AC

Queryables & Replies

Queryables are Zenoh's abstraction for data at rest and remote computation. They generalise both storage lookups and RPC under a single, location-transparent API.

Get (Requester)

let replies = session
    .get("sensors/**/temperature")
    .await
    .unwrap();
 
while let Ok(reply) = replies.recv_async().await {
    match reply.result() {
        Ok(sample) => println!("Got: {:?}", sample.payload()),
        Err(err)   => eprintln!("Error: {:?}", err),
    }
}

Queryable (Responder)

let queryable = session
    .declare_queryable("sensors/room1/temperature")
    .await
    .unwrap();
 
while let Ok(query) = queryable.recv_async().await {
    // Read the request parameters if any
    let params = query.parameters().to_string();
 
    query
        .reply(query.key_expr().clone(), "23.5°C".as_bytes())
        .await
        .unwrap();
}

Request / Reply Flow

The router fans the get() out to all matching queryables and collects replies, which stream back to the requester asynchronously.

Query fan-out and reply collection

Consolidated Replies

When querying a key expression that matches multiple resources, consolidation avoids returning stale data when multiple storages hold the same key:

let replies = session
    .get("sensors/**")
    .consolidation(ConsolidationMode::Latest)
    .await
    .unwrap();

Key Insight

Queryables blur the line between "get from storage" and "compute on demand". A queryable can:

  • Return a cached value (acting as a storage)
  • Compute a result on the fly (acting as a service)
  • Fan out to other Zenoh resources and aggregate results
PreviousPublishers & SubscribersNextStorages