enum StreamTimeoutMode {
    UNTIL_FIRST,
    // Maybe the default one
    UNTIL_NEXT,
    UNTIL_EOS // or UNTIL_LAST
}

StreamMessage<Object> stream = ...;
// Sets a timeout for each message to 5 seconds.
stream.timeout(5_seconds).subscribe(....);

// UNTIL_EOS will be useful for unary requests.
HttpRequest req = ...;
req.timeout(StreamTimeoutMode.UNTIL_EOS, 10_seconds).aggregate();
req.aggregate(10_seconds); // Shortcut

// UNTIL_NEXT will be useful for stream requests such as gRPC streams or WebSocket.
WebSocket input = ...;
input.timeout(UNTIL_NEXT, 3_seconds).subscribe(...);