Trait zerocopy::TryFromBytes
source · pub unsafe trait TryFromBytes {
Show 15 methods
// Provided methods
fn try_ref_from_bytes(
source: &[u8],
) -> Result<&Self, TryCastError<&[u8], Self>>
where Self: KnownLayout + Immutable { ... }
fn try_ref_from_prefix(
source: &[u8],
) -> Result<(&Self, &[u8]), TryCastError<&[u8], Self>>
where Self: KnownLayout + Immutable { ... }
fn try_ref_from_suffix(
source: &[u8],
) -> Result<(&[u8], &Self), TryCastError<&[u8], Self>>
where Self: KnownLayout + Immutable { ... }
fn try_mut_from_bytes(
bytes: &mut [u8],
) -> Result<&mut Self, TryCastError<&mut [u8], Self>>
where Self: KnownLayout { ... }
fn try_mut_from_prefix(
source: &mut [u8],
) -> Result<(&mut Self, &mut [u8]), TryCastError<&mut [u8], Self>>
where Self: KnownLayout { ... }
fn try_mut_from_suffix(
source: &mut [u8],
) -> Result<(&mut [u8], &mut Self), TryCastError<&mut [u8], Self>>
where Self: KnownLayout { ... }
fn try_ref_from_bytes_with_elems(
source: &[u8],
count: usize,
) -> Result<&Self, TryCastError<&[u8], Self>>
where Self: KnownLayout<PointerMetadata = usize> + Immutable { ... }
fn try_ref_from_prefix_with_elems(
source: &[u8],
count: usize,
) -> Result<(&Self, &[u8]), TryCastError<&[u8], Self>>
where Self: KnownLayout<PointerMetadata = usize> + Immutable { ... }
fn try_ref_from_suffix_with_elems(
source: &[u8],
count: usize,
) -> Result<(&[u8], &Self), TryCastError<&[u8], Self>>
where Self: KnownLayout<PointerMetadata = usize> + Immutable { ... }
fn try_mut_from_bytes_with_elems(
source: &mut [u8],
count: usize,
) -> Result<&mut Self, TryCastError<&mut [u8], Self>>
where Self: KnownLayout<PointerMetadata = usize> { ... }
fn try_mut_from_prefix_with_elems(
source: &mut [u8],
count: usize,
) -> Result<(&mut Self, &mut [u8]), TryCastError<&mut [u8], Self>>
where Self: KnownLayout<PointerMetadata = usize> { ... }
fn try_mut_from_suffix_with_elems(
source: &mut [u8],
count: usize,
) -> Result<(&mut [u8], &mut Self), TryCastError<&mut [u8], Self>>
where Self: KnownLayout<PointerMetadata = usize> { ... }
fn try_read_from_bytes(
source: &[u8],
) -> Result<Self, TryReadError<&[u8], Self>>
where Self: Sized { ... }
fn try_read_from_prefix(
source: &[u8],
) -> Result<(Self, &[u8]), TryReadError<&[u8], Self>>
where Self: Sized { ... }
fn try_read_from_suffix(
source: &[u8],
) -> Result<(&[u8], Self), TryReadError<&[u8], Self>>
where Self: Sized { ... }
}Expand description
Types for which some bit patterns are valid.
A memory region of the appropriate length which contains initialized bytes
can be viewed as a TryFromBytes type so long as the runtime value of those
bytes corresponds to a valid instance of that type. For example,
bool is TryFromBytes, so zerocopy can transmute a u8 into a
bool so long as it first checks that the value of the u8 is 0 or
1.
§Implementation
Do not implement this trait yourself! Instead, use
#[derive(TryFromBytes)]; e.g.:
#[derive(TryFromBytes)]
struct MyStruct {
...
}
#[derive(TryFromBytes)]
#[repr(u8)]
enum MyEnum {
...
}
#[derive(TryFromBytes, Immutable)]
union MyUnion {
...
}This derive ensures that the runtime check of whether bytes correspond to a valid instance is sound. You must implement this trait via the derive.
§What is a “valid instance”?
In Rust, each type has bit validity, which refers to the set of bit
patterns which may appear in an instance of that type. It is impossible for
safe Rust code to produce values which violate bit validity (ie, values
outside of the “valid” set of bit patterns). If unsafe code produces an
invalid value, this is considered undefined behavior.
Rust’s bit validity rules are currently being decided, which means that some types have three classes of bit patterns: those which are definitely valid, and whose validity is documented in the language; those which may or may not be considered valid at some point in the future; and those which are definitely invalid.
Zerocopy takes a conservative approach, and only considers a bit pattern to be valid if its validity is a documenteed guarantee provided by the language.
For most use cases, Rust’s current guarantees align with programmers’ intuitions about what ought to be valid. As a result, zerocopy’s conservatism should not affect most users.
If you are negatively affected by lack of support for a particular type, we encourage you to let us know by filing an issue.
§TryFromBytes is not symmetrical with IntoBytes
There are some types which implement both TryFromBytes and IntoBytes,
but for which TryFromBytes is not guaranteed to accept all byte sequences
produced by IntoBytes. In other words, for some T: TryFromBytes + IntoBytes, there exist values of t: T such that
TryFromBytes::try_ref_from_bytes(t.as_bytes()) == None. Code should not
generally assume that values produced by IntoBytes will necessarily be
accepted as valid by TryFromBytes.
§Safety
On its own, T: TryFromBytes does not make any guarantees about the layout
or representation of T. It merely provides the ability to perform a
validity check at runtime via methods like try_ref_from_bytes.
