin, Url};
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let url = Url::parse("foo:bar")?;
+    /// assert!(!url.origin().is_tuple());
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    #[inline]
+    pub fn origin(&self) -> Origin {
+        origin::url_origin(self)
+    }
+
+    /// Return the scheme of this URL, lower-cased, as an ASCII string without the ':' delimiter.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let url = Url::parse("file:///tmp/foo")?;
+    /// assert_eq!(url.scheme(), "file");
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    #[inline]
+    pub fn scheme(&self) -> &str {
+        self.slice(..self.scheme_end)
+    }
+
+    /// Return whether the URL has an 'authority',
+    /// which can contain a username, password, host, and port number.
+    ///
+    /// URLs that do *not* are either path-only like `unix:/run/foo.socket`
+    /// or cannot-be-a-base like `data:text/plain,Stuff`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let url = Url::parse("ftp://rms@example.com")?;
+    /// assert!(url.has_authority());
+    ///
+    /// let url = Url::parse("unix:/run/foo.socket")?;
+    /// assert!(!url.has_authority());
+    ///
+    /// let url = Url::parse("data:text/plain,Stuff")?;
+    /// assert!(!url.has_authority());
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    #[inline]
+    pub fn has_authority(&self) -> bool {
+        debug_assert!(self.byte_at(self.scheme_end) == b':');
+        self.slice(self.scheme_end..).starts_with("://")
+    }
+
+    /// Return whether this URL is a cannot-be-a-base URL,
+    /// meaning that parsing a relative URL string with this URL as the base will return an error.
+    ///
+    /// This is the case if the scheme and `:` delimiter are not followed by a `/` slash,
+    /// as is typically the case of `data:` and `mailto:` URLs.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let url = Url::parse("ftp://rms@example.com")?;
+    /// assert!(!url.cannot_be_a_base());
+    ///
+    /// let url = Url::parse("unix:/run/foo.socket")?;
+    /// assert!(!url.cannot_be_a_base());
+    ///
+    /// let url = Url::parse("data:text/plain,Stuff")?;
+    /// assert!(url.cannot_be_a_base());
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    #[inline]
+    pub fn cannot_be_a_base(&self) -> bool {
+        !self.slice(self.path_start..).starts_with('/')
+    }
+
+    /// Return the username for this URL (typically the empty string)
+    /// as a percent-encoded ASCII string.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let url = Url::parse("ftp://rms@example.com")?;
+    /// assert_eq!(url.username(), "rms");
+    ///
+    /// let url = Url::parse("ftp://:secret123@example.com")?;
+    /// assert_eq!(url.username(), "");
+    ///
+    /// let url = Url::parse("https://example.com")?;
+    /// assert_eq!(url.username(), "");
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    pub fn username(&self) -> &str {
+        if self.has_authority() {
+            self.slice(self.scheme_end + ("://".len() as u32)..self.username_end)
+        } else {
+            ""
+        }
+    }
+
+    /// Return the password for this URL, if any, as a percent-encoded ASCII string.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let url = Url::parse("ftp://rms:secret123@example.com")?;
+    /// assert_eq!(url.password(), Some("secret123"));
+    ///
+    /// let url = Url::parse("ftp://:secret123@example.com")?;
+    /// assert_eq!(url.password(), Some("secret123"));
+    ///
+    /// let url = Url::parse("ftp://rms@example.com")?;
+    /// assert_eq!(url.password(), None);
+    ///
+    /// let url = Url::parse("https://example.com")?;
+    /// assert_eq!(url.password(), None);
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    pub fn password(&self) -> Option<&str> {
+        // This ':' is not the one marking a port number since a host can not be empty.
+        // (Except for file: URLs, which do not have port numbers.)
+        if self.has_authority() && self.byte_at(self.username_end) == b':' {
+            debug_assert!(self.byte_at(self.host_start - 1) == b'@');
+            Some(self.slice(self.username_end + 1..self.host_start - 1))
+        } else {
+            None
+        }
+    }
+
+    /// Equivalent to `url.host().is_some()`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let url = Url::parse("ftp://rms@example.com")?;
+    /// assert!(url.has_host());
+    ///
+    /// let url = Url::parse("unix:/run/foo.socket")?;
+    /// assert!(!url.has_host());
+    ///
+    /// let url = Url::parse("data:text/plain,Stuff")?;
+    /// assert!(!url.has_host());
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    pub fn has_host(&self) -> bool {
+        !matches!(self.host, HostInternal::None)
+    }
+
+    /// Return the string representation of the host (domain or IP address) for this URL, if any.
+    ///
+    /// Non-ASCII domains are punycode-encoded per IDNA.
+    /// IPv6 addresses are given between `[` and `]` brackets.
+    ///
+    /// Cannot-be-a-base URLs (typical of `data:` and `mailto:`) and some `file:` URLs
+    /// don’t have a host.
+    ///
+    /// See also the `host` method.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let url = Url::parse("https://127.0.0.1/index.html")?;
+    /// assert_eq!(url.host_str(), Some("127.0.0.1"));
+    ///
+    /// let url = Url::parse("ftp://rms@example.com")?;
+    /// assert_eq!(url.host_str(), Some("example.com"));
+    ///
+    /// let url = Url::parse("unix:/run/foo.socket")?;
+    /// assert_eq!(url.host_str(), None);
+    ///
+    /// let url = Url::parse("data:text/plain,Stuff")?;
+    /// assert_eq!(url.host_str(), None);
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    pub fn host_str(&self) -> Option<&str> {
+        if self.has_host() {
+            Some(self.slice(self.host_start..self.host_end))
+        } else {
+            None
+        }
+    }
+
+    /// Return the parsed representation of the host for this URL.
+    /// Non-ASCII domain labels are punycode-encoded per IDNA.
+    ///
+    /// Cannot-be-a-base URLs (typical of `data:` and `mailto:`) and some `file:` URLs
+    /// don’t have a host.
+    ///
+    /// See also the `host_str` method.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let url = Url::parse("https://127.0.0.1/index.html")?;
+    /// assert!(url.host().is_some());
+    ///
+    /// let url = Url::parse("ftp://rms@example.com")?;
+    /// assert!(url.host().is_some());
+    ///
+    /// let url = Url::parse("unix:/run/foo.socket")?;
+    /// assert!(url.host().is_none());
+    ///
+    /// let url = Url::parse("data:text/plain,Stuff")?;
+    /// assert!(url.host().is_none());
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    pub fn host(&self) -> Option<Host<&str>> {
+        match self.host {
+            HostInternal::None => None,
+            HostInternal::Domain => Some(Host::Domain(self.slice(self.host_start..self.host_end))),
+            HostInternal::Ipv4(address) => Some(Host::Ipv4(address)),
+            HostInternal::Ipv6(address) => Some(Host::Ipv6(address)),
+        }
+    }
+
+    /// If this URL has a host and it is a domain name (not an IP address), return it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let url = Url::parse("https://127.0.0.1/")?;
+    /// assert_eq!(url.domain(), None);
+    ///
+    /// let url = Url::parse("mailto:rms@example.net")?;
+    /// assert_eq!(url.domain(), None);
+    ///
+    /// let url = Url::parse("https://example.com/")?;
+    /// assert_eq!(url.domain(), Some("example.com"));
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    pub fn domain(&self) -> Option<&str> {
+        match self.host {
+            HostInternal::Domain => Some(self.slice(self.host_start..self.host_end)),
+            _ => None,
+        }
+    }
+
+    /// Return the port number for this URL, if any.
+    ///
+    /// Note that default port numbers are never reflected by the serialization,
+    /// use the `port_or_known_default()` method if you want a default port number returned.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let url = Url::parse("https://example.com")?;
+    /// assert_eq!(url.port(), None);
+    ///
+    /// let url = Url::parse("https://example.com:443/")?;
+    /// assert_eq!(url.port(), None);
+    ///
+    /// let url = Url::parse("ssh://example.com:22")?;
+    /// assert_eq!(url.port(), Some(22));
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    #[inline]
+    pub fn port(&self) -> Option<u16> {
+        self.port
+    }
+
+    /// Return the port number for this URL, or the default port number if it is known.
+    ///
+    /// This method only knows the default port number
+    /// of the `http`, `https`, `ws`, `wss`, `ftp`, and `gopher` schemes.
+    ///
+    /// For URLs in these schemes, this method always returns `Some(_)`.
+    /// For other schemes, it is the same as `Url::port()`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let url = Url::parse("foo://example.com")?;
+    /// assert_eq!(url.port_or_known_default(), None);
+    ///
+    /// let url = Url::parse("foo://example.com:1456")?;
+    /// assert_eq!(url.port_or_known_default(), Some(1456));
+    ///
+    /// let url = Url::parse("https://example.com")?;
+    /// assert_eq!(url.port_or_known_default(), Some(443));
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    #[inline]
+    pub fn port_or_known_default(&self) -> Option<u16> {
+        self.port.or_else(|| parser::default_port(self.scheme()))
+    }
+
+    /// Resolve a URL’s host and port number to `SocketAddr`.
+    ///
+    /// If the URL has the default port number of a scheme that is unknown to this library,
+    /// `default_port_number` provides an opportunity to provide the actual port number.
+    /// In non-example code this should be implemented either simply as `|| None`,
+    /// or by matching on the URL’s `.scheme()`.
+    ///
+    /// If the host is a domain, it is resolved using the standard library’s DNS support.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// let url = url::Url::parse("https://example.net/").unwrap();
+    /// let addrs = url.socket_addrs(|| None).unwrap();
+    /// std::net::TcpStream::connect(&*addrs)
+    /// # ;
+    /// ```
+    ///
+    /// ```
+    /// /// With application-specific known default port numbers
+    /// fn socket_addrs(url: url::Url) -> std::io::Result<Vec<std::net::SocketAddr>> {
+    ///     url.socket_addrs(|| match url.scheme() {
+    ///         "socks5" | "socks5h" => Some(1080),
+    ///         _ => None,
+    ///     })
+    /// }
+    /// ```
+    pub fn socket_addrs(
+        &self,
+        default_port_number: impl Fn() -> Option<u16>,
+    ) -> io::Result<Vec<SocketAddr>> {
+        // Note: trying to avoid the Vec allocation by returning `impl AsRef<[SocketAddr]>`
+        // causes borrowck issues because the return value borrows `default_port_number`:
+        //
+        // https://github.com/rust-lang/rfcs/blob/master/text/1951-expand-impl-trait.md#scoping-for-type-and-lifetime-parameters
+        //
+        // > This RFC proposes that *all* type parameters are considered in scope
+        // > for `impl Trait` in return position
+
+        fn io_result<T>(opt: Option<T>, message: &str) -> io::Result<T> {
+            opt.ok_or_else(|| io::Error::new(io::ErrorKind::InvalidData, message))
+        }
+
+        let host = io_result(self.host(), "No host name in the URL")?;
+        let port = io_result(
+            self.port_or_known_default().or_else(default_port_number),
+            "No port number in the URL",
+        )?;
+        Ok(match host {
+            Host::Domain(domain) => (domain, port).to_socket_addrs()?.collect(),
+            Host::Ipv4(ip) => vec![(ip, port).into()],
+            Host::Ipv6(ip) => vec![(ip, port).into()],
+        })
+    }
+
+    /// Return the path for this URL, as a percent-encoded ASCII string.
+    /// For cannot-be-a-base URLs, this is an arbitrary string that doesn’t start with '/'.
+    /// For other URLs, this starts with a '/' slash
+    /// and continues with slash-separated path segments.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use url::{Url, ParseError};
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let url = Url::parse("https://example.com/api/versions?page=2")?;
+    /// assert_eq!(url.path(), "/api/versions");
+    ///
+    /// let url = Url::parse("https://example.com")?;
+    /// assert_eq!(url.path(), "/");
+    ///
+    /// let url = Url::parse("https://example.com/countries/việt nam")?;
+    /// assert_eq!(url.path(), "/countries/vi%E1%BB%87t%20nam");
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    pub fn path(&self) -> &str {
+        match (self.query_start, self.fragment_start) {
+            (None, None) => self.slice(self.path_start..),
+            (Some(next_component_start), _) | (None, Some(next_component_start)) => {
+                self.slice(self.path_start..next_component_start)
+            }
+        }
+    }
+
+    /// Unless this URL is cannot-be-a-base,
+    /// return an iterator of '/' slash-separated path segments,
+    /// each as a percent-encoded ASCII string.
+    ///
+    /// Return `None` for cannot-be-a-base URLs.
+    ///
+    /// When `Some` is returned, the iterator always contains at least one string
+    /// (which may be empty).
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use url::Url;
+    /// # use std::error::Error;
+    ///
+    /// # fn run() -> Result<(), Box<Error>> {
+    /// let url = Url::parse("https://example.com/foo/bar")?;
+    /// let mut path_segments = url.path_segments().ok_or_else(|| "cannot be base")?;
+    /// assert_eq!(path_segments.next(), Some("foo"));
+    /// assert_eq!(path_segments.next(), Some("bar"));
+    /// assert_eq!(path_segments.next(), None);
+    ///
+    /// let url = Url::parse("https://example.com")?;
+    /// let mut path_segments = url.path_segments().ok_or_else(|| "cannot be base")?;
+    /// assert_eq!(path_segments.next(), Some(""));
+    /// assert_eq!(path_segments.next(), None);
+    ///
+    /// let url = Url::parse("data:text/plain,HelloWorld")?;
+    /// assert!(url.path_segments().is_none());
+    ///
+    /// let url = Url::parse("https://example.com/countries/việt nam")?;
+    /// let mut path_segments = url.path_segments().ok_or_else(|| "cannot be base")?;
+    /// assert_eq!(path_segments.next(), Some("countries"));
+    /// assert_eq!(path_segments.next(), Some("vi%E1%BB%87t%20nam"));
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    pub fn path_segments(&self) -> Option<str::Split<char>> {
+        let path = self.path();
+        if path.starts_with('/') {
+            Some(path[1..].split('/'))
+        } else {
+            None
+        }
+    }
+
+    /// Return this URL’s query string, if any, as a percent-encoded ASCII string.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// fn run() -> Result<(), ParseError> {
+    /// let url = Url::parse("https://example.com/products?page=2")?;
+    /// let query = url.query();
+    /// assert_eq!(query, Some("page=2"));
+    ///
+    /// let url = Url::parse("https://example.com/products")?;
+    /// let query = url.query();
+    /// assert!(query.is_none());
+    ///
+    /// let url = Url::parse("https://example.com/?country=español")?;
+    /// let query = url.query();
+    /// assert_eq!(query, Some("country=espa%C3%B1ol"));
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    pub fn query(&self) -> Option<&str> {
+        match (self.query_start, self.fragment_start) {
+            (None, _) => None,
+            (Some(query_start), None) => {
+                debug_assert!(self.byte_at(query_start) == b'?');
+                Some(self.slice(query_start + 1..))
+            }
+            (Some(query_start), Some(fragment_start)) => {
+                debug_assert!(self.byte_at(query_start) == b'?');
+                Some(self.slice(query_start + 1..fragment_start))
+            }
+        }
+    }
+
+    /// Parse the URL’s query string, if any, as `application/x-www-form-urlencoded`
+    /// and return an iterator of (key, value) pairs.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use std::borrow::Cow;
+    ///
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let url = Url::parse("https://example.com/products?page=2&sort=desc")?;
+    /// let mut pairs = url.query_pairs();
+    ///
+    /// assert_eq!(pairs.count(), 2);
+    ///
+    /// assert_eq!(pairs.next(), Some((Cow::Borrowed("page"), Cow::Borrowed("2"))));
+    /// assert_eq!(pairs.next(), Some((Cow::Borrowed("sort"), Cow::Borrowed("desc"))));
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    ///
+
+    #[inline]
+    pub fn query_pairs(&self) -> form_urlencoded::Parse {
+        form_urlencoded::parse(self.query().unwrap_or("").as_bytes())
+    }
+
+    /// Return this URL’s fragment identifier, if any.
+    ///
+    /// A fragment is the part of the URL after the `#` symbol.
+    /// The fragment is optional and, if present, contains a fragment identifier
+    /// that identifies a secondary resource, such as a section heading
+    /// of a document.
+    ///
+    /// In HTML, the fragment identifier is usually the id attribute of a an element
+    /// that is scrolled to on load. Browsers typically will not send the fragment portion
+    /// of a URL to the server.
+    ///
+    /// **Note:** the parser did *not* percent-encode this component,
+    /// but the input may have been percent-encoded already.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let url = Url::parse("https://example.com/data.csv#row=4")?;
+    ///
+    /// assert_eq!(url.fragment(), Some("row=4"));
+    ///
+    /// let url = Url::parse("https://example.com/data.csv#cell=4,1-6,2")?;
+    ///
+    /// assert_eq!(url.fragment(), Some("cell=4,1-6,2"));
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    pub fn fragment(&self) -> Option<&str> {
+        self.fragment_start.map(|start| {
+            debug_assert!(self.byte_at(start) == b'#');
+            self.slice(start + 1..)
