Request-Response

The request-response (req-rep) pattern is used to connect a set of clients to a set of services. It can also be seen as a form of remote procedure call and a simple task distribution pattern.

graph LR
    C(Client)
    C -->|REQ| D(Server)
    D -->|REP| C

On the client side, messages containing the details of each procedure call are pushed by each client using a Request node. On the server side, a Response node is used to receive notifications of new requests. Responses can be evaluated using the SendResponse operator.

Warning

This pattern is strictly sequential: if multiple requests are sent to a Response socket, they will be handled by the server one at a time, in order of arrival. For asynchronous processing of requests, see the Router-Dealer pattern.

Example: Simple request-response

In the example below, a periodic timer sends counter updates as a request to the server. The server replies by formatting the input string with the prefix reply.