Struct FetchHeader 

pub struct FetchHeader {
    pub request_id: VarInt,
}

The head of a fetch stream: the stream type 0x05 and a Request ID.

Byte-identical to draft-19. What draft-20 widened is what the Request ID may name. Section 11.4.4: “all objects on the stream belong to the track requested in the message identified by Request ID”, where draft-19 said “the track requested in the Fetch message”. The widening is deliberate, because a fetch stream can now be a fill fetch stream whose Request ID names the SUBSCRIBE or the REQUEST_UPDATE that carried FILL_PARAMETERS (Section 5.1.3), not only a FETCH. Nothing on the stream says which, so a reader that keys a fetch stream by looking up a FETCH will fail to find one.

Two things a fill fetch stream does not have, which the draft leaves open

• No FETCH_OK, and therefore no End Location and no End Of Track. Section 5.1.3 says the fill is “delivered as a FETCH response” and Section 5.1.3.1 says there is no REQUEST_ERROR for it, so there is no OK either. How a subscriber learns the fill’s actual end, beyond the stream FINing, is unspecified; this codec treats the FIN as the only end signal and does not synthesize a FETCH_OK. Section 10.13’s rule that gaps between the last Object and the FETCH_OK’s Largest imply non-existence cannot be applied here, because there is no FETCH_OK to read it from.
• Failure is a stream reset, not an error message. Section 5.1.3.1: if the publisher must fail a fill it opens the stream and resets it immediately after the FETCH_HEADER. Resetting or cancelling a fill fetch stream does not affect the subscription, which keeps delivering.

Both are the caller’s to act on: neither is visible in a frame.

Fields

request_id: VarInt

Implementations

impl FetchHeader

pub fn decode(buf: &mut impl Buf) -> Result<Self, CodecError>

pub fn encode(&self, buf: &mut impl BufMut)

Trait Implementations

impl Clone for FetchHeader

fn clone(&self) -> FetchHeader

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for FetchHeader

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

Formats the value using the given formatter.