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//! 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
//! the `*read`-methods instead of the `*read_with` ones you must also implement
//!
//! # 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, MaybeUninit};
use core::ptr::copy_nonoverlapping;
use core::{result, str};
#[cfg(feature = "std")]
use std::ffi::{CStr, CString};
use crate::endian::Endian;
use crate::{error, Pread, Pwrite};
/// 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 {
matches!(self, StrCtx::Length(_))
}
}
/// 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
/// ##[cfg(feature = "std")] {
/// 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
/// ##[cfg(feature = "std")] {
/// 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, $endian:expr) => {{
assert!($dst.len() >= $size);
let bytes = if $endian.is_little() {
$n.to_le()
} else {
$n.to_be()
}
.to_ne_bytes();
unsafe {
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,
);
}
$typ::from_bits(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, self.to_bits(), 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: {src_len} dst len: {dst_len} offset: {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))
}
}
}
impl<'a, Ctx: Copy, T: TryFromCtx<'a, Ctx, Error = error::Error>, const N: usize>
TryFromCtx<'a, Ctx> for [T; N]
{
type Error = error::Error;
fn try_from_ctx(src: &'a [u8], ctx: Ctx) -> Result<(Self, usize), Self::Error> {
let mut offset = 0;
let mut buf: [MaybeUninit<T>; N] = core::array::from_fn(|_| MaybeUninit::uninit());
let mut error_ctx = None;
for (idx, element) in buf.iter_mut().enumerate() {
match src.gread_with::<T>(&mut offset, ctx) {
Ok(val) => {
*element = MaybeUninit::new(val);
}
Err(e) => {
error_ctx = Some((e, idx));
break;
}
}
}
if let Some((e, idx)) = error_ctx {
for element in &mut buf[0..idx].iter_mut() {
// SAFETY: Any element upto idx must have already been initialized, since
// we iterate until we encounter an error.
unsafe {
element.assume_init_drop();
}
}
Err(e)
} else {
// SAFETY: we initialized each element above by preading them out, correctness
// of the initialized element is guaranted by pread itself
Ok((buf.map(|element| unsafe { element.assume_init() }), offset))
}
}
}
impl<Ctx: Copy, T: TryIntoCtx<Ctx, Error = error::Error>, const N: usize> TryIntoCtx<Ctx>
for [T; N]
{
type Error = error::Error;
fn try_into_ctx(self, buf: &mut [u8], ctx: Ctx) -> Result<usize, Self::Error> {
let mut offset = 0;
for element in self {
buf.gwrite_with(element, &mut offset, ctx)?;
}
Ok(offset)
}
}
#[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)]
#[cfg(feature = "std")]
mod tests {
use super::*;
#[test]
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]
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);
}
}