Just a second...

Sending request messages to a session

A client session can send a request message containing typed data directly to a client session. The receiving client session can then send a response message containing typed data. The request and response messages are addressed through the same message path.

A control client session on the left. Diffusion in the centre. Another client session on the right. An arrow representing the request message goes from the control client session through a shape representing the message path inside the Diffusion server and continues to the other client session. An arrow representing the response message goes from the receiving client session back through the message path on the Diffusion server to the control client session.
When a request message is sent to a specific client session and that session responds, the following events occur:
  1. A control client session sends a request message to a client session, specifying the message path to send the message through and the session ID of the client session to send the request message to.
  2. The client session receives the request message through a request stream.
  3. The client session uses a responder to send a response to the request message.
  4. The control client session receives the response.

Both the request message and the response message contain typed values. The messages can contain data of one of the following types: JSON, binary, string, 64-bit integer, or double. The response message is not required to be the same data type as the request it responds to.

Sending a request to a session

Required permissions: send_to_session permission for the specified message path and register_handler permission

Usually, it is a control client session in your organization's backend that sends messages directly to other sessions.

Send the request message specifying the following information:
  • The session ID of the client session to send the request to
  • The message path to send the request and receive the response through
  • The request message
  • The datatype of the request message
  • The datatype of the response message
Apple
[session.messagingControl sendRequest:[PTDiffusionPrimitive requestWithLongLong:42]
                          toSessionId:sessionId
                                 path:message_path
         int64NumberCompletionHandler:^(NSNumber *response, NSError* error)
{
    if (error) {
        NSLog(@"Failed to send to %@. Error: %@", message_path, error);
    } else {
        NSLog(@"Received response: %@", response);
    }
}];
                    
Java and Android
//Establish client session and control session
final Session control = Diffusion.sessions().principal("control").password("password").open("ws://localhost:8080");
final Session client = Diffusion.sessions().principal("client").password("password").open("ws://localhost:8080");

//Obtain the Messaging and MessagingControl features
final MessagingControl messagingControl = control.feature("MessagingControl.class");
final Messaging messaging = client.feature(Messaging.class);

//Create a JSON object to send as a request
final JSON request = Diffusion.dataTypes().json().fromJsonString("\"hello\"");

//Create a local request stream for the client to receive direct requests from the control session
messaging.setRequestStream("foo", JSON.class, JSON.class, requestStream);

//Send the request to a message path "foo" and wait for (at most) 5 seconds until the response is received.
final JSON response = messagingControl.sendRequest(client.getSessionId(), "foo", request, JSON.class, JSON.class).get(5, TimeUnit.SECONDS);
                    
JavaScript
control.messages.sendRequest('foo', 'Hello client', session_id, diffusion.datatypes.json(), diffusion.datatypes.json())
                    

Responding to messages sent to a session

Required permissions: send_to_message_handler for the specified message path

Define a request stream to receive and respond to request messages that have a specific data type.

Apple
@interface NumberRequestStreamDelegate : NSObject<PTDiffusionNumberRequestStreamDelegate>
@end

@implementation NumberRequestStreamDelegate
- (void)    diffusionStream:(nonnull PTDiffusionStream *)stream
didReceiveRequestWithNumber:(nullable NSNumber *)number
                  responder:(nonnull PTDiffusionResponder *)responder
{
    // Do something when a request is received.
}

- (void)diffusionStream:(nonnull PTDiffusionStream *)stream
       didFailWithError:(nonnull NSError *)error
{
    // Do something if the stream fails.
}

- (void)diffusionDidCloseStream:(nonnull PTDiffusionStream *)stream
{
    // Do something if the stream closes.
}
                    
Java and Android
private final class JSONRequestStream implements Messaging.RequestStream<JSON, JSON> {

    @Override
    public void onClose() {
        ....
    }

    @Override
    public void onError(ErrorReason errorReason) {
        ....
    }

    @Override
    public void onRequest(String path, JSON request, Responder<JSON> responder) {
        ....
    }
}
                    
JavaScript
var handler = {
    onRequest : function(request, context, responder) {
        ....
        responder.respond(response);
    },
    onError : function(error) {},
    onClose : function() {}
}
                    

Add the request stream against a message path. You can only add one request stream for each message path.

Apple
// Ensure to maintain a strong reference to your request stream as it
// is referenced weakly by the Diffusion client library.
NumberRequestStreamDelegate *delegate = [NumberRequestStreamDelegate new];
PTDiffusionRequestStream *requestStream = [PTDiffusionPrimitive int64RequestStreamWithDelegate:delegate];
[session.messaging setRequestStream:requestStream forPath:message_path];
                    
Java and Android
messaging.setRequestStream("foo", JSON.class, JSON.class, requestStream);
                    
JavaScript
control.messages.setRequestStream("foo", diffusion.datatypes.json(), diffusion.datatypes.json(), request_stream);