+        })
+    }
+
+    fn mutate<F: FnOnce(&mut Parser) -> R, R>(&mut self, f: F) -> R {
+        let mut parser = Parser::for_setter(mem::replace(&mut self.serialization, String::new()));
+        let result = f(&mut parser);
+        self.serialization = parser.serialization;
+        result
+    }
+
+    /// Change this URL’s fragment identifier.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let mut url = Url::parse("https://example.com/data.csv")?;
+    /// assert_eq!(url.as_str(), "https://example.com/data.csv");
+
+    /// url.set_fragment(Some("cell=4,1-6,2"));
+    /// assert_eq!(url.as_str(), "https://example.com/data.csv#cell=4,1-6,2");
+    /// assert_eq!(url.fragment(), Some("cell=4,1-6,2"));
+    ///
+    /// url.set_fragment(None);
+    /// assert_eq!(url.as_str(), "https://example.com/data.csv");
+    /// assert!(url.fragment().is_none());
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    pub fn set_fragment(&mut self, fragment: Option<&str>) {
+        // Remove any previous fragment
+        if let Some(start) = self.fragment_start {
+            debug_assert!(self.byte_at(start) == b'#');
+            self.serialization.truncate(start as usize);
+        }
+        // Write the new one
+        if let Some(input) = fragment {
+            self.fragment_start = Some(to_u32(self.serialization.len()).unwrap());
+            self.serialization.push('#');
+            self.mutate(|parser| parser.parse_fragment(parser::Input::new(input)))
+        } else {
+            self.fragment_start = None
+        }
+    }
+
+    fn take_fragment(&mut self) -> Option<String> {
+        self.fragment_start.take().map(|start| {
+            debug_assert!(self.byte_at(start) == b'#');
+            let fragment = self.slice(start + 1..).to_owned();
+            self.serialization.truncate(start as usize);
+            fragment
+        })
+    }
+
+    fn restore_already_parsed_fragment(&mut self, fragment: Option<String>) {
+        if let Some(ref fragment) = fragment {
+            assert!(self.fragment_start.is_none());
+            self.fragment_start = Some(to_u32(self.serialization.len()).unwrap());
+            self.serialization.push('#');
+            self.serialization.push_str(fragment);
+        }
+    }
+
+    /// Change this URL’s query string.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let mut url = Url::parse("https://example.com/products")?;
+    /// assert_eq!(url.as_str(), "https://example.com/products");
+    ///
+    /// url.set_query(Some("page=2"));
+    /// assert_eq!(url.as_str(), "https://example.com/products?page=2");
+    /// assert_eq!(url.query(), Some("page=2"));
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    pub fn set_query(&mut self, query: Option<&str>) {
+        let fragment = self.take_fragment();
+
+        // Remove any previous query
+        if let Some(start) = self.query_start.take() {
+            debug_assert!(self.byte_at(start) == b'?');
+            self.serialization.truncate(start as usize);
+        }
+        // Write the new query, if any
+        if let Some(input) = query {
+            self.query_start = Some(to_u32(self.serialization.len()).unwrap());
+            self.serialization.push('?');
+            let scheme_type = SchemeType::from(self.scheme());
+            let scheme_end = self.scheme_end;
+            self.mutate(|parser| {
+                parser.parse_query(scheme_type, scheme_end, parser::Input::new(input))
+            });
+        }
+
+        self.restore_already_parsed_fragment(fragment);
+    }
+
+    /// Manipulate this URL’s query string, viewed as a sequence of name/value pairs
+    /// in `application/x-www-form-urlencoded` syntax.
+    ///
+    /// The return value has a method-chaining API:
+    ///
+    /// ```rust
+    /// # use url::{Url, ParseError};
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let mut url = Url::parse("https://example.net?lang=fr#nav")?;
+    /// assert_eq!(url.query(), Some("lang=fr"));
+    ///
+    /// url.query_pairs_mut().append_pair("foo", "bar");
+    /// assert_eq!(url.query(), Some("lang=fr&foo=bar"));
+    /// assert_eq!(url.as_str(), "https://example.net/?lang=fr&foo=bar#nav");
+    ///
+    /// url.query_pairs_mut()
+    ///     .clear()
+    ///     .append_pair("foo", "bar & baz")
+    ///     .append_pair("saisons", "\u{00C9}t\u{00E9}+hiver");
+    /// assert_eq!(url.query(), Some("foo=bar+%26+baz&saisons=%C3%89t%C3%A9%2Bhiver"));
+    /// assert_eq!(url.as_str(),
+    ///            "https://example.net/?foo=bar+%26+baz&saisons=%C3%89t%C3%A9%2Bhiver#nav");
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    ///
+    /// Note: `url.query_pairs_mut().clear();` is equivalent to `url.set_query(Some(""))`,
+    /// not `url.set_query(None)`.
+    ///
+    /// The state of `Url` is unspecified if this return value is leaked without being dropped.
+    pub fn query_pairs_mut(&mut self) -> form_urlencoded::Serializer<UrlQuery> {
+        let fragment = self.take_fragment();
+
+        let query_start;
+        if let Some(start) = self.query_start {
+            debug_assert!(self.byte_at(start) == b'?');
+            query_start = start as usize;
+        } else {
+            query_start = self.serialization.len();
+            self.query_start = Some(to_u32(query_start).unwrap());
+            self.serialization.push('?');
+        }
+
+        let query = UrlQuery {
+            url: Some(self),
+            fragment,
+        };
+        form_urlencoded::Serializer::for_suffix(query, query_start + "?".len())
+    }
+
+    fn take_after_path(&mut self) -> String {
+        match (self.query_start, self.fragment_start) {
+            (Some(i), _) | (None, Some(i)) => {
+                let after_path = self.slice(i..).to_owned();
+                self.serialization.truncate(i as usize);
+                after_path
+            }
+            (None, None) => String::new(),
+        }
+    }
+
+    /// Change this URL’s path.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let mut url = Url::parse("https://example.com")?;
+    /// url.set_path("api/comments");
+    /// assert_eq!(url.as_str(), "https://example.com/api/comments");
+    /// assert_eq!(url.path(), "/api/comments");
+    ///
+    /// let mut url = Url::parse("https://example.com/api")?;
+    /// url.set_path("data/report.csv");
+    /// assert_eq!(url.as_str(), "https://example.com/data/report.csv");
+    /// assert_eq!(url.path(), "/data/report.csv");
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    pub fn set_path(&mut self, mut path: &str) {
+        let after_path = self.take_after_path();
+        let old_after_path_pos = to_u32(self.serialization.len()).unwrap();
+        let cannot_be_a_base = self.cannot_be_a_base();
+        let scheme_type = SchemeType::from(self.scheme());
+        self.serialization.truncate(self.path_start as usize);
+        self.mutate(|parser| {
+            if cannot_be_a_base {
+                if path.starts_with('/') {
+                    parser.serialization.push_str("%2F");
+                    path = &path[1..];
+                }
+                parser.parse_cannot_be_a_base_path(parser::Input::new(path));
+            } else {
+                let mut has_host = true; // FIXME
+                parser.parse_path_start(scheme_type, &mut has_host, parser::Input::new(path));
+            }
+        });
+        self.restore_after_path(old_after_path_pos, &after_path);
+    }
+
+    /// Return an object with methods to manipulate this URL’s path segments.
+    ///
+    /// Return `Err(())` if this URL is cannot-be-a-base.
+    pub fn path_segments_mut(&mut self) -> Result<PathSegmentsMut, ()> {
+        if self.cannot_be_a_base() {
+            Err(())
+        } else {
+            Ok(path_segments::new(self))
+        }
+    }
+
+    fn restore_after_path(&mut self, old_after_path_position: u32, after_path: &str) {
+        let new_after_path_position = to_u32(self.serialization.len()).unwrap();
+        let adjust = |index: &mut u32| {
+            *index -= old_after_path_position;
+            *index += new_after_path_position;
+        };
+        if let Some(ref mut index) = self.query_start {
+            adjust(index)
+        }
+        if let Some(ref mut index) = self.fragment_start {
+            adjust(index)
+        }
+        self.serialization.push_str(after_path)
+    }
+
+    /// Change this URL’s port number.
+    ///
+    /// Note that default port numbers are not reflected in the serialization.
+    ///
+    /// If this URL is cannot-be-a-base, does not have a host, or has the `file` scheme;
+    /// do nothing and return `Err`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use url::Url;
+    /// # use std::error::Error;
+    ///
+    /// # fn run() -> Result<(), Box<Error>> {
+    /// let mut url = Url::parse("ssh://example.net:2048/")?;
+    ///
+    /// url.set_port(Some(4096)).map_err(|_| "cannot be base")?;
+    /// assert_eq!(url.as_str(), "ssh://example.net:4096/");
+    ///
+    /// url.set_port(None).map_err(|_| "cannot be base")?;
+    /// assert_eq!(url.as_str(), "ssh://example.net/");
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    ///
+    /// Known default port numbers are not reflected:
+    ///
+    /// ```rust
+    /// use url::Url;
+    /// # use std::error::Error;
+    ///
+    /// # fn run() -> Result<(), Box<Error>> {
+    /// let mut url = Url::parse("https://example.org/")?;
+    ///
+    /// url.set_port(Some(443)).map_err(|_| "cannot be base")?;
+    /// assert!(url.port().is_none());
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    ///
+    /// Cannot set port for cannot-be-a-base URLs:
+    ///
+    /// ```
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let mut url = Url::parse("mailto:rms@example.net")?;
+    ///
+    /// let result = url.set_port(Some(80));
+    /// assert!(result.is_err());
+    ///
+    /// let result = url.set_port(None);
+    /// assert!(result.is_err());
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    pub fn set_port(&mut self, mut port: Option<u16>) -> Result<(), ()> {
+        // has_host implies !cannot_be_a_base
+        if !self.has_host() || self.host() == Some(Host::Domain("")) || self.scheme() == "file" {
+            return Err(());
+        }
+        if port.is_some() && port == parser::default_port(self.scheme()) {
+            port = None
+        }
+        self.set_port_internal(port);
+        Ok(())
+    }
+
+    fn set_port_internal(&mut self, port: Option<u16>) {
+        match (self.port, port) {
+            (None, None) => {}
+            (Some(_), None) => {
+                self.serialization
+                    .drain(self.host_end as usize..self.path_start as usize);
+                let offset = self.path_start - self.host_end;
+                self.path_start = self.host_end;
+                if let Some(ref mut index) = self.query_start {
+                    *index -= offset
+                }
+                if let Some(ref mut index) = self.fragment_start {
+                    *index -= offset
+                }
+            }
+            (Some(old), Some(new)) if old == new => {}
+            (_, Some(new)) => {
+                let path_and_after = self.slice(self.path_start..).to_owned();
+                self.serialization.truncate(self.host_end as usize);
+                write!(&mut self.serialization, ":{}", new).unwrap();
+                let old_path_start = self.path_start;
+                let new_path_start = to_u32(self.serialization.len()).unwrap();
+                self.path_start = new_path_start;
+                let adjust = |index: &mut u32| {
+                    *index -= old_path_start;
+                    *index += new_path_start;
+                };
+                if let Some(ref mut index) = self.query_start {
+                    adjust(index)
+                }
+                if let Some(ref mut index) = self.fragment_start {
+                    adjust(index)
+                }
+                self.serialization.push_str(&path_and_after);
+            }
+        }
+        self.port = port;
+    }
+
+    /// Change this URL’s host.
+    ///
+    /// Removing the host (calling this with `None`)
+    /// will also remove any username, password, and port number.
+    ///
+    /// # Examples
+    ///
+    /// Change host:
+    ///
+    /// ```
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let mut url = Url::parse("https://example.net")?;
+    /// let result = url.set_host(Some("rust-lang.org"));
+    /// assert!(result.is_ok());
+    /// assert_eq!(url.as_str(), "https://rust-lang.org/");
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    ///
+    /// Remove host:
+    ///
+    /// ```
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let mut url = Url::parse("foo://example.net")?;
+    /// let result = url.set_host(None);
+    /// assert!(result.is_ok());
+    /// assert_eq!(url.as_str(), "foo:/");
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    ///
+    /// Cannot remove host for 'special' schemes (e.g. `http`):
+    ///
+    /// ```
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let mut url = Url::parse("https://example.net")?;
+    /// let result = url.set_host(None);
+    /// assert!(result.is_err());
+    /// assert_eq!(url.as_str(), "https://example.net/");
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    ///
+    /// Cannot change or remove host for cannot-be-a-base URLs:
+    ///
+    /// ```
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let mut url = Url::parse("mailto:rms@example.net")?;
+    ///
+    /// let result = url.set_host(Some("rust-lang.org"));
+    /// assert!(result.is_err());
+    /// assert_eq!(url.as_str(), "mailto:rms@example.net");
+    ///
+    /// let result = url.set_host(None);
+    /// assert!(result.is_err());
+    /// assert_eq!(url.as_str(), "mailto:rms@example.net");
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    ///
+    /// # Errors
+    ///
+    /// If this URL is cannot-be-a-base or there is an error parsing the given `host`,
+    /// a [`ParseError`] variant will be returned.
+    ///
+    /// [`ParseError`]: enum.ParseError.html
+    pub fn set_host(&mut self, host: Option<&str>) -> Result<(), ParseError> {
+        if self.cannot_be_a_base() {
+            return Err(ParseError::SetHostOnCannotBeABaseUrl);
+        }
+
+        if let Some(host) = host {
+            if host == "" && SchemeType::from(self.scheme()).is_special() {
+                return Err(ParseError::EmptyHost);
+            }
+            if SchemeType::from(self.scheme()).is_special() {
+                self.set_host_internal(Host::parse(host)?, None)
+            } else {
+                self.set_host_internal(Host::parse_opaque(host)?, None)
+            }
+        } else if self.has_host() {
+            if SchemeType::from(self.scheme()).is_special() {
+                return Err(ParseError::EmptyHost);
+            }
+            debug_assert!(self.byte_at(self.scheme_end) == b':');
+            debug_assert!(self.byte_at(self.path_start) == b'/');
+            let new_path_start = self.scheme_end + 1;
+            self.serialization
+                .drain(new_path_start as usize..self.path_start as usize);
+            let offset = self.path_start - new_path_start;
+            self.path_start = new_path_start;
+            self.username_end = new_path_start;
+            self.host_start = new_path_start;
+            self.host_end = new_path_start;
+            self.port = None;
+            if let Some(ref mut index) = self.query_start {
+                *index -= offset
+            }
+            if let Some(ref mut index) = self.fragment_start {
+                *index -= offset
+            }
+        }
+        Ok(())
+    }
+
+    /// opt_new_port: None means leave unchanged, Some(None) means remove any port number.
+    fn set_host_internal(&mut self, host: Host<String>, opt_new_port: Option<Option<u16>>) {
+        let old_suffix_pos = if opt_new_port.is_some() {
+            self.path_start
+        } else {
+            self.host_end
+        };
+        let suffix = self.slice(old_suffix_pos..).to_owned();
+        self.serialization.truncate(self.host_start as usize);
+        if !self.has_authority() {
+            debug_assert!(self.slice(self.scheme_end..self.host_start) == ":");
+            debug_assert!(self.username_end == self.host_start);
+            self.serialization.push('/');
+            self.serialization.push('/');
+            self.username_end += 2;
+            self.host_start += 2;
+        }
+        write!(&mut self.serialization, "{}", host).unwrap();
+        self.host_end = to_u32(self.serialization.len()).unwrap();
+        self.host = host.into();
+
+        if let Some(new_port) = opt_new_port {
+            self.port = new_port;
+            if let Some(port) = new_port {
+                write!(&mut self.serialization, ":{}", port).unwrap();
+            }
+        }
+        let new_suffix_pos = to_u32(self.serialization.len()).unwrap();
+        self.serialization.push_str(&suffix);
+
+        let adjust = |index: &mut u32| {
+            *index -= old_suffix_pos;
+            *index += new_suffix_pos;
+        };
+        adjust(&mut self.path_start);
+        if let Some(ref mut index) = self.query_start {
+            adjust(index)
+        }
+        if let Some(ref mut index) = self.fragment_start {
+            adjust(index)
+        }
+    }
+
+    /// Change this URL’s host to the given IP address.
+    ///
+    /// If this URL is cannot-be-a-base, do nothing and return `Err`.
