Struct Decoder 

pub struct Decoder<T> { /* private fields */ }

Reconstructs a JSON value from the snapshot and delta frames of a group.

The track-free core of Consumer, and the mirror of Encoder. The caller reads frames from wherever it likes and routes each one by its position in the group: the first frame of every group is a snapshot, the rest are deltas.

match frame.keyframe {
    true => decoder.snapshot(&frame.payload)?,
    false => decoder.delta(&frame.payload)?,
}
let value = decoder.decode()?;

Applying and materializing are separate on purpose. Frames must be applied in order (the merge patches and the DEFLATE window are both sequential), but a consumer catching up on a backlog only wants the value at the head, so it applies every frame and calls decode once. A caller that wants a value per frame just calls it every time.

Implementations

impl<T> Decoder<T>

pub fn new(config: ConsumerConfig) -> Self

Create a decoder with no value, awaiting its first snapshot.

pub fn snapshot(&mut self, payload: &[u8]) -> Result<()>

Apply a group’s first frame: a full snapshot that replaces the current value.

Also starts the group’s DEFLATE window, so this must be called at every group boundary, not only the first.

pub fn delta(&mut self, payload: &[u8]) -> Result<()>

Apply one of a group’s later frames: an RFC 7396 merge patch against the current value.

Errors with Error::MissingSnapshot when no snapshot has been applied yet, since a patch has nothing to apply to.

pub fn value(&self) -> Option<&Value>

The reconstructed value as raw JSON, or None before the first snapshot.

impl<T: DeserializeOwned> Decoder<T>

pub fn decode(&self) -> Result<Option<T>>

Materialize the reconstructed value as T, or None before the first snapshot.

Deserializing from the reconstructed Value rather than the frame bytes costs the line and column a parse error would carry, so the error is prefixed with the JSON path of the offending field instead. Without it a rejected field deep in a document reports only its own complaint, with nothing to say where it came from.