Adding upstream version 124.0.1.upstream/124.0.1

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

9 files changed, 2539 insertions, 0 deletions

diff --git a/third_party/rust/scroll/src/ctx.rs b/third_party/rust/scroll/src/ctx.rs
new file mode 100644
index 0000000000..1f982b82fa
--- /dev/null
+++ b/third_party/rust/scroll/src/ctx.rs
@@ -0,0 +1,897 @@
+//! Generic context-aware conversion traits, for automatic _downstream_ extension of `Pread`, et. al
+//!
+//! The context traits are arguably the center piece of the scroll crate. In simple terms they
+//! define how to actually read and write, respectively, a data type from a container, being able to
+//! take context into account.
+//!
+//! ### Reading
+//!
+//! Types implementing [TryFromCtx](trait.TryFromCtx.html) and it's infallible cousin [FromCtx](trait.FromCtx.html)
+//! allow a user of [Pread::pread](../trait.Pread.html#method.pread) or respectively
+//! [Cread::cread](../trait.Cread.html#method.cread) and
+//! [IOread::ioread](../trait.IOread.html#method.ioread) to read that data type from a data source one
+//! of the `*read` traits has been implemented for.
+//!
+//! Implementations of `TryFromCtx` specify a source (called `This`) and an `Error` type for failed
+//! reads. The source defines the kind of container the type can be read from, and defaults to
+//! `[u8]` for any type that implements `AsRef<[u8]>`.
+//!
+//! `FromCtx` is slightly more restricted; it requires the implementer to use `[u8]` as source and
+//! never fail, and thus does not have an `Error` type.
+//!
+//! Types chosen here are of relevance to `Pread` implementations; of course only a container which
+//! can produce a source of the type `This` can be used to read a `TryFromCtx` requiring it and the
+//! `Error` type returned in `Err` of `Pread::pread`'s Result.
+//!
+//! ### Writing
+//!
+//! [TryIntoCtx](trait.TryIntoCtx.html) and the infallible [IntoCtx](trait.IntoCtx.html) work
+//! similarly to the above traits, allowing [Pwrite::pwrite](../trait.Pwrite.html#method.pwrite) or
+//! respectively [Cwrite::cwrite](../trait.Cwrite.html#method.cwrite) and
+//! [IOwrite::iowrite](../trait.IOwrite.html#method.iowrite) to write data into a byte sink for
+//! which one of the `*write` traits has been implemented for.
+//!
+//! `IntoCtx` is similarly restricted as `FromCtx` is to `TryFromCtx`. And equally the types chosen
+//! affect usable `Pwrite` implementation.
+//!
+//! ### Context
+//!
+//! Each of the traits passes along a `Ctx` to the marshalling logic. This context type contains
+//! any additional information that may be required to successfully parse or write the data:
+//! Examples would be endianness to use, field lengths of a serialized struct, or delimiters to use
+//! when reading/writing `&str`. The context type can be any type but must derive
+//! [Copy](https://doc.rust-lang.org/std/marker/trait.Copy.html). In addition if you want to use
+//! the `*read`-methods instead of the `*read_with` ones you must also implement
+//! [default::Default](https://doc.rust-lang.org/std/default/trait.Default.html).
+//!
+//! # Example
+//!
+//! Let's expand on the [previous example](../index.html#complex-use-cases).
+//!
+//! ```rust
+//! use scroll::{self, ctx, Pread, Endian};
+//! use scroll::ctx::StrCtx;
+//!
+//! #[derive(Copy, Clone, PartialEq, Eq)]
+//! enum FieldSize {
+//!     U32,
+//!     U64
+//! }
+//!
+//! // Our custom context type. As said above it has to derive Copy.
+//! #[derive(Copy, Clone)]
+//! struct Context {
+//!     fieldsize: FieldSize,
+//!     endianess: Endian,
+//! }
+//!
+//! // Our custom data type
+//! struct Data<'b> {
+//!   // These u64 are encoded either as 32-bit or 64-bit wide ints. Which one it is is defined in
+//!   // the Context.
+//!   // Also, let's imagine they have a strict relationship: A < B < C otherwise the struct is
+//!   // invalid.
+//!   field_a: u64,
+//!   field_b: u64,
+//!   field_c: u64,
+//!
+//!   // Both of these are marshalled with a prefixed length.
+//!   name: &'b str,
+//!   value: &'b [u8],
+//! }
+//!
+//! #[derive(Debug)]
+//! enum Error {
+//!     // We'll return this custom error if the field* relationship doesn't hold
+//!     BadFieldMatchup,
+//!     Scroll(scroll::Error),
+//! }
+//!
+//! impl<'a> ctx::TryFromCtx<'a, Context> for Data<'a> {
+//!   type Error = Error;
+//!
+//!   // Using the explicit lifetime specification again you ensure that read data doesn't outlife
+//!   // its source buffer without having to resort to copying.
+//!   fn try_from_ctx (src: &'a [u8], ctx: Context)
+//!     // the `usize` returned here is the amount of bytes read.
+//!     -> Result<(Self, usize), Self::Error>
+//!   {
+//!     // The offset counter; gread and gread_with increment a given counter automatically so we
+//!     // don't have to manually care.
+//!     let offset = &mut 0;
+//!
+//!     let field_a;
+//!     let field_b;
+//!     let field_c;
+//!
+//!     // Switch the amount of bytes read depending on the parsing context
+//!     if ctx.fieldsize == FieldSize::U32 {
+//!       field_a = src.gread_with::<u32>(offset, ctx.endianess)? as u64;
+//!       field_b = src.gread_with::<u32>(offset, ctx.endianess)? as u64;
+//!       field_c = src.gread_with::<u32>(offset, ctx.endianess)? as u64;
+//!     } else {
+//!       field_a = src.gread_with::<u64>(offset, ctx.endianess)?;
+//!       field_b = src.gread_with::<u64>(offset, ctx.endianess)?;
+//!       field_c = src.gread_with::<u64>(offset, ctx.endianess)?;
+//!     }
+//!
+//!     // You can use type ascribition or turbofish operators, whichever you prefer.
+//!     let namelen = src.gread_with::<u16>(offset, ctx.endianess)? as usize;
+//!     let name: &str = src.gread_with(offset, scroll::ctx::StrCtx::Length(namelen))?;
+//!
+//!     let vallen = src.gread_with::<u16>(offset, ctx.endianess)? as usize;
+//!     let value = &src[*offset..(*offset+vallen)];
+//!
+//!     // Let's sanity check those fields, shall we?
+//!     if ! (field_a < field_b && field_b < field_c) {
+//!       return Err(Error::BadFieldMatchup);
+//!     }
+//!
+//!     Ok((Data { field_a, field_b, field_c, name, value }, *offset))
+//!   }
+//! }
+//!
+//! // In lieu of a complex byte buffer we hearken back to the venerable &[u8]; do note however
+//! // that the implementation of TryFromCtx did not specify such. In fact any type that implements
+//! // Pread can now read `Data` as it implements TryFromCtx.
+//! let bytes = b"\x00\x02\x03\x04\x01\x02\x03\x04\xde\xad\xbe\xef\x00\x08UserName\x00\x02\xCA\xFE";
+//!
+//! // We define an appropiate context, and get going
+//! let contextA = Context {
+//!     fieldsize: FieldSize::U32,
+//!     endianess: Endian::Big,
+//! };
+//! let data: Data = bytes.pread_with(0, contextA).unwrap();
+//!
+//! assert_eq!(data.field_a, 0x00020304);
+//! assert_eq!(data.field_b, 0x01020304);
+//! assert_eq!(data.field_c, 0xdeadbeef);
+//! assert_eq!(data.name, "UserName");
+//! assert_eq!(data.value, [0xCA, 0xFE]);
+//!
+//! // Here we have a context with a different FieldSize, changing parsing information at runtime.
+//! let contextB = Context {
+//!     fieldsize: FieldSize::U64,
+//!     endianess: Endian::Big,
+//! };
+//!
+//! // Which will of course error with a malformed input for the context
+//! let err: Result<Data, Error> = bytes.pread_with(0, contextB);
+//! assert!(err.is_err());
+//!
+//! let bytes_long = [0x00,0x00,0x00,0x00,0x00,0x02,0x03,0x04,0x00,0x00,0x00,0x00,0x01,0x02,0x03,
+//!                   0x04,0x00,0x00,0x00,0x00,0xde,0xad,0xbe,0xef,0x00,0x08,0x55,0x73,0x65,0x72,
+//!                   0x4e,0x61,0x6d,0x65,0x00,0x02,0xCA,0xFE];
+//!
+//! let data: Data = bytes_long.pread_with(0, contextB).unwrap();
+//!
+//! assert_eq!(data.field_a, 0x00020304);
+//! assert_eq!(data.field_b, 0x01020304);
+//! assert_eq!(data.field_c, 0xdeadbeef);
+//! assert_eq!(data.name, "UserName");
+//! assert_eq!(data.value, [0xCA, 0xFE]);
+//!
+//! // Ergonomic conversion, not relevant really.
+//! use std::convert::From;
+//! impl From<scroll::Error> for Error {
+//!   fn from(error: scroll::Error) -> Error {
+//!     Error::Scroll(error)
+//!   }
+//! }
+//! ```
+
+use core::mem::size_of;
+use core::mem::transmute;
+use core::ptr::copy_nonoverlapping;
+use core::result;
+use core::str;
+
+#[cfg(feature = "std")]
+use std::ffi::{CStr, CString};
+
+use crate::endian::Endian;
+use crate::error;
+
+/// A trait for measuring how large something is; for a byte sequence, it will be its length.
+pub trait MeasureWith<Ctx> {
+    /// How large is `Self`, given the `ctx`?
+    fn measure_with(&self, ctx: &Ctx) -> usize;
+}
+
+impl<Ctx> MeasureWith<Ctx> for [u8] {
+    #[inline]
+    fn measure_with(&self, _ctx: &Ctx) -> usize {
+        self.len()
+    }
+}
+
+impl<Ctx, T: AsRef<[u8]>> MeasureWith<Ctx> for T {
+    #[inline]
+    fn measure_with(&self, _ctx: &Ctx) -> usize {
+        self.as_ref().len()
+    }
+}
+
+/// The parsing context for converting a byte sequence to a `&str`
+///
+/// `StrCtx` specifies what byte delimiter to use, and defaults to C-style null terminators. Be careful.