You must not rely on the #[doc(hidden)] internals of TryFromBytes.
Future releases of zerocopy may make backwards-breaking changes to these
items, including changes that only affect soundness, which may cause code
which uses those items to silently become unsound.
Provided Methods§
sourcefn try_ref_from_bytes(source: &[u8]) -> Result<&Self, TryCastError<&[u8], Self>>where
Self: KnownLayout + Immutable,
fn try_ref_from_bytes(source: &[u8]) -> Result<&Self, TryCastError<&[u8], Self>>where
Self: KnownLayout + Immutable,
Attempts to interpret the given source as a &Self.
If the bytes of source are a valid instance of Self, this method
returns a reference to those bytes interpreted as a Self. If the
length of source is not a valid size of Self, or if
source is not appropriately aligned, or if source is not a valid
instance of Self, this returns Err. If Self: Unaligned, you can infallibly discard the alignment
error.
Self may be a sized type, a slice, or a slice DST.
§Compile-Time Assertions
This method cannot yet be used on unsized types whose dynamically-sized component is zero-sized. Attempting to use this method on such types results in a compile-time assertion error; e.g.:
use zerocopy::*;
#[derive(TryFromBytes, Immutable, KnownLayout)]
#[repr(C)]
struct ZSTy {
leading_sized: u16,
trailing_dst: [()],
}
let _ = ZSTy::try_ref_from_bytes(0u16.as_bytes()); // ⚠ Compile Error!§Examples
use zerocopy::TryFromBytes;
// The only valid value of this type is the byte `0xC0`
#[derive(TryFromBytes, KnownLayout, Immutable)]
#[repr(u8)]
enum C0 { xC0 = 0xC0 }
// The only valid value of this type is the byte sequence `0xC0C0`.
#[derive(TryFromBytes, KnownLayout, Immutable)]
#[repr(C)]
struct C0C0(C0, C0);
#[derive(TryFromBytes, KnownLayout, Immutable)]
#[repr(C)]
struct Packet {
magic_number: C0C0,
mug_size: u8,
temperature: u8,
marshmallows: [[u8; 2]],
}
let bytes = &[0xC0, 0xC0, 240, 77, 0, 1, 2, 3, 4, 5][..];
let packet = Packet::try_ref_from_bytes(bytes).unwrap();
assert_eq!(packet.mug_size, 240);
assert_eq!(packet.temperature, 77);
assert_eq!(packet.marshmallows, [[0, 1], [2, 3], [4, 5]]);
// These bytes are not valid instance of `Packet`.
let bytes = &[0x10, 0xC0, 240, 77, 0, 1, 2, 3, 4, 5][..];
assert!(Packet::try_ref_from_bytes(bytes).is_err());sourcefn try_ref_from_prefix(
source: &[u8],
) -> Result<(&Self, &[u8]), TryCastError<&[u8], Self>>where
Self: KnownLayout + Immutable,
fn try_ref_from_prefix(
source: &[u8],
) -> Result<(&Self, &[u8]), TryCastError<&[u8], Self>>where
Self: KnownLayout + Immutable,
Attempts to interpret the prefix of the given source as a &Self.
This method computes the largest possible size of Self
that can fit in the leading bytes of source. If that prefix is a valid
instance of Self, this method returns a reference to those bytes
interpreted as Self, and a reference to the remaining bytes. If there
are insufficient bytes, or if source is not appropriately aligned, or
if those bytes are not a valid instance of Self, this returns Err.
If Self: Unaligned, you can infallibly discard the
alignment error.
Self may be a sized type, a slice, or a slice DST.
§Compile-Time Assertions
This method cannot yet be used on unsized types whose dynamically-sized component is zero-sized. Attempting to use this method on such types results in a compile-time assertion error; e.g.:
use zerocopy::*;
#[derive(TryFromBytes, Immutable, KnownLayout)]
#[repr(C)]
struct ZSTy {
leading_sized: u16,
trailing_dst: [()],
}
let _ = ZSTy::try_ref_from_prefix(0u16.as_bytes()); // ⚠ Compile Error!§Examples
use zerocopy::TryFromBytes;
// The only valid value of this type is the byte `0xC0`
#[derive(TryFromBytes, KnownLayout, Immutable)]
#[repr(u8)]
enum C0 { xC0 = 0xC0 }
// The only valid value of this type is the bytes `0xC0C0`.
#[derive(TryFromBytes, KnownLayout, Immutable)]
#[repr(C)]
struct C0C0(C0, C0);
#[derive(TryFromBytes, KnownLayout, Immutable)]
#[repr(C)]
struct Packet {
magic_number: C0C0,
mug_size: u8,
temperature: u8,
marshmallows: [[u8; 2]],
}
// These are more bytes than are needed to encode a `Packet`.
let bytes = &[0xC0, 0xC0, 240, 77, 0, 1, 2, 3, 4, 5, 6][..];
let (packet, suffix) = Packet::try_ref_from_prefix(bytes).unwrap();
assert_eq!(packet.mug_size, 240);
assert_eq!(packet.temperature, 77);
assert_eq!(packet.marshmallows, [[0, 1], [2, 3], [4, 5]]);
assert_eq!(suffix, &[6u8][..]);
// These bytes are not valid instance of `Packet`.
let bytes = &[0x10, 0xC0, 240, 77, 0, 1, 2, 3, 4, 5, 6][..];
assert!(Packet::try_ref_from_prefix(bytes).is_err());sourcefn try_ref_from_suffix(
source: &[u8],
) -> Result<(&[u8], &Self), TryCastError<&[u8], Self>>where
Self: KnownLayout + Immutable,
fn try_ref_from_suffix(
source: &[u8],
) -> Result<(&[u8], &Self), TryCastError<&[u8], Self>>where
Self: KnownLayout + Immutable,
Attempts to interpret the suffix of the given source as a &Self.
