Enum capnp::serialize::NoAllocSliceSegments

pub enum NoAllocSliceSegments<'b> {
    SingleSegment {
        segment: &'b [u8],
    },
    MultipleSegments {
        message: &'b [u8],
    },
}

Segments read from a buffer, useful for when you have the message in a buffer and don’t want the extra copy of read_message.

NoAllocSliceSegments is similar to crate::serialize::SliceSegments but optimized for low memory embedded environment. It does not do heap allocations and consumes only one fat pointer worth of memory.

Performance considerations

Due to lack of heap allocations, NoAllocSliceSegments does not cache segments offset and length and has to parse message header every time NoAllocSliceSegments::get_segment is called. The parsing has O(N) complexity where N is total number of segments in the message. NoAllocSliceSegments has optimization for single segment messages: if message has only one segment, it will be parsed only once during creation and no parsing will be required on get_segment calls

Variants

SingleSegment

Fields

segment: &'b [u8]

MultipleSegments

Fields

message: &'b [u8]

Implementations

impl<'b> NoAllocSliceSegments<'b>

pub fn try_new(slice: &mut &'b [u8], options: ReaderOptions) -> Result<Self>

Reads a serialized message (including a segment table) from a buffer and takes ownership, without copying. The slice is allowed to extend beyond the end of the message. On success, updates slice to point to the remaining bytes beyond the end of the message.

ALIGNMENT: If the “unaligned” feature is enabled, then there are no alignment requirements on buffer. Otherwise, buffer must be 8-byte aligned (attempts to read the message will trigger errors).

Trait Implementations

impl<'b> ReaderSegments for NoAllocSliceSegments<'b>

fn get_segment(&self, idx: u32) -> Option<&[u8]>

Gets the segment with index idx. Returns None if idx is out of range.

fn len(&self) -> usize

Gets the number of segments.