+#[derive(Debug, Copy, Clone)]
+pub enum StrCtx {
+    Delimiter(u8),
+    DelimiterUntil(u8, usize),
+    Length(usize),
+}
+
+/// A C-style, null terminator based delimiter
+pub const NULL: u8 = 0;
+/// A space-based delimiter
+pub const SPACE: u8 = 0x20;
+/// A newline-based delimiter
+pub const RET: u8 = 0x0a;
+/// A tab-based delimiter
+pub const TAB: u8 = 0x09;
+
+impl Default for StrCtx {
+    #[inline]
+    fn default() -> Self {
+        StrCtx::Delimiter(NULL)
+    }
+}
+
+impl StrCtx {
+    pub fn len(&self) -> usize {
+        match *self {
+            StrCtx::Delimiter(_) | StrCtx::DelimiterUntil(_, _) => 1,
+            StrCtx::Length(_) => 0,
+        }
+    }
+
+    pub fn is_empty(&self) -> bool {
+        if let StrCtx::Length(_) = *self {
+            true
+        } else {
+            false
+        }
+    }
+}
+
+/// Reads `Self` from `This` using the context `Ctx`; must _not_ fail
+pub trait FromCtx<Ctx: Copy = (), This: ?Sized = [u8]> {
+    fn from_ctx(this: &This, ctx: Ctx) -> Self;
+}
+
+/// Tries to read `Self` from `This` using the context `Ctx`
+///
+/// # Implementing Your Own Reader
+/// If you want to implement your own reader for a type `Foo` from some kind of buffer (say
+/// `[u8]`), then you need to implement this trait
+///
+/// ```rust
+/// use scroll::{self, ctx, Pread};
+/// #[derive(Debug, PartialEq, Eq)]
+/// pub struct Foo(u16);
+///
+/// impl<'a> ctx::TryFromCtx<'a, scroll::Endian> for Foo {
+///      type Error = scroll::Error;
+///      fn try_from_ctx(this: &'a [u8], le: scroll::Endian) -> Result<(Self, usize), Self::Error> {
+///          if this.len() < 2 { return Err((scroll::Error::Custom("whatever".to_string())).into()) }
+///          let n = this.pread_with(0, le)?;
+///          Ok((Foo(n), 2))
+///      }
+/// }
+///
+/// let bytes: [u8; 4] = [0xde, 0xad, 0, 0];
+/// let foo = bytes.pread_with::<Foo>(0, scroll::LE).unwrap();
+/// assert_eq!(Foo(0xadde), foo);
+///
+/// let foo2 = bytes.pread_with::<Foo>(0, scroll::BE).unwrap();
+/// assert_eq!(Foo(0xdeadu16), foo2);
+/// ```
+///
+/// # Advanced: Using Your Own Error in `TryFromCtx`
+/// ```rust
+///  use scroll::{self, ctx, Pread};
+///  use std::error;
+///  use std::fmt::{self, Display};
+///  // make some kind of normal error which also can transformed from a scroll error
+///  #[derive(Debug)]
+///  pub struct ExternalError {}
+///
+///  impl Display for ExternalError {
+///      fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+///          write!(fmt, "ExternalError")
+///      }
+///  }
+///
+///  impl error::Error for ExternalError {
+///      fn description(&self) -> &str {
+///          "ExternalError"
+///      }
+///      fn cause(&self) -> Option<&dyn error::Error> { None}
+///  }
+///
+///  impl From<scroll::Error> for ExternalError {
+///      fn from(err: scroll::Error) -> Self {
+///          match err {
+///              _ => ExternalError{},
+///          }
+///      }
+///  }
+///  #[derive(Debug, PartialEq, Eq)]
+///  pub struct Foo(u16);
+///
+///  impl<'a> ctx::TryFromCtx<'a, scroll::Endian> for Foo {
+///      type Error = ExternalError;
+///      fn try_from_ctx(this: &'a [u8], le: scroll::Endian) -> Result<(Self, usize), Self::Error> {
+///          if this.len() <= 2 { return Err((ExternalError {}).into()) }
+///          let offset = &mut 0;
+///          let n = this.gread_with(offset, le)?;
+///          Ok((Foo(n), *offset))
+///      }
+///  }
+///
+/// let bytes: [u8; 4] = [0xde, 0xad, 0, 0];
+/// let foo: Result<Foo, ExternalError> = bytes.pread(0);
+/// ```
+pub trait TryFromCtx<'a, Ctx: Copy = (), This: ?Sized = [u8]>
+where
+    Self: 'a + Sized,
+{
+    type Error;
+    fn try_from_ctx(from: &'a This, ctx: Ctx) -> Result<(Self, usize), Self::Error>;
+}
+
+/// Writes `Self` into `This` using the context `Ctx`
+pub trait IntoCtx<Ctx: Copy = (), This: ?Sized = [u8]>: Sized {
+    fn into_ctx(self, _: &mut This, ctx: Ctx);
+}
+
+/// Tries to write `Self` into `This` using the context `Ctx`
+/// To implement writing into an arbitrary byte buffer, implement `TryIntoCtx`
+/// # Example
+/// ```rust
+/// use scroll::{self, ctx, LE, Endian, Pwrite};
+/// #[derive(Debug, PartialEq, Eq)]
+/// pub struct Foo(u16);
+///
+/// // this will use the default `DefaultCtx = scroll::Endian`
+/// impl ctx::TryIntoCtx<Endian> for Foo {
+///     // you can use your own error here too, but you will then need to specify it in fn generic parameters
+///     type Error = scroll::Error;
+///     // you can write using your own context type, see `leb128.rs`
+///     fn try_into_ctx(self, this: &mut [u8], le: Endian) -> Result<usize, Self::Error> {
+///         if this.len() < 2 { return Err((scroll::Error::Custom("whatever".to_string())).into()) }
+///         this.pwrite_with(self.0, 0, le)?;
+///         Ok(2)
+///     }
+/// }
+/// // now we can write a `Foo` into some buffer (in this case, a byte buffer, because that's what we implemented it for above)
+///
+/// let mut bytes: [u8; 4] = [0, 0, 0, 0];
+/// bytes.pwrite_with(Foo(0x7f), 1, LE).unwrap();
+/// ```
+pub trait TryIntoCtx<Ctx: Copy = (), This: ?Sized = [u8]>: Sized {
+    type Error;
+    fn try_into_ctx(self, _: &mut This, ctx: Ctx) -> Result<usize, Self::Error>;
+}
+
+/// Gets the size of `Self` with a `Ctx`, and in `Self::Units`. Implementors can then call `Gread` related functions
+///
+/// The rationale behind this trait is to:
+///
+/// 1. Prevent `gread` from being used, and the offset being modified based on simply the sizeof the value, which can be a misnomer, e.g., for Leb128, etc.
+/// 2. Allow a context based size, which is useful for 32/64 bit variants for various containers, etc.
+pub trait SizeWith<Ctx = ()> {
+    fn size_with(ctx: &Ctx) -> usize;
+}
+
+#[rustfmt::skip]
+macro_rules! signed_to_unsigned {
+    (i8) =>  {u8 };
+    (u8) =>  {u8 };
+    (i16) => {u16};
+    (u16) => {u16};
+    (i32) => {u32};
+    (u32) => {u32};
+    (i64) => {u64};
+    (u64) => {u64};
+    (i128) => {u128};
+    (u128) => {u128};
+    (f32) => {u32};
+    (f64) => {u64};
+}
+
+macro_rules! write_into {
+    ($typ:ty, $size:expr, $n:expr, $dst:expr, $endian:expr) => {{
+        unsafe {
+            assert!($dst.len() >= $size);
+            let bytes = transmute::<$typ, [u8; $size]>(if $endian.is_little() {
+                $n.to_le()
+            } else {
+                $n.to_be()
+            });
+            copy_nonoverlapping((&bytes).as_ptr(), $dst.as_mut_ptr(), $size);
+        }
+    }};
+}
+
+macro_rules! into_ctx_impl {
+    ($typ:tt, $size:expr) => {
+        impl IntoCtx<Endian> for $typ {
+            #[inline]
+            fn into_ctx(self, dst: &mut [u8], le: Endian) {
+                assert!(dst.len() >= $size);
+                write_into!($typ, $size, self, dst, le);
+            }
+        }
+        impl<'a> IntoCtx<Endian> for &'a $typ {
+            #[inline]
+            fn into_ctx(self, dst: &mut [u8], le: Endian) {
+                (*self).into_ctx(dst, le)
+            }
+        }
+        impl TryIntoCtx<Endian> for $typ
+        where
+            $typ: IntoCtx<Endian>,
+        {
+            type Error = error::Error;
+            #[inline]
+            fn try_into_ctx(self, dst: &mut [u8], le: Endian) -> error::Result<usize> {
+                if $size > dst.len() {
+                    Err(error::Error::TooBig {
+                        size: $size,
+                        len: dst.len(),
+                    })
+                } else {
+                    <$typ as IntoCtx<Endian>>::into_ctx(self, dst, le);
+                    Ok($size)
+                }
+            }
+        }
+        impl<'a> TryIntoCtx<Endian> for &'a $typ {
+            type Error = error::Error;
+            #[inline]
+            fn try_into_ctx(self, dst: &mut [u8], le: Endian) -> error::Result<usize> {
+                (*self).try_into_ctx(dst, le)
+            }
+        }
+    };
+}
+
+macro_rules! from_ctx_impl {
+    ($typ:tt, $size:expr) => {
+        impl<'a> FromCtx<Endian> for $typ {
+            #[inline]
+            fn from_ctx(src: &[u8], le: Endian) -> Self {
+                assert!(src.len() >= $size);
+                let mut data: signed_to_unsigned!($typ) = 0;
+                unsafe {
+                    copy_nonoverlapping(
+                        src.as_ptr(),
+                        &mut data as *mut signed_to_unsigned!($typ) as *mut u8,
+                        $size,
+                    );
+                }
+                (if le.is_little() {
+                    data.to_le()
+                } else {
+                    data.to_be()
+                }) as $typ
+            }
+        }
+
+        impl<'a> TryFromCtx<'a, Endian> for $typ
+        where
+            $typ: FromCtx<Endian>,
+        {
+            type Error = error::Error;
+            #[inline]
+            fn try_from_ctx(
+                src: &'a [u8],
+                le: Endian,
+            ) -> result::Result<(Self, usize), Self::Error> {
+                if $size > src.len() {
+                    Err(error::Error::TooBig {
+                        size: $size,
+                        len: src.len(),
+                    })
+                } else {
+                    Ok((FromCtx::from_ctx(&src, le), $size))
+                }
+            }
+        }
+        // as ref
+        impl<'a, T> FromCtx<Endian, T> for $typ
+        where
+            T: AsRef<[u8]>,
+        {
+            #[inline]
+            fn from_ctx(src: &T, le: Endian) -> Self {
+                let src = src.as_ref();
+                assert!(src.len() >= $size);
+                let mut data: signed_to_unsigned!($typ) = 0;
+                unsafe {
+                    copy_nonoverlapping(
+                        src.as_ptr(),
+                        &mut data as *mut signed_to_unsigned!($typ) as *mut u8,
+                        $size,
+                    );
+                }
+                (if le.is_little() {
+                    data.to_le()
+                } else {
+                    data.to_be()
+                }) as $typ
+            }
+        }
+
+        impl<'a, T> TryFromCtx<'a, Endian, T> for $typ
+        where
+            $typ: FromCtx<Endian, T>,
+            T: AsRef<[u8]>,
+        {
+            type Error = error::Error;
+            #[inline]
+            fn try_from_ctx(src: &'a T, le: Endian) -> result::Result<(Self, usize), Self::Error> {
+                let src = src.as_ref();
+                Self::try_from_ctx(src, le)
+            }
+        }
+    };
+}
+
+macro_rules! ctx_impl {
+    ($typ:tt, $size:expr) => {
+        from_ctx_impl!($typ, $size);
+    };
+}
+
+ctx_impl!(u8, 1);
+ctx_impl!(i8, 1);
+ctx_impl!(u16, 2);
+ctx_impl!(i16, 2);
+ctx_impl!(u32, 4);
+ctx_impl!(i32, 4);
+ctx_impl!(u64, 8);
+ctx_impl!(i64, 8);
+ctx_impl!(u128, 16);
+ctx_impl!(i128, 16);
+
+macro_rules! from_ctx_float_impl {
+    ($typ:tt, $size:expr) => {
+        impl<'a> FromCtx<Endian> for $typ {
+            #[inline]
+            fn from_ctx(src: &[u8], le: Endian) -> Self {
+                assert!(src.len() >= ::core::mem::size_of::<Self>());
+                let mut data: signed_to_unsigned!($typ) = 0;
+                unsafe {
+                    copy_nonoverlapping(
+                        src.as_ptr(),
+                        &mut data as *mut signed_to_unsigned!($typ) as *mut u8,
+                        $size,
+                    );
+                    transmute(if le.is_little() {
+                        data.to_le()
+                    } else {
+                        data.to_be()
+                    })
+                }
+            }
+        }
+        impl<'a> TryFromCtx<'a, Endian> for $typ
+        where
+            $typ: FromCtx<Endian>,
+        {
+            type Error = error::Error;
+            #[inline]
+            fn try_from_ctx(
+                src: &'a [u8],
+                le: Endian,
+            ) -> result::Result<(Self, usize), Self::Error> {
+                if $size > src.len() {
+                    Err(error::Error::TooBig {
+                        size: $size,
+                        len: src.len(),
+                    })
+                } else {
+                    Ok((FromCtx::from_ctx(src, le), $size))
+                }
+            }
+        }
+    };
+}
+
+from_ctx_float_impl!(f32, 4);
+from_ctx_float_impl!(f64, 8);
+
+into_ctx_impl!(u8, 1);
+into_ctx_impl!(i8, 1);
+into_ctx_impl!(u16, 2);
+into_ctx_impl!(i16, 2);
+into_ctx_impl!(u32, 4);
+into_ctx_impl!(i32, 4);
+into_ctx_impl!(u64, 8);
+into_ctx_impl!(i64, 8);
+into_ctx_impl!(u128, 16);
+into_ctx_impl!(i128, 16);
+
+macro_rules! into_ctx_float_impl {
+    ($typ:tt, $size:expr) => {
+        impl IntoCtx<Endian> for $typ {
+            #[inline]