This method computes the largest possible size of Self
that can fit in the trailing bytes of source. If that suffix is a
valid instance of Self, this method returns a reference to those bytes
interpreted as Self, and a reference to the preceding bytes. If there
are insufficient bytes, or if the suffix of source would not be
appropriately aligned, or if the suffix is not a valid instance of
Self, this returns Err. If Self: Unaligned, you
can infallibly discard the alignment error.
Self may be a sized type, a slice, or a slice DST.
§Compile-Time Assertions
This method cannot yet be used on unsized types whose dynamically-sized component is zero-sized. Attempting to use this method on such types results in a compile-time assertion error; e.g.:
use zerocopy::*;
#[derive(TryFromBytes, Immutable, KnownLayout)]
#[repr(C)]
struct ZSTy {
leading_sized: u16,
trailing_dst: [()],
}
let _ = ZSTy::try_ref_from_suffix(0u16.as_bytes()); // ⚠ Compile Error!§Examples
use zerocopy::TryFromBytes;
// The only valid value of this type is the byte `0xC0`
#[derive(TryFromBytes, KnownLayout, Immutable)]
#[repr(u8)]
enum C0 { xC0 = 0xC0 }
// The only valid value of this type is the bytes `0xC0C0`.
#[derive(TryFromBytes, KnownLayout, Immutable)]
#[repr(C)]
struct C0C0(C0, C0);
#[derive(TryFromBytes, KnownLayout, Immutable)]
#[repr(C)]
struct Packet {
magic_number: C0C0,
mug_size: u8,
temperature: u8,
marshmallows: [[u8; 2]],
}
// These are more bytes than are needed to encode a `Packet`.
let bytes = &[0, 0xC0, 0xC0, 240, 77, 2, 3, 4, 5, 6, 7][..];
let (prefix, packet) = Packet::try_ref_from_suffix(bytes).unwrap();
assert_eq!(packet.mug_size, 240);
assert_eq!(packet.temperature, 77);
assert_eq!(packet.marshmallows, [[2, 3], [4, 5], [6, 7]]);
assert_eq!(prefix, &[0u8][..]);
// These bytes are not valid instance of `Packet`.
let bytes = &[0, 1, 2, 3, 4, 5, 6, 77, 240, 0xC0, 0x10][..];
assert!(Packet::try_ref_from_suffix(bytes).is_err());sourcefn try_mut_from_bytes(
bytes: &mut [u8],
) -> Result<&mut Self, TryCastError<&mut [u8], Self>>where
Self: KnownLayout,
fn try_mut_from_bytes(
bytes: &mut [u8],
) -> Result<&mut Self, TryCastError<&mut [u8], Self>>where
Self: KnownLayout,
Attempts to interpret the given source as a &mut Self without
copying.
If the bytes of source are a valid instance of Self, this method
returns a reference to those bytes interpreted as a Self. If the
length of source is not a valid size of Self, or if
source is not appropriately aligned, or if source is not a valid
instance of Self, this returns Err. If Self: Unaligned, you can infallibly discard the alignment
error.
Self may be a sized type, a slice, or a slice DST.
§Compile-Time Assertions
This method cannot yet be used on unsized types whose dynamically-sized component is zero-sized. Attempting to use this method on such types results in a compile-time assertion error; e.g.:
use zerocopy::*;
#[derive(TryFromBytes, KnownLayout)]
#[repr(C)]
struct ZSTy {
leading_sized: [u8; 2],
trailing_dst: [()],
}
let mut source = [85, 85];
let _ = ZSTy::try_mut_from_bytes(&mut source[..]); // ⚠ Compile Error!§Examples
use zerocopy::TryFromBytes;
// The only valid value of this type is the byte `0xC0`
#[derive(TryFromBytes, KnownLayout)]
#[repr(u8)]
enum C0 { xC0 = 0xC0 }
// The only valid value of this type is the bytes `0xC0C0`.
#[derive(TryFromBytes, KnownLayout)]
#[repr(C)]
struct C0C0(C0, C0);
#[derive(TryFromBytes, KnownLayout)]
#[repr(C)]
struct Packet {
magic_number: C0C0,
mug_size: u8,
temperature: u8,
marshmallows: [[u8; 2]],
}
let bytes = &mut [0xC0, 0xC0, 240, 77, 0, 1, 2, 3, 4, 5][..];
let packet = Packet::try_mut_from_bytes(bytes).unwrap();
assert_eq!(packet.mug_size, 240);
assert_eq!(packet.temperature, 77);
assert_eq!(packet.marshmallows, [[0, 1], [2, 3], [4, 5]]);
packet.temperature = 111;
assert_eq!(bytes, [0xC0, 0xC0, 240, 111, 0, 1, 2, 3, 4, 5]);
// These bytes are not valid instance of `Packet`.
let bytes = &mut [0x10, 0xC0, 240, 77, 0, 1, 2, 3, 4, 5, 6][..];
assert!(Packet::try_mut_from_bytes(bytes).is_err());sourcefn try_mut_from_prefix(
source: &mut [u8],
) -> Result<(&mut Self, &mut [u8]), TryCastError<&mut [u8], Self>>where
Self: KnownLayout,
fn try_mut_from_prefix(
source: &mut [u8],
) -> Result<(&mut Self, &mut [u8]), TryCastError<&mut [u8], Self>>where
Self: KnownLayout,
Attempts to interpret the prefix of the given source as a &mut Self.