+    ///
+    /// Compared to `Url::set_host`, this skips the host parser.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use url::{Url, ParseError};
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let mut url = Url::parse("http://example.com")?;
+    /// url.set_ip_host("127.0.0.1".parse().unwrap());
+    /// assert_eq!(url.host_str(), Some("127.0.0.1"));
+    /// assert_eq!(url.as_str(), "http://127.0.0.1/");
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    ///
+    /// Cannot change URL's from mailto(cannot-be-base) to ip:
+    ///
+    /// ```rust
+    /// use url::{Url, ParseError};
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let mut url = Url::parse("mailto:rms@example.com")?;
+    /// let result = url.set_ip_host("127.0.0.1".parse().unwrap());
+    ///
+    /// assert_eq!(url.as_str(), "mailto:rms@example.com");
+    /// assert!(result.is_err());
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    ///
+    pub fn set_ip_host(&mut self, address: IpAddr) -> Result<(), ()> {
+        if self.cannot_be_a_base() {
+            return Err(());
+        }
+
+        let address = match address {
+            IpAddr::V4(address) => Host::Ipv4(address),
+            IpAddr::V6(address) => Host::Ipv6(address),
+        };
+        self.set_host_internal(address, None);
+        Ok(())
+    }
+
+    /// Change this URL’s password.
+    ///
+    /// If this URL is cannot-be-a-base or does not have a host, do nothing and return `Err`.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use url::{Url, ParseError};
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let mut url = Url::parse("mailto:rmz@example.com")?;
+    /// let result = url.set_password(Some("secret_password"));
+    /// assert!(result.is_err());
+    ///
+    /// let mut url = Url::parse("ftp://user1:secret1@example.com")?;
+    /// let result = url.set_password(Some("secret_password"));
+    /// assert_eq!(url.password(), Some("secret_password"));
+    ///
+    /// let mut url = Url::parse("ftp://user2:@example.com")?;
+    /// let result = url.set_password(Some("secret2"));
+    /// assert!(result.is_ok());
+    /// assert_eq!(url.password(), Some("secret2"));
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    pub fn set_password(&mut self, password: Option<&str>) -> Result<(), ()> {
+        // has_host implies !cannot_be_a_base
+        if !self.has_host() || self.host() == Some(Host::Domain("")) || self.scheme() == "file" {
+            return Err(());
+        }
+        if let Some(password) = password {
+            let host_and_after = self.slice(self.host_start..).to_owned();
+            self.serialization.truncate(self.username_end as usize);
+            self.serialization.push(':');
+            self.serialization
+                .extend(utf8_percent_encode(password, USERINFO));
+            self.serialization.push('@');
+
+            let old_host_start = self.host_start;
+            let new_host_start = to_u32(self.serialization.len()).unwrap();
+            let adjust = |index: &mut u32| {
+                *index -= old_host_start;
+                *index += new_host_start;
+            };
+            self.host_start = new_host_start;
+            adjust(&mut self.host_end);
+            adjust(&mut self.path_start);
+            if let Some(ref mut index) = self.query_start {
+                adjust(index)
+            }
+            if let Some(ref mut index) = self.fragment_start {
+                adjust(index)
+            }
+
+            self.serialization.push_str(&host_and_after);
+        } else if self.byte_at(self.username_end) == b':' {
+            // If there is a password to remove
+            let has_username_or_password = self.byte_at(self.host_start - 1) == b'@';
+            debug_assert!(has_username_or_password);
+            let username_start = self.scheme_end + 3;
+            let empty_username = username_start == self.username_end;
+            let start = self.username_end; // Remove the ':'
+            let end = if empty_username {
+                self.host_start // Remove the '@' as well
+            } else {
+                self.host_start - 1 // Keep the '@' to separate the username from the host
+            };
+            self.serialization.drain(start as usize..end as usize);
+            let offset = end - start;
+            self.host_start -= offset;
+            self.host_end -= offset;
+            self.path_start -= offset;
+            if let Some(ref mut index) = self.query_start {
+                *index -= offset
+            }
+            if let Some(ref mut index) = self.fragment_start {
+                *index -= offset
+            }
+        }
+        Ok(())
+    }
+
+    /// Change this URL’s username.
+    ///
+    /// If this URL is cannot-be-a-base or does not have a host, do nothing and return `Err`.
+    /// # Examples
+    ///
+    /// Cannot setup username from mailto(cannot-be-base)
+    ///
+    /// ```rust
+    /// use url::{Url, ParseError};
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let mut url = Url::parse("mailto:rmz@example.com")?;
+    /// let result = url.set_username("user1");
+    /// assert_eq!(url.as_str(), "mailto:rmz@example.com");
+    /// assert!(result.is_err());
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    ///
+    /// Setup username to user1
+    ///
+    /// ```rust
+    /// use url::{Url, ParseError};
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let mut url = Url::parse("ftp://:secre1@example.com/")?;
+    /// let result = url.set_username("user1");
+    /// assert!(result.is_ok());
+    /// assert_eq!(url.username(), "user1");
+    /// assert_eq!(url.as_str(), "ftp://user1:secre1@example.com/");
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    pub fn set_username(&mut self, username: &str) -> Result<(), ()> {
+        // has_host implies !cannot_be_a_base
+        if !self.has_host() || self.host() == Some(Host::Domain("")) || self.scheme() == "file" {
+            return Err(());
+        }
+        let username_start = self.scheme_end + 3;
+        debug_assert!(self.slice(self.scheme_end..username_start) == "://");
+        if self.slice(username_start..self.username_end) == username {
+            return Ok(());
+        }
+        let after_username = self.slice(self.username_end..).to_owned();
+        self.serialization.truncate(username_start as usize);
+        self.serialization
+            .extend(utf8_percent_encode(username, USERINFO));
+
+        let mut removed_bytes = self.username_end;
+        self.username_end = to_u32(self.serialization.len()).unwrap();
+        let mut added_bytes = self.username_end;
+
+        let new_username_is_empty = self.username_end == username_start;
+        match (new_username_is_empty, after_username.chars().next()) {
+            (true, Some('@')) => {
+                removed_bytes += 1;
+                self.serialization.push_str(&after_username[1..]);
+            }
+            (false, Some('@')) | (_, Some(':')) | (true, _) => {
+                self.serialization.push_str(&after_username);
+            }
+            (false, _) => {
+                added_bytes += 1;
+                self.serialization.push('@');
+                self.serialization.push_str(&after_username);
+            }
+        }
+
+        let adjust = |index: &mut u32| {
+            *index -= removed_bytes;
+            *index += added_bytes;
+        };
+        adjust(&mut self.host_start);
+        adjust(&mut self.host_end);
+        adjust(&mut self.path_start);
+        if let Some(ref mut index) = self.query_start {
+            adjust(index)
+        }
+        if let Some(ref mut index) = self.fragment_start {
+            adjust(index)
+        }
+        Ok(())
+    }
+
+    /// Change this URL’s scheme.
+    ///
+    /// Do nothing and return `Err` if:
+    ///
+    /// * The new scheme is not in `[a-zA-Z][a-zA-Z0-9+.-]+`
+    /// * This URL is cannot-be-a-base and the new scheme is one of
+    ///   `http`, `https`, `ws`, `wss`, `ftp`, or `gopher`
+    ///
+    /// # Examples
+    ///
+    /// Change the URL’s scheme from `https` to `foo`:
+    ///
+    /// ```
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let mut url = Url::parse("https://example.net")?;
+    /// let result = url.set_scheme("foo");
+    /// assert_eq!(url.as_str(), "foo://example.net/");
+    /// assert!(result.is_ok());
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    ///
+    ///
+    /// Cannot change URL’s scheme from `https` to `foõ`:
+    ///
+    /// ```
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let mut url = Url::parse("https://example.net")?;
+    /// let result = url.set_scheme("foõ");
+    /// assert_eq!(url.as_str(), "https://example.net/");
+    /// assert!(result.is_err());
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    ///
+    /// Cannot change URL’s scheme from `mailto` (cannot-be-a-base) to `https`:
+    ///
+    /// ```
+    /// use url::Url;
+    /// # use url::ParseError;
+    ///
+    /// # fn run() -> Result<(), ParseError> {
+    /// let mut url = Url::parse("mailto:rms@example.net")?;
+    /// let result = url.set_scheme("https");
+    /// assert_eq!(url.as_str(), "mailto:rms@example.net");
+    /// assert!(result.is_err());
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    pub fn set_scheme(&mut self, scheme: &str) -> Result<(), ()> {
+        let mut parser = Parser::for_setter(String::new());
+        let remaining = parser.parse_scheme(parser::Input::new(scheme))?;
+        if !remaining.is_empty()
+            || (!self.has_host() && SchemeType::from(&parser.serialization).is_special())
+        {
+            return Err(());
+        }
+        let old_scheme_end = self.scheme_end;
+        let new_scheme_end = to_u32(parser.serialization.len()).unwrap();
+        let adjust = |index: &mut u32| {
+            *index -= old_scheme_end;
+            *index += new_scheme_end;
+        };
+
+        self.scheme_end = new_scheme_end;
+        adjust(&mut self.username_end);
+        adjust(&mut self.host_start);
+        adjust(&mut self.host_end);
+        adjust(&mut self.path_start);
+        if let Some(ref mut index) = self.query_start {
+            adjust(index)
+        }
+        if let Some(ref mut index) = self.fragment_start {
+            adjust(index)
+        }
+
+        parser.serialization.push_str(self.slice(old_scheme_end..));
+        self.serialization = parser.serialization;
+        Ok(())
+    }
+
+    /// Convert a file name as `std::path::Path` into an URL in the `file` scheme.
+    ///
+    /// This returns `Err` if the given path is not absolute or,
+    /// on Windows, if the prefix is not a disk prefix (e.g. `C:`) or a UNC prefix (`\\`).
+    ///
+    /// # Examples
+    ///
+    /// On Unix-like platforms:
+    ///
+    /// ```
+    /// # if cfg!(unix) {
+    /// use url::Url;
+    ///
+    /// # fn run() -> Result<(), ()> {
+    /// let url = Url::from_file_path("/tmp/foo.txt")?;
+    /// assert_eq!(url.as_str(), "file:///tmp/foo.txt");
+    ///
+    /// let url = Url::from_file_path("../foo.txt");
+    /// assert!(url.is_err());
+    ///
+    /// let url = Url::from_file_path("https://google.com/");
+    /// assert!(url.is_err());
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// # }
+    /// ```
+    #[cfg(any(unix, windows, target_os = "redox"))]
+    pub fn from_file_path<P: AsRef<Path>>(path: P) -> Result<Url, ()> {
+        let mut serialization = "file://".to_owned();
+        let host_start = serialization.len() as u32;
+        let (host_end, host) = path_to_file_url_segments(path.as_ref(), &mut serialization)?;
+        Ok(Url {
+            serialization,
+            scheme_end: "file".len() as u32,
+            username_end: host_start,
+            host_start,
+            host_end,
+            host,
+            port: None,
+            path_start: host_end,
+            query_start: None,
+            fragment_start: None,
+        })
+    }
+
+    /// Convert a directory name as `std::path::Path` into an URL in the `file` scheme.
+    ///
+    /// This returns `Err` if the given path is not absolute or,
+    /// on Windows, if the prefix is not a disk prefix (e.g. `C:`) or a UNC prefix (`\\`).
+    ///
+    /// Compared to `from_file_path`, this ensure that URL’s the path has a trailing slash
+    /// so that the entire path is considered when using this URL as a base URL.
+    ///
+    /// For example:
+    ///
+    /// * `"index.html"` parsed with `Url::from_directory_path(Path::new("/var/www"))`
+    ///   as the base URL is `file:///var/www/index.html`
+    /// * `"index.html"` parsed with `Url::from_file_path(Path::new("/var/www"))`
+    ///   as the base URL is `file:///var/index.html`, which might not be what was intended.
+    ///
+    /// Note that `std::path` does not consider trailing slashes significant
+    /// and usually does not include them (e.g. in `Path::parent()`).
+    #[cfg(any(unix, windows, target_os = "redox"))]
+    pub fn from_directory_path<P: AsRef<Path>>(path: P) -> Result<Url, ()> {
+        let mut url = Url::from_file_path(path)?;
+        if !url.serialization.ends_with('/') {
+            url.serialization.push('/')
+        }
+        Ok(url)
+    }
+
+    /// Serialize with Serde using the internal representation of the `Url` struct.
+    ///
+    /// The corresponding `deserialize_internal` method sacrifices some invariant-checking
+    /// for speed, compared to the `Deserialize` trait impl.
+    ///
+    /// This method is only available if the `serde` Cargo feature is enabled.
+    #[cfg(feature = "serde")]
+    #[deny(unused)]
+    pub fn serialize_internal<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+    {
+        use serde::Serialize;
+        // Destructuring first lets us ensure that adding or removing fields forces this method
+        // to be updated
+        let Url {
+            ref serialization,
+            ref scheme_end,
+            ref username_end,
+            ref host_start,
+            ref host_end,
+            ref host,
+            ref port,
+            ref path_start,
+            ref query_start,
+            ref fragment_start,
+        } = *self;
+        (
+            serialization,
+            scheme_end,
+            username_end,
+            host_start,
+            host_end,
+            host,
+            port,
+            path_start,
+            query_start,
+            fragment_start,
+        )
+            .serialize(serializer)
+    }
+
+    /// Serialize with Serde using the internal representation of the `Url` struct.
+    ///
+    /// The corresponding `deserialize_internal` method sacrifices some invariant-checking
+    /// for speed, compared to the `Deserialize` trait impl.
+    ///
+    /// This method is only available if the `serde` Cargo feature is enabled.
+    #[cfg(feature = "serde")]
+    #[deny(unused)]
+    pub fn deserialize_internal<'de, D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        use serde::de::{Deserialize, Error, Unexpected};
+        let (
+            serialization,
+            scheme_end,
+            username_end,
+            host_start,
+            host_end,
+            host,
+            port,
+            path_start,
+            query_start,
+            fragment_start,
+        ) = Deserialize::deserialize(deserializer)?;
+        let url = Url {
+            serialization,
+            scheme_end,
+            username_end,
+            host_start,
+            host_end,
+            host,
+            port,
+            path_start,
+            query_start,
+            fragment_start,
+        };
+        if cfg!(debug_assertions) {
+            url.check_invariants().map_err(|reason| {
+                let reason: &str = &reason;
+                Error::invalid_value(Unexpected::Other("value"), &reason)
+            })?
+        }
+        Ok(url)
+    }
+
+    /// Assuming the URL is in the `file` scheme or similar,
+    /// convert its path to an absolute `std::path::Path`.
+    ///
+    /// **Note:** This does not actually check the URL’s `scheme`,
+    /// and may give nonsensical results for other schemes.
+    /// It is the user’s responsibility to check the URL’s scheme before calling this.
+    ///
+    /// ```
+    /// # use url::Url;
+    /// # let url = Url::parse("file:///etc/passwd").unwrap();
+    /// let path = url.to_file_path();
+    /// ```
+    ///
+    /// Returns `Err` if the host is neither empty nor `"localhost"` (except on Windows, where
+    /// `file:` URLs may have a non-local host),
+    /// or if `Path::new_opt()` returns `None`.
+    /// (That is, if the percent-decoded path contains a NUL byte or,
+    /// for a Windows path, is not UTF-8.)
+    #[inline]
+    #[cfg(any(unix, windows, target_os = "redox"))]
+    pub fn to_file_path(&self) -> Result<PathBuf, ()> {
+        if let Some(segments) = self.path_segments() {
+            let host = match self.host() {
+                None | Some(Host::Domain("localhost")) => None,
+                Some(_) if cfg!(windows) && self.scheme() == "file" => {
+                    Some(&self.serialization[self.host_start as usize..self.host_end as usize])
+                }
+                _ => return Err(()),
+            };
+
+            return file_url_segments_to_pathbuf(host, segments);
+        }
+        Err(())
+    }
+
+    // Private helper methods:
+
+    #[inline]
+    fn slice<R>(&self, range: R) -> &str
+    where
+        R: RangeArg,
+    {
+        range.slice_of(&self.serialization)
+    }
+
+    #[inline]
+    fn byte_at(&self, i: u32) -> u8 {
+        self.serialization.as_bytes()[i as usize]
+    }
+}
+
+/// Parse a string as an URL, without a base URL or encoding override.
+impl str::FromStr for Url {
+    type Err = ParseError;
+
+    #[inline]
+    fn from_str(input: &str) -> Result<Url, ::ParseError> {
+        Url::parse(input)
+    }
+}
+
+/// Display the serialization of this URL.
+impl fmt::Display for Url {
+    #[inline]
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Display::fmt(&self.serialization, formatter)
+    }
+}
+
+/// Debug the serialization of this URL.
+impl fmt::Debug for Url {
+    #[inline]
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&self.serialization, formatter)
+    }
+}
+
+/// URLs compare like their serialization.
+impl Eq for Url {}
+
+/// URLs compare like their serialization.
+impl PartialEq for Url {
+    #[inline]
+    fn eq(&self, other: &Self) -> bool {
+        self.serialization == other.serialization
+    }
+}
+
+/// URLs compare like their serialization.
+impl Ord for Url {
+    #[inline]
+    fn cmp(&self, other: &Self) -> cmp::Ordering {
+        self.serialization.cmp(&other.serialization)
+    }
+}
+
+/// URLs compare like their serialization.