+            fn into_ctx(self, dst: &mut [u8], le: Endian) {
+                assert!(dst.len() >= $size);
+                write_into!(
+                    signed_to_unsigned!($typ),
+                    $size,
+                    transmute::<$typ, signed_to_unsigned!($typ)>(self),
+                    dst,
+                    le
+                );
+            }
+        }
+        impl<'a> IntoCtx<Endian> for &'a $typ {
+            #[inline]
+            fn into_ctx(self, dst: &mut [u8], le: Endian) {
+                (*self).into_ctx(dst, le)
+            }
+        }
+        impl TryIntoCtx<Endian> for $typ
+        where
+            $typ: IntoCtx<Endian>,
+        {
+            type Error = error::Error;
+            #[inline]
+            fn try_into_ctx(self, dst: &mut [u8], le: Endian) -> error::Result<usize> {
+                if $size > dst.len() {
+                    Err(error::Error::TooBig {
+                        size: $size,
+                        len: dst.len(),
+                    })
+                } else {
+                    <$typ as IntoCtx<Endian>>::into_ctx(self, dst, le);
+                    Ok($size)
+                }
+            }
+        }
+        impl<'a> TryIntoCtx<Endian> for &'a $typ {
+            type Error = error::Error;
+            #[inline]
+            fn try_into_ctx(self, dst: &mut [u8], le: Endian) -> error::Result<usize> {
+                (*self).try_into_ctx(dst, le)
+            }
+        }
+    };
+}
+
+into_ctx_float_impl!(f32, 4);
+into_ctx_float_impl!(f64, 8);
+
+impl<'a> TryFromCtx<'a, StrCtx> for &'a str {
+    type Error = error::Error;
+    #[inline]
+    /// Read a `&str` from `src` using `delimiter`
+    fn try_from_ctx(src: &'a [u8], ctx: StrCtx) -> Result<(Self, usize), Self::Error> {
+        let len = match ctx {
+            StrCtx::Length(len) => len,
+            StrCtx::Delimiter(delimiter) => src.iter().take_while(|c| **c != delimiter).count(),
+            StrCtx::DelimiterUntil(delimiter, len) => {
+                if len > src.len() {
+                    return Err(error::Error::TooBig {
+                        size: len,
+                        len: src.len(),
+                    });
+                };
+                src.iter()
+                    .take_while(|c| **c != delimiter)
+                    .take(len)
+                    .count()
+            }
+        };
+
+        if len > src.len() {
+            return Err(error::Error::TooBig {
+                size: len,
+                len: src.len(),
+            });
+        };
+
+        match str::from_utf8(&src[..len]) {
+            Ok(res) => Ok((res, len + ctx.len())),
+            Err(_) => Err(error::Error::BadInput {
+                size: src.len(),
+                msg: "invalid utf8",
+            }),
+        }
+    }
+}
+
+impl<'a, T> TryFromCtx<'a, StrCtx, T> for &'a str
+where
+    T: AsRef<[u8]>,
+{
+    type Error = error::Error;
+    #[inline]
+    fn try_from_ctx(src: &'a T, ctx: StrCtx) -> result::Result<(Self, usize), Self::Error> {
+        let src = src.as_ref();
+        TryFromCtx::try_from_ctx(src, ctx)
+    }
+}
+
+impl<'a> TryIntoCtx for &'a [u8] {
+    type Error = error::Error;
+    #[inline]
+    fn try_into_ctx(self, dst: &mut [u8], _ctx: ()) -> error::Result<usize> {
+        let src_len = self.len() as isize;
+        let dst_len = dst.len() as isize;
+        // if src_len < 0 || dst_len < 0 || offset < 0 {
+        //     return Err(error::Error::BadOffset(format!("requested operation has negative casts: src len: {} dst len: {} offset: {}", src_len, dst_len, offset)).into())
+        // }
+        if src_len > dst_len {
+            Err(error::Error::TooBig {
+                size: self.len(),
+                len: dst.len(),
+            })
+        } else {
+            unsafe { copy_nonoverlapping(self.as_ptr(), dst.as_mut_ptr(), src_len as usize) };
+            Ok(self.len())
+        }
+    }
+}
+
+// TODO: make TryIntoCtx use StrCtx for awesomeness
+impl<'a> TryIntoCtx for &'a str {
+    type Error = error::Error;
+    #[inline]
+    fn try_into_ctx(self, dst: &mut [u8], _ctx: ()) -> error::Result<usize> {
+        let bytes = self.as_bytes();
+        TryIntoCtx::try_into_ctx(bytes, dst, ())
+    }
+}
+
+// TODO: we can make this compile time without size_of call, but compiler probably does that anyway
+macro_rules! sizeof_impl {
+    ($ty:ty) => {
+        impl SizeWith<Endian> for $ty {
+            #[inline]
+            fn size_with(_ctx: &Endian) -> usize {
+                size_of::<$ty>()
+            }
+        }
+    };
+}
+
+sizeof_impl!(u8);
+sizeof_impl!(i8);
+sizeof_impl!(u16);
+sizeof_impl!(i16);
+sizeof_impl!(u32);
+sizeof_impl!(i32);
+sizeof_impl!(u64);
+sizeof_impl!(i64);
+sizeof_impl!(u128);
+sizeof_impl!(i128);
+sizeof_impl!(f32);
+sizeof_impl!(f64);
+
+impl<'a> TryFromCtx<'a, usize> for &'a [u8] {
+    type Error = error::Error;
+    #[inline]
+    fn try_from_ctx(src: &'a [u8], size: usize) -> result::Result<(Self, usize), Self::Error> {
+        if size > src.len() {
+            Err(error::Error::TooBig {
+                size,
+                len: src.len(),
+            })
+        } else {
+            Ok((&src[..size], size))
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl<'a> TryFromCtx<'a> for &'a CStr {
+    type Error = error::Error;
+    #[inline]
+    fn try_from_ctx(src: &'a [u8], _ctx: ()) -> result::Result<(Self, usize), Self::Error> {
+        let null_byte = match src.iter().position(|b| *b == 0) {
+            Some(ix) => ix,
+            None => {
+                return Err(error::Error::BadInput {
+                    size: 0,
+                    msg: "The input doesn't contain a null byte",
+                })
+            }
+        };
+
+        let cstr = unsafe { CStr::from_bytes_with_nul_unchecked(&src[..=null_byte]) };
+        Ok((cstr, null_byte + 1))
+    }
+}
+
+#[cfg(feature = "std")]
+impl<'a> TryFromCtx<'a> for CString {
+    type Error = error::Error;
+    #[inline]
+    fn try_from_ctx(src: &'a [u8], _ctx: ()) -> result::Result<(Self, usize), Self::Error> {
+        let (raw, bytes_read) = <&CStr as TryFromCtx>::try_from_ctx(src, _ctx)?;
+        Ok((raw.to_owned(), bytes_read))
+    }
+}
+
+#[cfg(feature = "std")]
+impl<'a> TryIntoCtx for &'a CStr {
+    type Error = error::Error;
+    #[inline]
+    fn try_into_ctx(self, dst: &mut [u8], _ctx: ()) -> error::Result<usize> {
+        let data = self.to_bytes_with_nul();
+
+        if dst.len() < data.len() {
+            Err(error::Error::TooBig {
+                size: dst.len(),
+                len: data.len(),
+            })
+        } else {
+            unsafe {
+                copy_nonoverlapping(data.as_ptr(), dst.as_mut_ptr(), data.len());
+            }
+
+            Ok(data.len())
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl TryIntoCtx for CString {
+    type Error = error::Error;
+    #[inline]
+    fn try_into_ctx(self, dst: &mut [u8], _ctx: ()) -> error::Result<usize> {
+        self.as_c_str().try_into_ctx(dst, ())
+    }
+}
+
+// example of marshalling to bytes, let's wait until const is an option
+// impl FromCtx for [u8; 10] {
+//     fn from_ctx(bytes: &[u8], _ctx: Endian) -> Self {
+//         let mut dst: Self = [0; 10];
+//         assert!(bytes.len() >= dst.len());
+//         unsafe {
+//             copy_nonoverlapping(bytes.as_ptr(), dst.as_mut_ptr(), dst.len());
+//         }
+//         dst
+//     }
+// }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    #[cfg(feature = "std")]
+    fn parse_a_cstr() {
+        let src = CString::new("Hello World").unwrap();
+        let as_bytes = src.as_bytes_with_nul();
+
+        let (got, bytes_read) = <&CStr as TryFromCtx>::try_from_ctx(as_bytes, ()).unwrap();
+
+        assert_eq!(bytes_read, as_bytes.len());
+        assert_eq!(got, src.as_c_str());
+    }
+
+    #[test]
+    #[cfg(feature = "std")]
+    fn round_trip_a_c_str() {
+        let src = CString::new("Hello World").unwrap();
+        let src = src.as_c_str();
+        let as_bytes = src.to_bytes_with_nul();
+
+        let mut buffer = vec![0; as_bytes.len()];
+        let bytes_written = src.try_into_ctx(&mut buffer, ()).unwrap();
+        assert_eq!(bytes_written, as_bytes.len());
+
+        let (got, bytes_read) = <&CStr as TryFromCtx>::try_from_ctx(&buffer, ()).unwrap();
+
+        assert_eq!(bytes_read, as_bytes.len());
+        assert_eq!(got, src);
+    }
+}
diff --git a/third_party/rust/scroll/src/endian.rs b/third_party/rust/scroll/src/endian.rs
new file mode 100644
index 0000000000..06d7a1dc1c
--- /dev/null
+++ b/third_party/rust/scroll/src/endian.rs
@@ -0,0 +1,51 @@
+#[derive(PartialEq, Eq, Copy, Debug, Clone)]
+/// The endianness (byte order) of a stream of bytes
+pub enum Endian {
+    Little,
+    Big,
+}
+
+/// Little Endian byte order context
+pub const LE: Endian = Endian::Little;
+/// Big Endian byte order context
+pub const BE: Endian = Endian::Big;
+/// Network byte order context
+pub const NETWORK: Endian = Endian::Big;
+#[cfg(target_endian = "little")]
+/// The machine's native byte order
+pub const NATIVE: Endian = LE;
+#[cfg(target_endian = "big")]
+/// The machine's native byte order
+pub const NATIVE: Endian = BE;
+
+impl Default for Endian {
+    #[inline]
+    fn default() -> Self {
+        NATIVE
+    }
+}
+
+impl From<bool> for Endian {
+    #[inline]
+    fn from(little_endian: bool) -> Self {
+        if little_endian {
+            LE
+        } else {
+            BE
+        }
+    }
+}
+
+impl Endian {
+    #[inline]
+    pub fn network() -> Endian {
+        NETWORK
+    }
+    #[inline]
+    pub fn is_little(&self) -> bool {
+        match *self {
+            LE => true,
+            _ => false,
+        }
+    }
+}
diff --git a/third_party/rust/scroll/src/error.rs b/third_party/rust/scroll/src/error.rs
new file mode 100644
index 0000000000..7740254774
--- /dev/null
+++ b/third_party/rust/scroll/src/error.rs
@@ -0,0 +1,84 @@
+use core::fmt::{self, Display};
+use core::result;
+
+#[cfg(feature = "std")]
+use std::error;
+#[cfg(feature = "std")]
+use std::io;
+
+#[derive(Debug)]
+/// A custom Scroll error
+pub enum Error {
+    /// The type you tried to read was too big
+    TooBig {
+        size: usize,
+        len: usize,
+    },
+    /// The requested offset to read/write at is invalid
+    BadOffset(usize),
+    BadInput {
+        size: usize,
+        msg: &'static str,
+    },
+    #[cfg(feature = "std")]
+    /// A custom Scroll error for reporting messages to clients
+    Custom(String),
+    #[cfg(feature = "std")]
+    /// Returned when IO based errors are encountered
+    IO(io::Error),
+}
+
+#[cfg(feature = "std")]
+impl error::Error for Error {
+    fn description(&self) -> &str {
+        match *self {
+            Error::TooBig { .. } => "TooBig",
+            Error::BadOffset(_) => "BadOffset",
+            Error::BadInput { .. } => "BadInput",
+            Error::Custom(_) => "Custom",
+            Error::IO(_) => "IO",
+        }
+    }
+    fn cause(&self) -> Option<&dyn error::Error> {
+        match *self {
+            Error::TooBig { .. } => None,
+            Error::BadOffset(_) => None,
+            Error::BadInput { .. } => None,
+            Error::Custom(_) => None,
+            Error::IO(ref io) => io.source(),
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl From<io::Error> for Error {
+    fn from(err: io::Error) -> Error {
+        Error::IO(err)
+    }
+}
+
+impl Display for Error {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            Error::TooBig { ref size, ref len } => {
+                write!(fmt, "type is too big ({}) for {}", size, len)
+            }
+            Error::BadOffset(ref offset) => {
+                write!(fmt, "bad offset {}", offset)
+            }
+            Error::BadInput { ref msg, ref size } => {
+                write!(fmt, "bad input {} ({})", msg, size)
+            }
+            #[cfg(feature = "std")]
+            Error::Custom(ref msg) => {
+                write!(fmt, "{}", msg)
+            }
+            #[cfg(feature = "std")]
+            Error::IO(ref err) => {
+                write!(fmt, "{}", err)
+            }
+        }
+    }
+}
+
+pub type Result<T> = result::Result<T, Error>;
diff --git a/third_party/rust/scroll/src/greater.rs b/third_party/rust/scroll/src/greater.rs
new file mode 100644
index 0000000000..353aab7c4c
--- /dev/null
+++ b/third_party/rust/scroll/src/greater.rs
@@ -0,0 +1,169 @@
+use core::ops::{Index, IndexMut, RangeFrom};
+
+use crate::ctx::{FromCtx, IntoCtx};
+
+/// Core-read - core, no_std friendly trait for reading basic traits from byte buffers. Cannot fail
+/// unless the buffer is too small, in which case an assert fires and the program panics.