This method computes the largest possible size of Self
that can fit in the leading bytes of source. If that prefix is a valid
instance of Self, this method returns a reference to those bytes
interpreted as Self, and a reference to the remaining bytes. If there
are insufficient bytes, or if source is not appropriately aligned, or
if the bytes are not a valid instance of Self, this returns Err. If
Self: Unaligned, you can infallibly discard the
alignment error.
Self may be a sized type, a slice, or a slice DST.
§Compile-Time Assertions
This method cannot yet be used on unsized types whose dynamically-sized component is zero-sized. Attempting to use this method on such types results in a compile-time assertion error; e.g.:
use zerocopy::*;
#[derive(TryFromBytes, KnownLayout)]
#[repr(C)]
struct ZSTy {
leading_sized: [u8; 2],
trailing_dst: [()],
}
let mut source = [85, 85];
let _ = ZSTy::try_mut_from_prefix(&mut source[..]); // ⚠ Compile Error!§Examples
use zerocopy::TryFromBytes;
// The only valid value of this type is the byte `0xC0`
#[derive(TryFromBytes, KnownLayout)]
#[repr(u8)]
enum C0 { xC0 = 0xC0 }
// The only valid value of this type is the bytes `0xC0C0`.
#[derive(TryFromBytes, KnownLayout)]
#[repr(C)]
struct C0C0(C0, C0);
#[derive(TryFromBytes, KnownLayout)]
#[repr(C)]
struct Packet {
magic_number: C0C0,
mug_size: u8,
temperature: u8,
marshmallows: [[u8; 2]],
}
// These are more bytes than are needed to encode a `Packet`.
let bytes = &mut [0xC0, 0xC0, 240, 77, 0, 1, 2, 3, 4, 5, 6][..];
let (packet, suffix) = Packet::try_mut_from_prefix(bytes).unwrap();
assert_eq!(packet.mug_size, 240);
assert_eq!(packet.temperature, 77);
assert_eq!(packet.marshmallows, [[0, 1], [2, 3], [4, 5]]);
assert_eq!(suffix, &[6u8][..]);
packet.temperature = 111;
suffix[0] = 222;
assert_eq!(bytes, [0xC0, 0xC0, 240, 111, 0, 1, 2, 3, 4, 5, 222]);
// These bytes are not valid instance of `Packet`.
let bytes = &mut [0x10, 0xC0, 240, 77, 0, 1, 2, 3, 4, 5, 6][..];
assert!(Packet::try_mut_from_prefix(bytes).is_err());sourcefn try_mut_from_suffix(
source: &mut [u8],
) -> Result<(&mut [u8], &mut Self), TryCastError<&mut [u8], Self>>where
Self: KnownLayout,
fn try_mut_from_suffix(
source: &mut [u8],
) -> Result<(&mut [u8], &mut Self), TryCastError<&mut [u8], Self>>where
Self: KnownLayout,
Attempts to interpret the suffix of the given source as a &mut Self.
This method computes the largest possible size of Self
that can fit in the trailing bytes of source. If that suffix is a
valid instance of Self, this method returns a reference to those bytes
interpreted as Self, and a reference to the preceding bytes. If there
are insufficient bytes, or if the suffix of source would not be
appropriately aligned, or if the suffix is not a valid instance of
Self, this returns Err. If Self: Unaligned, you
can infallibly discard the alignment error.
Self may be a sized type, a slice, or a slice DST.
§Compile-Time Assertions
This method cannot yet be used on unsized types whose dynamically-sized component is zero-sized. Attempting to use this method on such types results in a compile-time assertion error; e.g.:
use zerocopy::*;
#[derive(TryFromBytes, KnownLayout)]
#[repr(C)]
struct ZSTy {
leading_sized: u16,
trailing_dst: [()],
}
let mut source = [85, 85];
let _ = ZSTy::try_mut_from_suffix(&mut source[..]); // ⚠ Compile Error!§Examples
use zerocopy::TryFromBytes;
// The only valid value of this type is the byte `0xC0`
#[derive(TryFromBytes, KnownLayout)]
#[repr(u8)]
enum C0 { xC0 = 0xC0 }
// The only valid value of this type is the bytes `0xC0C0`.
#[derive(TryFromBytes, KnownLayout)]
#[repr(C)]
struct C0C0(C0, C0);
#[derive(TryFromBytes, KnownLayout)]
#[repr(C)]
struct Packet {
magic_number: C0C0,
mug_size: u8,
temperature: u8,
marshmallows: [[u8; 2]],
}
// These are more bytes than are needed to encode a `Packet`.
let bytes = &mut [0, 0xC0, 0xC0, 240, 77, 2, 3, 4, 5, 6, 7][..];
let (prefix, packet) = Packet::try_mut_from_suffix(bytes).unwrap();
assert_eq!(packet.mug_size, 240);
assert_eq!(packet.temperature, 77);
assert_eq!(packet.marshmallows, [[2, 3], [4, 5], [6, 7]]);
assert_eq!(prefix, &[0u8][..]);
prefix[0] = 111;
packet.temperature = 222;
assert_eq!(bytes, [111, 0xC0, 0xC0, 240, 222, 2, 3, 4, 5, 6, 7]);
// These bytes are not valid instance of `Packet`.
let bytes = &mut [0, 1, 2, 3, 4, 5, 6, 77, 240, 0xC0, 0x10][..];
assert!(Packet::try_mut_from_suffix(bytes).is_err());sourcefn try_ref_from_bytes_with_elems(
source: &[u8],
count: usize,
) -> Result<&Self, TryCastError<&[u8], Self>>
fn try_ref_from_bytes_with_elems( source: &[u8], count: usize, ) -> Result<&Self, TryCastError<&[u8], Self>>
Attempts to interpret the given source as a &Self with a DST length
equal to count.