+impl PartialOrd for Url {
+    #[inline]
+    fn partial_cmp(&self, other: &Self) -> Option<cmp::Ordering> {
+        self.serialization.partial_cmp(&other.serialization)
+    }
+}
+
+/// URLs hash like their serialization.
+impl hash::Hash for Url {
+    #[inline]
+    fn hash<H>(&self, state: &mut H)
+    where
+        H: hash::Hasher,
+    {
+        hash::Hash::hash(&self.serialization, state)
+    }
+}
+
+/// Return the serialization of this URL.
+impl AsRef<str> for Url {
+    #[inline]
+    fn as_ref(&self) -> &str {
+        &self.serialization
+    }
+}
+
+trait RangeArg {
+    fn slice_of<'a>(&self, s: &'a str) -> &'a str;
+}
+
+impl RangeArg for Range<u32> {
+    #[inline]
+    fn slice_of<'a>(&self, s: &'a str) -> &'a str {
+        &s[self.start as usize..self.end as usize]
+    }
+}
+
+impl RangeArg for RangeFrom<u32> {
+    #[inline]
+    fn slice_of<'a>(&self, s: &'a str) -> &'a str {
+        &s[self.start as usize..]
+    }
+}
+
+impl RangeArg for RangeTo<u32> {
+    #[inline]
+    fn slice_of<'a>(&self, s: &'a str) -> &'a str {
+        &s[..self.end as usize]
+    }
+}
+
+/// Serializes this URL into a `serde` stream.
+///
+/// This implementation is only available if the `serde` Cargo feature is enabled.
+#[cfg(feature = "serde")]
+impl serde::Serialize for Url {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+    {
+        serializer.serialize_str(self.as_str())
+    }
+}
+
+/// Deserializes this URL from a `serde` stream.
+///
+/// This implementation is only available if the `serde` Cargo feature is enabled.
+#[cfg(feature = "serde")]
+impl<'de> serde::Deserialize<'de> for Url {
+    fn deserialize<D>(deserializer: D) -> Result<Url, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        use serde::de::{Error, Unexpected, Visitor};
+
+        struct UrlVisitor;
+
+        impl<'de> Visitor<'de> for UrlVisitor {
+            type Value = Url;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str("a string representing an URL")
+            }
+
+            fn visit_str<E>(self, s: &str) -> Result<Self::Value, E>
+            where
+                E: Error,
+            {
+                Url::parse(s)
+                    .map_err(|err| Error::invalid_value(Unexpected::Str(s), &err.description()))
+            }
+        }
+
+        deserializer.deserialize_str(UrlVisitor)
+    }
+}
+
+#[cfg(any(unix, target_os = "redox"))]
+fn path_to_file_url_segments(
+    path: &Path,
+    serialization: &mut String,
+) -> Result<(u32, HostInternal), ()> {
+    use std::os::unix::prelude::OsStrExt;
+    if !path.is_absolute() {
+        return Err(());
+    }
+    let host_end = to_u32(serialization.len()).unwrap();
+    let mut empty = true;
+    // skip the root component
+    for component in path.components().skip(1) {
+        empty = false;
+        serialization.push('/');
+        serialization.extend(percent_encode(
+            component.as_os_str().as_bytes(),
+            PATH_SEGMENT,
+        ));
+    }
+    if empty {
+        // An URL’s path must not be empty.
+        serialization.push('/');
+    }
+    Ok((host_end, HostInternal::None))
+}
+
+#[cfg(windows)]
+fn path_to_file_url_segments(
+    path: &Path,
+    serialization: &mut String,
+) -> Result<(u32, HostInternal), ()> {
+    path_to_file_url_segments_windows(path, serialization)
+}
+
+// Build this unconditionally to alleviate https://github.com/servo/rust-url/issues/102
+#[cfg_attr(not(windows), allow(dead_code))]
+fn path_to_file_url_segments_windows(
+    path: &Path,
+    serialization: &mut String,
+) -> Result<(u32, HostInternal), ()> {
+    use std::path::{Component, Prefix};
+    if !path.is_absolute() {
+        return Err(());
+    }
+    let mut components = path.components();
+
+    let host_end;
+    let host_internal;
+    match components.next() {
+        Some(Component::Prefix(ref p)) => match p.kind() {
+            Prefix::Disk(letter) | Prefix::VerbatimDisk(letter) => {
+                host_end = to_u32(serialization.len()).unwrap();
+                host_internal = HostInternal::None;
+                serialization.push('/');
+                serialization.push(letter as char);
+                serialization.push(':');
+            }
+            Prefix::UNC(server, share) | Prefix::VerbatimUNC(server, share) => {
+                let host = Host::parse(server.to_str().ok_or(())?).map_err(|_| ())?;
+                write!(serialization, "{}", host).unwrap();
+                host_end = to_u32(serialization.len()).unwrap();
+                host_internal = host.into();
+                serialization.push('/');
+                let share = share.to_str().ok_or(())?;
+                serialization.extend(percent_encode(share.as_bytes(), PATH_SEGMENT));
+            }
+            _ => return Err(()),
+        },
+
+        _ => return Err(()),
+    }
+
+    for component in components {
+        if component == Component::RootDir {
+            continue;
+        }
+        // FIXME: somehow work with non-unicode?
+        let component = component.as_os_str().to_str().ok_or(())?;
+        serialization.push('/');
+        serialization.extend(percent_encode(component.as_bytes(), PATH_SEGMENT));
+    }
+    Ok((host_end, host_internal))
+}
+
+#[cfg(any(unix, target_os = "redox"))]
+fn file_url_segments_to_pathbuf(
+    host: Option<&str>,
+    segments: str::Split<char>,
+) -> Result<PathBuf, ()> {
+    use std::ffi::OsStr;
+    use std::os::unix::prelude::OsStrExt;
+
+    if host.is_some() {
+        return Err(());
+    }
+
+    let mut bytes = if cfg!(target_os = "redox") {
+        b"file:".to_vec()
+    } else {
+        Vec::new()
+    };
+    for segment in segments {
+        bytes.push(b'/');
+        bytes.extend(percent_decode(segment.as_bytes()));
+    }
+    let os_str = OsStr::from_bytes(&bytes);
+    let path = PathBuf::from(os_str);
+    debug_assert!(
+        path.is_absolute(),
+        "to_file_path() failed to produce an absolute Path"
+    );
+    Ok(path)
+}
+
+#[cfg(windows)]
+fn file_url_segments_to_pathbuf(
+    host: Option<&str>,
+    segments: str::Split<char>,
+) -> Result<PathBuf, ()> {
+    file_url_segments_to_pathbuf_windows(host, segments)
+}
+
+// Build this unconditionally to alleviate https://github.com/servo/rust-url/issues/102
+#[cfg_attr(not(windows), allow(dead_code))]
+fn file_url_segments_to_pathbuf_windows(
+    host: Option<&str>,
+    mut segments: str::Split<char>,
+) -> Result<PathBuf, ()> {
+    let mut string = if let Some(host) = host {
+        r"\\".to_owned() + host
+    } else {
+        let first = segments.next().ok_or(())?;
+
+        match first.len() {
+            2 => {
+                if !first.starts_with(parser::ascii_alpha) || first.as_bytes()[1] != b':' {
+                    return Err(());
+                }
+
+                first.to_owned()
+            }
+
+            4 => {
+                if !first.starts_with(parser::ascii_alpha) {
+                    return Err(());
+                }
+                let bytes = first.as_bytes();
+                if bytes[1] != b'%' || bytes[2] != b'3' || (bytes[3] != b'a' && bytes[3] != b'A') {
+                    return Err(());
+                }
+
+                first[0..1].to_owned() + ":"
+            }
+
+            _ => return Err(()),
+        }
+    };
+
+    for segment in segments {
+        string.push('\\');
+
+        // Currently non-unicode windows paths cannot be represented
+        match String::from_utf8(percent_decode(segment.as_bytes()).collect()) {
+            Ok(s) => string.push_str(&s),
+            Err(..) => return Err(()),
+        }
+    }
+    let path = PathBuf::from(string);
+    debug_assert!(
+        path.is_absolute(),
+        "to_file_path() failed to produce an absolute Path"
+    );
+    Ok(path)
+}
+
+/// Implementation detail of `Url::query_pairs_mut`. Typically not used directly.
+#[derive(Debug)]
+pub struct UrlQuery<'a> {
+    url: Option<&'a mut Url>,
+    fragment: Option<String>,
+}
+
+impl<'a> Drop for UrlQuery<'a> {
+    fn drop(&mut self) {
+        if let Some(url) = self.url.take() {
+            url.restore_already_parsed_fragment(self.fragment.take())
+        }
+    }
+}
diff --git a/third_party/rust/url/src/origin.rs b/third_party/rust/url/src/origin.rs
new file mode 100644
index 0000000000..3223709dde
--- /dev/null
+++ b/third_party/rust/url/src/origin.rs
@@ -0,0 +1,113 @@
+// Copyright 2016 The rust-url developers.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use host::Host;
+use idna::domain_to_unicode;
+use parser::default_port;
+use std::sync::atomic::{AtomicUsize, Ordering};
+use Url;
+
+pub fn url_origin(url: &Url) -> Origin {
+    let scheme = url.scheme();
+    match scheme {
+        "blob" => {
+            let result = Url::parse(url.path());
+            match result {
+                Ok(ref url) => url_origin(url),
+                Err(_) => Origin::new_opaque(),
+            }
+        }
+        "ftp" | "gopher" | "http" | "https" | "ws" | "wss" => Origin::Tuple(
+            scheme.to_owned(),
+            url.host().unwrap().to_owned(),
+            url.port_or_known_default().unwrap(),
+        ),
+        // TODO: Figure out what to do if the scheme is a file
+        "file" => Origin::new_opaque(),
+        _ => Origin::new_opaque(),
+    }
+}
+
+/// The origin of an URL
+///
+/// Two URLs with the same origin are considered
+/// to originate from the same entity and can therefore trust
+/// each other.
+///
+/// The origin is determined based on the scheme as follows:
+///
+/// - If the scheme is "blob" the origin is the origin of the
+///   URL contained in the path component. If parsing fails,
+///   it is an opaque origin.
+/// - If the scheme is "ftp", "gopher", "http", "https", "ws", or "wss",
+///   then the origin is a tuple of the scheme, host, and port.
+/// - If the scheme is anything else, the origin is opaque, meaning
+///   the URL does not have the same origin as any other URL.
+///
+/// For more information see <https://url.spec.whatwg.org/#origin>
+#[derive(PartialEq, Eq, Hash, Clone, Debug)]
+pub enum Origin {
+    /// A globally unique identifier
+    Opaque(OpaqueOrigin),
+
+    /// Consists of the URL's scheme, host and port
+    Tuple(String, Host<String>, u16),
+}
+
+impl Origin {
+    /// Creates a new opaque origin that is only equal to itself.
+    pub fn new_opaque() -> Origin {
+        static COUNTER: AtomicUsize = AtomicUsize::new(0);
+        Origin::Opaque(OpaqueOrigin(COUNTER.fetch_add(1, Ordering::SeqCst)))
+    }
+
+    /// Return whether this origin is a (scheme, host, port) tuple
+    /// (as opposed to an opaque origin).
+    pub fn is_tuple(&self) -> bool {
+        matches!(*self, Origin::Tuple(..))
+    }
+
+    /// <https://html.spec.whatwg.org/multipage/#ascii-serialisation-of-an-origin>
+    pub fn ascii_serialization(&self) -> String {
+        match *self {
+            Origin::Opaque(_) => "null".to_owned(),
+            Origin::Tuple(ref scheme, ref host, port) => {
+                if default_port(scheme) == Some(port) {
+                    format!("{}://{}", scheme, host)
+                } else {
+                    format!("{}://{}:{}", scheme, host, port)
+                }
+            }
+        }
+    }
+
+    /// <https://html.spec.whatwg.org/multipage/#unicode-serialisation-of-an-origin>
+    pub fn unicode_serialization(&self) -> String {
+        match *self {
+            Origin::Opaque(_) => "null".to_owned(),
+            Origin::Tuple(ref scheme, ref host, port) => {
+                let host = match *host {
+                    Host::Domain(ref domain) => {
+                        let (domain, _errors) = domain_to_unicode(domain);
+                        Host::Domain(domain)
+                    }
+                    _ => host.clone(),
+                };
+                if default_port(scheme) == Some(port) {
+                    format!("{}://{}", scheme, host)
+                } else {
+                    format!("{}://{}:{}", scheme, host, port)
+                }
+            }
+        }
+    }
+}
+
+/// Opaque identifier for URLs that have file or other schemes
+#[derive(Eq, PartialEq, Hash, Clone, Debug)]
+pub struct OpaqueOrigin(usize);
diff --git a/third_party/rust/url/src/parser.rs b/third_party/rust/url/src/parser.rs
new file mode 100644
index 0000000000..e2ea36bfab
--- /dev/null
+++ b/third_party/rust/url/src/parser.rs
@@ -0,0 +1,1426 @@
+// Copyright 2013-2016 The rust-url developers.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::error::Error;
+use std::fmt::{self, Formatter, Write};
+use std::str;
+
+use host::{Host, HostInternal};
+use percent_encoding::{percent_encode, utf8_percent_encode, AsciiSet, CONTROLS};
+use query_encoding::EncodingOverride;
+use Url;
+
+/// https://url.spec.whatwg.org/#fragment-percent-encode-set
+const FRAGMENT: &AsciiSet = &CONTROLS.add(b' ').add(b'"').add(b'<').add(b'>').add(b'`');
+
+/// https://url.spec.whatwg.org/#path-percent-encode-set
+const PATH: &AsciiSet = &FRAGMENT.add(b'#').add(b'?').add(b'{').add(b'}');
+
+/// https://url.spec.whatwg.org/#userinfo-percent-encode-set
+pub(crate) const USERINFO: &AsciiSet = &PATH
+    .add(b'/')
+    .add(b':')
+    .add(b';')
+    .add(b'=')
+    .add(b'@')
+    .add(b'[')
+    .add(b'\\')
+    .add(b']')
+    .add(b'^')
+    .add(b'|');
+
+pub(crate) const PATH_SEGMENT: &AsciiSet = &PATH.add(b'/').add(b'%');
+
+// The backslash (\) character is treated as a path separator in special URLs
+// so it needs to be additionally escaped in that case.
+pub(crate) const SPECIAL_PATH_SEGMENT: &AsciiSet = &PATH_SEGMENT.add(b'\\');
+
+// https://url.spec.whatwg.org/#query-state
+const QUERY: &AsciiSet = &CONTROLS.add(b' ').add(b'"').add(b'#').add(b'<').add(b'>');
+const SPECIAL_QUERY: &AsciiSet = &QUERY.add(b'\'');
+
+pub type ParseResult<T> = Result<T, ParseError>;
+
+macro_rules! simple_enum_error {
+    ($($name: ident => $description: expr,)+) => {
+        /// Errors that can occur during parsing.
+        ///
+        /// This may be extended in the future so exhaustive matching is
+        /// discouraged with an unused variant.
+        #[derive(PartialEq, Eq, Clone, Copy, Debug)]
+        pub enum ParseError {
+            $(
+                $name,
+            )+
+            /// Unused variant enable non-exhaustive matching
+            #[doc(hidden)]
+            __FutureProof,
+        }
+
+        impl Error for ParseError {
+            fn description(&self) -> &str {
+                match *self {
+                    $(
+                        ParseError::$name => $description,
+                    )+
+                    ParseError::__FutureProof => {
+                        unreachable!("Don't abuse the FutureProof!");
+                    }
+                }
+            }
+        }
+    }
+}
+
+simple_enum_error! {
+    EmptyHost => "empty host",
+    IdnaError => "invalid international domain name",
+    InvalidPort => "invalid port number",
+    InvalidIpv4Address => "invalid IPv4 address",
+    InvalidIpv6Address => "invalid IPv6 address",
+    InvalidDomainCharacter => "invalid domain character",
+    RelativeUrlWithoutBase => "relative URL without a base",
+    RelativeUrlWithCannotBeABaseBase => "relative URL with a cannot-be-a-base base",
+    SetHostOnCannotBeABaseUrl => "a cannot-be-a-base URL doesn’t have a host to set",
+    Overflow => "URLs more than 4 GB are not supported",
+}
+
+impl fmt::Display for ParseError {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        fmt::Display::fmt(self.description(), f)
+    }
+}
+
+impl From<::idna::Errors> for ParseError {
+    fn from(_: ::idna::Errors) -> ParseError {
+        ParseError::IdnaError
+    }
+}
+
+macro_rules! syntax_violation_enum {
+    ($($name: ident => $description: expr,)+) => {
+        /// Non-fatal syntax violations that can occur during parsing.
+        ///
+        /// This may be extended in the future so exhaustive matching is
+        /// discouraged with an unused variant.
