Adding upstream version 115.7.0esr.upstream/115.7.0esr

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

1 files changed, 1031 insertions, 0 deletions

diff --git a/third_party/rust/arbitrary/src/unstructured.rs b/third_party/rust/arbitrary/src/unstructured.rs
new file mode 100644
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--- /dev/null
+++ b/third_party/rust/arbitrary/src/unstructured.rs
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+// Copyright © 2019 The Rust Fuzz Project 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.
+
+//! Wrappers around raw, unstructured bytes.
+
+use crate::{Arbitrary, Error, Result};
+use std::marker::PhantomData;
+use std::ops::ControlFlow;
+use std::{mem, ops};
+
+/// A source of unstructured data.
+///
+/// An `Unstructured` helps `Arbitrary` implementations interpret raw data
+/// (typically provided by a fuzzer) as a "DNA string" that describes how to
+/// construct the `Arbitrary` type. The goal is that a small change to the "DNA
+/// string" (the raw data wrapped by an `Unstructured`) results in a small
+/// change to the generated `Arbitrary` instance. This helps a fuzzer
+/// efficiently explore the `Arbitrary`'s input space.
+///
+/// `Unstructured` is deterministic: given the same raw data, the same series of
+/// API calls will return the same results (modulo system resource constraints,
+/// like running out of memory). However, `Unstructured` does not guarantee
+/// anything beyond that: it makes not guarantee that it will yield bytes from
+/// the underlying data in any particular order.
+///
+/// You shouldn't generally need to use an `Unstructured` unless you are writing
+/// a custom `Arbitrary` implementation by hand, instead of deriving it. Mostly,
+/// you should just be passing it through to nested `Arbitrary::arbitrary`
+/// calls.
+///
+/// # Example
+///
+/// Imagine you were writing a color conversion crate. You might want to write
+/// fuzz tests that take a random RGB color and assert various properties, run
+/// functions and make sure nothing panics, etc.
+///
+/// Below is what translating the fuzzer's raw input into an `Unstructured` and
+/// using that to generate an arbitrary RGB color might look like:
+///
+/// ```
+/// # #[cfg(feature = "derive")] fn foo() {
+/// use arbitrary::{Arbitrary, Unstructured};
+///
+/// /// An RGB color.
+/// #[derive(Arbitrary)]
+/// pub struct Rgb {
+///     r: u8,
+///     g: u8,
+///     b: u8,
+/// }
+///
+/// // Get the raw bytes from the fuzzer.
+/// #   let get_input_from_fuzzer = || &[];
+/// let raw_data: &[u8] = get_input_from_fuzzer();
+///
+/// // Wrap it in an `Unstructured`.
+/// let mut unstructured = Unstructured::new(raw_data);
+///
+/// // Generate an `Rgb` color and run our checks.
+/// if let Ok(rgb) = Rgb::arbitrary(&mut unstructured) {
+/// #   let run_my_color_conversion_checks = |_| {};
+///     run_my_color_conversion_checks(rgb);
+/// }
+/// # }
+/// ```
+pub struct Unstructured<'a> {
+    data: &'a [u8],
+}
+
+impl<'a> Unstructured<'a> {
+    /// Create a new `Unstructured` from the given raw data.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use arbitrary::Unstructured;
+    ///
+    /// let u = Unstructured::new(&[1, 2, 3, 4]);
+    /// ```
+    pub fn new(data: &'a [u8]) -> Self {
+        Unstructured { data }
+    }
+
+    /// Get the number of remaining bytes of underlying data that are still
+    /// available.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use arbitrary::{Arbitrary, Unstructured};
+    ///
+    /// let mut u = Unstructured::new(&[1, 2, 3]);
+    ///
+    /// // Initially have three bytes of data.
+    /// assert_eq!(u.len(), 3);
+    ///
+    /// // Generating a `bool` consumes one byte from the underlying data, so
+    /// // we are left with two bytes afterwards.
+    /// let _ = bool::arbitrary(&mut u);
+    /// assert_eq!(u.len(), 2);
+    /// ```
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.data.len()
+    }
+
+    /// Is the underlying unstructured data exhausted?
+    ///
+    /// `unstructured.is_empty()` is the same as `unstructured.len() == 0`.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use arbitrary::{Arbitrary, Unstructured};
+    ///
+    /// let mut u = Unstructured::new(&[1, 2, 3, 4]);
+    ///
+    /// // Initially, we are not empty.
+    /// assert!(!u.is_empty());
+    ///
+    /// // Generating a `u32` consumes all four bytes of the underlying data, so
+    /// // we become empty afterwards.
