Publishers & Subscribers

The pub/sub abstraction in Zenoh provides location-transparent data in motion.

Publishers

A publisher declares intent to produce data on a key expression:

let publisher = session
    .declare_publisher("robots/*/pose")
    .await
    .unwrap();
 
// Send data
publisher.put(payload_bytes).await.unwrap();
 
// With metadata
publisher
    .put(payload_bytes)
    .encoding(Encoding::APPLICATION_JSON)
    .await
    .unwrap();

Declaring a publisher (rather than using session.put() directly) allows the router to pre-compute routes, improving throughput.

Subscribers

let subscriber = session
    .declare_subscriber("robots/**")
    .await
    .unwrap();
 
// Async handler
while let Ok(sample) = subscriber.recv_async().await {
    println!("Key: {}", sample.key_expr());
}
 
// Callback handler
let _subscriber = session
    .declare_subscriber("robots/**")
    .callback(|sample| println!("Got: {}", sample.key_expr()))
    .await
    .unwrap();

Data Flow

The router matches each publication against all active subscriber key expressions and delivers only to those that intersect.

Pub/sub fan-out through the router

Sample

Every received message is a Sample containing:

Field	Type	Description
`key_expr()`	`KeyExpr`	The exact key the data was published on
`payload()`	`ZBytes`	The raw payload
`encoding()`	`Encoding`	Payload type hint
`timestamp()`	`Option<Timestamp>`	Optional HLC timestamp
`kind()`	`SampleKind`	`Put` or `Delete`

Delete

Publish a deletion (e.g., to remove a key from storages):

session.delete("robots/robot-42/pose").await.unwrap();