Struct FetchObjectWriter 

pub struct FetchObjectWriter { /* private fields */ }

Re-encodes resolved fetch Objects onto one FETCH stream.

The exact inverse of FetchObjectReader, and it exists for one caller: something that has read a stream and is writing a different stream from the same Objects. Draft-16 Section 10.4.4.1 lets an Object leave out its Group ID, Object ID, Subgroup ID and Priority and take the prior Object’s, so removing an Object changes what the Objects after it are read against: a field the survivor left off has to appear, and a flag bit with it.

Every field draft-16 puts on the wire here is the absolute value rather than a difference — the deltas arrive at draft-18. What is stateful is the omission, and that is enough to make removal a re-encode.

Why this is not a general encoder

Every Object it writes came off a stream, so the caller holds the Object’s own FetchObjectHeader beside its resolved FetchObjectLocation. The header is used as the preference: wherever the original shape still says the same thing against the new predecessor it is kept, so a stream with nothing removed is reproduced byte for byte.

Implementations

impl FetchObjectWriter

pub fn new() -> Self

A writer positioned before the first Object of a fetch stream, with no prior Object for anything to be written against.

pub fn header_for( &self, original: &FetchObjectHeader, location: &FetchObjectLocation, ) -> Result<FetchObjectHeader, CodecError>

The header that encodes location against everything written so far, starting from the shape original arrived in.

Does not advance the writer — Self::write_object_header is the call that does both.

Errors

CodecError::InvalidField for an Object with neither a Subgroup ID nor the Datagram bit, and where a value does not fit a variable-length integer.

pub fn write_object_header( &mut self, original: &FetchObjectHeader, location: &FetchObjectLocation, out: &mut impl BufMut, ) -> Result<FetchObjectHeader, CodecError>

Encode location against everything written so far and advance.

Writes the header only. The payload is original.payload_length bytes and is the caller’s to copy, unchanged.

Errors

CodecError::InvalidField for an Object with no encoding; the writer is left untouched when this happens.

pub fn advance( &mut self, written: &FetchObjectHeader, location: &FetchObjectLocation, )

Record what was written as the predecessor of whatever comes next.

Mirrors FetchObjectReader::resolve exactly, including the two places draft-16 differs from the drafts after it: a Datagram-forwarded Object clears the running Subgroup ID rather than leaving it standing, and an Object that states no Priority leaves the running one alone.

Public because a re-emitting caller has a second way of putting a frame on the wire: when the framing it arrived in still encodes the same meaning against the frame before it, its own bytes are forwarded untouched — no header is produced and nothing is copied. The writer still has to move, or the frame after it is encoded against a predecessor one frame stale. written is then the Object’s own header, which is what was put on the wire.

Trait Implementations

impl Clone for FetchObjectWriter

fn clone(&self) -> FetchObjectWriter

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for FetchObjectWriter

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for FetchObjectWriter

fn default() -> FetchObjectWriter

Returns the “default value” for a type.