+///
+/// If your type implements [FromCtx](ctx/trait.FromCtx.html) then you can `cread::<YourType>(offset)`.
+///
+/// # Example
+///
+/// ```rust
+/// use scroll::{ctx, Cread, LE};
+///
+/// #[repr(packed)]
+/// struct Bar {
+///     foo: i32,
+///     bar: u32,
+/// }
+///
+/// impl ctx::FromCtx<scroll::Endian> for Bar {
+///     fn from_ctx(bytes: &[u8], ctx: scroll::Endian) -> Self {
+///         use scroll::Cread;
+///         Bar { foo: bytes.cread_with(0, ctx), bar: bytes.cread_with(4, ctx) }
+///     }
+/// }
+///
+/// let bytes = [0xff, 0xff, 0xff, 0xff, 0xef,0xbe,0xad,0xde,];
+/// let bar = bytes.cread_with::<Bar>(0, LE);
+/// // Remember that you need to copy out fields from packed structs
+/// // with a `{}` block instead of borrowing them directly
+/// // ref: https://github.com/rust-lang/rust/issues/46043
+/// assert_eq!({bar.foo}, -1);
+/// assert_eq!({bar.bar}, 0xdeadbeef);
+/// ```
+pub trait Cread<Ctx, I = usize>: Index<I> + Index<RangeFrom<I>>
+where
+    Ctx: Copy,
+{
+    /// Reads a value from `Self` at `offset` with `ctx`. Cannot fail.
+    /// If the buffer is too small for the value requested, this will panic.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use scroll::{Cread, BE, LE};
+    /// use std::i64::MAX;
+    ///
+    /// let bytes = [0x7f,0xff,0xff,0xff,0xff,0xff,0xff,0xff, 0xef,0xbe,0xad,0xde,];
+    /// let foo = bytes.cread_with::<i64>(0, BE);
+    /// let bar = bytes.cread_with::<u32>(8, LE);
+    /// assert_eq!(foo, MAX);
+    /// assert_eq!(bar, 0xdeadbeef);
+    /// ```
+    #[inline]
+    fn cread_with<N: FromCtx<Ctx, <Self as Index<RangeFrom<I>>>::Output>>(
+        &self,
+        offset: I,
+        ctx: Ctx,
+    ) -> N {
+        N::from_ctx(&self[offset..], ctx)
+    }
+    /// Reads a value implementing `FromCtx` from `Self` at `offset`,
+    /// with the **target machine**'s endianness.
+    /// For the primitive types, this will be the **target machine**'s endianness.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use scroll::Cread;
+    ///
+    /// let bytes = [0x01,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0xef,0xbe,0x00,0x00,];
+    /// let foo = bytes.cread::<i64>(0);
+    /// let bar = bytes.cread::<u32>(8);
+    /// #[cfg(target_endian = "little")]
+    /// assert_eq!(foo, 1);
+    /// #[cfg(target_endian = "big")]
+    /// assert_eq!(foo, 0x100_0000_0000_0000);
+    ///
+    /// #[cfg(target_endian = "little")]
+    /// assert_eq!(bar, 0xbeef);
+    /// #[cfg(target_endian = "big")]
+    /// assert_eq!(bar, 0xefbe0000);
+    /// ```
+    #[inline]
+    fn cread<N: FromCtx<Ctx, <Self as Index<RangeFrom<I>>>::Output>>(&self, offset: I) -> N
+    where
+        Ctx: Default,
+    {
+        let ctx = Ctx::default();
+        N::from_ctx(&self[offset..], ctx)
+    }
+}
+
+impl<Ctx: Copy, I, R: ?Sized + Index<I> + Index<RangeFrom<I>>> Cread<Ctx, I> for R {}
+
+/// Core-write - core, no_std friendly trait for writing basic types into byte buffers. Cannot fail
+/// unless the buffer is too small, in which case an assert fires and the program panics.
+/// Similar to [Cread](trait.Cread.html), if your type implements [IntoCtx](ctx/trait.IntoCtx.html)
+/// then you can `cwrite(your_type, offset)`.
+///
+/// # Example
+///
+/// ```rust
+/// use scroll::{ctx, Cwrite};
+///
+/// #[repr(packed)]
+/// struct Bar {
+///     foo: i32,
+///     bar: u32,
+/// }
+///
+/// impl ctx::IntoCtx<scroll::Endian> for Bar {
+///     fn into_ctx(self, bytes: &mut [u8], ctx: scroll::Endian) {
+///         use scroll::Cwrite;
+///         bytes.cwrite_with(self.foo, 0, ctx);
+///         bytes.cwrite_with(self.bar, 4, ctx);
+///     }
+/// }
+///
+/// let bar = Bar { foo: -1, bar: 0xdeadbeef };
+/// let mut bytes = [0x0; 16];
+/// bytes.cwrite::<Bar>(bar, 0);
+/// ```
+pub trait Cwrite<Ctx: Copy, I = usize>: Index<I> + IndexMut<RangeFrom<I>> {
+    /// Writes `n` into `Self` at `offset`; uses default context.
+    /// For the primitive types, this will be the **target machine**'s endianness.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use scroll::{Cwrite, Cread};
+    /// let mut bytes = [0x0; 16];
+    /// bytes.cwrite::<i64>(42, 0);
+    /// bytes.cwrite::<u32>(0xdeadbeef, 8);
+    ///
+    /// assert_eq!(bytes.cread::<i64>(0), 42);
+    /// assert_eq!(bytes.cread::<u32>(8), 0xdeadbeef);
+    #[inline]
+    fn cwrite<N: IntoCtx<Ctx, <Self as Index<RangeFrom<I>>>::Output>>(&mut self, n: N, offset: I)
+    where
+        Ctx: Default,
+    {
+        let ctx = Ctx::default();
+        n.into_ctx(self.index_mut(offset..), ctx)
+    }
+    /// Writes `n` into `Self` at `offset` with `ctx`
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use scroll::{Cwrite, Cread, LE, BE};
+    /// let mut bytes = [0x0; 0x10];
+    /// bytes.cwrite_with::<i64>(42, 0, LE);
+    /// bytes.cwrite_with::<u32>(0xdeadbeef, 8, BE);
+    /// assert_eq!(bytes.cread_with::<i64>(0, LE), 42);
+    /// assert_eq!(bytes.cread_with::<u32>(8, LE), 0xefbeadde);
+    #[inline]
+    fn cwrite_with<N: IntoCtx<Ctx, <Self as Index<RangeFrom<I>>>::Output>>(
+        &mut self,
+        n: N,
+        offset: I,
+        ctx: Ctx,
+    ) {
+        n.into_ctx(self.index_mut(offset..), ctx)
+    }
+}
+
+impl<Ctx: Copy, I, W: ?Sized + Index<I> + IndexMut<RangeFrom<I>>> Cwrite<Ctx, I> for W {}
diff --git a/third_party/rust/scroll/src/leb128.rs b/third_party/rust/scroll/src/leb128.rs
new file mode 100644
index 0000000000..43f50b95f1
--- /dev/null
+++ b/third_party/rust/scroll/src/leb128.rs
@@ -0,0 +1,249 @@
+use crate::ctx::TryFromCtx;
+use crate::error;
+use crate::Pread;
+use core::convert::{AsRef, From};
+use core::result;
+use core::u8;
+
+#[derive(Debug, PartialEq, Copy, Clone)]
+/// An unsigned leb128 integer
+pub struct Uleb128 {
+    value: u64,
+    count: usize,
+}
+
+impl Uleb128 {
+    #[inline]
+    /// Return how many bytes this Uleb128 takes up in memory
+    pub fn size(&self) -> usize {
+        self.count
+    }
+    #[inline]
+    /// Read a variable length u64 from `bytes` at `offset`
+    pub fn read(bytes: &[u8], offset: &mut usize) -> error::Result<u64> {
+        let tmp = bytes.pread::<Uleb128>(*offset)?;
+        *offset += tmp.size();
+        Ok(tmp.into())
+    }
+}
+
+impl AsRef<u64> for Uleb128 {
+    fn as_ref(&self) -> &u64 {
+        &self.value
+    }
+}
+
+impl From<Uleb128> for u64 {
+    #[inline]
+    fn from(uleb128: Uleb128) -> u64 {
+        uleb128.value
+    }
+}
+
+#[derive(Debug, PartialEq, Copy, Clone)]
+/// An signed leb128 integer
+pub struct Sleb128 {
+    value: i64,
+    count: usize,
+}
+
+impl Sleb128 {
+    #[inline]
+    /// Return how many bytes this Sleb128 takes up in memory
+    pub fn size(&self) -> usize {
+        self.count
+    }
+    #[inline]
+    /// Read a variable length i64 from `bytes` at `offset`
+    pub fn read(bytes: &[u8], offset: &mut usize) -> error::Result<i64> {
+        let tmp = bytes.pread::<Sleb128>(*offset)?;
+        *offset += tmp.size();
+        Ok(tmp.into())
+    }
+}
+
+impl AsRef<i64> for Sleb128 {
+    fn as_ref(&self) -> &i64 {
+        &self.value
+    }
+}
+
+impl From<Sleb128> for i64 {
+    #[inline]
+    fn from(sleb128: Sleb128) -> i64 {
+        sleb128.value
+    }
+}
+
+// Below implementation heavily adapted from: https://github.com/fitzgen/leb128
+const CONTINUATION_BIT: u8 = 1 << 7;
+const SIGN_BIT: u8 = 1 << 6;
+
+#[inline]
+fn mask_continuation(byte: u8) -> u8 {
+    byte & !CONTINUATION_BIT
+}
+
+// #[inline]
+// fn mask_continuation_u64(val: u64) -> u8 {
+//     let byte = val & (u8::MAX as u64);
+//     mask_continuation(byte as u8)
+// }
+
+impl<'a> TryFromCtx<'a> for Uleb128 {
+    type Error = error::Error;
+    #[inline]
+    fn try_from_ctx(src: &'a [u8], _ctx: ()) -> result::Result<(Self, usize), Self::Error> {
+        let mut result = 0;
+        let mut shift = 0;
+        let mut count = 0;
+        loop {
+            let byte: u8 = src.pread(count)?;
+
+            if shift == 63 && byte != 0x00 && byte != 0x01 {
+                return Err(error::Error::BadInput {
+                    size: src.len(),
+                    msg: "failed to parse",
+                });
+            }
+
+            let low_bits = u64::from(mask_continuation(byte));
+            result |= low_bits << shift;
+
+            count += 1;
+            shift += 7;
+
+            if byte & CONTINUATION_BIT == 0 {
+                return Ok((
+                    Uleb128 {
+                        value: result,
+                        count,
+                    },
+                    count,
+                ));
+            }
+        }
+    }
+}
+
+impl<'a> TryFromCtx<'a> for Sleb128 {
+    type Error = error::Error;
+    #[inline]
+    fn try_from_ctx(src: &'a [u8], _ctx: ()) -> result::Result<(Self, usize), Self::Error> {
+        let o = 0;
+        let offset = &mut 0;
+        let mut result = 0;
+        let mut shift = 0;
+        let size = 64;
+        let mut byte: u8;
+        loop {
+            byte = src.gread(offset)?;
+
+            if shift == 63 && byte != 0x00 && byte != 0x7f {
+                return Err(error::Error::BadInput {
+                    size: src.len(),
+                    msg: "failed to parse",
+                });
+            }
+
+            let low_bits = i64::from(mask_continuation(byte));
+            result |= low_bits << shift;
+            shift += 7;
+
+            if byte & CONTINUATION_BIT == 0 {
+                break;
+            }
+        }
+
+        if shift < size && (SIGN_BIT & byte) == SIGN_BIT {
+            // Sign extend the result.