+    /// let _ = u32::arbitrary(&mut u);
+    /// assert!(u.is_empty());
+    /// ```
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    /// Generate an arbitrary instance of `A`.
+    ///
+    /// This is simply a helper method that is equivalent to `<A as
+    /// Arbitrary>::arbitrary(self)`. This helper is a little bit more concise,
+    /// and can be used in situations where Rust's type inference will figure
+    /// out what `A` should be.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # #[cfg(feature="derive")] fn foo() -> arbitrary::Result<()> {
+    /// use arbitrary::{Arbitrary, Unstructured};
+    ///
+    /// #[derive(Arbitrary)]
+    /// struct MyType {
+    ///     // ...
+    /// }
+    ///
+    /// fn do_stuff(value: MyType) {
+    /// #   let _ = value;
+    ///     // ...
+    /// }
+    ///
+    /// let mut u = Unstructured::new(&[1, 2, 3, 4]);
+    ///
+    /// // Rust's type inference can figure out that `value` should be of type
+    /// // `MyType` here:
+    /// let value = u.arbitrary()?;
+    /// do_stuff(value);
+    /// # Ok(()) }
+    /// ```
+    pub fn arbitrary<A>(&mut self) -> Result<A>
+    where
+        A: Arbitrary<'a>,
+    {
+        <A as Arbitrary<'a>>::arbitrary(self)
+    }
+
+    /// Get the number of elements to insert when building up a collection of
+    /// arbitrary `ElementType`s.
+    ///
+    /// This uses the [`<ElementType as
+    /// Arbitrary>::size_hint`][crate::Arbitrary::size_hint] method to smartly
+    /// choose a length such that we most likely have enough underlying bytes to
+    /// construct that many arbitrary `ElementType`s.
+    ///
+    /// This should only be called within an `Arbitrary` implementation.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use arbitrary::{Arbitrary, Result, Unstructured};
+    /// # pub struct MyCollection<T> { _t: std::marker::PhantomData<T> }
+    /// # impl<T> MyCollection<T> {
+    /// #     pub fn with_capacity(capacity: usize) -> Self { MyCollection { _t: std::marker::PhantomData } }
+    /// #     pub fn insert(&mut self, element: T) {}
+    /// # }
+    ///
+    /// impl<'a, T> Arbitrary<'a> for MyCollection<T>
+    /// where
+    ///     T: Arbitrary<'a>,
+    /// {
+    ///     fn arbitrary(u: &mut Unstructured<'a>) -> Result<Self> {
+    ///         // Get the number of `T`s we should insert into our collection.
+    ///         let len = u.arbitrary_len::<T>()?;
+    ///
+    ///         // And then create a collection of that length!
+    ///         let mut my_collection = MyCollection::with_capacity(len);
+    ///         for _ in 0..len {
+    ///             let element = T::arbitrary(u)?;
+    ///             my_collection.insert(element);
+    ///         }
+    ///
+    ///         Ok(my_collection)
+    ///     }
+    /// }
+    /// ```
+    pub fn arbitrary_len<ElementType>(&mut self) -> Result<usize>
+    where
+        ElementType: Arbitrary<'a>,
+    {
+        let byte_size = self.arbitrary_byte_size()?;
+        let (lower, upper) = <ElementType as Arbitrary>::size_hint(0);
+        let elem_size = upper.unwrap_or(lower * 2);
+        let elem_size = std::cmp::max(1, elem_size);
+        Ok(byte_size / elem_size)
+    }
+
+    fn arbitrary_byte_size(&mut self) -> Result<usize> {
+        if self.data.is_empty() {
+            Ok(0)
+        } else if self.data.len() == 1 {
+            self.data = &[];
+            Ok(0)
+        } else {
+            // Take lengths from the end of the data, since the `libFuzzer` folks
+            // found that this lets fuzzers more efficiently explore the input
+            // space.
+            //
+            // https://github.com/rust-fuzz/libfuzzer-sys/blob/0c450753/libfuzzer/utils/FuzzedDataProvider.h#L92-L97
+
+            // We only consume as many bytes as necessary to cover the entire
+            // range of the byte string.