+        #[derive(PartialEq, Eq, Clone, Copy, Debug)]
+        pub enum SyntaxViolation {
+            $(
+                $name,
+            )+
+            /// Unused variant enable non-exhaustive matching
+            #[doc(hidden)]
+            __FutureProof,
+        }
+
+        impl SyntaxViolation {
+            pub fn description(&self) -> &'static str {
+                match *self {
+                    $(
+                        SyntaxViolation::$name => $description,
+                    )+
+                    SyntaxViolation::__FutureProof => {
+                        unreachable!("Don't abuse the FutureProof!");
+                    }
+                }
+            }
+        }
+    }
+}
+
+syntax_violation_enum! {
+    Backslash => "backslash",
+    C0SpaceIgnored =>
+        "leading or trailing control or space character are ignored in URLs",
+    EmbeddedCredentials =>
+        "embedding authentication information (username or password) \
+         in an URL is not recommended",
+    ExpectedDoubleSlash => "expected //",
+    ExpectedFileDoubleSlash => "expected // after file:",
+    FileWithHostAndWindowsDrive => "file: with host and Windows drive letter",
+    NonUrlCodePoint => "non-URL code point",
+    NullInFragment => "NULL characters are ignored in URL fragment identifiers",
+    PercentDecode => "expected 2 hex digits after %",
+    TabOrNewlineIgnored => "tabs or newlines are ignored in URLs",
+    UnencodedAtSign => "unencoded @ sign in username or password",
+}
+
+impl fmt::Display for SyntaxViolation {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        fmt::Display::fmt(self.description(), f)
+    }
+}
+
+#[derive(Copy, Clone)]
+pub enum SchemeType {
+    File,
+    SpecialNotFile,
+    NotSpecial,
+}
+
+impl SchemeType {
+    pub fn is_special(&self) -> bool {
+        !matches!(*self, SchemeType::NotSpecial)
+    }
+
+    pub fn is_file(&self) -> bool {
+        matches!(*self, SchemeType::File)
+    }
+
+    pub fn from(s: &str) -> Self {
+        match s {
+            "http" | "https" | "ws" | "wss" | "ftp" | "gopher" => SchemeType::SpecialNotFile,
+            "file" => SchemeType::File,
+            _ => SchemeType::NotSpecial,
+        }
+    }
+}
+
+pub fn default_port(scheme: &str) -> Option<u16> {
+    match scheme {
+        "http" | "ws" => Some(80),
+        "https" | "wss" => Some(443),
+        "ftp" => Some(21),
+        "gopher" => Some(70),
+        _ => None,
+    }
+}
+
+#[derive(Clone)]
+pub struct Input<'i> {
+    chars: str::Chars<'i>,
+}
+
+impl<'i> Input<'i> {
+    pub fn new(input: &'i str) -> Self {
+        Input::with_log(input, None)
+    }
+
+    pub fn with_log(original_input: &'i str, vfn: Option<&dyn Fn(SyntaxViolation)>) -> Self {
+        let input = original_input.trim_matches(c0_control_or_space);
+        if let Some(vfn) = vfn {
+            if input.len() < original_input.len() {
+                vfn(SyntaxViolation::C0SpaceIgnored)
+            }
+            if input.chars().any(|c| matches!(c, '\t' | '\n' | '\r')) {
+                vfn(SyntaxViolation::TabOrNewlineIgnored)
+            }
+        }
+        Input {
+            chars: input.chars(),
+        }
+    }
+
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.clone().next().is_none()
+    }
+
+    #[inline]
+    fn starts_with<P: Pattern>(&self, p: P) -> bool {
+        p.split_prefix(&mut self.clone())
+    }
+
+    #[inline]
+    pub fn split_prefix<P: Pattern>(&self, p: P) -> Option<Self> {
+        let mut remaining = self.clone();
+        if p.split_prefix(&mut remaining) {
+            Some(remaining)
+        } else {
+            None
+        }
+    }
+
+    #[inline]
+    fn split_first(&self) -> (Option<char>, Self) {
+        let mut remaining = self.clone();
+        (remaining.next(), remaining)
+    }
+
+    #[inline]
+    fn count_matching<F: Fn(char) -> bool>(&self, f: F) -> (u32, Self) {
+        let mut count = 0;
+        let mut remaining = self.clone();
+        loop {
+            let mut input = remaining.clone();
+            if matches!(input.next(), Some(c) if f(c)) {
+                remaining = input;
+                count += 1;
+            } else {
+                return (count, remaining);
+            }
+        }
+    }
+
+    #[inline]
+    fn next_utf8(&mut self) -> Option<(char, &'i str)> {
+        loop {
+            let utf8 = self.chars.as_str();
+            match self.chars.next() {
+                Some(c) => {
+                    if !matches!(c, '\t' | '\n' | '\r') {
+                        return Some((c, &utf8[..c.len_utf8()]));
+                    }
+                }
+                None => return None,
+            }
+        }
+    }
+}
+
+pub trait Pattern {
+    fn split_prefix<'i>(self, input: &mut Input<'i>) -> bool;
+}
+
+impl Pattern for char {
+    fn split_prefix<'i>(self, input: &mut Input<'i>) -> bool {
+        input.next() == Some(self)
+    }
+}
+
+impl<'a> Pattern for &'a str {
+    fn split_prefix<'i>(self, input: &mut Input<'i>) -> bool {
+        for c in self.chars() {
+            if input.next() != Some(c) {
+                return false;
+            }
+        }
+        true
+    }
+}
+
+impl<F: FnMut(char) -> bool> Pattern for F {
+    fn split_prefix<'i>(self, input: &mut Input<'i>) -> bool {
+        input.next().map_or(false, self)
+    }
+}
+
+impl<'i> Iterator for Input<'i> {
+    type Item = char;
+    fn next(&mut self) -> Option<char> {
+        self.chars
+            .by_ref()
+            .find(|&c| !matches!(c, '\t' | '\n' | '\r'))
+    }
+}
+
+pub struct Parser<'a> {
+    pub serialization: String,
+    pub base_url: Option<&'a Url>,
+    pub query_encoding_override: EncodingOverride<'a>,
+    pub violation_fn: Option<&'a dyn Fn(SyntaxViolation)>,
+    pub context: Context,
+}
+
+#[derive(PartialEq, Eq, Copy, Clone)]
+pub enum Context {
+    UrlParser,
+    Setter,
+    PathSegmentSetter,
+}
+
+impl<'a> Parser<'a> {
+    fn log_violation(&self, v: SyntaxViolation) {
+        if let Some(f) = self.violation_fn {
+            f(v)
+        }
+    }
+
+    fn log_violation_if(&self, v: SyntaxViolation, test: impl FnOnce() -> bool) {
+        if let Some(f) = self.violation_fn {
+            if test() {
+                f(v)
+            }
+        }
+    }
+
+    pub fn for_setter(serialization: String) -> Parser<'a> {
+        Parser {
+            serialization,
+            base_url: None,
+            query_encoding_override: None,
+            violation_fn: None,
+            context: Context::Setter,
+        }
+    }
+
+    /// https://url.spec.whatwg.org/#concept-basic-url-parser
+    pub fn parse_url(mut self, input: &str) -> ParseResult<Url> {
+        let input = Input::with_log(input, self.violation_fn);
+        if let Ok(remaining) = self.parse_scheme(input.clone()) {
+            return self.parse_with_scheme(remaining);
+        }
+
+        // No-scheme state
+        if let Some(base_url) = self.base_url {
+            if input.starts_with('#') {
+                self.fragment_only(base_url, input)
+            } else if base_url.cannot_be_a_base() {
+                Err(ParseError::RelativeUrlWithCannotBeABaseBase)
+            } else {
+                let scheme_type = SchemeType::from(base_url.scheme());
+                if scheme_type.is_file() {
+                    self.parse_file(input, scheme_type, Some(base_url))
+                } else {
+                    self.parse_relative(input, scheme_type, base_url)
+                }
+            }
+        } else {
+            Err(ParseError::RelativeUrlWithoutBase)
+        }
+    }
+
+    pub fn parse_scheme<'i>(&mut self, mut input: Input<'i>) -> Result<Input<'i>, ()> {
+        if input.is_empty() || !input.starts_with(ascii_alpha) {
+            return Err(());
+        }
+        debug_assert!(self.serialization.is_empty());
+        while let Some(c) = input.next() {
+            match c {
+                'a'..='z' | 'A'..='Z' | '0'..='9' | '+' | '-' | '.' => {
+                    self.serialization.push(c.to_ascii_lowercase())
+                }
+                ':' => return Ok(input),
+                _ => {
+                    self.serialization.clear();
+                    return Err(());
+                }
+            }
+        }
+        // EOF before ':'
+        if self.context == Context::Setter {
+            Ok(input)
+        } else {
+            self.serialization.clear();
+            Err(())
+        }
+    }
+
+    fn parse_with_scheme(mut self, input: Input) -> ParseResult<Url> {
+        use SyntaxViolation::{ExpectedDoubleSlash, ExpectedFileDoubleSlash};
+        let scheme_end = to_u32(self.serialization.len())?;
+        let scheme_type = SchemeType::from(&self.serialization);
+        self.serialization.push(':');
+        match scheme_type {
+            SchemeType::File => {
+                self.log_violation_if(ExpectedFileDoubleSlash, || !input.starts_with("//"));
+                let base_file_url = self.base_url.and_then(|base| {
+                    if base.scheme() == "file" {
+                        Some(base)
+                    } else {
+                        None
+                    }
+                });
+                self.serialization.clear();
+                self.parse_file(input, scheme_type, base_file_url)
+            }
+            SchemeType::SpecialNotFile => {
+                // special relative or authority state
+                let (slashes_count, remaining) = input.count_matching(|c| matches!(c, '/' | '\\'));
+                if let Some(base_url) = self.base_url {
+                    if slashes_count < 2
+                        && base_url.scheme() == &self.serialization[..scheme_end as usize]
+                    {
+                        // "Cannot-be-a-base" URLs only happen with "not special" schemes.
+                        debug_assert!(!base_url.cannot_be_a_base());
+                        self.serialization.clear();
+                        return self.parse_relative(input, scheme_type, base_url);
+                    }
+                }
+                // special authority slashes state
+                self.log_violation_if(ExpectedDoubleSlash, || {
+                    input
+                        .clone()
+                        .take_while(|&c| matches!(c, '/' | '\\'))
+                        .collect::<String>()
+                        != "//"
+                });
+                self.after_double_slash(remaining, scheme_type, scheme_end)
+            }
+            SchemeType::NotSpecial => self.parse_non_special(input, scheme_type, scheme_end),
+        }
+    }
+
+    /// Scheme other than file, http, https, ws, ws, ftp, gopher.
+    fn parse_non_special(
+        mut self,
+        input: Input,
+        scheme_type: SchemeType,
+        scheme_end: u32,
+    ) -> ParseResult<Url> {
+        // path or authority state (
+        if let Some(input) = input.split_prefix("//") {
+            return self.after_double_slash(input, scheme_type, scheme_end);
+        }
+        // Anarchist URL (no authority)
+        let path_start = to_u32(self.serialization.len())?;
+        let username_end = path_start;
+        let host_start = path_start;
+        let host_end = path_start;
+        let host = HostInternal::None;
+        let port = None;
+        let remaining = if let Some(input) = input.split_prefix('/') {
+            let path_start = self.serialization.len();
+            self.serialization.push('/');
+            self.parse_path(scheme_type, &mut false, path_start, input)
+        } else {
+            self.parse_cannot_be_a_base_path(input)
+        };
+        self.with_query_and_fragment(
+            scheme_type,
+            scheme_end,
+            username_end,
+            host_start,
+            host_end,
+            host,
+            port,
+            path_start,
+            remaining,
+        )
+    }
+
+    fn parse_file(
+        mut self,
+        input: Input,
+        scheme_type: SchemeType,
+        mut base_file_url: Option<&Url>,
+    ) -> ParseResult<Url> {
+        use SyntaxViolation::Backslash;
+        // file state
+        debug_assert!(self.serialization.is_empty());
+        let (first_char, input_after_first_char) = input.split_first();
+        match first_char {
+            None => {
+                if let Some(base_url) = base_file_url {
+                    // Copy everything except the fragment
+                    let before_fragment = match base_url.fragment_start {
+                        Some(i) => &base_url.serialization[..i as usize],
+                        None => &*base_url.serialization,
+                    };
+                    self.serialization.push_str(before_fragment);
+                    Ok(Url {
+                        serialization: self.serialization,
+                        fragment_start: None,
+                        ..*base_url
+                    })
+                } else {
+                    self.serialization.push_str("file:///");
+                    let scheme_end = "file".len() as u32;
+                    let path_start = "file://".len() as u32;
+                    Ok(Url {
+                        serialization: self.serialization,
+                        scheme_end,
+                        username_end: path_start,
+                        host_start: path_start,
+                        host_end: path_start,
+                        host: HostInternal::None,
+                        port: None,
+                        path_start,
+                        query_start: None,
+                        fragment_start: None,
+                    })
+                }
+            }
+            Some('?') => {
+                if let Some(base_url) = base_file_url {
+                    // Copy everything up to the query string
+                    let before_query = match (base_url.query_start, base_url.fragment_start) {
+                        (None, None) => &*base_url.serialization,
+                        (Some(i), _) | (None, Some(i)) => base_url.slice(..i),
+                    };
+                    self.serialization.push_str(before_query);
+                    let (query_start, fragment_start) =
+                        self.parse_query_and_fragment(scheme_type, base_url.scheme_end, input)?;
+                    Ok(Url {
+                        serialization: self.serialization,
+                        query_start,
+                        fragment_start,
+                        ..*base_url
+                    })
+                } else {
+                    self.serialization.push_str("file:///");
+                    let scheme_end = "file".len() as u32;
+                    let path_start = "file://".len() as u32;
+                    let (query_start, fragment_start) =
+                        self.parse_query_and_fragment(scheme_type, scheme_end, input)?;
+                    Ok(Url {
+                        serialization: self.serialization,
+                        scheme_end,
+                        username_end: path_start,
+                        host_start: path_start,
+                        host_end: path_start,
+                        host: HostInternal::None,
+                        port: None,
+                        path_start,
+                        query_start,
+                        fragment_start,
+                    })
+                }
+            }
+            Some('#') => {
+                if let Some(base_url) = base_file_url {
+                    self.fragment_only(base_url, input)
+                } else {
+                    self.serialization.push_str("file:///");
+                    let scheme_end = "file".len() as u32;
+                    let path_start = "file://".len() as u32;
+                    let fragment_start = "file:///".len() as u32;
+                    self.serialization.push('#');
+                    self.parse_fragment(input_after_first_char);
+                    Ok(Url {
+                        serialization: self.serialization,
+                        scheme_end,
+                        username_end: path_start,
+                        host_start: path_start,
+                        host_end: path_start,
+                        host: HostInternal::None,
+                        port: None,
+                        path_start,
+                        query_start: None,
+                        fragment_start: Some(fragment_start),
+                    })
+                }
+            }
+            Some('/') | Some('\\') => {
+                self.log_violation_if(Backslash, || first_char == Some('\\'));
+                // file slash state
+                let (next_char, input_after_next_char) = input_after_first_char.split_first();
+                self.log_violation_if(Backslash, || next_char == Some('\\'));
+                if matches!(next_char, Some('/') | Some('\\')) {
+                    // file host state
+                    self.serialization.push_str("file://");
+                    let scheme_end = "file".len() as u32;
+                    let host_start = "file://".len() as u32;
+                    let (path_start, mut host, remaining) =
+                        self.parse_file_host(input_after_next_char)?;
+                    let mut host_end = to_u32(self.serialization.len())?;
+                    let mut has_host = !matches!(host, HostInternal::None);
+                    let remaining = if path_start {
+                        self.parse_path_start(SchemeType::File, &mut has_host, remaining)
+                    } else {
+                        let path_start = self.serialization.len();
+                        self.serialization.push('/');
+                        self.parse_path(SchemeType::File, &mut has_host, path_start, remaining)
+                    };
+                    // For file URLs that have a host and whose path starts
+                    // with the windows drive letter we just remove the host.