+            result |= !0 << shift;
+        }
+        let count = *offset - o;
+        Ok((
+            Sleb128 {
+                value: result,
+                count,
+            },
+            count,
+        ))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::super::LE;
+    use super::{Sleb128, Uleb128};
+
+    const CONTINUATION_BIT: u8 = 1 << 7;
+    //const SIGN_BIT: u8 = 1 << 6;
+
+    #[test]
+    fn uleb_size() {
+        use super::super::Pread;
+        let buf = [2u8 | CONTINUATION_BIT, 1];
+        let bytes = &buf[..];
+        let num = bytes.pread::<Uleb128>(0).unwrap();
+        println!("num: {:?}", &num);
+        assert_eq!(130u64, num.into());
+        assert_eq!(num.size(), 2);
+
+        let buf = [0x00, 0x01];
+        let bytes = &buf[..];
+        let num = bytes.pread::<Uleb128>(0).unwrap();
+        println!("num: {:?}", &num);
+        assert_eq!(0u64, num.into());
+        assert_eq!(num.size(), 1);
+
+        let buf = [0x21];
+        let bytes = &buf[..];
+        let num = bytes.pread::<Uleb128>(0).unwrap();
+        println!("num: {:?}", &num);
+        assert_eq!(0x21u64, num.into());
+        assert_eq!(num.size(), 1);
+    }
+
+    #[test]
+    fn uleb128() {
+        use super::super::Pread;
+        let buf = [2u8 | CONTINUATION_BIT, 1];
+        let bytes = &buf[..];
+        let num = bytes.pread::<Uleb128>(0).expect("Should read Uleb128");
+        assert_eq!(130u64, num.into());
+        assert_eq!(
+            386,
+            bytes.pread_with::<u16>(0, LE).expect("Should read number")
+        );
+    }
+
+    #[test]
+    fn uleb128_overflow() {
+        use super::super::Pread;
+        let buf = [
+            2u8 | CONTINUATION_BIT,
+            2 | CONTINUATION_BIT,
+            2 | CONTINUATION_BIT,
+            2 | CONTINUATION_BIT,
+            2 | CONTINUATION_BIT,
+            2 | CONTINUATION_BIT,
+            2 | CONTINUATION_BIT,
+            2 | CONTINUATION_BIT,
+            2 | CONTINUATION_BIT,
+            2 | CONTINUATION_BIT,
+            1,
+        ];
+        let bytes = &buf[..];
+        assert!(bytes.pread::<Uleb128>(0).is_err());
+    }
+
+    #[test]
+    fn sleb128() {
+        use super::super::Pread;
+        let bytes = [0x7fu8 | CONTINUATION_BIT, 0x7e];
+        let num: i64 = bytes
+            .pread::<Sleb128>(0)
+            .expect("Should read Sleb128")
+            .into();
+        assert_eq!(-129, num);
+    }
+}
diff --git a/third_party/rust/scroll/src/lesser.rs b/third_party/rust/scroll/src/lesser.rs
new file mode 100644
index 0000000000..46ef4c5b11
--- /dev/null
+++ b/third_party/rust/scroll/src/lesser.rs
@@ -0,0 +1,178 @@
+use crate::ctx::{FromCtx, IntoCtx, SizeWith};
+use std::io::{Read, Result, Write};
+
+/// An extension trait to `std::io::Read` streams; mainly targeted at reading primitive types with
+/// a known size.
+///
+/// Requires types to implement [`FromCtx`](ctx/trait.FromCtx.html) and [`SizeWith`](ctx/trait.SizeWith.html).
+///
+/// **NB** You should probably add `repr(C)` and be very careful how you implement
+/// [`SizeWith`](ctx/trait.SizeWith.html), otherwise you will get IO errors failing to fill entire
+/// buffer (the size you specified in `SizeWith`), or out of bound errors (depending on your impl)
+/// in `from_ctx`.
+///
+/// Warning: Currently ioread/write uses a small 256-byte buffer and can not read/write larger types
+///
+/// # Example
+/// ```rust
+/// use std::io::Cursor;
+/// use scroll::{self, ctx, LE, Pread, IOread};
+///
+/// #[repr(packed)]
+/// struct Foo {
+///     foo: i64,
+///     bar: u32,
+/// }
+///
+/// impl ctx::FromCtx<scroll::Endian> for Foo {
+///     fn from_ctx(bytes: &[u8], ctx: scroll::Endian) -> Self {
+///         Foo { foo: bytes.pread_with::<i64>(0, ctx).unwrap(), bar: bytes.pread_with::<u32>(8, ctx).unwrap() }
+///     }
+/// }
+///
+/// impl ctx::SizeWith<scroll::Endian> for Foo {
+///     // our parsing context doesn't influence our size
+///     fn size_with(_: &scroll::Endian) -> usize {
+///         ::std::mem::size_of::<Foo>()
+///     }
+/// }
+///
+/// let bytes_ = [0x0b,0x0b,0x00,0x00,0x00,0x00,0x00,0x00, 0xef,0xbe,0x00,0x00,];
+/// let mut bytes = Cursor::new(bytes_);
+/// let foo = bytes.ioread_with::<i64>(LE).unwrap();
+/// let bar = bytes.ioread_with::<u32>(LE).unwrap();
+/// assert_eq!(foo, 0xb0b);
+/// assert_eq!(bar, 0xbeef);
+/// let error = bytes.ioread_with::<f64>(LE);
+/// assert!(error.is_err());
+/// let mut bytes = Cursor::new(bytes_);
+/// let foo_ = bytes.ioread_with::<Foo>(LE).unwrap();
+/// // Remember that you need to copy out fields from packed structs
+/// // with a `{}` block instead of borrowing them directly
+/// // ref: https://github.com/rust-lang/rust/issues/46043
+/// assert_eq!({foo_.foo}, foo);
+/// assert_eq!({foo_.bar}, bar);
+/// ```
+///
+pub trait IOread<Ctx: Copy>: Read {
+    /// Reads the type `N` from `Self`, with a default parsing context.
+    /// For the primitive numeric types, this will be at the host machine's endianness.
+    ///
+    /// # Example
+    /// ```rust
+    /// use scroll::IOread;
+    /// use std::io::Cursor;
+    /// let bytes = [0xef, 0xbe];
+    /// let mut bytes = Cursor::new(&bytes[..]);
+    /// let beef = bytes.ioread::<u16>().unwrap();
+    ///
+    /// #[cfg(target_endian = "little")]
+    /// assert_eq!(0xbeef, beef);
+    /// #[cfg(target_endian = "big")]
+    /// assert_eq!(0xefbe, beef);
+    /// ```
+    #[inline]
+    fn ioread<N: FromCtx<Ctx> + SizeWith<Ctx>>(&mut self) -> Result<N>
+    where
+        Ctx: Default,
+    {
+        let ctx = Ctx::default();
+        self.ioread_with(ctx)
+    }
+
+    /// Reads the type `N` from `Self`, with the parsing context `ctx`.
+    /// **NB**: this will panic if the type you're reading has a size greater than 256. Plans are to have this allocate in larger cases.
+    ///
+    /// For the primitive numeric types, this will be at the host machine's endianness.
+    ///
+    /// # Example
+    /// ```rust
+    /// use scroll::{IOread, LE, BE};
+    /// use std::io::Cursor;
+    /// let bytes = [0xef, 0xbe, 0xb0, 0xb0, 0xfe, 0xed, 0xde, 0xad];
+    /// let mut bytes = Cursor::new(&bytes[..]);
+    /// let beef = bytes.ioread_with::<u16>(LE).unwrap();
+    /// assert_eq!(0xbeef, beef);
+    /// let b0 = bytes.ioread::<u8>().unwrap();
+    /// assert_eq!(0xb0, b0);
+    /// let b0 = bytes.ioread::<u8>().unwrap();
+    /// assert_eq!(0xb0, b0);
+    /// let feeddead = bytes.ioread_with::<u32>(BE).unwrap();
+    /// assert_eq!(0xfeeddead, feeddead);
+    /// ```
+    #[inline]
+    fn ioread_with<N: FromCtx<Ctx> + SizeWith<Ctx>>(&mut self, ctx: Ctx) -> Result<N> {
+        let mut scratch = [0u8; 256];
+        let size = N::size_with(&ctx);
+        let mut buf = &mut scratch[0..size];
+        self.read_exact(&mut buf)?;
+        Ok(N::from_ctx(buf, ctx))
+    }
+}
+
+/// Types that implement `Read` get methods defined in `IOread`
+/// for free.
+impl<Ctx: Copy, R: Read + ?Sized> IOread<Ctx> for R {}
+
+/// An extension trait to `std::io::Write` streams; this only serializes simple types, like `u8`, `i32`, `f32`, `usize`, etc.
+///
+/// To write custom types with a single `iowrite::<YourType>` call, implement [`IntoCtx`](ctx/trait.IntoCtx.html) and [`SizeWith`](ctx/trait.SizeWith.html) for `YourType`.
+pub trait IOwrite<Ctx: Copy>: Write {
+    /// Writes the type `N` into `Self`, with the parsing context `ctx`.
+    /// **NB**: this will panic if the type you're writing has a size greater than 256. Plans are to have this allocate in larger cases.
+    ///
+    /// For the primitive numeric types, this will be at the host machine's endianness.
+    ///
+    /// # Example
+    /// ```rust
+    /// use scroll::IOwrite;
+    /// use std::io::Cursor;
+    ///
+    /// let mut bytes = [0x0u8; 4];
+    /// let mut bytes = Cursor::new(&mut bytes[..]);
+    /// bytes.iowrite(0xdeadbeef as u32).unwrap();
+    ///
+    /// #[cfg(target_endian = "little")]
+    /// assert_eq!(bytes.into_inner(), [0xef, 0xbe, 0xad, 0xde,]);
+    /// #[cfg(target_endian = "big")]
+    /// assert_eq!(bytes.into_inner(), [0xde, 0xad, 0xbe, 0xef,]);
+    /// ```
+    #[inline]
+    fn iowrite<N: SizeWith<Ctx> + IntoCtx<Ctx>>(&mut self, n: N) -> Result<()>
+    where
+        Ctx: Default,
+    {
+        let ctx = Ctx::default();
+        self.iowrite_with(n, ctx)
+    }
+
+    /// Writes the type `N` into `Self`, with the parsing context `ctx`.
+    /// **NB**: this will panic if the type you're writing has a size greater than 256. Plans are to have this allocate in larger cases.
+    ///
+    /// For the primitive numeric types, this will be at the host machine's endianness.
+    ///
+    /// # Example
+    /// ```rust
+    /// use scroll::{IOwrite, LE, BE};
+    /// use std::io::{Write, Cursor};
+    ///
+    /// let mut bytes = [0x0u8; 10];
+    /// let mut cursor = Cursor::new(&mut bytes[..]);
+    /// cursor.write_all(b"hello").unwrap();
+    /// cursor.iowrite_with(0xdeadbeef as u32, BE).unwrap();
+    /// assert_eq!(cursor.into_inner(), [0x68, 0x65, 0x6c, 0x6c, 0x6f, 0xde, 0xad, 0xbe, 0xef, 0x0]);
+    /// ```
+    #[inline]
+    fn iowrite_with<N: SizeWith<Ctx> + IntoCtx<Ctx>>(&mut self, n: N, ctx: Ctx) -> Result<()> {
+        let mut buf = [0u8; 256];
+        let size = N::size_with(&ctx);
+        let buf = &mut buf[0..size];
+        n.into_ctx(buf, ctx);
+        self.write_all(buf)?;
+        Ok(())
+    }
+}
+
+/// Types that implement `Write` get methods defined in `IOwrite`
+/// for free.
+impl<Ctx: Copy, W: Write + ?Sized> IOwrite<Ctx> for W {}
diff --git a/third_party/rust/scroll/src/lib.rs b/third_party/rust/scroll/src/lib.rs
new file mode 100644
index 0000000000..dcb58e7564
--- /dev/null
+++ b/third_party/rust/scroll/src/lib.rs
@@ -0,0 +1,637 @@
+//! # Scroll
+//!
+//! ```text, no_run
+//!         _______________
+//!    ()==(              (@==()
+//!         '______________'|
+//!           |             |
+//!           |   ἀρετή     |
+//!         __)_____________|
+//!    ()==(               (@==()
+//!         '--------------'
+//!
+//! ```
+//!
+//! Scroll is a library for easily and efficiently reading/writing types from data containers like
+//! byte arrays.
+//!
+//! ## Easily:
+//!
+//! Scroll sets down a number of traits:
+//!
+//! [FromCtx](ctx/trait.FromCtx.html), [IntoCtx](ctx/trait.IntoCtx.html),
+//! [TryFromCtx](ctx/trait.TryFromCtx.html) and [TryIntoCtx](ctx/trait.TryIntoCtx.html) — further
+//! explained in the [ctx module](ctx/index.html); to be implemented on custom types to allow
+//! reading, writing, and potentially fallible reading/writing respectively.