+            // Note: We cast to u64 so we don't overflow when checking std::u32::MAX + 4 on 32-bit archs
+            let len = if self.data.len() as u64 <= std::u8::MAX as u64 + 1 {
+                let bytes = 1;
+                let max_size = self.data.len() - bytes;
+                let (rest, for_size) = self.data.split_at(max_size);
+                self.data = rest;
+                Self::int_in_range_impl(0..=max_size as u8, for_size.iter().copied())?.0 as usize
+            } else if self.data.len() as u64 <= std::u16::MAX as u64 + 2 {
+                let bytes = 2;
+                let max_size = self.data.len() - bytes;
+                let (rest, for_size) = self.data.split_at(max_size);
+                self.data = rest;
+                Self::int_in_range_impl(0..=max_size as u16, for_size.iter().copied())?.0 as usize
+            } else if self.data.len() as u64 <= std::u32::MAX as u64 + 4 {
+                let bytes = 4;
+                let max_size = self.data.len() - bytes;
+                let (rest, for_size) = self.data.split_at(max_size);
+                self.data = rest;
+                Self::int_in_range_impl(0..=max_size as u32, for_size.iter().copied())?.0 as usize
+            } else {
+                let bytes = 8;
+                let max_size = self.data.len() - bytes;
+                let (rest, for_size) = self.data.split_at(max_size);
+                self.data = rest;
+                Self::int_in_range_impl(0..=max_size as u64, for_size.iter().copied())?.0 as usize
+            };
+
+            Ok(len)
+        }
+    }
+
+    /// Generate an integer within the given range.
+    ///
+    /// Do not use this to generate the size of a collection. Use
+    /// `arbitrary_len` instead.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `range.start > range.end`. That is, the given range must be
+    /// non-empty.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use arbitrary::{Arbitrary, Unstructured};
+    ///
+    /// let mut u = Unstructured::new(&[1, 2, 3, 4]);
+    ///
+    /// let x: i32 = u.int_in_range(-5_000..=-1_000)
+    ///     .expect("constructed `u` with enough bytes to generate an `i32`");
+    ///
+    /// assert!(-5_000 <= x);
+    /// assert!(x <= -1_000);
+    /// ```
+    pub fn int_in_range<T>(&mut self, range: ops::RangeInclusive<T>) -> Result<T>
+    where
+        T: Int,
+    {
+        let (result, bytes_consumed) = Self::int_in_range_impl(range, self.data.iter().cloned())?;
+        self.data = &self.data[bytes_consumed..];
+        Ok(result)
+    }
+
+    fn int_in_range_impl<T>(
+        range: ops::RangeInclusive<T>,
+        mut bytes: impl Iterator<Item = u8>,
+    ) -> Result<(T, usize)>
+    where
+        T: Int,
+    {
+        let start = *range.start();
+        let end = *range.end();
+        assert!(
+            start <= end,
+            "`arbitrary::Unstructured::int_in_range` requires a non-empty range"
+        );
+
+        // When there is only one possible choice, don't waste any entropy from
+        // the underlying data.
+        if start == end {
+            return Ok((start, 0));
+        }
+
+        // From here on out we work with the unsigned representation. All of the
+        // operations performed below work out just as well whether or not `T`
+        // is a signed or unsigned integer.
+        let start = start.to_unsigned();
+        let end = end.to_unsigned();
+
+        let delta = end.wrapping_sub(start);
+        debug_assert_ne!(delta, T::Unsigned::ZERO);
+
+        // Compute an arbitrary integer offset from the start of the range. We
+        // do this by consuming `size_of(T)` bytes from the input to create an
+        // arbitrary integer and then clamping that int into our range bounds
+        // with a modulo operation.
+        let mut arbitrary_int = T::Unsigned::ZERO;
+        let mut bytes_consumed: usize = 0;
+
+        while (bytes_consumed < mem::size_of::<T>())
+            && (delta >> T::Unsigned::from_usize(bytes_consumed * 8)) > T::Unsigned::ZERO
+        {
+            let byte = match bytes.next() {
+                None => break,
+                Some(b) => b,
+            };
+            bytes_consumed += 1;
+
+            // Combine this byte into our arbitrary integer, but avoid
+            // overflowing the shift for `u8` and `i8`.
+            arbitrary_int = if mem::size_of::<T>() == 1 {
+                T::Unsigned::from_u8(byte)
+            } else {
+                (arbitrary_int << 8) | T::Unsigned::from_u8(byte)
+            };
+        }
+
+        let offset = if delta == T::Unsigned::MAX {
+            arbitrary_int
+        } else {
+            arbitrary_int % (delta.checked_add(T::Unsigned::ONE).unwrap())
+        };
+
+        // Finally, we add `start` to our offset from `start` to get the result
+        // actual value within the range.
+        let result = start.wrapping_add(offset);
+
+        // And convert back to our maybe-signed representation.
+        let result = T::from_unsigned(result);
+        debug_assert!(*range.start() <= result);
+        debug_assert!(result <= *range.end());
+
+        Ok((result, bytes_consumed))
+    }
+
+    /// Choose one of the given choices.