This method attempts to return a reference to source interpreted as a
Self with count trailing elements. If the length of source is not
equal to the size of Self with count elements, if source is not
appropriately aligned, or if source does not contain a valid instance
of Self, this returns Err. If Self: Unaligned,
you can infallibly discard the alignment error.
§Examples
use zerocopy::TryFromBytes;
// The only valid value of this type is the byte `0xC0`
#[derive(TryFromBytes, KnownLayout, Immutable)]
#[repr(u8)]
enum C0 { xC0 = 0xC0 }
// The only valid value of this type is the bytes `0xC0C0`.
#[derive(TryFromBytes, KnownLayout, Immutable)]
#[repr(C)]
struct C0C0(C0, C0);
#[derive(TryFromBytes, KnownLayout, Immutable)]
#[repr(C)]
struct Packet {
magic_number: C0C0,
mug_size: u8,
temperature: u8,
marshmallows: [[u8; 2]],
}
let bytes = &[0xC0, 0xC0, 240, 77, 2, 3, 4, 5, 6, 7][..];
let packet = Packet::try_ref_from_bytes_with_elems(bytes, 3).unwrap();
assert_eq!(packet.mug_size, 240);
assert_eq!(packet.temperature, 77);
assert_eq!(packet.marshmallows, [[2, 3], [4, 5], [6, 7]]);
// These bytes are not valid instance of `Packet`.
let bytes = &[0, 1, 2, 3, 4, 5, 6, 77, 240, 0xC0, 0xC0][..];
assert!(Packet::try_ref_from_bytes_with_elems(bytes, 3).is_err());Since an explicit count is provided, this method supports types with
zero-sized trailing slice elements. Methods such as try_ref_from_bytes
which do not take an explicit count do not support such types.
use core::num::NonZeroU16;
use zerocopy::*;
#[derive(TryFromBytes, Immutable, KnownLayout)]
#[repr(C)]
struct ZSTy {
leading_sized: NonZeroU16,
trailing_dst: [()],
}
let src = &[85, 85][..];
let zsty = ZSTy::try_ref_from_bytes_with_elems(src, 42).unwrap();
assert_eq!(zsty.trailing_dst.len(), 42);sourcefn try_ref_from_prefix_with_elems(
source: &[u8],
count: usize,
) -> Result<(&Self, &[u8]), TryCastError<&[u8], Self>>
fn try_ref_from_prefix_with_elems( source: &[u8], count: usize, ) -> Result<(&Self, &[u8]), TryCastError<&[u8], Self>>
Attempts to interpret the prefix of the given source as a &Self with
a DST length equal to count.
This method attempts to return a reference to the prefix of source
interpreted as a Self with count trailing elements, and a reference
to the remaining bytes. If the length of source is less than the size
of Self with count elements, if source is not appropriately
aligned, or if the prefix of source does not contain a valid instance
of Self, this returns Err. If Self: Unaligned,
you can infallibly discard the alignment error.
§Examples
use zerocopy::TryFromBytes;
// The only valid value of this type is the byte `0xC0`
#[derive(TryFromBytes, KnownLayout, Immutable)]
#[repr(u8)]
enum C0 { xC0 = 0xC0 }
// The only valid value of this type is the bytes `0xC0C0`.
#[derive(TryFromBytes, KnownLayout, Immutable)]
#[repr(C)]
struct C0C0(C0, C0);
#[derive(TryFromBytes, KnownLayout, Immutable)]
#[repr(C)]
struct Packet {
magic_number: C0C0,
mug_size: u8,
temperature: u8,
marshmallows: [[u8; 2]],
}
let bytes = &[0xC0, 0xC0, 240, 77, 2, 3, 4, 5, 6, 7, 8][..];
let (packet, suffix) = Packet::try_ref_from_prefix_with_elems(bytes, 3).unwrap();
assert_eq!(packet.mug_size, 240);
assert_eq!(packet.temperature, 77);
assert_eq!(packet.marshmallows, [[2, 3], [4, 5], [6, 7]]);
assert_eq!(suffix, &[8u8][..]);
// These bytes are not valid instance of `Packet`.
let bytes = &mut [0, 1, 2, 3, 4, 5, 6, 7, 8, 77, 240, 0xC0, 0xC0][..];
assert!(Packet::try_ref_from_prefix_with_elems(bytes, 3).is_err());Since an explicit count is provided, this method supports types with
zero-sized trailing slice elements. Methods such as try_ref_from_prefix
which do not take an explicit count do not support such types.
use core::num::NonZeroU16;
use zerocopy::*;
#[derive(TryFromBytes, Immutable, KnownLayout)]
#[repr(C)]
struct ZSTy {
leading_sized: NonZeroU16,
trailing_dst: [()],
}
let src = &[85, 85][..];
let (zsty, _) = ZSTy::try_ref_from_prefix_with_elems(src, 42).unwrap();
assert_eq!(zsty.trailing_dst.len(), 42);sourcefn try_ref_from_suffix_with_elems(
source: &[u8],
count: usize,
) -> Result<(&[u8], &Self), TryCastError<&[u8], Self>>
fn try_ref_from_suffix_with_elems( source: &[u8], count: usize, ) -> Result<(&[u8], &Self), TryCastError<&[u8], Self>>
Attempts to interpret the suffix of the given source as a &Self with
a DST length equal to count.
