Defines StreamLD’s server-to-server replication binding over WebSockets — the transport a downstream server uses to mirror an upstream stream in full, in order, with explicit resumption. Part of the StreamLD module.
Unlike the SSE binding (StreamLD SSE Binding), which serves a single browser
client, the WebSocket replication binding is intended for one server
mirroring another server’s stream in full. There is no browser-platform
reconnection help available on this transport, so resumption is handled
entirely in-protocol.
2. Join and backlog
A replicating server opens a WebSocket connection and sends a join request
carrying a `streamld:SubscriptionRequest` (see StreamLD Core, The Event Envelope). The upstream server responds with either
every already-buffered `streamld:ReplicationFrame` with `streamld:cursor` greater than
the requested `streamld:after` value, in ascending cursor order, or
a `streamld:GapSignal`, per the same rule as StreamLD Core, Gap handling, if the
requested cursor is not resolvable.
3. Live frames
After a successful join, the upstream server pushes one
`streamld:ReplicationFrame` per subsequent append, in cursor order. A
replicating server MUST persist the highest cursor it has durably stored, so
that a reconnect after a network interruption can resume from that persisted
cursor rather than the beginning of the stream.
Conformance
Document conventions
Conformance requirements are expressed
with a combination of descriptive assertions
and RFC 2119 terminology.
The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL”
in the normative parts of this document
are to be interpreted as described in RFC 2119.
However, for readability,
these words do not appear in all uppercase letters in this specification.
All of the text of this specification is normative
except sections explicitly marked as non-normative, examples, and notes. [RFC2119]
Examples in this specification are introduced with the words “for example”
or are set apart from the normative text
with class="example",
like this:
This is an example of an informative example.
Informative notes begin with the word “Note”
and are set apart from the normative text
with class="note",
like this: