publish message without exchange declaration

lib/src/client/channel.dart

@@ -43,10 +43,14 @@ abstract class Channel {
   /// returned future will fail with a [ExchangeNotFoundException] if the exchange does not exist.
   ///
   /// The [durable] flag will enable the exchange to persist across server restarts.
+  ///
+  /// The [declare] flag can be set to false to skip the exchange declaration step
+  /// for clients with read-only access to the broker.
   Future<Exchange> exchange(String name, ExchangeType type,
       {bool passive = false,
       bool durable = false,
       bool noWait = false,
+      bool declare = true,
       Map<String, Object> arguments});
 
   /// Setup the [prefetchSize] and [prefetchCount] QoS parameters. The value

lib/src/client/impl/channel_impl.dart

@@ -563,6 +563,7 @@ class _ChannelImpl implements Channel {
       {bool passive = false,
       bool durable = false,
       bool noWait = false,
+      bool declare = true,
       Map<String, Object>? arguments}) {
     if (name.isEmpty) {
       throw ArgumentError("The name of the exchange cannot be empty");
@@ -579,6 +580,12 @@ class _ChannelImpl implements Channel {
       ..arguments = arguments;
 
     Completer<Exchange> opCompleter = Completer<Exchange>();
+
+    if (!declare) {
+      opCompleter.complete(_ExchangeImpl(this, name, type));
+      return opCompleter.future;
+    }
+
     writeMessage(exchangeRequest,
         completer: opCompleter,
         futurePayload: _ExchangeImpl(this, name, type),

test/lib/exchange_test.dart

@@ -203,6 +203,38 @@ main({bool enableLogger = true}) {
       await boundQueue.unbind(exchange, "");
     });
 
+    test("publish to exchange without exchange declaration", () async {
+      Completer testCompleter = Completer();
+
+      // Use the second client to define the queue and the exchange in advance
+      Channel channel2 = await client2.channel();
+      Queue queue = await channel2.queue("q_test_ro");
+      Exchange exchange = await channel2.exchange("exc_test_ro", ExchangeType.FANOUT);
+      queue.bind(exchange, '');
+
+      // Pretend we are a RO consumer that cannot declare the exchange but
+      // should still be able to publish to it.
+      Channel channel = await client.channel();
+      Exchange exchangeRo = await channel
+          .exchange("exc_test_ro", ExchangeType.FANOUT, declare: false);
+
+      expect(exchangeRo.channel, const TypeMatcher<Channel>());
+      expect(exchangeRo.type, equals(ExchangeType.FANOUT));
+      expect(exchangeRo.name, "exc_test_ro");
+
+      exchangeRo.publish("Test payload", "");
+
+      Consumer consumer = await queue.consume();
+      consumer.listen((AmqpMessage reply) {
+        expect(reply.payloadAsString, equals("Test payload"));
+
+        // Pass!
+        testCompleter.complete();
+      });
+
+      return testCompleter.future;
+    });
+
     group("exceptions", () {
       test("missing exchange name", () async {
         Channel channel = await client.channel();