Message

Message<H, T> hands a handler the decoded payload and its parsed header contract as one input.

chunk.headers is the contract and chunk.body the payload. The contract parses the way Headers<T> parses it, and a contract that does not parse is a decode failure. A batch handler takes &[Message<H, T>], so each element keeps its own headers. A reply typed Message<H, T> carries its headers the same way.

Example

Macros

examples/typed_headers.rs

/// The payload and its contract arrive decoded together.
#[subscriber("chunks")]
async fn store(chunk: &Message<ChunkMeta, Chunk>) -> HandlerOutcome {
    let meta = &chunk.headers;
    if meta.chunk_no >= meta.chunks_total {
        // A chunk past the end of its task.
        return HandlerOutcome::drop();
    }
    tracing::info!(meta.task_id, meta.chunk_no, chunk.body.size, "stored");
    HandlerOutcome::ack()
}

Manual

examples/manual/typed_headers.rs

/// The payload and its contract arrive decoded together.
struct Store;

impl Handle<Message<ChunkMeta, Chunk>> for Store {
    fn handle(
        &self,
        chunk: &Message<ChunkMeta, Chunk>,
        _outs: &(),
        _ctx: &mut Context<'_>,
    ) -> impl Future<Output = Result<(), HandlerOutcome>> {
        let meta = &chunk.headers;
        if meta.chunk_no >= meta.chunks_total {
            // A chunk past the end of its task.
            return ready(Err(HandlerOutcome::drop()));
        }
        tracing::info!(meta.task_id, meta.chunk_no, chunk.body.size, "stored");
        ready(Ok(()))
    }
}