+//!
+//! [Pread](trait.Pread.html) and [Pwrite](trait.Pwrite.html) which are implemented on data
+//! containers such as byte arrays to define how to read or respectively write types implementing
+//! the *Ctx traits above.
+//! In addition scroll also defines [IOread](trait.IOread.html) and
+//! [IOwrite](trait.IOwrite.html) with additional constraits that then allow reading and writing
+//! from `std::io` [Read](https://doc.rust-lang.org/nightly/std/io/trait.Read.html) and
+//! [Write](https://doc.rust-lang.org/nightly/std/io/trait.Write.html).
+//!
+//!
+//! In most cases you can use [scroll_derive](https://docs.rs/scroll_derive) to derive sensible
+//! defaults for `Pread`, `Pwrite`, their IO counterpart and `SizeWith`.  More complex situations
+//! call for manual implementation of those traits; refer to [the ctx module](ctx/index.html) for
+//! details.
+//!
+//!
+//! ## Efficiently:
+//!
+//! Reading Slices — including [&str](https://doc.rust-lang.org/std/primitive.str.html) — supports
+//! zero-copy. Scroll is designed with a `no_std` context in mind; every dependency on `std` is
+//! cfg-gated and errors need not allocate.
+//!
+//! Reads by default take only immutable references wherever possible, allowing for trivial
+//! parallelization.
+//!
+//! # Examples
+//!
+//! Let's start with a simple example
+//!
+//! ```rust
+//! use scroll::{ctx, Pread};
+//!
+//! // Let's first define some data, cfg-gated so our assertions later on hold.
+//! #[cfg(target_endian = "little")]
+//! let bytes: [u8; 4] = [0xde, 0xad, 0xbe, 0xef];
+//! #[cfg(target_endian = "big")]
+//! let bytes: [u8; 4] = [0xef, 0xbe, 0xad, 0xde];
+//!
+//! // We can read a u32 from the array `bytes` at offset 0.
+//! // This will use a default context for the type being parsed;
+//! // in the case of u32 this defines to use the host's endianess.
+//! let number = bytes.pread::<u32>(0).unwrap();
+//! assert_eq!(number, 0xefbeadde);
+//!
+//!
+//! // Similarly we can also read a single byte at offset 2
+//! // This time using type ascription instead of the turbofish (::<>) operator.
+//! let byte: u8 = bytes.pread(2).unwrap();
+//! #[cfg(target_endian = "little")]
+//! assert_eq!(byte, 0xbe);
+//! #[cfg(target_endian = "big")]
+//! assert_eq!(byte, 0xad);
+//!
+//!
+//! // If required we can also provide a specific parsing context; e.g. if we want to explicitly
+//! // define the endianess to use:
+//! let be_number: u32 = bytes.pread_with(0, scroll::BE).unwrap();
+//! #[cfg(target_endian = "little")]
+//! assert_eq!(be_number, 0xdeadbeef);
+//! #[cfg(target_endian = "big")]
+//! assert_eq!(be_number, 0xefbeadde);
+//!
+//! let be_number16 = bytes.pread_with::<u16>(1, scroll::BE).unwrap();
+//! #[cfg(target_endian = "little")]
+//! assert_eq!(be_number16, 0xadbe);
+//! #[cfg(target_endian = "big")]
+//! assert_eq!(be_number16, 0xbead);
+//!
+//!
+//! // Reads may fail; in this example due to a too large read for the given container.
+//! // Scroll's error type does not by default allocate to work in environments like no_std.
+//! let byte_err: scroll::Result<i64> = bytes.pread(0);
+//! assert!(byte_err.is_err());
+//!
+//!
+//! // We can parse out custom datatypes, or types with lifetimes, as long as they implement
+//! // the conversion traits `TryFromCtx/FromCtx`.
+//! // Here we use the default context for &str which parses are C-style '\0'-delimited string.
+//! let hello: &[u8] = b"hello world\0more words";
+//! let hello_world: &str = hello.pread(0).unwrap();
+//! assert_eq!("hello world", hello_world);
+//!
+//! // We can again provide a custom context; for example to parse Space-delimited strings.
+//! // As you can see while we still call `pread` changing the context can influence the output —
+//! // instead of splitting at '\0' we split at spaces
+//! let hello2: &[u8] = b"hello world\0more words";
+//! let world: &str = hello2.pread_with(6, ctx::StrCtx::Delimiter(ctx::SPACE)).unwrap();
+//! assert_eq!("world\0more", world);
+//! ```
+//!
+//! ## `std::io` API
+//!
+//! Scroll also allows reading from `std::io`. For this the types to read need to implement
+//! [FromCtx](ctx/trait.FromCtx.html) and [SizeWith](ctx/trait.SizeWith.html).
+//!
+//! ```rust
+//! use std::io::Cursor;
+//! use scroll::{IOread, ctx, Endian};
+//! let bytes = [0x01,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0xef,0xbe,0x00,0x00,];
+//! let mut cursor = Cursor::new(bytes);
+//!
+//! // IOread uses std::io::Read methods, thus the Cursor will be incremented on these reads:
+//! let prev = cursor.position();
+//!
+//! let integer = cursor.ioread_with::<u64>(Endian::Little).unwrap();
+//!
+//! let after = cursor.position();
+//!
+//! assert!(prev < after);
+//!
+//! // SizeWith allows us to define a context-sensitive size of a read type:
+//! // Contexts can have different instantiations; e.g. the `Endian` context can be either Little or
+//! // Big. This is useful if for example the context contains the word-size of fields to be
+//! // read/written, e.g. switching between ELF32 or ELF64 at runtime.
+//! let size = <u64 as ctx::SizeWith<Endian>>::size_with(&Endian::Little) as u64;
+//! assert_eq!(prev + size, after);
+//! ```
+//!
+//! In the same vein as IOread we can use IOwrite to write a type to anything implementing
+//! `std::io::Write`:
+//!
+//! ```rust
+//! use std::io::Cursor;
+//! use scroll::{IOwrite};
+//!
+//! let mut bytes = [0x0u8; 5];
+//! let mut cursor = Cursor::new(&mut bytes[..]);
+//!
+//! // This of course once again increments the cursor position
+//! cursor.iowrite_with(0xdeadbeef as u32, scroll::BE).unwrap();
+//!
+//! assert_eq!(cursor.into_inner(), [0xde, 0xad, 0xbe, 0xef, 0x0]);
+//! ```
+//!
+//! ## Complex use cases
+//!
+//! Scoll is designed to be highly adaptable while providing a strong abstraction between the types
+//! being read/written and the data container containing them.
+//!
+//! In this example we'll define a custom Data and allow it to be read from an arbitrary byte
+//! buffer.
+//!
+//! ```rust
+//! use scroll::{self, ctx, Pread, Endian};
+//! use scroll::ctx::StrCtx;
+//!
+//! // Our custom context type. In a more complex situation you could for example store details on
+//! // how to write or read your type, field-sizes or other information.
+//! // In this simple example we could also do without using a custom context in the first place.
+//! #[derive(Copy, Clone)]
+//! struct Context(Endian);
+//!
+//! // Our custom data type
+//! struct Data<'zerocopy> {
+//!   // This is only a reference to the actual data; we make use of scroll's zero-copy capability
+//!   name: &'zerocopy str,
+//!   id: u32,
+//! }
+//!
+//! // To allow for safe zero-copying scroll allows to specify lifetimes explicitly:
+//! // The context
+//! impl<'a> ctx::TryFromCtx<'a, Context> for Data<'a> {
+//!   // If necessary you can set a custom error type here, which will be returned by Pread/Pwrite
+//!   type Error = scroll::Error;
+//!
+//!   // Using the explicit lifetime specification again you ensure that read data doesn't outlife
+//!   // its source buffer without having to resort to copying.
+//!   fn try_from_ctx (src: &'a [u8], ctx: Context)
+//!     // the `usize` returned here is the amount of bytes read.
+//!     -> Result<(Self, usize), Self::Error>
+//!   {
+//!     let offset = &mut 0;
+//!
+//!     let id = src.gread_with(offset, ctx.0)?;
+//!
+//!     // In a more serious application you would validate data here of course.
+//!     let namelen: u16 = src.gread_with(offset, ctx.0)?;
+//!     let name = src.gread_with::<&str>(offset, StrCtx::Length(namelen as usize))?;
+//!
+//!     Ok((Data { name: name, id: id }, *offset))
+//!   }
+//! }
+//!
+//! // In lieu of a complex byte buffer we hearken back to a simple &[u8]; the default source
+//! // of TryFromCtx. However, any type that implements Pread to produce a &[u8] can now read
+//! // `Data` thanks to it's implementation of TryFromCtx.
+//! let bytes = b"\x01\x02\x03\x04\x00\x08UserName";
+//! let data: Data = bytes.pread_with(0, Context(Endian::Big)).unwrap();
+//!
+//! assert_eq!(data.id, 0x01020304);
+//! assert_eq!(data.name.to_string(), "UserName".to_string());
+//! ```
+//!
+//! For further explanation of the traits and how to implement them manually refer to
+//! [Pread](trait.Pread.html) and [TryFromCtx](ctx/trait.TryFromCtx.html).