+    ///
+    /// This should only be used inside of `Arbitrary` implementations.
+    ///
+    /// Returns an error if there is not enough underlying data to make a
+    /// choice or if no choices are provided.
+    ///
+    /// # Examples
+    ///
+    /// Selecting from an array of choices:
+    ///
+    /// ```
+    /// use arbitrary::Unstructured;
+    ///
+    /// let mut u = Unstructured::new(&[1, 2, 3, 4, 5, 6, 7, 8, 9, 0]);
+    /// let choices = ['a', 'b', 'c', 'd', 'e', 'f', 'g'];
+    ///
+    /// let choice = u.choose(&choices).unwrap();
+    ///
+    /// println!("chose {}", choice);
+    /// ```
+    ///
+    /// An error is returned if no choices are provided:
+    ///
+    /// ```
+    /// use arbitrary::Unstructured;
+    ///
+    /// let mut u = Unstructured::new(&[1, 2, 3, 4, 5, 6, 7, 8, 9, 0]);
+    /// let choices: [char; 0] = [];
+    ///
+    /// let result = u.choose(&choices);
+    ///
+    /// assert!(result.is_err());
+    /// ```
+    pub fn choose<'b, T>(&mut self, choices: &'b [T]) -> Result<&'b T> {
+        let idx = self.choose_index(choices.len())?;
+        Ok(&choices[idx])
+    }
+
+    /// Choose a value in `0..len`.
+    ///
+    /// Returns an error if the `len` is zero.
+    ///
+    /// # Examples
+    ///
+    /// Using Fisher–Yates shuffle shuffle to gerate an arbitrary permutation.
+    ///
+    /// [Fisher–Yates shuffle]: https://en.wikipedia.org/wiki/Fisher–Yates_shuffle
+    ///
+    /// ```
+    /// use arbitrary::Unstructured;
+    ///
+    /// let mut u = Unstructured::new(&[1, 2, 3, 4, 5, 6, 7, 8, 9, 0]);
+    /// let mut permutation = ['a', 'b', 'c', 'd', 'e', 'f', 'g'];
+    /// let mut to_permute = &mut permutation[..];
+    /// while to_permute.len() > 1 {
+    ///     let idx = u.choose_index(to_permute.len()).unwrap();
+    ///     to_permute.swap(0, idx);
+    ///     to_permute = &mut to_permute[1..];
+    /// }
+    ///
+    /// println!("permutation: {:?}", permutation);
+    /// ```
+    ///
+    /// An error is returned if the length is zero:
+    ///
+    /// ```
+    /// use arbitrary::Unstructured;
+    ///
+    /// let mut u = Unstructured::new(&[1, 2, 3, 4, 5, 6, 7, 8, 9, 0]);
+    /// let array: [i32; 0] = [];
+    ///
+    /// let result = u.choose_index(array.len());
+    ///
+    /// assert!(result.is_err());
+    /// ```
+    pub fn choose_index(&mut self, len: usize) -> Result<usize> {
+        if len == 0 {
+            return Err(Error::EmptyChoose);
+        }
+        let idx = self.int_in_range(0..=len - 1)?;
+        Ok(idx)
+    }
+
+    /// Generate a boolean according to the given ratio.
+    ///
+    /// # Panics
+    ///
+    /// Panics when the numerator and denominator do not meet these constraints:
+    ///
+    /// * `0 < numerator <= denominator`
+    ///
+    /// # Example
+    ///
+    /// Generate a boolean that is `true` five sevenths of the time:
+    ///
+    /// ```
+    /// # fn foo() -> arbitrary::Result<()> {
+    /// use arbitrary::Unstructured;
+    ///
+    /// # let my_data = [1, 2, 3, 4, 5, 6, 7, 8, 9, 0];
+    /// let mut u = Unstructured::new(&my_data);
+    ///
+    /// if u.ratio(5, 7)? {
+    ///     // Take this branch 5/7 of the time.
+    /// }
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn ratio<T>(&mut self, numerator: T, denominator: T) -> Result<bool>
+    where
+        T: Int,
+    {
+        assert!(T::ZERO < numerator);
+        assert!(numerator <= denominator);
+        let x = self.int_in_range(T::ONE..=denominator)?;
+        Ok(x <= numerator)
+    }
+
+    /// Fill a `buffer` with bytes from the underlying raw data.
+    ///
+    /// This should only be called within an `Arbitrary` implementation. This is
+    /// a very low-level operation. You should generally prefer calling nested
+    /// `Arbitrary` implementations like `<Vec<u8>>::arbitrary` and
+    /// `String::arbitrary` over using this method directly.