This method attempts to return a reference to the suffix of source
interpreted as a Self with count trailing elements, and a reference
to the preceding bytes. If the length of source is less than the size
of Self with count elements, if the suffix of source is not
appropriately aligned, or if the suffix of source does not contain a
valid instance of Self, this returns Err. If Self: Unaligned, you can infallibly discard the alignment
error.
§Examples
use zerocopy::TryFromBytes;
// The only valid value of this type is the byte `0xC0`
#[derive(TryFromBytes, KnownLayout, Immutable)]
#[repr(u8)]
enum C0 { xC0 = 0xC0 }
// The only valid value of this type is the bytes `0xC0C0`.
#[derive(TryFromBytes, KnownLayout, Immutable)]
#[repr(C)]
struct C0C0(C0, C0);
#[derive(TryFromBytes, KnownLayout, Immutable)]
#[repr(C)]
struct Packet {
magic_number: C0C0,
mug_size: u8,
temperature: u8,
marshmallows: [[u8; 2]],
}
let bytes = &[123, 0xC0, 0xC0, 240, 77, 2, 3, 4, 5, 6, 7][..];
let (prefix, packet) = Packet::try_ref_from_suffix_with_elems(bytes, 3).unwrap();
assert_eq!(packet.mug_size, 240);
assert_eq!(packet.temperature, 77);
assert_eq!(packet.marshmallows, [[2, 3], [4, 5], [6, 7]]);
assert_eq!(prefix, &[123u8][..]);
// These bytes are not valid instance of `Packet`.
let bytes = &[0, 1, 2, 3, 4, 5, 6, 7, 8, 77, 240, 0xC0, 0xC0][..];
assert!(Packet::try_ref_from_suffix_with_elems(bytes, 3).is_err());Since an explicit count is provided, this method supports types with
zero-sized trailing slice elements. Methods such as try_ref_from_prefix
which do not take an explicit count do not support such types.
use core::num::NonZeroU16;
use zerocopy::*;
#[derive(TryFromBytes, Immutable, KnownLayout)]
#[repr(C)]
struct ZSTy {
leading_sized: NonZeroU16,
trailing_dst: [()],
}
let src = &[85, 85][..];
let (_, zsty) = ZSTy::try_ref_from_suffix_with_elems(src, 42).unwrap();
assert_eq!(zsty.trailing_dst.len(), 42);sourcefn try_mut_from_bytes_with_elems(
source: &mut [u8],
count: usize,
) -> Result<&mut Self, TryCastError<&mut [u8], Self>>where
Self: KnownLayout<PointerMetadata = usize>,
fn try_mut_from_bytes_with_elems(
source: &mut [u8],
count: usize,
) -> Result<&mut Self, TryCastError<&mut [u8], Self>>where
Self: KnownLayout<PointerMetadata = usize>,
Attempts to interpret the given source as a &mut Self with a DST
length equal to count.
This method attempts to return a reference to source interpreted as a
Self with count trailing elements. If the length of source is not
equal to the size of Self with count elements, if source is not
appropriately aligned, or if source does not contain a valid instance
of Self, this returns Err. If Self: Unaligned,
you can infallibly discard the alignment error.
§Examples
use zerocopy::TryFromBytes;
// The only valid value of this type is the byte `0xC0`
#[derive(TryFromBytes, KnownLayout)]
#[repr(u8)]
enum C0 { xC0 = 0xC0 }
// The only valid value of this type is the bytes `0xC0C0`.
#[derive(TryFromBytes, KnownLayout)]
#[repr(C)]
struct C0C0(C0, C0);
#[derive(TryFromBytes, KnownLayout)]
#[repr(C)]
struct Packet {
magic_number: C0C0,
mug_size: u8,
temperature: u8,
marshmallows: [[u8; 2]],
}
let bytes = &mut [0xC0, 0xC0, 240, 77, 2, 3, 4, 5, 6, 7][..];
let packet = Packet::try_mut_from_bytes_with_elems(bytes, 3).unwrap();
assert_eq!(packet.mug_size, 240);
assert_eq!(packet.temperature, 77);
assert_eq!(packet.marshmallows, [[2, 3], [4, 5], [6, 7]]);
packet.temperature = 111;
assert_eq!(bytes, [0xC0, 0xC0, 240, 111, 2, 3, 4, 5, 6, 7]);
// These bytes are not valid instance of `Packet`.
let bytes = &mut [0, 1, 2, 3, 4, 5, 6, 77, 240, 0xC0, 0xC0][..];
assert!(Packet::try_mut_from_bytes_with_elems(bytes, 3).is_err());Since an explicit count is provided, this method supports types with
zero-sized trailing slice elements. Methods such as try_mut_from_bytes
which do not take an explicit count do not support such types.
use core::num::NonZeroU16;
use zerocopy::*;
#[derive(TryFromBytes, KnownLayout)]
#[repr(C)]
struct ZSTy {
leading_sized: NonZeroU16,
trailing_dst: [()],
}
let src = &mut [85, 85][..];
let zsty = ZSTy::try_mut_from_bytes_with_elems(src, 42).unwrap();
assert_eq!(zsty.trailing_dst.len(), 42);sourcefn try_mut_from_prefix_with_elems(
source: &mut [u8],
count: usize,
) -> Result<(&mut Self, &mut [u8]), TryCastError<&mut [u8], Self>>where
Self: KnownLayout<PointerMetadata = usize>,
fn try_mut_from_prefix_with_elems(
source: &mut [u8],
count: usize,
) -> Result<(&mut Self, &mut [u8]), TryCastError<&mut [u8], Self>>where
Self: KnownLayout<PointerMetadata = usize>,
Attempts to interpret the prefix of the given source as a &mut Self
with a DST length equal to count.