+
+#![cfg_attr(not(feature = "std"), no_std)]
+
+#[cfg(feature = "derive")]
+#[allow(unused_imports)]
+pub use scroll_derive::{IOread, IOwrite, Pread, Pwrite, SizeWith};
+
+#[cfg(feature = "std")]
+extern crate core;
+
+pub mod ctx;
+mod endian;
+mod error;
+mod greater;
+mod leb128;
+#[cfg(feature = "std")]
+mod lesser;
+mod pread;
+mod pwrite;
+
+pub use crate::endian::*;
+pub use crate::error::*;
+pub use crate::greater::*;
+pub use crate::leb128::*;
+#[cfg(feature = "std")]
+pub use crate::lesser::*;
+pub use crate::pread::*;
+pub use crate::pwrite::*;
+
+#[doc(hidden)]
+pub mod export {
+    pub use ::core::mem;
+    pub use ::core::result;
+}
+
+#[allow(unused)]
+macro_rules! doc_comment {
+    ($x:expr) => {
+        #[doc = $x]
+        #[doc(hidden)]
+        mod readme_tests {}
+    };
+}
+
+#[cfg(feature = "derive")]
+doc_comment!(include_str!("../README.md"));
+
+#[cfg(test)]
+mod tests {
+    #[allow(overflowing_literals)]
+    use super::LE;
+
+    #[test]
+    fn test_measure_with_bytes() {
+        use super::ctx::MeasureWith;
+        let bytes: [u8; 4] = [0xef, 0xbe, 0xad, 0xde];
+        assert_eq!(bytes.measure_with(&()), 4);
+    }
+
+    #[test]
+    fn test_measurable() {
+        use super::ctx::SizeWith;
+        assert_eq!(8, u64::size_with(&LE));
+    }
+
+    //////////////////////////////////////////////////////////////
+    // begin pread_with
+    //////////////////////////////////////////////////////////////
+
+    macro_rules! pwrite_test {
+        ($write:ident, $read:ident, $deadbeef:expr) => {
+            #[test]
+            fn $write() {
+                use super::{Pread, Pwrite, BE};
+                let mut bytes: [u8; 8] = [0, 0, 0, 0, 0, 0, 0, 0];
+                let b = &mut bytes[..];
+                b.pwrite_with::<$read>($deadbeef, 0, LE).unwrap();
+                assert_eq!(b.pread_with::<$read>(0, LE).unwrap(), $deadbeef);
+                b.pwrite_with::<$read>($deadbeef, 0, BE).unwrap();
+                assert_eq!(b.pread_with::<$read>(0, BE).unwrap(), $deadbeef);
+            }
+        };
+    }
+
+    pwrite_test!(pwrite_and_pread_roundtrip_u16, u16, 0xbeef);
+    pwrite_test!(pwrite_and_pread_roundtrip_i16, i16, 0x7eef);
+    pwrite_test!(pwrite_and_pread_roundtrip_u32, u32, 0xbeefbeef);
+    pwrite_test!(pwrite_and_pread_roundtrip_i32, i32, 0x7eefbeef);
+    pwrite_test!(pwrite_and_pread_roundtrip_u64, u64, 0xbeefbeef7eef7eef);
+    pwrite_test!(pwrite_and_pread_roundtrip_i64, i64, 0x7eefbeef7eef7eef);
+
+    #[test]
+    fn pread_with_be() {
+        use super::Pread;
+        let bytes: [u8; 2] = [0x7e, 0xef];
+        let b = &bytes[..];
+        let byte: u16 = b.pread_with(0, super::BE).unwrap();
+        assert_eq!(0x7eef, byte);
+        let bytes: [u8; 2] = [0xde, 0xad];
+        let dead: u16 = bytes.pread_with(0, super::BE).unwrap();
+        assert_eq!(0xdead, dead);
+    }
+
+    #[test]
+    fn pread() {
+        use super::Pread;
+        let bytes: [u8; 2] = [0x7e, 0xef];
+        let b = &bytes[..];
+        let byte: u16 = b.pread(0).unwrap();
+        #[cfg(target_endian = "little")]
+        assert_eq!(0xef7e, byte);
+        #[cfg(target_endian = "big")]
+        assert_eq!(0x7eef, byte);
+    }
+
+    #[test]
+    fn pread_slice() {
+        use super::ctx::StrCtx;
+        use super::Pread;
+        let bytes: [u8; 2] = [0x7e, 0xef];
+        let b = &bytes[..];
+        let iserr: Result<&str, _> = b.pread_with(0, StrCtx::Length(3));
+        assert!(iserr.is_err());
+        // let bytes2: &[u8]  = b.pread_with(0, 2).unwrap();
+        // assert_eq!(bytes2.len(), bytes[..].len());
+        // for i in 0..bytes2.len() {
+        //     assert_eq!(bytes2[i], bytes[i])
+        // }
+    }
+
+    #[test]
+    fn pread_str() {
+        use super::ctx::*;
+        use super::Pread;
+        let bytes: [u8; 2] = [0x2e, 0x0];
+        let b = &bytes[..];
+        let s: &str = b.pread(0).unwrap();
+        println!("str: {}", s);
+        assert_eq!(s.len(), bytes[..].len() - 1);
+        let bytes: &[u8] = b"hello, world!\0some_other_things";
+        let hello_world: &str = bytes.pread_with(0, StrCtx::Delimiter(NULL)).unwrap();
+        println!("{:?}", &hello_world);
+        assert_eq!(hello_world.len(), 13);
+        let hello: &str = bytes.pread_with(0, StrCtx::Delimiter(SPACE)).unwrap();
+        println!("{:?}", &hello);
+        assert_eq!(hello.len(), 6);
+        // this could result in underflow so we just try it
+        let _error = bytes.pread_with::<&str>(6, StrCtx::Delimiter(SPACE));
+        let error = bytes.pread_with::<&str>(7, StrCtx::Delimiter(SPACE));
+        println!("{:?}", &error);
+        assert!(error.is_ok());
+    }
+
+    #[test]
+    fn pread_str_weird() {
+        use super::ctx::*;
+        use super::Pread;
+        let bytes: &[u8] = b"";
+        let hello_world = bytes.pread_with::<&str>(0, StrCtx::Delimiter(NULL));
+        println!("1 {:?}", &hello_world);
+        assert_eq!(hello_world.is_err(), true);
+        let error = bytes.pread_with::<&str>(7, StrCtx::Delimiter(SPACE));
+        println!("2 {:?}", &error);
+        assert!(error.is_err());
+        let bytes: &[u8] = b"\0";
+        let null = bytes.pread::<&str>(0).unwrap();
+        println!("3 {:?}", &null);
+        assert_eq!(null.len(), 0);
+    }
+
+    #[test]
+    fn pwrite_str_and_bytes() {
+        use super::ctx::*;
+        use super::{Pread, Pwrite};
+        let astring: &str = "lol hello_world lal\0ala imabytes";
+        let mut buffer = [0u8; 33];
+        buffer.pwrite(astring, 0).unwrap();
+        {
+            let hello_world = buffer
+                .pread_with::<&str>(4, StrCtx::Delimiter(SPACE))
+                .unwrap();
+            assert_eq!(hello_world, "hello_world");
+        }
+        let bytes: &[u8] = b"more\0bytes";
+        buffer.pwrite(bytes, 0).unwrap();
+        let more = bytes
+            .pread_with::<&str>(0, StrCtx::Delimiter(NULL))
+            .unwrap();
+        assert_eq!(more, "more");
+        let bytes = bytes
+            .pread_with::<&str>(more.len() + 1, StrCtx::Delimiter(NULL))
+            .unwrap();
+        assert_eq!(bytes, "bytes");
+    }
+
+    use std::error;
+    use std::fmt::{self, Display};
+
+    #[derive(Debug)]
+    pub struct ExternalError {}
+
+    impl Display for ExternalError {
+        fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+            write!(fmt, "ExternalError")
+        }
+    }
+
+    impl error::Error for ExternalError {
+        fn description(&self) -> &str {
+            "ExternalError"
+        }
+        fn cause(&self) -> Option<&dyn error::Error> {
+            None
+        }
+    }
+
+    impl From<super::Error> for ExternalError {
+        fn from(err: super::Error) -> Self {
+            //use super::Error::*;
+            match err {
+                _ => ExternalError {},
+            }
+        }
+    }
+
+    #[derive(Debug, PartialEq, Eq)]
+    pub struct Foo(u16);
+
+    impl super::ctx::TryIntoCtx<super::Endian> for Foo {
+        type Error = ExternalError;
+        fn try_into_ctx(self, this: &mut [u8], le: super::Endian) -> Result<usize, Self::Error> {
+            use super::Pwrite;
+            if this.len() < 2 {
+                return Err((ExternalError {}).into());
+            }
+            this.pwrite_with(self.0, 0, le)?;
+            Ok(2)
+        }
+    }
+
+    impl<'a> super::ctx::TryFromCtx<'a, super::Endian> for Foo {
+        type Error = ExternalError;
+        fn try_from_ctx(this: &'a [u8], le: super::Endian) -> Result<(Self, usize), Self::Error> {
+            use super::Pread;
+            if this.len() > 2 {
+                return Err((ExternalError {}).into());
+            }
+            let n = this.pread_with(0, le)?;
+            Ok((Foo(n), 2))
+        }
+    }
+
+    #[test]
+    fn pread_with_iter_bytes() {
+        use super::Pread;
+        let mut bytes_to: [u8; 8] = [0, 0, 0, 0, 0, 0, 0, 0];
+        let bytes_from: [u8; 8] = [1, 2, 3, 4, 5, 6, 7, 8];
+        let bytes_to = &mut bytes_to[..];
+        let bytes_from = &bytes_from[..];
+        for i in 0..bytes_from.len() {
+            bytes_to[i] = bytes_from.pread(i).unwrap();
+        }
+        assert_eq!(bytes_to, bytes_from);
+    }
+
+    //////////////////////////////////////////////////////////////
+    // end pread_with
+    //////////////////////////////////////////////////////////////
+
+    //////////////////////////////////////////////////////////////
+    // begin gread_with
+    //////////////////////////////////////////////////////////////
+    macro_rules! g_test {
+        ($read:ident, $deadbeef:expr, $typ:ty) => {
+            #[test]
+            fn $read() {
+                use super::Pread;
+                let bytes: [u8; 8] = [0xf, 0xe, 0xe, 0xb, 0xd, 0xa, 0xe, 0xd];
+                let mut offset = 0;
+                let deadbeef: $typ = bytes.gread_with(&mut offset, LE).unwrap();
+                assert_eq!(deadbeef, $deadbeef as $typ);
+                assert_eq!(offset, ::std::mem::size_of::<$typ>());
+            }
+        };
+    }
+
+    g_test!(simple_gread_u16, 0xe0f, u16);
+    g_test!(simple_gread_u32, 0xb0e0e0f, u32);
+    g_test!(simple_gread_u64, 0xd0e0a0d0b0e0e0f, u64);
+    g_test!(simple_gread_i64, 940700423303335439, i64);
+
+    macro_rules! simple_float_test {
+        ($read:ident, $deadbeef:expr, $typ:ty) => {
+            #[test]
+            fn $read() {
+                use super::Pread;
+                let bytes: [u8; 8] = [0u8, 0, 0, 0, 0, 0, 224, 63];
+                let mut offset = 0;
+                let deadbeef: $typ = bytes.gread_with(&mut offset, LE).unwrap();
+                assert_eq!(deadbeef, $deadbeef as $typ);
+                assert_eq!(offset, ::std::mem::size_of::<$typ>());
+            }
+        };
+    }
+
+    simple_float_test!(gread_f32, 0.0, f32);
+    simple_float_test!(gread_f64, 0.5, f64);
+
+    macro_rules! g_read_write_test {
+        ($read:ident, $val:expr, $typ:ty) => {
+            #[test]
+            fn $read() {
+                use super::{Pread, Pwrite, BE, LE};
+                let mut buffer = [0u8; 16];
+                let offset = &mut 0;
+                buffer.gwrite_with($val.clone(), offset, LE).unwrap();
+                let o2 = &mut 0;
+                let val: $typ = buffer.gread_with(o2, LE).unwrap();
+                assert_eq!(val, $val);
+                assert_eq!(*offset, ::std::mem::size_of::<$typ>());
+                assert_eq!(*o2, ::std::mem::size_of::<$typ>());
+                assert_eq!(*o2, *offset);
+                buffer.gwrite_with($val.clone(), offset, BE).unwrap();
+                let val: $typ = buffer.gread_with(o2, BE).unwrap();
+                assert_eq!(val, $val);
+            }
+        };
+    }
+
+    g_read_write_test!(gread_gwrite_f64_1, 0.25f64, f64);
+    g_read_write_test!(gread_gwrite_f64_2, 0.5f64, f64);
+    g_read_write_test!(gread_gwrite_f64_3, 0.064, f64);
+
+    g_read_write_test!(gread_gwrite_f32_1, 0.25f32, f32);
+    g_read_write_test!(gread_gwrite_f32_2, 0.5f32, f32);
+    g_read_write_test!(gread_gwrite_f32_3, 0.0f32, f32);
+
+    g_read_write_test!(gread_gwrite_i64_1, 0i64, i64);
+    g_read_write_test!(gread_gwrite_i64_2, -1213213211111i64, i64);
+    g_read_write_test!(gread_gwrite_i64_3, -3000i64, i64);
+
+    g_read_write_test!(gread_gwrite_i32_1, 0i32, i32);
+    g_read_write_test!(gread_gwrite_i32_2, -1213213232, i32);
+    g_read_write_test!(gread_gwrite_i32_3, -3000i32, i32);
+
+    // useful for ferreting out problems with impls
+    #[test]
+    fn gread_with_iter_bytes() {
+        use super::Pread;
+        let mut bytes_to: [u8; 8] = [0, 0, 0, 0, 0, 0, 0, 0];
+        let bytes_from: [u8; 8] = [1, 2, 3, 4, 5, 6, 7, 8];
+        let bytes_to = &mut bytes_to[..];
+        let bytes_from = &bytes_from[..];
+        let mut offset = &mut 0;
+        for i in 0..bytes_from.len() {
+            bytes_to[i] = bytes_from.gread(&mut offset).unwrap();
+        }
+        assert_eq!(bytes_to, bytes_from);
+        assert_eq!(*offset, bytes_to.len());
+    }
+
+    #[test]
+    fn gread_inout() {
+        use super::Pread;
+        let mut bytes_to: [u8; 8] = [0, 0, 0, 0, 0, 0, 0, 0];
+        let bytes_from: [u8; 8] = [1, 2, 3, 4, 5, 6, 7, 8];
+        let bytes = &bytes_from[..];
+        let offset = &mut 0;
+        bytes.gread_inout(offset, &mut bytes_to[..]).unwrap();
+        assert_eq!(bytes_to, bytes_from);
+        assert_eq!(*offset, bytes_to.len());
+    }
+
+    #[test]
+    fn gread_with_byte() {
+        use super::Pread;
+        let bytes: [u8; 1] = [0x7f];
+        let b = &bytes[..];
+        let offset = &mut 0;
+        let byte: u8 = b.gread(offset).unwrap();
+        assert_eq!(0x7f, byte);
+        assert_eq!(*offset, 1);
+    }
+
+    #[test]
+    fn gread_slice() {
+        use super::ctx::StrCtx;
+        use super::Pread;
+        let bytes: [u8; 2] = [0x7e, 0xef];
+        let b = &bytes[..];
+        let offset = &mut 0;
+        let res = b.gread_with::<&str>(offset, StrCtx::Length(3));
+        assert!(res.is_err());
+        *offset = 0;
+        let astring: [u8; 3] = [0x45, 042, 0x44];
+        let string = astring.gread_with::<&str>(offset, StrCtx::Length(2));
+        match &string {
+            &Ok(_) => {}
+            &Err(ref err) => {
+                println!("{}", &err);
+                panic!();
+            }
+        }
+        assert_eq!(string.unwrap(), "E*");
+        *offset = 0;
+        let bytes2: &[u8] = b.gread_with(offset, 2).unwrap();
+        assert_eq!(*offset, 2);
+        assert_eq!(bytes2.len(), bytes[..].len());
+        for i in 0..bytes2.len() {
+            assert_eq!(bytes2[i], bytes[i])
+        }
+    }
+
+    /////////////////////////////////////////////////////////////////
+    // end gread_with
+    /////////////////////////////////////////////////////////////////
+}
diff --git a/third_party/rust/scroll/src/pread.rs b/third_party/rust/scroll/src/pread.rs
new file mode 100644
index 0000000000..72ba877054
--- /dev/null
+++ b/third_party/rust/scroll/src/pread.rs
@@ -0,0 +1,178 @@
+use core::result;
+
+use crate::ctx::TryFromCtx;
+use crate::error;
+
+/// A very generic, contextual pread interface in Rust.