+    ///
+    /// If this `Unstructured` does not have enough underlying data to fill the
+    /// whole `buffer`, it pads the buffer out with zeros.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use arbitrary::Unstructured;
+    ///
+    /// let mut u = Unstructured::new(&[1, 2, 3, 4]);
+    ///
+    /// let mut buf = [0; 2];
+    ///
+    /// assert!(u.fill_buffer(&mut buf).is_ok());
+    /// assert_eq!(buf, [1, 2]);
+    ///
+    /// assert!(u.fill_buffer(&mut buf).is_ok());
+    /// assert_eq!(buf, [3, 4]);
+    ///
+    /// assert!(u.fill_buffer(&mut buf).is_ok());
+    /// assert_eq!(buf, [0, 0]);
+    /// ```
+    pub fn fill_buffer(&mut self, buffer: &mut [u8]) -> Result<()> {
+        let n = std::cmp::min(buffer.len(), self.data.len());
+        buffer[..n].copy_from_slice(&self.data[..n]);
+        for byte in buffer[n..].iter_mut() {
+            *byte = 0;
+        }
+        self.data = &self.data[n..];
+        Ok(())
+    }
+
+    /// Provide `size` bytes from the underlying raw data.
+    ///
+    /// This should only be called within an `Arbitrary` implementation. This is
+    /// a very low-level operation. You should generally prefer calling nested
+    /// `Arbitrary` implementations like `<Vec<u8>>::arbitrary` and
+    /// `String::arbitrary` over using this method directly.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use arbitrary::Unstructured;
+    ///
+    /// let mut u = Unstructured::new(&[1, 2, 3, 4]);
+    ///
+    /// assert!(u.bytes(2).unwrap() == &[1, 2]);
+    /// assert!(u.bytes(2).unwrap() == &[3, 4]);
+    /// ```
+    pub fn bytes(&mut self, size: usize) -> Result<&'a [u8]> {
+        if self.data.len() < size {
+            return Err(Error::NotEnoughData);
+        }
+
+        let (for_buf, rest) = self.data.split_at(size);
+        self.data = rest;
+        Ok(for_buf)
+    }
+
+    /// Peek at `size` number of bytes of the underlying raw input.
+    ///
+    /// Does not consume the bytes, only peeks at them.
+    ///
+    /// Returns `None` if there are not `size` bytes left in the underlying raw
+    /// input.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use arbitrary::Unstructured;
+    ///
+    /// let u = Unstructured::new(&[1, 2, 3]);
+    ///
+    /// assert_eq!(u.peek_bytes(0).unwrap(), []);
+    /// assert_eq!(u.peek_bytes(1).unwrap(), [1]);
+    /// assert_eq!(u.peek_bytes(2).unwrap(), [1, 2]);
+    /// assert_eq!(u.peek_bytes(3).unwrap(), [1, 2, 3]);
+    ///
+    /// assert!(u.peek_bytes(4).is_none());
+    /// ```
+    pub fn peek_bytes(&self, size: usize) -> Option<&'a [u8]> {
+        self.data.get(..size)
+    }
+
+    /// Consume all of the rest of the remaining underlying bytes.
+    ///
+    /// Returns a slice of all the remaining, unconsumed bytes.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use arbitrary::Unstructured;
+    ///
+    /// let mut u = Unstructured::new(&[1, 2, 3]);
+    ///
+    /// let mut remaining = u.take_rest();
+    ///
+    /// assert_eq!(remaining, [1, 2, 3]);
+    /// ```
+    pub fn take_rest(mut self) -> &'a [u8] {
+        mem::take(&mut self.data)
+    }
+
+    /// Provide an iterator over elements for constructing a collection
+    ///
+    /// This is useful for implementing [`Arbitrary::arbitrary`] on collections
+    /// since the implementation is simply `u.arbitrary_iter()?.collect()`
+    pub fn arbitrary_iter<'b, ElementType: Arbitrary<'a>>(
+        &'b mut self,
+    ) -> Result<ArbitraryIter<'a, 'b, ElementType>> {
+        Ok(ArbitraryIter {
+            u: &mut *self,
+            _marker: PhantomData,
+        })
+    }
+
+    /// Provide an iterator over elements for constructing a collection from
+    /// all the remaining bytes.