This method attempts to return a reference to the prefix of source
interpreted as a Self with count trailing elements, and a reference
to the remaining bytes. If the length of source is less than the size
of Self with count elements, if source is not appropriately
aligned, or if the prefix of source does not contain a valid instance
of Self, this returns Err. If Self: Unaligned,
you can infallibly discard the alignment error.
§Examples
use zerocopy::TryFromBytes;
// The only valid value of this type is the byte `0xC0`
#[derive(TryFromBytes, KnownLayout)]
#[repr(u8)]
enum C0 { xC0 = 0xC0 }
// The only valid value of this type is the bytes `0xC0C0`.
#[derive(TryFromBytes, KnownLayout)]
#[repr(C)]
struct C0C0(C0, C0);
#[derive(TryFromBytes, KnownLayout)]
#[repr(C)]
struct Packet {
magic_number: C0C0,
mug_size: u8,
temperature: u8,
marshmallows: [[u8; 2]],
}
let bytes = &mut [0xC0, 0xC0, 240, 77, 2, 3, 4, 5, 6, 7, 8][..];
let (packet, suffix) = Packet::try_mut_from_prefix_with_elems(bytes, 3).unwrap();
assert_eq!(packet.mug_size, 240);
assert_eq!(packet.temperature, 77);
assert_eq!(packet.marshmallows, [[2, 3], [4, 5], [6, 7]]);
assert_eq!(suffix, &[8u8][..]);
packet.temperature = 111;
suffix[0] = 222;
assert_eq!(bytes, [0xC0, 0xC0, 240, 111, 2, 3, 4, 5, 6, 7, 222]);
// These bytes are not valid instance of `Packet`.
let bytes = &mut [0, 1, 2, 3, 4, 5, 6, 7, 8, 77, 240, 0xC0, 0xC0][..];
assert!(Packet::try_mut_from_prefix_with_elems(bytes, 3).is_err());Since an explicit count is provided, this method supports types with
zero-sized trailing slice elements. Methods such as try_mut_from_prefix
which do not take an explicit count do not support such types.
use core::num::NonZeroU16;
use zerocopy::*;
#[derive(TryFromBytes, KnownLayout)]
#[repr(C)]
struct ZSTy {
leading_sized: NonZeroU16,
trailing_dst: [()],
}
let src = &mut [85, 85][..];
let (zsty, _) = ZSTy::try_mut_from_prefix_with_elems(src, 42).unwrap();
assert_eq!(zsty.trailing_dst.len(), 42);sourcefn try_mut_from_suffix_with_elems(
source: &mut [u8],
count: usize,
) -> Result<(&mut [u8], &mut Self), TryCastError<&mut [u8], Self>>where
Self: KnownLayout<PointerMetadata = usize>,
fn try_mut_from_suffix_with_elems(
source: &mut [u8],
count: usize,
) -> Result<(&mut [u8], &mut Self), TryCastError<&mut [u8], Self>>where
Self: KnownLayout<PointerMetadata = usize>,
Attempts to interpret the suffix of the given source as a &mut Self
with a DST length equal to count.
This method attempts to return a reference to the suffix of source
interpreted as a Self with count trailing elements, and a reference
to the preceding bytes. If the length of source is less than the size
of Self with count elements, if the suffix of source is not
appropriately aligned, or if the suffix of source does not contain a
valid instance of Self, this returns Err. If Self: Unaligned, you can infallibly discard the alignment
error.
§Examples
use zerocopy::TryFromBytes;
// The only valid value of this type is the byte `0xC0`
#[derive(TryFromBytes, KnownLayout)]
#[repr(u8)]
enum C0 { xC0 = 0xC0 }
// The only valid value of this type is the bytes `0xC0C0`.
#[derive(TryFromBytes, KnownLayout)]
#[repr(C)]
struct C0C0(C0, C0);
#[derive(TryFromBytes, KnownLayout)]
#[repr(C)]
struct Packet {
magic_number: C0C0,
mug_size: u8,
temperature: u8,
marshmallows: [[u8; 2]],
}
let bytes = &mut [123, 0xC0, 0xC0, 240, 77, 2, 3, 4, 5, 6, 7][..];
let (prefix, packet) = Packet::try_mut_from_suffix_with_elems(bytes, 3).unwrap();
assert_eq!(packet.mug_size, 240);
assert_eq!(packet.temperature, 77);
assert_eq!(packet.marshmallows, [[2, 3], [4, 5], [6, 7]]);
assert_eq!(prefix, &[123u8][..]);
prefix[0] = 111;
packet.temperature = 222;
assert_eq!(bytes, [111, 0xC0, 0xC0, 240, 222, 2, 3, 4, 5, 6, 7]);
// These bytes are not valid instance of `Packet`.
