diff options
Diffstat (limited to 'third_party/rust/object/src/read/read_ref.rs')
| -rw-r--r-- | third_party/rust/object/src/read/read_ref.rs | 137 |
1 files changed, 137 insertions, 0 deletions
diff --git a/third_party/rust/object/src/read/read_ref.rs b/third_party/rust/object/src/read/read_ref.rs new file mode 100644 index 0000000000..2f547a4e2c --- /dev/null +++ b/third_party/rust/object/src/read/read_ref.rs @@ -0,0 +1,137 @@ +#![allow(clippy::len_without_is_empty)] + +use core::convert::TryInto; +use core::ops::Range; +use core::{mem, result}; + +use crate::pod::{from_bytes, slice_from_bytes, Pod}; + +type Result<T> = result::Result<T, ()>; + +/// A trait for reading references to `Pod` types from a block of data. +/// +/// This allows parsers to handle both of these cases: +/// - the block of data exists in memory, and it is desirable +/// to use references to this block instead of copying it, +/// - the block of data exists in storage, and it is desirable +/// to read on demand to minimize I/O and memory usage. +/// +/// The methods accept `self` by value because `Self` is expected to behave +/// similar to a reference: it may be a reference with a lifetime of `'a`, +/// or it may be a wrapper of a reference. +/// +/// The `Clone` and `Copy` bounds are for convenience, and since `Self` is +/// expected to be similar to a reference, these are easily satisfied. +/// +/// Object file parsers typically use offsets to locate the structures +/// in the block, and will most commonly use the `*_at` methods to +/// read a structure at a known offset. +/// +/// Occasionally file parsers will need to treat the block as a stream, +/// and so convenience methods are provided that update an offset with +/// the size that was read. +// +// An alternative would be for methods to accept `&mut self` and use a +// `seek` method instead of the `offset` parameters, but this is less +// convenient for implementers. +pub trait ReadRef<'a>: Clone + Copy { + /// The total size of the block of data. + fn len(self) -> Result<u64>; + + /// Get a reference to a `u8` slice at the given offset. + /// + /// Returns an error if offset or size are out of bounds. + fn read_bytes_at(self, offset: u64, size: u64) -> Result<&'a [u8]>; + + /// Get a reference to a delimited `u8` slice which starts at range.start. + /// + /// Does not include the delimiter. + /// + /// Returns an error if the range is out of bounds or the delimiter is + /// not found in the range. + fn read_bytes_at_until(self, range: Range<u64>, delimiter: u8) -> Result<&'a [u8]>; + + /// Get a reference to a `u8` slice at the given offset, and update the offset. + /// + /// Returns an error if offset or size are out of bounds. + fn read_bytes(self, offset: &mut u64, size: u64) -> Result<&'a [u8]> { + let bytes = self.read_bytes_at(*offset, size)?; + *offset = offset.wrapping_add(size); + Ok(bytes) + } + + /// Get a reference to a `Pod` type at the given offset, and update the offset. + /// + /// Returns an error if offset or size are out of bounds. + /// + /// The default implementation uses `read_bytes`, and returns an error if + /// `read_bytes` does not return bytes with the correct alignment for `T`. + /// Implementors may want to provide their own implementation that ensures + /// the alignment can be satisified. Alternatively, only use this method with + /// types that do not need alignment (see the `unaligned` feature of this crate). + fn read<T: Pod>(self, offset: &mut u64) -> Result<&'a T> { + let size = mem::size_of::<T>().try_into().map_err(|_| ())?; + let bytes = self.read_bytes(offset, size)?; + let (t, _) = from_bytes(bytes)?; + Ok(t) + } + + /// Get a reference to a `Pod` type at the given offset. + /// + /// Returns an error if offset or size are out of bounds. + /// + /// Also see the `read` method for information regarding alignment of `T`. + fn read_at<T: Pod>(self, mut offset: u64) -> Result<&'a T> { + self.read(&mut offset) + } + + /// Get a reference to a slice of a `Pod` type at the given offset, and update the offset. + /// + /// Returns an error if offset or size are out of bounds. + /// + /// Also see the `read` method for information regarding alignment of `T`. + fn read_slice<T: Pod>(self, offset: &mut u64, count: usize) -> Result<&'a [T]> { + let size = count + .checked_mul(mem::size_of::<T>()) + .ok_or(())? + .try_into() + .map_err(|_| ())?; + let bytes = self.read_bytes(offset, size)?; + let (t, _) = slice_from_bytes(bytes, count)?; + Ok(t) + } + + /// Get a reference to a slice of a `Pod` type at the given offset. + /// + /// Returns an error if offset or size are out of bounds. + /// + /// Also see the `read` method for information regarding alignment of `T`. + fn read_slice_at<T: Pod>(self, mut offset: u64, count: usize) -> Result<&'a [T]> { + self.read_slice(&mut offset, count) + } +} + +impl<'a> ReadRef<'a> for &'a [u8] { + fn len(self) -> Result<u64> { + self.len().try_into().map_err(|_| ()) + } + + fn read_bytes_at(self, offset: u64, size: u64) -> Result<&'a [u8]> { + let offset: usize = offset.try_into().map_err(|_| ())?; + let size: usize = size.try_into().map_err(|_| ())?; + self.get(offset..).ok_or(())?.get(..size).ok_or(()) + } + + fn read_bytes_at_until(self, range: Range<u64>, delimiter: u8) -> Result<&'a [u8]> { + let start: usize = range.start.try_into().map_err(|_| ())?; + let end: usize = range.end.try_into().map_err(|_| ())?; + let bytes = self.get(start..end).ok_or(())?; + match memchr::memchr(delimiter, bytes) { + Some(len) => { + // This will never fail. + bytes.get(..len).ok_or(()) + } + None => Err(()), + } + } +} |