The `from_bytes*` family of functions expect a slice of the exact same size as the requested type. This can be sometimes cumbersome for callers that deal with dynamic stream of data that needs to be manually cut before each invocation of `from_bytes`.
To simplify such callers, introduce a new `from_bytes*_prefix` family of methods, which split the input slice at the index required for the equivalent `from_bytes` method to succeed, and return its result alongside with the remainder of the slice. This design is inspired by zerocopy's `try_*_from_prefix` family of methods. Signed-off-by: Alexandre Courbot <[email protected]> --- rust/kernel/transmute.rs | 60 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 60 insertions(+) diff --git a/rust/kernel/transmute.rs b/rust/kernel/transmute.rs index cfc37d81adf2..00cd3092c7cc 100644 --- a/rust/kernel/transmute.rs +++ b/rust/kernel/transmute.rs @@ -58,6 +58,26 @@ fn from_bytes(bytes: &[u8]) -> Option<&Self> } } + /// Converts the beginning of `bytes` to a reference to `Self`. + /// + /// This method is similar to [`Self::from_bytes`], with the difference that `bytes` does not + /// need to be the same size of `Self` - the appropriate portion is cut from the beginning of + /// `bytes`, and the remainder returned alongside the result. + fn from_bytes_prefix(bytes: &[u8]) -> Option<(&Self, &[u8])> + where + Self: Sized, + { + if bytes.len() < size_of::<Self>() { + None + } else { + // We checked that `bytes.len() >= size_of::<Self>`, thus `split_at` cannot panic. + // TODO: replace with `split_at_checked` once the MSRV is >= 1.80. + let (prefix, remainder) = bytes.split_at(size_of::<Self>()); + + Self::from_bytes(prefix).map(|s| (s, remainder)) + } + } + /// Converts a mutable slice of bytes to a reference to `Self`. /// /// Succeeds if the reference is properly aligned, and the size of `bytes` is equal to that of @@ -80,6 +100,26 @@ fn from_bytes_mut(bytes: &mut [u8]) -> Option<&mut Self> } } + /// Converts the beginning of `bytes` to a mutable reference to `Self`. + /// + /// This method is similar to [`Self::from_bytes_mut`], with the difference that `bytes` does + /// not need to be the same size of `Self` - the appropriate portion is cut from the beginning + /// of `bytes`, and the remainder returned alongside the result. + fn from_bytes_mut_prefix(bytes: &mut [u8]) -> Option<(&mut Self, &mut [u8])> + where + Self: AsBytes + Sized, + { + if bytes.len() < size_of::<Self>() { + None + } else { + // We checked that `bytes.len() >= size_of::<Self>`, thus `split_at_mut` cannot panic. + // TODO: replace with `split_at_mut_checked` once the MSRV is >= 1.80. + let (prefix, remainder) = bytes.split_at_mut(size_of::<Self>()); + + Self::from_bytes_mut(prefix).map(|s| (s, remainder)) + } + } + /// Creates an owned instance of `Self` by copying `bytes`. /// /// Unlike [`FromBytes::from_bytes`], which requires aligned input, this method can be used on @@ -97,6 +137,26 @@ fn from_bytes_copy(bytes: &[u8]) -> Option<Self> None } } + + /// Creates an owned instance of `Self` from the beginning of `bytes`. + /// + /// This method is similar to [`Self::from_bytes_copy`], with the difference that `bytes` does + /// not need to be the same size of `Self` - the appropriate portion is cut from the beginning + /// of `bytes`, and the remainder returned alongside the result. + fn from_bytes_copy_prefix(bytes: &[u8]) -> Option<(Self, &[u8])> + where + Self: Sized, + { + if bytes.len() < size_of::<Self>() { + None + } else { + // We checked that `bytes.len() >= size_of::<Self>`, thus `split_at` cannot panic. + // TODO: replace with `split_at_checked` once the MSRV is >= 1.80. + let (prefix, remainder) = bytes.split_at(size_of::<Self>()); + + Self::from_bytes_copy(prefix).map(|s| (s, remainder)) + } + } } macro_rules! impl_frombytes { -- 2.51.0
