Struct Fetch 

pub struct Fetch {
    pub request_id: VarInt,
    pub track_namespace: TrackNamespace,
    pub track_name: Vec<u8>,
    pub parameters: Vec<KeyValuePair>,
}

FETCH (0x16), rebuilt in draft-20 (Section 10.13, Figure 16).

FETCH Message {
  Type (vi64) = 0x16,
  Length (16),
  Request ID (vi64),
  Track Namespace (..),
  Track Name Length (vi64),
  Track Name (..),
  Number of Parameters (vi64),
  Parameters (..) ...
}

What went, and why draft-19’s shape cannot be ported

Draft-19’s FETCH opened with a Fetch Type that chose between a Standalone Fetch — a namespace, a name and an inline Start Location / End Location pair — and a Joining Fetch of two varints. Draft-20 deleted the field, both structures, the Fetch Type registry and the whole joining mechanism, and promoted the namespace and the name to fields of FETCH itself, in the positions they held inside the old Standalone Fetch. What is left is byte-identical to Subscribe apart from the type code.

The range now travels in the LOCATION_FILTER parameter (Section 5.1.2). A FETCH with none covers {0,0} through Largest Object, inclusive.

INVALID_RANGE and a relative start

Section 10.13 keeps draft-19’s rule: “If no Objects have been published for the track or Start Location is greater than the Largest Object” then “the publisher MUST return REQUEST_ERROR with error code INVALID_RANGE”. A relative start — the one-field LOCATION_FILTER with StartGroup = 0, which resolves to the Next Group — is by construction greater than Largest Object, so read literally the rule rejects every relative-start FETCH. That is plainly not the intent and the text carves out nothing, so this codec does not apply the Start-greater-than-Largest test to a relative start, and neither should a caller. Nothing here can enforce either reading: the test needs Largest Object, which is track state rather than anything in this frame, so the decision belongs to the endpoint and is recorded here because this is where the filter arrives.

The codepoint did not change. A draft-19 decoder fed one of these reads the Number of Track Namespace Fields count as a Fetch Type and mis-parses without complaint; there is no in-band version signal to catch it. That is why draft-20 has a FETCH decoder of its own rather than sharing draft-19’s.

Fields

request_id: VarInt

track_namespace: TrackNamespace

track_name: Vec<u8>

parameters: Vec<KeyValuePair>

Trait Implementations

impl Clone for Fetch

fn clone(&self) -> Fetch

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Fetch

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

Formats the value using the given formatter.

impl Eq for Fetch

impl PartialEq for Fetch

fn eq(&self, other: &Fetch) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for Fetch