+                    if !has_host {
+                        self.serialization
+                            .drain(host_start as usize..host_end as usize);
+                        host_end = host_start;
+                        host = HostInternal::None;
+                    }
+                    let (query_start, fragment_start) =
+                        self.parse_query_and_fragment(scheme_type, scheme_end, remaining)?;
+                    Ok(Url {
+                        serialization: self.serialization,
+                        scheme_end,
+                        username_end: host_start,
+                        host_start,
+                        host_end,
+                        host,
+                        port: None,
+                        path_start: host_end,
+                        query_start,
+                        fragment_start,
+                    })
+                } else {
+                    self.serialization.push_str("file:///");
+                    let scheme_end = "file".len() as u32;
+                    let path_start = "file://".len();
+                    if let Some(base_url) = base_file_url {
+                        let first_segment = base_url.path_segments().unwrap().next().unwrap();
+                        // FIXME: *normalized* drive letter
+                        if is_windows_drive_letter(first_segment) {
+                            self.serialization.push_str(first_segment);
+                            self.serialization.push('/');
+                        }
+                    }
+                    let remaining = self.parse_path(
+                        SchemeType::File,
+                        &mut false,
+                        path_start,
+                        input_after_first_char,
+                    );
+                    let (query_start, fragment_start) =
+                        self.parse_query_and_fragment(scheme_type, scheme_end, remaining)?;
+                    let path_start = path_start as u32;
+                    Ok(Url {
+                        serialization: self.serialization,
+                        scheme_end,
+                        username_end: path_start,
+                        host_start: path_start,
+                        host_end: path_start,
+                        host: HostInternal::None,
+                        port: None,
+                        path_start,
+                        query_start,
+                        fragment_start,
+                    })
+                }
+            }
+            _ => {
+                if starts_with_windows_drive_letter_segment(&input) {
+                    base_file_url = None;
+                }
+                if let Some(base_url) = base_file_url {
+                    let before_query = match (base_url.query_start, base_url.fragment_start) {
+                        (None, None) => &*base_url.serialization,
+                        (Some(i), _) | (None, Some(i)) => base_url.slice(..i),
+                    };
+                    self.serialization.push_str(before_query);
+                    self.pop_path(SchemeType::File, base_url.path_start as usize);
+                    let remaining = self.parse_path(
+                        SchemeType::File,
+                        &mut true,
+                        base_url.path_start as usize,
+                        input,
+                    );
+                    self.with_query_and_fragment(
+                        SchemeType::File,
+                        base_url.scheme_end,
+                        base_url.username_end,
+                        base_url.host_start,
+                        base_url.host_end,
+                        base_url.host,
+                        base_url.port,
+                        base_url.path_start,
+                        remaining,
+                    )
+                } else {
+                    self.serialization.push_str("file:///");
+                    let scheme_end = "file".len() as u32;
+                    let path_start = "file://".len();
+                    let remaining =
+                        self.parse_path(SchemeType::File, &mut false, path_start, input);
+                    let (query_start, fragment_start) =
+                        self.parse_query_and_fragment(SchemeType::File, scheme_end, remaining)?;
+                    let path_start = path_start as u32;
+                    Ok(Url {
+                        serialization: self.serialization,
+                        scheme_end,
+                        username_end: path_start,
+                        host_start: path_start,
+                        host_end: path_start,
+                        host: HostInternal::None,
+                        port: None,
+                        path_start,
+                        query_start,
+                        fragment_start,
+                    })
+                }
+            }
+        }
+    }
+
+    fn parse_relative(
+        mut self,
+        input: Input,
+        scheme_type: SchemeType,
+        base_url: &Url,
+    ) -> ParseResult<Url> {
+        // relative state
+        debug_assert!(self.serialization.is_empty());
+        let (first_char, input_after_first_char) = input.split_first();
+        match first_char {
+            None => {
+                // Copy everything except the fragment
+                let before_fragment = match base_url.fragment_start {
+                    Some(i) => &base_url.serialization[..i as usize],
+                    None => &*base_url.serialization,
+                };
+                self.serialization.push_str(before_fragment);
+                Ok(Url {
+                    serialization: self.serialization,
+                    fragment_start: None,
+                    ..*base_url
+                })
+            }
+            Some('?') => {
+                // Copy everything up to the query string
+                let before_query = match (base_url.query_start, base_url.fragment_start) {
+                    (None, None) => &*base_url.serialization,
+                    (Some(i), _) | (None, Some(i)) => base_url.slice(..i),
+                };
+                self.serialization.push_str(before_query);
+                let (query_start, fragment_start) =
+                    self.parse_query_and_fragment(scheme_type, base_url.scheme_end, input)?;
+                Ok(Url {
+                    serialization: self.serialization,
+                    query_start,
+                    fragment_start,
+                    ..*base_url
+                })
+            }
+            Some('#') => self.fragment_only(base_url, input),
+            Some('/') | Some('\\') => {
+                let (slashes_count, remaining) = input.count_matching(|c| matches!(c, '/' | '\\'));
+                if slashes_count >= 2 {
+                    self.log_violation_if(SyntaxViolation::ExpectedDoubleSlash, || {
+                        input
+                            .clone()
+                            .take_while(|&c| matches!(c, '/' | '\\'))
+                            .collect::<String>()
+                            != "//"
+                    });
+                    let scheme_end = base_url.scheme_end;
+                    debug_assert!(base_url.byte_at(scheme_end) == b':');
+                    self.serialization
+                        .push_str(base_url.slice(..scheme_end + 1));
+                    return self.after_double_slash(remaining, scheme_type, scheme_end);
+                }
+                let path_start = base_url.path_start;
+                debug_assert!(base_url.byte_at(path_start) == b'/');
+                self.serialization
+                    .push_str(base_url.slice(..path_start + 1));
+                let remaining = self.parse_path(
+                    scheme_type,
+                    &mut true,
+                    path_start as usize,
+                    input_after_first_char,
+                );
+                self.with_query_and_fragment(
+                    scheme_type,
+                    base_url.scheme_end,
+                    base_url.username_end,
+                    base_url.host_start,
+                    base_url.host_end,
+                    base_url.host,
+                    base_url.port,
+                    base_url.path_start,
+                    remaining,
+                )
+            }
+            _ => {
+                let before_query = match (base_url.query_start, base_url.fragment_start) {
+                    (None, None) => &*base_url.serialization,
+                    (Some(i), _) | (None, Some(i)) => base_url.slice(..i),
+                };
+                self.serialization.push_str(before_query);
+                // FIXME spec says just "remove last entry", not the "pop" algorithm
+                self.pop_path(scheme_type, base_url.path_start as usize);
+                let remaining =
+                    self.parse_path(scheme_type, &mut true, base_url.path_start as usize, input);
+                self.with_query_and_fragment(
+                    scheme_type,
+                    base_url.scheme_end,
+                    base_url.username_end,
+                    base_url.host_start,
+                    base_url.host_end,
+                    base_url.host,
+                    base_url.port,
+                    base_url.path_start,
+                    remaining,
+                )
+            }
+        }
+    }
+
+    fn after_double_slash(
+        mut self,
+        input: Input,
+        scheme_type: SchemeType,
+        scheme_end: u32,
+    ) -> ParseResult<Url> {
+        self.serialization.push('/');
+        self.serialization.push('/');
+        // authority state
+        let (username_end, remaining) = self.parse_userinfo(input, scheme_type)?;
+        // host state
+        let host_start = to_u32(self.serialization.len())?;
+        let (host_end, host, port, remaining) =
+            self.parse_host_and_port(remaining, scheme_end, scheme_type)?;
+        // path state
+        let path_start = to_u32(self.serialization.len())?;
+        let remaining = self.parse_path_start(scheme_type, &mut true, remaining);
+        self.with_query_and_fragment(
+            scheme_type,
+            scheme_end,
+            username_end,
+            host_start,
+            host_end,
+            host,
+            port,
+            path_start,
+            remaining,
+        )
+    }
+
+    /// Return (username_end, remaining)
+    fn parse_userinfo<'i>(
+        &mut self,
+        mut input: Input<'i>,
+        scheme_type: SchemeType,
+    ) -> ParseResult<(u32, Input<'i>)> {
+        let mut last_at = None;
+        let mut remaining = input.clone();
+        let mut char_count = 0;
+        while let Some(c) = remaining.next() {
+            match c {
+                '@' => {
+                    if last_at.is_some() {
+                        self.log_violation(SyntaxViolation::UnencodedAtSign)
+                    } else {
+                        self.log_violation(SyntaxViolation::EmbeddedCredentials)
+                    }
+                    last_at = Some((char_count, remaining.clone()))
+                }
+                '/' | '?' | '#' => break,
+                '\\' if scheme_type.is_special() => break,
+                _ => (),
+            }
+            char_count += 1;
+        }
+        let (mut userinfo_char_count, remaining) = match last_at {
+            None => return Ok((to_u32(self.serialization.len())?, input)),
+            Some((0, remaining)) => return Ok((to_u32(self.serialization.len())?, remaining)),
+            Some(x) => x,
+        };
+
+        let mut username_end = None;
+        let mut has_password = false;
+        let mut has_username = false;
+        while userinfo_char_count > 0 {
+            let (c, utf8_c) = input.next_utf8().unwrap();
+            userinfo_char_count -= 1;
+            if c == ':' && username_end.is_none() {
+                // Start parsing password
+                username_end = Some(to_u32(self.serialization.len())?);
+                // We don't add a colon if the password is empty
+                if userinfo_char_count > 0 {
+                    self.serialization.push(':');
+                    has_password = true;
+                }
+            } else {
+                if !has_password {
+                    has_username = true;
+                }
+                self.check_url_code_point(c, &input);
+                self.serialization
+                    .extend(utf8_percent_encode(utf8_c, USERINFO));
+            }
+        }
+        let username_end = match username_end {
+            Some(i) => i,
+            None => to_u32(self.serialization.len())?,
+        };
+        if has_username || has_password {
+            self.serialization.push('@');
+        }
+        Ok((username_end, remaining))
+    }
+
+    fn parse_host_and_port<'i>(
+        &mut self,
+        input: Input<'i>,
+        scheme_end: u32,
+        scheme_type: SchemeType,
+    ) -> ParseResult<(u32, HostInternal, Option<u16>, Input<'i>)> {
+        let (host, remaining) = Parser::parse_host(input, scheme_type)?;
+        write!(&mut self.serialization, "{}", host).unwrap();
+        let host_end = to_u32(self.serialization.len())?;
+        let (port, remaining) = if let Some(remaining) = remaining.split_prefix(':') {
+            let scheme = || default_port(&self.serialization[..scheme_end as usize]);
+            Parser::parse_port(remaining, scheme, self.context)?
+        } else {
+            (None, remaining)
+        };
+        if let Some(port) = port {
+            write!(&mut self.serialization, ":{}", port).unwrap()
+        }
+        Ok((host_end, host.into(), port, remaining))
+    }
+
+    pub fn parse_host(
+        mut input: Input,
+        scheme_type: SchemeType,
+    ) -> ParseResult<(Host<String>, Input)> {
+        // Undo the Input abstraction here to avoid allocating in the common case
+        // where the host part of the input does not contain any tab or newline
+        let input_str = input.chars.as_str();
+        let mut inside_square_brackets = false;
+        let mut has_ignored_chars = false;
+        let mut non_ignored_chars = 0;
+        let mut bytes = 0;
+        for c in input_str.chars() {
+            match c {
+                ':' if !inside_square_brackets => break,
+                '\\' if scheme_type.is_special() => break,
+                '/' | '?' | '#' => break,
+                '\t' | '\n' | '\r' => {
+                    has_ignored_chars = true;
+                }
+                '[' => {
+                    inside_square_brackets = true;
+                    non_ignored_chars += 1
+                }
+                ']' => {
+                    inside_square_brackets = false;
+                    non_ignored_chars += 1
+                }
+                _ => non_ignored_chars += 1,
+            }
+            bytes += c.len_utf8();
+        }
+        let replaced: String;
+        let host_str;
+        {
+            let host_input = input.by_ref().take(non_ignored_chars);
+            if has_ignored_chars {
+                replaced = host_input.collect();
+                host_str = &*replaced
+            } else {
+                for _ in host_input {}
+                host_str = &input_str[..bytes]
+            }
+        }
+        if scheme_type.is_special() && host_str.is_empty() {
+            return Err(ParseError::EmptyHost);
+        }
+        if !scheme_type.is_special() {
+            let host = Host::parse_opaque(host_str)?;
+            return Ok((host, input));
+        }
+        let host = Host::parse(host_str)?;
+        Ok((host, input))
+    }
+
+    pub(crate) fn parse_file_host<'i>(
+        &mut self,
+        input: Input<'i>,
+    ) -> ParseResult<(bool, HostInternal, Input<'i>)> {
+        // Undo the Input abstraction here to avoid allocating in the common case
+        // where the host part of the input does not contain any tab or newline
+        let input_str = input.chars.as_str();
+        let mut has_ignored_chars = false;
+        let mut non_ignored_chars = 0;
+        let mut bytes = 0;
+        for c in input_str.chars() {
+            match c {
+                '/' | '\\' | '?' | '#' => break,
+                '\t' | '\n' | '\r' => has_ignored_chars = true,
+                _ => non_ignored_chars += 1,
+            }
+            bytes += c.len_utf8();
+        }
+        let replaced: String;
+        let host_str;
+        let mut remaining = input.clone();
+        {
+            let host_input = remaining.by_ref().take(non_ignored_chars);
+            if has_ignored_chars {
+                replaced = host_input.collect();
+                host_str = &*replaced
+            } else {
+                for _ in host_input {}
+                host_str = &input_str[..bytes]
+            }
+        }
+        if is_windows_drive_letter(host_str) {
+            return Ok((false, HostInternal::None, input));
+        }
+        let host = if host_str.is_empty() {
+            HostInternal::None
+        } else {
+            match Host::parse(host_str)? {
+                Host::Domain(ref d) if d == "localhost" => HostInternal::None,
+                host => {
+                    write!(&mut self.serialization, "{}", host).unwrap();
+                    host.into()
+                }
+            }
+        };
+        Ok((true, host, remaining))
+    }
+
+    pub fn parse_port<P>(
+        mut input: Input,
+        default_port: P,
+        context: Context,
+    ) -> ParseResult<(Option<u16>, Input)>
+    where
+        P: Fn() -> Option<u16>,
+    {
+        let mut port: u32 = 0;
+        let mut has_any_digit = false;
+        while let (Some(c), remaining) = input.split_first() {
+            if let Some(digit) = c.to_digit(10) {
+                port = port * 10 + digit;
+                if port > ::std::u16::MAX as u32 {
+                    return Err(ParseError::InvalidPort);
+                }
+                has_any_digit = true;
+            } else if context == Context::UrlParser && !matches!(c, '/' | '\\' | '?' | '#') {
+                return Err(ParseError::InvalidPort);
+            } else {
+                break;
+            }
+            input = remaining;
+        }
+        let mut opt_port = Some(port as u16);
+        if !has_any_digit || opt_port == default_port() {
+            opt_port = None;
+        }
+        Ok((opt_port, input))
+    }
+
+    pub fn parse_path_start<'i>(
+        &mut self,
+        scheme_type: SchemeType,
+        has_host: &mut bool,
+        mut input: Input<'i>,
+    ) -> Input<'i> {
+        // Path start state
+        match input.split_first() {
+            (Some('/'), remaining) => input = remaining,
+            (Some('\\'), remaining) => {
+                if scheme_type.is_special() {
+                    self.log_violation(SyntaxViolation::Backslash);
+                    input = remaining
+                }
+            }
+            _ => {}
+        }
+        let path_start = self.serialization.len();
+        self.serialization.push('/');
+        self.parse_path(scheme_type, has_host, path_start, input)
+    }
+
+    pub fn parse_path<'i>(
+        &mut self,
+        scheme_type: SchemeType,
+        has_host: &mut bool,
+        path_start: usize,
+        mut input: Input<'i>,
+    ) -> Input<'i> {
+        // Relative path state
+        debug_assert!(self.serialization.ends_with('/'));
+        loop {
+            let segment_start = self.serialization.len();
+            let mut ends_with_slash = false;
+            loop {
+                let input_before_c = input.clone();
+                let (c, utf8_c) = if let Some(x) = input.next_utf8() {
+                    x
+                } else {
+                    break;
+                };
+                match c {
+                    '/' if self.context != Context::PathSegmentSetter => {
+                        ends_with_slash = true;
+                        break;
+                    }
+                    '\\' if self.context != Context::PathSegmentSetter
+                        && scheme_type.is_special() =>
+                    {
+                        self.log_violation(SyntaxViolation::Backslash);
+                        ends_with_slash = true;
+                        break;
+                    }
+                    '?' | '#' if self.context == Context::UrlParser => {
+                        input = input_before_c;
+                        break;
+                    }
+                    _ => {
+                        self.check_url_code_point(c, &input);
+                        if self.context == Context::PathSegmentSetter {
+                            if scheme_type.is_special() {
+                                self.serialization
+                                    .extend(utf8_percent_encode(utf8_c, SPECIAL_PATH_SEGMENT));
+                            } else {
+                                self.serialization
+                                    .extend(utf8_percent_encode(utf8_c, PATH_SEGMENT));
+                            }
+                        } else {
+                            self.serialization.extend(utf8_percent_encode(utf8_c, PATH));
+                        }
+                    }
+                }
+            }
+            match &self.serialization[segment_start..] {
+                ".." | "%2e%2e" | "%2e%2E" | "%2E%2e" | "%2E%2E" | "%2e." | "%2E." | ".%2e"
+                | ".%2E" => {
+                    debug_assert!(self.serialization.as_bytes()[segment_start - 1] == b'/');
+                    self.serialization.truncate(segment_start - 1); // Truncate "/.."