+///
+/// Like [Pwrite](trait.Pwrite.html) — but for reading!
+///
+/// Implementing `Pread` on a data store allows you to then read almost arbitrarily complex types
+/// efficiently.
+///
+/// To this end the Pread trait works in conjuction with the [TryFromCtx](ctx/trait.TryFromCtx.html);
+/// The `TryFromCtx` trait implemented on a type defines how to convert data to an object of that
+/// type, the Pread trait implemented on a data store defines how to extract said data from that
+/// store.
+///
+/// It should be noted though that in this context, data does not necessarily mean `&[u8]` —
+/// `Pread` and `TryFromCtx` are generic over what 'data' means and could be implemented instead
+/// over chunks of memory or any other indexable type — but scroll does come with a set of powerful
+/// blanket implementations for data being a continous block of byte-addressable memory.
+///
+/// Pread provides two main groups of functions: pread and gread.
+///
+/// `pread` is the basic function that simply extracts a given type from a given data store - either
+/// using a provided Context in the case of [pread_with](trait.Pread.html#method.pread_with) or
+/// with the default context for the given type in the case of [pread](trait.Pread.html#method.pread)
+///
+/// `gread` does in addition to that update the offset it's currently at, allowing for a cursored
+/// read — `gread_inout` expands on that and reads a number of continous types from the data store.
+/// gread again comes with `_with` variants to allow using a specific context.
+///
+/// Since pread and friends are very generic functions their types are rather complex, but very
+/// much understandable; `TryFromCtx` is generic over `Ctx` ([described
+/// here](ctx/index.html#context)), `Output` and `Error`. The Error type is hopefully
+/// self-explanatory, however the `Output` type is rather important; it defines what Pread extracts
+/// from the data store and has to match up with what `TryFromCtx` expects as input to convert into
+/// the resulting type. scroll defaults to `&[u8]` here.
+///
+/// Unless you need to implement your own data store — that is either can't convert to `&[u8]` or
+/// have a data that does not expose a `&[u8]` — you will probably want to implement
+/// [TryFromCtx](ctx/trait.TryFromCtx.html) on your Rust types to be extracted.
+///
+pub trait Pread<Ctx: Copy, E> {
+    #[inline]
+    /// Reads a value from `self` at `offset` with a default `Ctx`. For the primitive numeric values, this will read at the machine's endianness.
+    /// # Example
+    /// ```rust
+    /// use scroll::Pread;
+    /// let bytes = [0x7fu8; 0x01];
+    /// let byte = bytes.pread::<u8>(0).unwrap();
+    fn pread<'a, N: TryFromCtx<'a, Ctx, Self, Error = E>>(
+        &'a self,
+        offset: usize,
+    ) -> result::Result<N, E>
+    where
+        Ctx: Default,
+    {
+        self.pread_with(offset, Ctx::default())
+    }
+
+    #[inline]
+    /// Reads a value from `self` at `offset` with the given `ctx`
+    /// # Example
+    /// ```rust
+    /// use scroll::Pread;
+    /// let bytes: [u8; 2] = [0xde, 0xad];
+    /// let dead: u16 = bytes.pread_with(0, scroll::BE).unwrap();
+    /// assert_eq!(dead, 0xdeadu16);
+    fn pread_with<'a, N: TryFromCtx<'a, Ctx, Self, Error = E>>(
+        &'a self,
+        offset: usize,
+        ctx: Ctx,
+    ) -> result::Result<N, E> {
+        let mut ignored = offset;
+        self.gread_with(&mut ignored, ctx)
+    }
+
+    #[inline]
+    /// Reads a value from `self` at `offset` with a default `Ctx`. For the primitive numeric values, this will read at the machine's endianness. Updates the offset
+    /// # Example
+    /// ```rust
+    /// use scroll::Pread;
+    /// let offset = &mut 0;
+    /// let bytes = [0x7fu8; 0x01];
+    /// let byte = bytes.gread::<u8>(offset).unwrap();
+    /// assert_eq!(*offset, 1);
+    fn gread<'a, N: TryFromCtx<'a, Ctx, Self, Error = E>>(
+        &'a self,
+        offset: &mut usize,
+    ) -> result::Result<N, E>
+    where
+        Ctx: Default,
+    {
+        let ctx = Ctx::default();
+        self.gread_with(offset, ctx)
+    }
+
+    /// Reads a value from `self` at `offset` with the given `ctx`, and updates the offset.
+    /// # Example
+    /// ```rust
+    /// use scroll::Pread;
+    /// let offset = &mut 0;
+    /// let bytes: [u8; 2] = [0xde, 0xad];
+    /// let dead: u16 = bytes.gread_with(offset, scroll::BE).unwrap();
+    /// assert_eq!(dead, 0xdeadu16);
+    /// assert_eq!(*offset, 2);
+    fn gread_with<'a, N: TryFromCtx<'a, Ctx, Self, Error = E>>(
+        &'a self,
+        offset: &mut usize,
+        ctx: Ctx,
+    ) -> result::Result<N, E>;
+
+    /// Tries to write `inout.len()` `N`s into `inout` from `Self` starting at `offset`, using the default context for `N`, and updates the offset.
+    /// # Example
+    /// ```rust
+    /// use scroll::Pread;
+    /// let mut bytes: Vec<u8> = vec![0, 0];
+    /// let offset = &mut 0;
+    /// let bytes_from: [u8; 2] = [0x48, 0x49];
+    /// bytes_from.gread_inout(offset, &mut bytes).unwrap();
+    /// assert_eq!(&bytes, &bytes_from);
+    /// assert_eq!(*offset, 2);
+    #[inline]
+    fn gread_inout<'a, N: TryFromCtx<'a, Ctx, Self, Error = E>>(
+        &'a self,
+        offset: &mut usize,
+        inout: &mut [N],
+    ) -> result::Result<(), E>
+    where
+        Ctx: Default,
+    {
+        for i in inout.iter_mut() {
+            *i = self.gread(offset)?;
+        }
+        Ok(())
+    }
+
+    /// Tries to write `inout.len()` `N`s into `inout` from `Self` starting at `offset`, using the context `ctx`
+    /// # Example
+    /// ```rust
+    /// use scroll::{ctx, LE, Pread};
+    /// let mut bytes: Vec<u8> = vec![0, 0];
+    /// let offset = &mut 0;
+    /// let bytes_from: [u8; 2] = [0x48, 0x49];
+    /// bytes_from.gread_inout_with(offset, &mut bytes, LE).unwrap();
+    /// assert_eq!(&bytes, &bytes_from);
+    /// assert_eq!(*offset, 2);
+    #[inline]
+    fn gread_inout_with<'a, N: TryFromCtx<'a, Ctx, Self, Error = E>>(
+        &'a self,
+        offset: &mut usize,
+        inout: &mut [N],
+        ctx: Ctx,
+    ) -> result::Result<(), E> {
+        for i in inout.iter_mut() {
+            *i = self.gread_with(offset, ctx)?;
+        }
+        Ok(())
+    }
+}
+
+impl<Ctx: Copy, E: From<error::Error>> Pread<Ctx, E> for [u8] {
+    fn gread_with<'a, N: TryFromCtx<'a, Ctx, Self, Error = E>>(
+        &'a self,
+        offset: &mut usize,
+        ctx: Ctx,
+    ) -> result::Result<N, E> {
+        let start = *offset;
+        if start >= self.len() {
+            return Err(error::Error::BadOffset(start).into());
+        }
+        N::try_from_ctx(&self[start..], ctx).map(|(n, size)| {
+            *offset += size;
+            n
+        })
+    }
+}
diff --git a/third_party/rust/scroll/src/pwrite.rs b/third_party/rust/scroll/src/pwrite.rs
new file mode 100644
index 0000000000..ab6d96157d
--- /dev/null
+++ b/third_party/rust/scroll/src/pwrite.rs
@@ -0,0 +1,96 @@
+use core::result;
+
+use crate::ctx::TryIntoCtx;
+use crate::error;
+
+/// A very generic, contextual pwrite interface in Rust.
+///
+/// Like [Pread](trait.Pread.html) — but for writing!
+///
+/// Implementing `Pwrite` on a data store allows you to then write almost arbitrarily complex types
+/// efficiently.
+///
+/// To this end the Pwrite trait works in conjuction with the [TryIntoCtx](ctx/trait.TryIntoCtx.html);
+/// The `TryIntoCtx` trait implemented on a type defines how to convert said type into data that
+/// an implementation of Pwrite can … well … write.
+///
+/// As with [Pread](trait.Pread.html) 'data' does not necessarily mean `&[u8]` but can be any
+/// indexable type. In fact much of the documentation of `Pread` applies to `Pwrite` as well just
+/// with 'read' switched for 'write' and 'From' switched with 'Into' so if you haven't yet you
+/// should read the documentation of `Pread` first.
+///
+/// Unless you need to implement your own data store — that is either can't convert to `&[u8]` or
+/// have a data that does not expose a `&mut [u8]` — you will probably want to implement
+/// [TryIntoCtx](ctx/trait.TryIntoCtx.html) on your Rust types to be written.
+///
+pub trait Pwrite<Ctx: Copy, E> {
+    #[inline]
+    fn pwrite<N: TryIntoCtx<Ctx, Self, Error = E>>(
+        &mut self,
+        n: N,
+        offset: usize,
+    ) -> result::Result<usize, E>
+    where
+        Ctx: Default,
+    {
+        self.pwrite_with(n, offset, Ctx::default())
+    }
+
+    /// Write `N` at offset `I` with context `Ctx`
+    /// # Example
+    /// ```
+    /// use scroll::{Pwrite, Pread, LE};
+    /// let mut bytes: [u8; 8] = [0, 0, 0, 0, 0, 0, 0, 0];
+    /// bytes.pwrite_with::<u32>(0xbeefbeef, 0, LE).unwrap();
+    /// assert_eq!(bytes.pread_with::<u32>(0, LE).unwrap(), 0xbeefbeef);
+    fn pwrite_with<N: TryIntoCtx<Ctx, Self, Error = E>>(
+        &mut self,
+        n: N,
+        offset: usize,
+        ctx: Ctx,
+    ) -> result::Result<usize, E>;
+
+    /// Write `n` into `self` at `offset`, with a default `Ctx`. Updates the offset.
+    #[inline]
+    fn gwrite<N: TryIntoCtx<Ctx, Self, Error = E>>(
+        &mut self,
+        n: N,
+        offset: &mut usize,
+    ) -> result::Result<usize, E>
+    where
+        Ctx: Default,
+    {
+        let ctx = Ctx::default();
+        self.gwrite_with(n, offset, ctx)
+    }
+
+    /// Write `n` into `self` at `offset`, with the `ctx`. Updates the offset.
+    #[inline]
+    fn gwrite_with<N: TryIntoCtx<Ctx, Self, Error = E>>(
+        &mut self,
+        n: N,
+        offset: &mut usize,
+        ctx: Ctx,
+    ) -> result::Result<usize, E> {
+        let o = *offset;
+        self.pwrite_with(n, o, ctx).map(|size| {
+            *offset += size;
+            size
+        })
+    }
+}
+
+impl<Ctx: Copy, E: From<error::Error>> Pwrite<Ctx, E> for [u8] {
+    fn pwrite_with<N: TryIntoCtx<Ctx, Self, Error = E>>(
+        &mut self,
+        n: N,
+        offset: usize,
+        ctx: Ctx,
+    ) -> result::Result<usize, E> {
+        if offset >= self.len() {
+            return Err(error::Error::BadOffset(offset).into());
+        }
+        let dst = &mut self[offset..];
+        n.try_into_ctx(dst, ctx)
+    }
+}