let bytes = &mut [0, 1, 2, 3, 4, 5, 6, 7, 8, 77, 240, 0xC0, 0xC0][..];
assert!(Packet::try_mut_from_suffix_with_elems(bytes, 3).is_err());Since an explicit count is provided, this method supports types with
zero-sized trailing slice elements. Methods such as try_mut_from_prefix
which do not take an explicit count do not support such types.
use core::num::NonZeroU16;
use zerocopy::*;
#[derive(TryFromBytes, KnownLayout)]
#[repr(C)]
struct ZSTy {
leading_sized: NonZeroU16,
trailing_dst: [()],
}
let src = &mut [85, 85][..];
let (_, zsty) = ZSTy::try_mut_from_suffix_with_elems(src, 42).unwrap();
assert_eq!(zsty.trailing_dst.len(), 42);sourcefn try_read_from_bytes(source: &[u8]) -> Result<Self, TryReadError<&[u8], Self>>where
Self: Sized,
fn try_read_from_bytes(source: &[u8]) -> Result<Self, TryReadError<&[u8], Self>>where
Self: Sized,
Attempts to read the given source as a Self.
If source.len() != size_of::<Self>() or the bytes are not a valid
instance of Self, this returns Err.
§Examples
use zerocopy::TryFromBytes;
// The only valid value of this type is the byte `0xC0`
#[derive(TryFromBytes)]
#[repr(u8)]
enum C0 { xC0 = 0xC0 }
// The only valid value of this type is the bytes `0xC0C0`.
#[derive(TryFromBytes)]
#[repr(C)]
struct C0C0(C0, C0);
#[derive(TryFromBytes)]
#[repr(C)]
struct Packet {
magic_number: C0C0,
mug_size: u8,
temperature: u8,
}
let bytes = &[0xC0, 0xC0, 240, 77][..];
let packet = Packet::try_read_from_bytes(bytes).unwrap();
assert_eq!(packet.mug_size, 240);
assert_eq!(packet.temperature, 77);
// These bytes are not valid instance of `Packet`.
let bytes = &mut [0x10, 0xC0, 240, 77][..];
assert!(Packet::try_read_from_bytes(bytes).is_err());sourcefn try_read_from_prefix(
source: &[u8],
) -> Result<(Self, &[u8]), TryReadError<&[u8], Self>>where
Self: Sized,
fn try_read_from_prefix(
source: &[u8],
) -> Result<(Self, &[u8]), TryReadError<&[u8], Self>>where
Self: Sized,
Attempts to read a Self from the prefix of the given source.
This attempts to read a Self from the first size_of::<Self>() bytes
of source, returning that Self and any remaining bytes. If
source.len() < size_of::<Self>() or the bytes are not a valid instance
of Self, it returns Err.
§Examples
use zerocopy::TryFromBytes;
// The only valid value of this type is the byte `0xC0`
#[derive(TryFromBytes)]
#[repr(u8)]
enum C0 { xC0 = 0xC0 }
// The only valid value of this type is the bytes `0xC0C0`.
#[derive(TryFromBytes)]
#[repr(C)]
struct C0C0(C0, C0);
#[derive(TryFromBytes)]
#[repr(C)]
struct Packet {
magic_number: C0C0,
mug_size: u8,
temperature: u8,
}
// These are more bytes than are needed to encode a `Packet`.
let bytes = &[0xC0, 0xC0, 240, 77, 0, 1, 2, 3, 4, 5, 6][..];
let (packet, suffix) = Packet::try_read_from_prefix(bytes).unwrap();
assert_eq!(packet.mug_size, 240);
assert_eq!(packet.temperature, 77);
assert_eq!(suffix, &[0u8, 1, 2, 3, 4, 5, 6][..]);
// These bytes are not valid instance of `Packet`.
let bytes = &[0x10, 0xC0, 240, 77, 0, 1, 2, 3, 4, 5, 6][..];
assert!(Packet::try_read_from_prefix(bytes).is_err());sourcefn try_read_from_suffix(
source: &[u8],
) -> Result<(&[u8], Self), TryReadError<&[u8], Self>>where
Self: Sized,
fn try_read_from_suffix(
source: &[u8],
) -> Result<(&[u8], Self), TryReadError<&[u8], Self>>where
Self: Sized,
Attempts to read a Self from the suffix of the given source.
This attempts to read a Self from the last size_of::<Self>() bytes
of source, returning that Self and any preceding bytes. If
source.len() < size_of::<Self>() or the bytes are not a valid instance
of Self, it returns Err.
§Examples
use zerocopy::TryFromBytes;
// The only valid value of this type is the byte `0xC0`
#[derive(TryFromBytes)]
#[repr(u8)]
enum C0 { xC0 = 0xC0 }
// The only valid value of this type is the bytes `0xC0C0`.
#[derive(TryFromBytes)]
#[repr(C)]
struct C0C0(C0, C0);
#[derive(TryFromBytes)]
#[repr(C)]
struct Packet {
magic_number: C0C0,
mug_size: u8,
temperature: u8,
}
// These are more bytes than are needed to encode a `Packet`.
let bytes = &[0, 1, 2, 3, 4, 5, 0xC0, 0xC0, 240, 77][..];
let (prefix, packet) = Packet::try_read_from_suffix(bytes).unwrap();
assert_eq!(packet.mug_size, 240);
assert_eq!(packet.temperature, 77);
assert_eq!(prefix, &[0u8, 1, 2, 3, 4, 5][..]);
// These bytes are not valid instance of `Packet`.
let bytes = &[0, 1, 2, 3, 4, 5, 0x10, 0xC0, 240, 77][..];
assert!(Packet::try_read_from_suffix(bytes).is_err());