+                    self.pop_path(scheme_type, path_start);
+                    if !self.serialization[path_start..].ends_with('/') {
+                        self.serialization.push('/')
+                    }
+                }
+                "." | "%2e" | "%2E" => {
+                    self.serialization.truncate(segment_start);
+                }
+                _ => {
+                    if scheme_type.is_file()
+                        && is_windows_drive_letter(&self.serialization[path_start + 1..])
+                    {
+                        if self.serialization.ends_with('|') {
+                            self.serialization.pop();
+                            self.serialization.push(':');
+                        }
+                        if *has_host {
+                            self.log_violation(SyntaxViolation::FileWithHostAndWindowsDrive);
+                            *has_host = false; // FIXME account for this in callers
+                        }
+                    }
+                    if ends_with_slash {
+                        self.serialization.push('/')
+                    }
+                }
+            }
+            if !ends_with_slash {
+                break;
+            }
+        }
+        input
+    }
+
+    /// https://url.spec.whatwg.org/#pop-a-urls-path
+    fn pop_path(&mut self, scheme_type: SchemeType, path_start: usize) {
+        if self.serialization.len() > path_start {
+            let slash_position = self.serialization[path_start..].rfind('/').unwrap();
+            // + 1 since rfind returns the position before the slash.
+            let segment_start = path_start + slash_position + 1;
+            // Don’t pop a Windows drive letter
+            // FIXME: *normalized* Windows drive letter
+            if !(scheme_type.is_file()
+                && is_windows_drive_letter(&self.serialization[segment_start..]))
+            {
+                self.serialization.truncate(segment_start);
+            }
+        }
+    }
+
+    pub fn parse_cannot_be_a_base_path<'i>(&mut self, mut input: Input<'i>) -> Input<'i> {
+        loop {
+            let input_before_c = input.clone();
+            match input.next_utf8() {
+                Some(('?', _)) | Some(('#', _)) if self.context == Context::UrlParser => {
+                    return input_before_c
+                }
+                Some((c, utf8_c)) => {
+                    self.check_url_code_point(c, &input);
+                    self.serialization
+                        .extend(utf8_percent_encode(utf8_c, CONTROLS));
+                }
+                None => return input,
+            }
+        }
+    }
+
+    fn with_query_and_fragment(
+        mut self,
+        scheme_type: SchemeType,
+        scheme_end: u32,
+        username_end: u32,
+        host_start: u32,
+        host_end: u32,
+        host: HostInternal,
+        port: Option<u16>,
+        path_start: u32,
+        remaining: Input,
+    ) -> ParseResult<Url> {
+        let (query_start, fragment_start) =
+            self.parse_query_and_fragment(scheme_type, scheme_end, remaining)?;
+        Ok(Url {
+            serialization: self.serialization,
+            scheme_end,
+            username_end,
+            host_start,
+            host_end,
+            host,
+            port,
+            path_start,
+            query_start,
+            fragment_start,
+        })
+    }
+
+    /// Return (query_start, fragment_start)
+    fn parse_query_and_fragment(
+        &mut self,
+        scheme_type: SchemeType,
+        scheme_end: u32,
+        mut input: Input,
+    ) -> ParseResult<(Option<u32>, Option<u32>)> {
+        let mut query_start = None;
+        match input.next() {
+            Some('#') => {}
+            Some('?') => {
+                query_start = Some(to_u32(self.serialization.len())?);
+                self.serialization.push('?');
+                let remaining = self.parse_query(scheme_type, scheme_end, input);
+                if let Some(remaining) = remaining {
+                    input = remaining
+                } else {
+                    return Ok((query_start, None));
+                }
+            }
+            None => return Ok((None, None)),
+            _ => panic!("Programming error. parse_query_and_fragment() called without ? or #"),
+        }
+
+        let fragment_start = to_u32(self.serialization.len())?;
+        self.serialization.push('#');
+        self.parse_fragment(input);
+        Ok((query_start, Some(fragment_start)))
+    }
+
+    pub fn parse_query<'i>(
+        &mut self,
+        scheme_type: SchemeType,
+        scheme_end: u32,
+        mut input: Input<'i>,
+    ) -> Option<Input<'i>> {
+        let mut query = String::new(); // FIXME: use a streaming decoder instead
+        let mut remaining = None;
+        while let Some(c) = input.next() {
+            if c == '#' && self.context == Context::UrlParser {
+                remaining = Some(input);
+                break;
+            } else {
+                self.check_url_code_point(c, &input);
+                query.push(c);
+            }
+        }
+
+        let encoding = match &self.serialization[..scheme_end as usize] {
+            "http" | "https" | "file" | "ftp" | "gopher" => self.query_encoding_override,
+            _ => None,
+        };
+        let query_bytes = ::query_encoding::encode(encoding, &query);
+        let set = if scheme_type.is_special() {
+            SPECIAL_QUERY
+        } else {
+            QUERY
+        };
+        self.serialization.extend(percent_encode(&query_bytes, set));
+        remaining
+    }
+
+    fn fragment_only(mut self, base_url: &Url, mut input: Input) -> ParseResult<Url> {
+        let before_fragment = match base_url.fragment_start {
+            Some(i) => base_url.slice(..i),
+            None => &*base_url.serialization,
+        };
+        debug_assert!(self.serialization.is_empty());
+        self.serialization
+            .reserve(before_fragment.len() + input.chars.as_str().len());
+        self.serialization.push_str(before_fragment);
+        self.serialization.push('#');
+        let next = input.next();
+        debug_assert!(next == Some('#'));
+        self.parse_fragment(input);
+        Ok(Url {
+            serialization: self.serialization,
+            fragment_start: Some(to_u32(before_fragment.len())?),
+            ..*base_url
+        })
+    }
+
+    pub fn parse_fragment(&mut self, mut input: Input) {
+        while let Some((c, utf8_c)) = input.next_utf8() {
+            if c == '\0' {
+                self.log_violation(SyntaxViolation::NullInFragment)
+            } else {
+                self.check_url_code_point(c, &input);
+                self.serialization.extend(utf8_percent_encode(
+                    utf8_c,
+                    // FIXME: tests fail when we use the FRAGMENT set here
+                    // as defined in the spec as of 2019-07-17,
+                    // likely because tests are out of date.
+                    // See https://github.com/servo/rust-url/issues/290
+                    CONTROLS,
+                ));
+            }
+        }
+    }
+
+    fn check_url_code_point(&self, c: char, input: &Input) {
+        if let Some(vfn) = self.violation_fn {
+            if c == '%' {
+                let mut input = input.clone();
+                if !matches!((input.next(), input.next()), (Some(a), Some(b))
+                             if is_ascii_hex_digit(a) && is_ascii_hex_digit(b))
+                {
+                    vfn(SyntaxViolation::PercentDecode)
+                }
+            } else if !is_url_code_point(c) {
+                vfn(SyntaxViolation::NonUrlCodePoint)
+            }
+        }
+    }
+}
+
+#[inline]
+fn is_ascii_hex_digit(c: char) -> bool {
+    matches!(c, 'a'..='f' | 'A'..='F' | '0'..='9')
+}
+
+// Non URL code points:
+// U+0000 to U+0020 (space)
+// " # % < > [ \ ] ^ ` { | }
+// U+007F to U+009F
+// surrogates
+// U+FDD0 to U+FDEF
+// Last two of each plane: U+__FFFE to U+__FFFF for __ in 00 to 10 hex
+#[inline]
+fn is_url_code_point(c: char) -> bool {
+    matches!(c,
+        'a'..='z' |
+        'A'..='Z' |
+        '0'..='9' |
+        '!' | '$' | '&' | '\'' | '(' | ')' | '*' | '+' | ',' | '-' |
+        '.' | '/' | ':' | ';' | '=' | '?' | '@' | '_' | '~' |
+        '\u{A0}'..='\u{D7FF}' | '\u{E000}'..='\u{FDCF}' | '\u{FDF0}'..='\u{FFFD}' |
+        '\u{10000}'..='\u{1FFFD}' | '\u{20000}'..='\u{2FFFD}' |
+        '\u{30000}'..='\u{3FFFD}' | '\u{40000}'..='\u{4FFFD}' |
+        '\u{50000}'..='\u{5FFFD}' | '\u{60000}'..='\u{6FFFD}' |
+        '\u{70000}'..='\u{7FFFD}' | '\u{80000}'..='\u{8FFFD}' |
+        '\u{90000}'..='\u{9FFFD}' | '\u{A0000}'..='\u{AFFFD}' |
+        '\u{B0000}'..='\u{BFFFD}' | '\u{C0000}'..='\u{CFFFD}' |
+        '\u{D0000}'..='\u{DFFFD}' | '\u{E1000}'..='\u{EFFFD}' |
+        '\u{F0000}'..='\u{FFFFD}' | '\u{100000}'..='\u{10FFFD}')
+}
+
+/// https://url.spec.whatwg.org/#c0-controls-and-space
+#[inline]
+fn c0_control_or_space(ch: char) -> bool {
+    ch <= ' ' // U+0000 to U+0020
+}
+
+/// https://url.spec.whatwg.org/#ascii-alpha
+#[inline]
+pub fn ascii_alpha(ch: char) -> bool {
+    matches!(ch, 'a'..='z' | 'A'..='Z')
+}
+
+#[inline]
+pub fn to_u32(i: usize) -> ParseResult<u32> {
+    if i <= ::std::u32::MAX as usize {
+        Ok(i as u32)
+    } else {
+        Err(ParseError::Overflow)
+    }
+}
+
+/// Wether the scheme is file:, the path has a single segment, and that segment
+/// is a Windows drive letter
+fn is_windows_drive_letter(segment: &str) -> bool {
+    segment.len() == 2 && starts_with_windows_drive_letter(segment)
+}
+
+fn starts_with_windows_drive_letter(s: &str) -> bool {
+    ascii_alpha(s.as_bytes()[0] as char) && matches!(s.as_bytes()[1], b':' | b'|')
+}
+
+fn starts_with_windows_drive_letter_segment(input: &Input) -> bool {
+    let mut input = input.clone();
+    matches!((input.next(), input.next(), input.next()), (Some(a), Some(b), Some(c))
+             if ascii_alpha(a) && matches!(b, ':' | '|') && matches!(c, '/' | '\\' | '?' | '#'))
+}
diff --git a/third_party/rust/url/src/path_segments.rs b/third_party/rust/url/src/path_segments.rs
new file mode 100644
index 0000000000..97055e777c
--- /dev/null
+++ b/third_party/rust/url/src/path_segments.rs
@@ -0,0 +1,229 @@
+// Copyright 2016 The rust-url developers.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use parser::{self, to_u32, SchemeType};
+use std::str;
+use Url;
+
+/// Exposes methods to manipulate the path of an URL that is not cannot-be-base.
+///
+/// The path always starts with a `/` slash, and is made of slash-separated segments.
+/// There is always at least one segment (which may be the empty string).
+///
+/// Examples:
+///
+/// ```rust
+/// use url::Url;
+/// # use std::error::Error;
+///
+/// # fn run() -> Result<(), Box<Error>> {
+/// let mut url = Url::parse("mailto:me@example.com")?;
+/// assert!(url.path_segments_mut().is_err());
+///
+/// let mut url = Url::parse("http://example.net/foo/index.html")?;
+/// url.path_segments_mut().map_err(|_| "cannot be base")?
+///     .pop().push("img").push("2/100%.png");
+/// assert_eq!(url.as_str(), "http://example.net/foo/img/2%2F100%25.png");
+/// # Ok(())
+/// # }
+/// # run().unwrap();
+/// ```
+#[derive(Debug)]
+pub struct PathSegmentsMut<'a> {
+    url: &'a mut Url,
+    after_first_slash: usize,
+    after_path: String,
+    old_after_path_position: u32,
+}
+
+// Not re-exported outside the crate
+pub fn new(url: &mut Url) -> PathSegmentsMut {
+    let after_path = url.take_after_path();
+    let old_after_path_position = to_u32(url.serialization.len()).unwrap();
+    debug_assert!(url.byte_at(url.path_start) == b'/');
+    PathSegmentsMut {
+        after_first_slash: url.path_start as usize + "/".len(),
+        url,
+        old_after_path_position,
+        after_path,
+    }
+}
+
+impl<'a> Drop for PathSegmentsMut<'a> {
+    fn drop(&mut self) {
+        self.url
+            .restore_after_path(self.old_after_path_position, &self.after_path)
+    }
+}
+
+impl<'a> PathSegmentsMut<'a> {
+    /// Remove all segments in the path, leaving the minimal `url.path() == "/"`.
+    ///
+    /// Returns `&mut Self` so that method calls can be chained.
+    ///
+    /// Example:
+    ///
+    /// ```rust
+    /// use url::Url;
+    /// # use std::error::Error;
+    ///
+    /// # fn run() -> Result<(), Box<Error>> {
+    /// let mut url = Url::parse("https://github.com/servo/rust-url/")?;
+    /// url.path_segments_mut().map_err(|_| "cannot be base")?
+    ///     .clear().push("logout");
+    /// assert_eq!(url.as_str(), "https://github.com/logout");
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    pub fn clear(&mut self) -> &mut Self {
+        self.url.serialization.truncate(self.after_first_slash);
+        self
+    }
+
+    /// Remove the last segment of this URL’s path if it is empty,
+    /// except if these was only one segment to begin with.
+    ///
+    /// In other words, remove one path trailing slash, if any,
+    /// unless it is also the initial slash (so this does nothing if `url.path() == "/")`.
+    ///
+    /// Returns `&mut Self` so that method calls can be chained.
+    ///
+    /// Example:
+    ///
+    /// ```rust
+    /// use url::Url;
+    /// # use std::error::Error;
+    ///
+    /// # fn run() -> Result<(), Box<Error>> {
+    /// let mut url = Url::parse("https://github.com/servo/rust-url/")?;
+    /// url.path_segments_mut().map_err(|_| "cannot be base")?
+    ///     .push("pulls");
+    /// assert_eq!(url.as_str(), "https://github.com/servo/rust-url//pulls");
+    ///
+    /// let mut url = Url::parse("https://github.com/servo/rust-url/")?;
+    /// url.path_segments_mut().map_err(|_| "cannot be base")?
+    ///     .pop_if_empty().push("pulls");
+    /// assert_eq!(url.as_str(), "https://github.com/servo/rust-url/pulls");
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    pub fn pop_if_empty(&mut self) -> &mut Self {
+        if self.url.serialization[self.after_first_slash..].ends_with('/') {
+            self.url.serialization.pop();
+        }
+        self
+    }
+
+    /// Remove the last segment of this URL’s path.
+    ///
+    /// If the path only has one segment, make it empty such that `url.path() == "/"`.
+    ///
+    /// Returns `&mut Self` so that method calls can be chained.
+    pub fn pop(&mut self) -> &mut Self {
+        let last_slash = self.url.serialization[self.after_first_slash..]
+            .rfind('/')
+            .unwrap_or(0);
+        self.url
+            .serialization
+            .truncate(self.after_first_slash + last_slash);
+        self
+    }
+
+    /// Append the given segment at the end of this URL’s path.
+    ///
+    /// See the documentation for `.extend()`.
+    ///
+    /// Returns `&mut Self` so that method calls can be chained.
+    pub fn push(&mut self, segment: &str) -> &mut Self {
+        self.extend(Some(segment))
+    }
+
+    /// Append each segment from the given iterator at the end of this URL’s path.
+    ///
+    /// Each segment is percent-encoded like in `Url::parse` or `Url::join`,
+    /// except that `%` and `/` characters are also encoded (to `%25` and `%2F`).
+    /// This is unlike `Url::parse` where `%` is left as-is in case some of the input
+    /// is already percent-encoded, and `/` denotes a path segment separator.)
+    ///
+    /// Note that, in addition to slashes between new segments,
+    /// this always adds a slash between the existing path and the new segments
+    /// *except* if the existing path is `"/"`.
+    /// If the previous last segment was empty (if the path had a trailing slash)
+    /// the path after `.extend()` will contain two consecutive slashes.
+    /// If that is undesired, call `.pop_if_empty()` first.
+    ///
+    /// To obtain a behavior similar to `Url::join`, call `.pop()` unconditionally first.
+    ///
+    /// Returns `&mut Self` so that method calls can be chained.
+    ///
+    /// Example:
+    ///
+    /// ```rust
+    /// use url::Url;
+    /// # use std::error::Error;
+    ///
+    /// # fn run() -> Result<(), Box<Error>> {
+    /// let mut url = Url::parse("https://github.com/")?;
+    /// let org = "servo";
+    /// let repo = "rust-url";
+    /// let issue_number = "188";
+    /// url.path_segments_mut().map_err(|_| "cannot be base")?
