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use core::result; use core::ops::{Index, RangeFrom}; use crate::ctx::{TryFromCtx, MeasureWith}; use crate::error; /// A very generic, contextual pread interface in Rust. Allows completely parallelized reads, as `Self` is immutable /// /// Don't be scared! The `Pread` definition _is_ terrifying, but it is definitely tractable. Essentially, `E` is the error, `Ctx` the parsing context, `I` is the indexing type, `TryCtx` is the "offset + ctx" Context given to the `TryFromCtx` trait bounds, and `SliceCtx` is the "offset + size + ctx" context given to the `TryRefFromCtx` trait bound. /// /// # 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 [TryFromCtx](trait.TryFromCtx.html) /// /// ```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 transform a scroll error ideally (quick_error, error_chain allow this automatically nowadays) /// #[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<&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 Pread<Ctx, E> : Index<usize> + Index<RangeFrom<usize>> + MeasureWith<Ctx> where Ctx: Copy, E: From<error::Error>, { #[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 as Index<RangeFrom<usize>>>::Output, Error = E>>(&'a self, offset: usize) -> result::Result<N, E> where <Self as Index<RangeFrom<usize>>>::Output: 'a, 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 as Index<RangeFrom<usize>>>::Output, Error = E>>(&'a self, offset: usize, ctx: Ctx) -> result::Result<N, E> where <Self as Index<RangeFrom<usize>>>::Output: 'a { let len = self.measure_with(&ctx); if offset >= len { return Err(error::Error::BadOffset(offset).into()) } N::try_from_ctx(&self[offset..], ctx).and_then(|(n, _)| Ok(n)) } #[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 as Index<RangeFrom<usize>>>::Output, Error = E>>(&'a self, offset: &mut usize) -> result::Result<N, E> where Ctx: Default, <Self as Index<RangeFrom<usize>>>::Output: 'a { 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); #[inline] fn gread_with<'a, N: TryFromCtx<'a, Ctx, <Self as Index<RangeFrom<usize>>>::Output, Error = E>> (&'a self, offset: &mut usize, ctx: Ctx) -> result::Result<N, E> where <Self as Index<RangeFrom<usize>>>::Output: 'a { let o = *offset; // self.pread_with(o, ctx).and_then(|(n, size)| { // *offset += size; // Ok(n) // }) let len = self.measure_with(&ctx); if o >= len { return Err(error::Error::BadOffset(o).into()) } N::try_from_ctx(&self[o..], ctx).and_then(|(n, size)| { *offset += size; Ok(n) }) } /// Trys 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>(&'a self, offset: &mut usize, inout: &mut [N]) -> result::Result<(), E> where N: TryFromCtx<'a, Ctx, <Self as Index<RangeFrom<usize>>>::Output, Error = E>, Ctx: Default, <Self as Index<RangeFrom<usize>>>::Output: 'a { for i in inout.iter_mut() { *i = self.gread(offset)?; } Ok(()) } /// Trys 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>(&'a self, offset: &mut usize, inout: &mut [N], ctx: Ctx) -> result::Result<(), E> where N: TryFromCtx<'a, Ctx, <Self as Index<RangeFrom<usize>>>::Output, Error = E>, <Self as Index<RangeFrom<usize>>>::Output: 'a { for i in inout.iter_mut() { *i = self.gread_with(offset, ctx)?; } Ok(()) } } impl<Ctx: Copy, E: From<error::Error>, R: ?Sized + Index<usize> + Index<RangeFrom<usize>> + MeasureWith<Ctx>> Pread<Ctx, E> for R {}