+    ///
+    /// This is useful for implementing [`Arbitrary::arbitrary_take_rest`] on collections
+    /// since the implementation is simply `u.arbitrary_take_rest_iter()?.collect()`
+    pub fn arbitrary_take_rest_iter<ElementType: Arbitrary<'a>>(
+        self,
+    ) -> Result<ArbitraryTakeRestIter<'a, ElementType>> {
+        let (lower, upper) = ElementType::size_hint(0);
+
+        let elem_size = upper.unwrap_or(lower * 2);
+        let elem_size = std::cmp::max(1, elem_size);
+        let size = self.len() / elem_size;
+        Ok(ArbitraryTakeRestIter {
+            size,
+            u: Some(self),
+            _marker: PhantomData,
+        })
+    }
+
+    /// Call the given function an arbitrary number of times.
+    ///
+    /// The function is given this `Unstructured` so that it can continue to
+    /// generate arbitrary data and structures.
+    ///
+    /// You may optionaly specify minimum and maximum bounds on the number of
+    /// times the function is called.
+    ///
+    /// You may break out of the loop early by returning
+    /// `Ok(std::ops::ControlFlow::Break)`. To continue the loop, return
+    /// `Ok(std::ops::ControlFlow::Continue)`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `min > max`.
+    ///
+    /// # Example
+    ///
+    /// Call a closure that generates an arbitrary type inside a context an
+    /// arbitrary number of times:
+    ///
+    /// ```
+    /// use arbitrary::{Result, Unstructured};
+    /// use std::ops::ControlFlow;
+    ///
+    /// enum Type {
+    ///     /// A boolean type.
+    ///     Bool,
+    ///
+    ///     /// An integer type.
+    ///     Int,
+    ///
+    ///     /// A list of the `i`th type in this type's context.
+    ///     List(usize),
+    /// }
+    ///
+    /// fn arbitrary_types_context(u: &mut Unstructured) -> Result<Vec<Type>> {
+    ///     let mut context = vec![];
+    ///
+    ///     u.arbitrary_loop(Some(10), Some(20), |u| {
+    ///         let num_choices = if context.is_empty() {
+    ///             2
+    ///         } else {
+    ///             3
+    ///         };
+    ///         let ty = match u.int_in_range::<u8>(1..=num_choices)? {
+    ///             1 => Type::Bool,
+    ///             2 => Type::Int,
+    ///             3 => Type::List(u.int_in_range(0..=context.len() - 1)?),
+    ///             _ => unreachable!(),
+    ///         };
+    ///         context.push(ty);
+    ///         Ok(ControlFlow::Continue(()))
+    ///     })?;
+    ///
+    ///     // The number of loop iterations are constrained by the min/max
+    ///     // bounds that we provided.
+    ///     assert!(context.len() >= 10);
+    ///     assert!(context.len() <= 20);
+    ///
+    ///     Ok(context)
+    /// }
+    /// ```
+    pub fn arbitrary_loop(
+        &mut self,
+        min: Option<u32>,
+        max: Option<u32>,
+        mut f: impl FnMut(&mut Self) -> Result<ControlFlow<(), ()>>,
+    ) -> Result<()> {
+        let min = min.unwrap_or(0);
+        let max = max.unwrap_or(u32::MAX);
+
+        for _ in 0..self.int_in_range(min..=max)? {
+            match f(self)? {
+                ControlFlow::Continue(_) => continue,
+                ControlFlow::Break(_) => break,
+            }
+        }
+
+        Ok(())
+    }
+}
+
+/// Utility iterator produced by [`Unstructured::arbitrary_iter`]
+pub struct ArbitraryIter<'a, 'b, ElementType> {
+    u: &'b mut Unstructured<'a>,
+    _marker: PhantomData<ElementType>,
+}
+
+impl<'a, 'b, ElementType: Arbitrary<'a>> Iterator for ArbitraryIter<'a, 'b, ElementType> {
+    type Item = Result<ElementType>;
+    fn next(&mut self) -> Option<Result<ElementType>> {
+        let keep_going = self.u.arbitrary().unwrap_or(false);
+        if keep_going {
+            Some(Arbitrary::arbitrary(self.u))
+        } else {
+            None
+        }
+    }
+}
+
+/// Utility iterator produced by [`Unstructured::arbitrary_take_rest_iter`]
+pub struct ArbitraryTakeRestIter<'a, ElementType> {
+    u: Option<Unstructured<'a>>,
+    size: usize,
+    _marker: PhantomData<ElementType>,
+}
+
+impl<'a, ElementType: Arbitrary<'a>> Iterator for ArbitraryTakeRestIter<'a, ElementType> {
+    type Item = Result<ElementType>;
+    fn next(&mut self) -> Option<Result<ElementType>> {
+        if let Some(mut u) = self.u.take() {
+            if self.size == 1 {
+                Some(Arbitrary::arbitrary_take_rest(u))
+            } else if self.size == 0 {
+                None
+            } else {
+                self.size -= 1;
+                let ret = Arbitrary::arbitrary(&mut u);
+                self.u = Some(u);
+                Some(ret)
+            }
+        } else {
+            None
+        }
+    }
+}
+
+/// A trait that is implemented for all of the primitive integers:
+///
+/// * `u8`
+/// * `u16`
+/// * `u32`
+/// * `u64`
+/// * `u128`
+/// * `usize`
+/// * `i8`
+/// * `i16`
+/// * `i32`
+/// * `i64`
+/// * `i128`
+/// * `isize`
+///
+/// Don't implement this trait yourself.