+    ///     .extend(&[org, repo, "issues", issue_number]);
+    /// assert_eq!(url.as_str(), "https://github.com/servo/rust-url/issues/188");
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    ///
+    /// In order to make sure that parsing the serialization of an URL gives the same URL,
+    /// a segment is ignored if it is `"."` or `".."`:
+    ///
+    /// ```rust
+    /// use url::Url;
+    /// # use std::error::Error;
+    ///
+    /// # fn run() -> Result<(), Box<Error>> {
+    /// let mut url = Url::parse("https://github.com/servo")?;
+    /// url.path_segments_mut().map_err(|_| "cannot be base")?
+    ///     .extend(&["..", "rust-url", ".", "pulls"]);
+    /// assert_eq!(url.as_str(), "https://github.com/servo/rust-url/pulls");
+    /// # Ok(())
+    /// # }
+    /// # run().unwrap();
+    /// ```
+    pub fn extend<I>(&mut self, segments: I) -> &mut Self
+    where
+        I: IntoIterator,
+        I::Item: AsRef<str>,
+    {
+        let scheme_type = SchemeType::from(self.url.scheme());
+        let path_start = self.url.path_start as usize;
+        self.url.mutate(|parser| {
+            parser.context = parser::Context::PathSegmentSetter;
+            for segment in segments {
+                let segment = segment.as_ref();
+                if matches!(segment, "." | "..") {
+                    continue;
+                }
+                if parser.serialization.len() > path_start + 1 {
+                    parser.serialization.push('/');
+                }
+                let mut has_host = true; // FIXME account for this?
+                parser.parse_path(
+                    scheme_type,
+                    &mut has_host,
+                    path_start,
+                    parser::Input::new(segment),
+                );
+            }
+        });
+        self
+    }
+}
diff --git a/third_party/rust/url/src/query_encoding.rs b/third_party/rust/url/src/query_encoding.rs
new file mode 100644
index 0000000000..76aed15a7b
--- /dev/null
+++ b/third_party/rust/url/src/query_encoding.rs
@@ -0,0 +1,35 @@
+// Copyright 2019 The rust-url developers.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::borrow::Cow;
+
+pub type EncodingOverride<'a> = Option<&'a dyn Fn(&str) -> Cow<[u8]>>;
+
+pub(crate) fn encode<'a>(encoding_override: EncodingOverride, input: &'a str) -> Cow<'a, [u8]> {
+    if let Some(o) = encoding_override {
+        return o(input);
+    }
+    input.as_bytes().into()
+}
+
+pub(crate) fn decode_utf8_lossy(input: Cow<[u8]>) -> Cow<str> {
+    match input {
+        Cow::Borrowed(bytes) => String::from_utf8_lossy(bytes),
+        Cow::Owned(bytes) => {
+            let raw_utf8: *const [u8];
+            match String::from_utf8_lossy(&bytes) {
+                Cow::Borrowed(utf8) => raw_utf8 = utf8.as_bytes(),
+                Cow::Owned(s) => return s.into(),
+            }
+            // from_utf8_lossy returned a borrow of `bytes` unchanged.
+            debug_assert!(raw_utf8 == &*bytes as *const [u8]);
+            // Reuse the existing `Vec` allocation.
+            unsafe { String::from_utf8_unchecked(bytes) }.into()
+        }
+    }
+}
diff --git a/third_party/rust/url/src/quirks.rs b/third_party/rust/url/src/quirks.rs
new file mode 100644
index 0000000000..285ee21b65
--- /dev/null
+++ b/third_party/rust/url/src/quirks.rs
@@ -0,0 +1,226 @@
+// Copyright 2016 The rust-url developers.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Getters and setters for URL components implemented per https://url.spec.whatwg.org/#api
+//!
+//! Unless you need to be interoperable with web browsers,
+//! you probably want to use `Url` method instead.
+
+use parser::{default_port, Context, Input, Parser, SchemeType};
+use {idna, Host, ParseError, Position, Url};
+
+/// https://url.spec.whatwg.org/#dom-url-domaintoascii
+pub fn domain_to_ascii(domain: &str) -> String {
+    match Host::parse(domain) {
+        Ok(Host::Domain(domain)) => domain,
+        _ => String::new(),
+    }
+}
+
+/// https://url.spec.whatwg.org/#dom-url-domaintounicode
+pub fn domain_to_unicode(domain: &str) -> String {
+    match Host::parse(domain) {
+        Ok(Host::Domain(ref domain)) => {
+            let (unicode, _errors) = idna::domain_to_unicode(domain);
+            unicode
+        }
+        _ => String::new(),
+    }
+}
+
+/// Getter for https://url.spec.whatwg.org/#dom-url-href
+pub fn href(url: &Url) -> &str {
+    url.as_str()
+}
+
+/// Setter for https://url.spec.whatwg.org/#dom-url-href
+pub fn set_href(url: &mut Url, value: &str) -> Result<(), ParseError> {
+    *url = Url::parse(value)?;
+    Ok(())
+}
+
+/// Getter for https://url.spec.whatwg.org/#dom-url-origin
+pub fn origin(url: &Url) -> String {
+    url.origin().ascii_serialization()
+}
+
+/// Getter for https://url.spec.whatwg.org/#dom-url-protocol
+#[inline]
+pub fn protocol(url: &Url) -> &str {
+    &url.as_str()[..url.scheme().len() + ":".len()]
+}
+
+/// Setter for https://url.spec.whatwg.org/#dom-url-protocol
+pub fn set_protocol(url: &mut Url, mut new_protocol: &str) -> Result<(), ()> {
+    // The scheme state in the spec ignores everything after the first `:`,
+    // but `set_scheme` errors if there is more.
+    if let Some(position) = new_protocol.find(':') {
+        new_protocol = &new_protocol[..position];
+    }
+    url.set_scheme(new_protocol)
+}
+
+/// Getter for https://url.spec.whatwg.org/#dom-url-username
+#[inline]
+pub fn username(url: &Url) -> &str {
+    url.username()
+}
+
+/// Setter for https://url.spec.whatwg.org/#dom-url-username
+pub fn set_username(url: &mut Url, new_username: &str) -> Result<(), ()> {
+    url.set_username(new_username)
+}
+
+/// Getter for https://url.spec.whatwg.org/#dom-url-password
+#[inline]
+pub fn password(url: &Url) -> &str {
+    url.password().unwrap_or("")
+}
+
+/// Setter for https://url.spec.whatwg.org/#dom-url-password
+pub fn set_password(url: &mut Url, new_password: &str) -> Result<(), ()> {
+    url.set_password(if new_password.is_empty() {
+        None
+    } else {
+        Some(new_password)
+    })
+}
+
+/// Getter for https://url.spec.whatwg.org/#dom-url-host
+#[inline]
+pub fn host(url: &Url) -> &str {
+    &url[Position::BeforeHost..Position::AfterPort]
+}
+
+/// Setter for https://url.spec.whatwg.org/#dom-url-host
+pub fn set_host(url: &mut Url, new_host: &str) -> Result<(), ()> {
+    if url.cannot_be_a_base() {
+        return Err(());
+    }
+    let host;
+    let opt_port;
+    {
+        let scheme = url.scheme();
+        let result = Parser::parse_host(Input::new(new_host), SchemeType::from(scheme));
+        match result {
+            Ok((h, remaining)) => {
+                host = h;
+                opt_port = if let Some(remaining) = remaining.split_prefix(':') {
+                    Parser::parse_port(remaining, || default_port(scheme), Context::Setter)
+                        .ok()
+                        .map(|(port, _remaining)| port)
+                } else {
+                    None
+                };
+            }
+            Err(_) => return Err(()),
+        }
+    }
+    url.set_host_internal(host, opt_port);
+    Ok(())
+}
+
+/// Getter for https://url.spec.whatwg.org/#dom-url-hostname
+#[inline]
+pub fn hostname(url: &Url) -> &str {
+    url.host_str().unwrap_or("")
+}
+
+/// Setter for https://url.spec.whatwg.org/#dom-url-hostname
+pub fn set_hostname(url: &mut Url, new_hostname: &str) -> Result<(), ()> {
+    if url.cannot_be_a_base() {
+        return Err(());
+    }
+    let result = Parser::parse_host(Input::new(new_hostname), SchemeType::from(url.scheme()));
+    if let Ok((host, _remaining)) = result {
+        url.set_host_internal(host, None);
+        Ok(())
+    } else {
+        Err(())
+    }
+}
+
+/// Getter for https://url.spec.whatwg.org/#dom-url-port
+#[inline]
+pub fn port(url: &Url) -> &str {
+    &url[Position::BeforePort..Position::AfterPort]
+}
+
+/// Setter for https://url.spec.whatwg.org/#dom-url-port
+pub fn set_port(url: &mut Url, new_port: &str) -> Result<(), ()> {
+    let result;
+    {
+        // has_host implies !cannot_be_a_base
+        let scheme = url.scheme();
+        if !url.has_host() || url.host() == Some(Host::Domain("")) || scheme == "file" {
+            return Err(());
+        }
+        result = Parser::parse_port(
+            Input::new(new_port),
+            || default_port(scheme),
+            Context::Setter,
+        )
+    }
+    if let Ok((new_port, _remaining)) = result {
+        url.set_port_internal(new_port);
+        Ok(())
+    } else {
+        Err(())
+    }
+}
+
+/// Getter for https://url.spec.whatwg.org/#dom-url-pathname
+#[inline]
+pub fn pathname(url: &Url) -> &str {
+    url.path()
+}
+
+/// Setter for https://url.spec.whatwg.org/#dom-url-pathname
+pub fn set_pathname(url: &mut Url, new_pathname: &str) {
+    if !url.cannot_be_a_base() {
+        url.set_path(new_pathname)
+    }
+}
+
+/// Getter for https://url.spec.whatwg.org/#dom-url-search
+pub fn search(url: &Url) -> &str {
+    trim(&url[Position::AfterPath..Position::AfterQuery])
+}
+
+/// Setter for https://url.spec.whatwg.org/#dom-url-search
+pub fn set_search(url: &mut Url, new_search: &str) {
+    url.set_query(match new_search {
+        "" => None,
+        _ if new_search.starts_with('?') => Some(&new_search[1..]),
+        _ => Some(new_search),
+    })
+}
+
+/// Getter for https://url.spec.whatwg.org/#dom-url-hash
+pub fn hash(url: &Url) -> &str {
+    trim(&url[Position::AfterQuery..])
+}
+
+/// Setter for https://url.spec.whatwg.org/#dom-url-hash
+pub fn set_hash(url: &mut Url, new_hash: &str) {
+    if url.scheme() != "javascript" {
+        url.set_fragment(match new_hash {
+            "" => None,
+            _ if new_hash.starts_with('#') => Some(&new_hash[1..]),
+            _ => Some(new_hash),
+        })
+    }
+}
+
+fn trim(s: &str) -> &str {
+    if s.len() == 1 {
+        ""
+    } else {
+        s
+    }
+}
diff --git a/third_party/rust/url/src/slicing.rs b/third_party/rust/url/src/slicing.rs
new file mode 100644
index 0000000000..2d7f78e6f8
--- /dev/null
+++ b/third_party/rust/url/src/slicing.rs
@@ -0,0 +1,187 @@
+// Copyright 2016 The rust-url developers.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::ops::{Index, Range, RangeFrom, RangeFull, RangeTo};
+use Url;
+
+impl Index<RangeFull> for Url {
+    type Output = str;
+    fn index(&self, _: RangeFull) -> &str {
+        &self.serialization
+    }
+}
+
+impl Index<RangeFrom<Position>> for Url {
+    type Output = str;
+    fn index(&self, range: RangeFrom<Position>) -> &str {
+        &self.serialization[self.index(range.start)..]
+    }
+}
+
+impl Index<RangeTo<Position>> for Url {
+    type Output = str;
+    fn index(&self, range: RangeTo<Position>) -> &str {
+        &self.serialization[..self.index(range.end)]
+    }
+}
+
+impl Index<Range<Position>> for Url {
+    type Output = str;
+    fn index(&self, range: Range<Position>) -> &str {
+        &self.serialization[self.index(range.start)..self.index(range.end)]
+    }
+}
+
+/// Indicates a position within a URL based on its components.
+///
+/// A range of positions can be used for slicing `Url`:
+///
+/// ```rust
+/// # use url::{Url, Position};
+/// # fn something(some_url: Url) {
+/// let serialization: &str = &some_url[..];
+/// let serialization_without_fragment: &str = &some_url[..Position::AfterQuery];
+/// let authority: &str = &some_url[Position::BeforeUsername..Position::AfterPort];
+/// let data_url_payload: &str = &some_url[Position::BeforePath..Position::AfterQuery];
+/// let scheme_relative: &str = &some_url[Position::BeforeUsername..];
+/// # }
+/// ```
+///
+/// In a pseudo-grammar (where `[`…`]?` makes a sub-sequence optional),
+/// URL components and delimiters that separate them are:
+///
+/// ```notrust
+/// url =
+///     scheme ":"
+///     [ "//" [ username [ ":" password ]? "@" ]? host [ ":" port ]? ]?
+///     path [ "?" query ]? [ "#" fragment ]?
+/// ```
+///
+/// When a given component is not present,
+/// its "before" and "after" position are the same
+/// (so that `&some_url[BeforeFoo..AfterFoo]` is the empty string)
+/// and component ordering is preserved
+/// (so that a missing query "is between" a path and a fragment).
+///
+/// The end of a component and the start of the next are either the same or separate
+/// by a delimiter.
+/// (Not that the initial `/` of a path is considered part of the path here, not a delimiter.)
+/// For example, `&url[..BeforeFragment]` would include a `#` delimiter (if present in `url`),
+/// so `&url[..AfterQuery]` might be desired instead.
+///
+/// `BeforeScheme` and `AfterFragment` are always the start and end of the entire URL,
+/// so `&url[BeforeScheme..X]` is the same as `&url[..X]`
+/// and `&url[X..AfterFragment]` is the same as `&url[X..]`.
+#[derive(Copy, Clone, Debug)]
+pub enum Position {
+    BeforeScheme,
+    AfterScheme,
+    BeforeUsername,
+    AfterUsername,
+    BeforePassword,
+    AfterPassword,
+    BeforeHost,
+    AfterHost,
+    BeforePort,
+    AfterPort,
+    BeforePath,
+    AfterPath,
+    BeforeQuery,
+    AfterQuery,
+    BeforeFragment,
+    AfterFragment,
+}
+
+impl Url {
+    #[inline]
+    fn index(&self, position: Position) -> usize {
+        match position {
+            Position::BeforeScheme => 0,
+
+            Position::AfterScheme => self.scheme_end as usize,
+
+            Position::BeforeUsername => {
+                if self.has_authority() {
+                    self.scheme_end as usize + "://".len()
+                } else {
+                    debug_assert!(self.byte_at(self.scheme_end) == b':');
+                    debug_assert!(self.scheme_end + ":".len() as u32 == self.username_end);
+                    self.scheme_end as usize + ":".len()
+                }
+            }
+
+            Position::AfterUsername => self.username_end as usize,
+
+            Position::BeforePassword => {
+                if self.has_authority() && self.byte_at(self.username_end) == b':' {
+                    self.username_end as usize + ":".len()
+                } else {
+                    debug_assert!(self.username_end == self.host_start);
+                    self.username_end as usize
+                }
+            }
+
+            Position::AfterPassword => {
+                if self.has_authority() && self.byte_at(self.username_end) == b':' {
+                    debug_assert!(self.byte_at(self.host_start - "@".len() as u32) == b'@');
+                    self.host_start as usize - "@".len()
+                } else {
+                    debug_assert!(self.username_end == self.host_start);
+                    self.host_start as usize
+                }
+            }
+
+            Position::BeforeHost => self.host_start as usize,
+
+            Position::AfterHost => self.host_end as usize,
+
+            Position::BeforePort => {
+                if self.port.is_some() {
+                    debug_assert!(self.byte_at(self.host_end) == b':');
+                    self.host_end as usize + ":".len()
+                } else {
+                    self.host_end as usize
+                }
+            }
+
+            Position::AfterPort => self.path_start as usize,
+
+            Position::BeforePath => self.path_start as usize,
+
+            Position::AfterPath => match (self.query_start, self.fragment_start) {
+                (Some(q), _) => q as usize,
+                (None, Some(f)) => f as usize,
+                (None, None) => self.serialization.len(),
+            },
+
+            Position::BeforeQuery => match (self.query_start, self.fragment_start) {
+                (Some(q), _) => {
+                    debug_assert!(self.byte_at(q) == b'?');
+                    q as usize + "?".len()
+                }
+                (None, Some(f)) => f as usize,
+                (None, None) => self.serialization.len(),
+            },
+
+            Position::AfterQuery => match self.fragment_start {
+                None => self.serialization.len(),
+                Some(f) => f as usize,
+            },
+
+            Position::BeforeFragment => match self.fragment_start {
+                Some(f) => {
+                    debug_assert!(self.byte_at(f) == b'#');
+                    f as usize + "#".len()
+                }
+                None => self.serialization.len(),
+            },
+
+            Position::AfterFragment => self.serialization.len(),
+        }
+    }
+}