Module window 

Sliding-window JSON publishing over moq-net tracks.

A window is an ordered run of records the publisher appends to the back of and drops from the front of. Unlike stream, which preserves a log forever in one group, and snapshot, which keeps only the latest value, a window keeps a bounded stretch of records and lets a reader join it at any point.

Why a log can’t do this

The obvious alternative is an append-only log that rolls its group and re-seeds the new one with the records it still holds. That breaks the reader: re-seeded records are indistinguishable from new ones, so a reader that was keeping up receives them twice. This mode exists to make the restatement explicit, so a reader can tell “you already have these” from “here is another one”.

On the wire

The first frame of every group names the retained offset and a decodable records suffix. Its optional start identifies the suffix when a checkpoint bound omits older records. Later frames are tagged push and pop ops, positional against the group header. Indices stop at 2^53 - 1, the largest integer represented exactly by both implementations.

Trimming is therefore an op, not a group boundary. Dropping a record costs one small frame inside the shared compression window instead of a roll that would throw that window away.

Group boundaries are invisible

The publisher rolls a group when the ops in it outgrow ProducerConfig::op_ratio times the header that opened it, exactly as snapshot rolls on its delta budget. That is purely a compression decision: there is no caller-driven cut and no age bound, and a Consumer never surfaces it. A header restating records a reader already has yields nothing, so however often the publisher rolls, the reader sees one continuous stream of Events. ProducerConfig::checkpoint_records bounds the suffix repeated on each roll for a long-lived window.

What a reader is told

A reader gets Event::Push when a record arrives, Event::Pop when a contiguous range leaves, and Event::Skip when a range was dropped before this reader saw it. A reader that keeps up sees pushes and pops; one that falls a group behind learns from the header’s offset which records it will never get, rather than silently missing them.

Choosing a layer

Producer and Consumer own a track. Encoder and Decoder are the same logic without it, for when something else is already in charge of the track; the encoder owns the retained window and says where the group boundaries fall, and the decoder turns frames into events.

Structs

Consumer

Consumes a sliding window of JSON records from a track, yielding one event per change.

ConsumerConfig

Configuration for a Decoder, and so for the Consumer wrapping one.

Decoder

Reconstructs window events from frame payloads.

Encoded

One encoded frame, and the group boundary it implies.

Encoder

Encodes window edits into frame payloads, deciding where the group boundaries fall.

Group

Decodes one MoQ group’s frames while borrowing the continuous window state.

Pending

An encoded frame the caller has not yet acknowledged writing.

Producer

Publishes a sliding window of JSON records over a track.

ProducerConfig

Configuration for an Encoder and the Producer wrapping one.

Enums

Event

One change to the window, as the consumer sees it.