+pub trait Int:
+    Copy
+    + std::fmt::Debug
+    + PartialOrd
+    + Ord
+    + ops::Sub<Self, Output = Self>
+    + ops::Rem<Self, Output = Self>
+    + ops::Shr<Self, Output = Self>
+    + ops::Shl<usize, Output = Self>
+    + ops::BitOr<Self, Output = Self>
+{
+    #[doc(hidden)]
+    type Unsigned: Int;
+
+    #[doc(hidden)]
+    const ZERO: Self;
+
+    #[doc(hidden)]
+    const ONE: Self;
+
+    #[doc(hidden)]
+    const MAX: Self;
+
+    #[doc(hidden)]
+    fn from_u8(b: u8) -> Self;
+
+    #[doc(hidden)]
+    fn from_usize(u: usize) -> Self;
+
+    #[doc(hidden)]
+    fn checked_add(self, rhs: Self) -> Option<Self>;
+
+    #[doc(hidden)]
+    fn wrapping_add(self, rhs: Self) -> Self;
+
+    #[doc(hidden)]
+    fn wrapping_sub(self, rhs: Self) -> Self;
+
+    #[doc(hidden)]
+    fn to_unsigned(self) -> Self::Unsigned;
+
+    #[doc(hidden)]
+    fn from_unsigned(unsigned: Self::Unsigned) -> Self;
+}
+
+macro_rules! impl_int {
+    ( $( $ty:ty : $unsigned_ty: ty ; )* ) => {
+        $(
+            impl Int for $ty {
+                type Unsigned = $unsigned_ty;
+
+                const ZERO: Self = 0;
+
+                const ONE: Self = 1;
+
+                const MAX: Self = Self::MAX;
+
+                fn from_u8(b: u8) -> Self {
+                    b as Self
+                }
+
+                fn from_usize(u: usize) -> Self {
+                    u as Self
+                }
+
+                fn checked_add(self, rhs: Self) -> Option<Self> {
+                    <$ty>::checked_add(self, rhs)
+                }
+
+                fn wrapping_add(self, rhs: Self) -> Self {
+                    <$ty>::wrapping_add(self, rhs)
+                }
+
+                fn wrapping_sub(self, rhs: Self) -> Self {
+                    <$ty>::wrapping_sub(self, rhs)
+                }
+
+                fn to_unsigned(self) -> Self::Unsigned {
+                    self as $unsigned_ty
+                }
+
+                fn from_unsigned(unsigned: $unsigned_ty) -> Self {
+                    unsigned as Self
+                }
+            }
+        )*
+    }
+}
+
+impl_int! {
+    u8: u8;
+    u16: u16;
+    u32: u32;
+    u64: u64;
+    u128: u128;
+    usize: usize;
+    i8: u8;
+    i16: u16;
+    i32: u32;
+    i64: u64;
+    i128: u128;
+    isize: usize;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_byte_size() {
+        let mut u = Unstructured::new(&[1, 2, 3, 4, 5, 6, 7, 8, 9, 6]);
+        // Should take one byte off the end
+        assert_eq!(u.arbitrary_byte_size().unwrap(), 6);
+        assert_eq!(u.len(), 9);
+        let mut v = vec![];
+        v.resize(260, 0);
+        v.push(1);
+        v.push(4);
+        let mut u = Unstructured::new(&v);
+        // Should read two bytes off the end
+        assert_eq!(u.arbitrary_byte_size().unwrap(), 0x104);
+        assert_eq!(u.len(), 260);
+    }
+
+    #[test]
+    fn int_in_range_of_one() {
+        let mut u = Unstructured::new(&[1, 2, 3, 4, 5, 6, 7, 8, 9, 6]);
+        let x = u.int_in_range(0..=0).unwrap();
+        assert_eq!(x, 0);
+        let choice = *u.choose(&[42]).unwrap();
+        assert_eq!(choice, 42)
+    }
+
+    #[test]
+    fn int_in_range_uses_minimal_amount_of_bytes() {
+        let mut u = Unstructured::new(&[1, 2]);
+        assert_eq!(1, u.int_in_range::<u8>(0..=u8::MAX).unwrap());
+        assert_eq!(u.len(), 1);
+
+        let mut u = Unstructured::new(&[1, 2]);
+        assert_eq!(1, u.int_in_range::<u32>(0..=u8::MAX as u32).unwrap());
+        assert_eq!(u.len(), 1);
+
+        let mut u = Unstructured::new(&[1]);
+        assert_eq!(1, u.int_in_range::<u32>(0..=u8::MAX as u32 + 1).unwrap());
+        assert!(u.is_empty());
+    }
+
+    #[test]
+    fn int_in_range_in_bounds() {
+        for input in u8::MIN..=u8::MAX {
+            let input = [input];
+
+            let mut u = Unstructured::new(&input);
+            let x = u.int_in_range(1..=u8::MAX).unwrap();
+            assert_ne!(x, 0);
+
+            let mut u = Unstructured::new(&input);
+            let x = u.int_in_range(0..=u8::MAX - 1).unwrap();
+            assert_ne!(x, u8::MAX);
+        }
+    }
+
+    #[test]
+    fn int_in_range_covers_unsigned_range() {
+        // Test that we generate all values within the range given to
+        // `int_in_range`.
+
+        let mut full = [false; u8::MAX as usize + 1];
+        let mut no_zero = [false; u8::MAX as usize];
+        let mut no_max = [false; u8::MAX as usize];
+        let mut narrow = [false; 10];
+
+        for input in u8::MIN..=u8::MAX {
+            let input = [input];
+
+            let mut u = Unstructured::new(&input);
+            let x = u.int_in_range(0..=u8::MAX).unwrap();
+            full[x as usize] = true;
+
+            let mut u = Unstructured::new(&input);
+            let x = u.int_in_range(1..=u8::MAX).unwrap();
+            no_zero[x as usize - 1] = true;
+
+            let mut u = Unstructured::new(&input);
+            let x = u.int_in_range(0..=u8::MAX - 1).unwrap();
+            no_max[x as usize] = true;
+
+            let mut u = Unstructured::new(&input);
+            let x = u.int_in_range(100..=109).unwrap();
+            narrow[x as usize - 100] = true;
+        }
+
+        for (i, covered) in full.iter().enumerate() {
+            assert!(covered, "full[{}] should have been generated", i);
+        }
+        for (i, covered) in no_zero.iter().enumerate() {
+            assert!(covered, "no_zero[{}] should have been generated", i);
+        }
+        for (i, covered) in no_max.iter().enumerate() {
+            assert!(covered, "no_max[{}] should have been generated", i);
+        }
+        for (i, covered) in narrow.iter().enumerate() {
+            assert!(covered, "narrow[{}] should have been generated", i);
+        }
+    }
+
+    #[test]
+    fn int_in_range_covers_signed_range() {
+        // Test that we generate all values within the range given to
+        // `int_in_range`.
+
+        let mut full = [false; u8::MAX as usize + 1];
+        let mut no_min = [false; u8::MAX as usize];
+        let mut no_max = [false; u8::MAX as usize];
+        let mut narrow = [false; 21];
+
+        let abs_i8_min: isize = 128;
+
+        for input in 0..=u8::MAX {
+            let input = [input];
+
+            let mut u = Unstructured::new(&input);
+            let x = u.int_in_range(i8::MIN..=i8::MAX).unwrap();
+            full[(x as isize + abs_i8_min) as usize] = true;
+
+            let mut u = Unstructured::new(&input);
+            let x = u.int_in_range(i8::MIN + 1..=i8::MAX).unwrap();
+            no_min[(x as isize + abs_i8_min - 1) as usize] = true;
+
+            let mut u = Unstructured::new(&input);
+            let x = u.int_in_range(i8::MIN..=i8::MAX - 1).unwrap();
+            no_max[(x as isize + abs_i8_min) as usize] = true;
+
+            let mut u = Unstructured::new(&input);
+            let x = u.int_in_range(-10..=10).unwrap();
+            narrow[(x as isize + 10) as usize] = true;
+        }
+
+        for (i, covered) in full.iter().enumerate() {
+            assert!(covered, "full[{}] should have been generated", i);
+        }
+        for (i, covered) in no_min.iter().enumerate() {
+            assert!(covered, "no_min[{}] should have been generated", i);
+        }
+        for (i, covered) in no_max.iter().enumerate() {
+            assert!(covered, "no_max[{}] should have been generated", i);
+        }
+        for (i, covered) in narrow.iter().enumerate() {
+            assert!(covered, "narrow[{}] should have been generated", i);
+        }
+    }
+}