fixes OverflowException if UnicstProcessr request and onNext race

rsocket-core/src/main/java/io/rsocket/core/RequestOperator.java

@@ -93,7 +93,6 @@ public Context currentContext() {
 
   @Override
   public void request(long n) {
-    this.s.request(n);
     if (!firstRequest) {
       try {
         this.hookOnRemainingRequests(n);
@@ -115,6 +114,15 @@ public void request(long n) {
       if (firstLoop) {
         firstLoop = false;
         try {
+          // since in all the scenarios where RequestOperator is used, the
+          // CorePublisher is either UnicastProcessor or UnicastProcessor.next()
+          // we are free to propagate unbounded demand to that publisher right after
+          // the first request happens. UnicastProcessor is only there to allow sending signals from
+          // the
+          // connection to a real subscriber and does not have to check the real demand
+          // For more info see
+          // https://github.com/rsocket/rsocket/blob/master/Protocol.md#handling-the-unexpected
+          this.s.request(Long.MAX_VALUE);
           this.hookOnFirstRequest(n);
         } catch (Throwable throwable) {
           onError(throwable);

rsocket-core/src/test/java/io/rsocket/core/RSocketRequesterTest.java

@@ -1142,6 +1142,51 @@ public void testWorkaround858() {
     rule.assertHasNoLeaks();
   }
 
+  @ParameterizedTest
+  @ValueSource(strings = {"stream", "channel"})
+  // see https://github.com/rsocket/rsocket-java/issues/959
+  public void testWorkaround959(String type) {
+    for (int i = 1; i < 20000; i += 2) {
+      ByteBuf buffer = rule.alloc().buffer();
+      buffer.writeCharSequence("test", CharsetUtil.UTF_8);
+
+      final AssertSubscriber<Payload> assertSubscriber = new AssertSubscriber<>(3);
+      if (type.equals("stream")) {
+        rule.socket.requestStream(ByteBufPayload.create(buffer)).subscribe(assertSubscriber);
+      } else if (type.equals("channel")) {
+        rule.socket
+            .requestChannel(Flux.just(ByteBufPayload.create(buffer)))
+            .subscribe(assertSubscriber);
+      }
+
+      final ByteBuf payloadFrame =
+          PayloadFrameCodec.encode(
+              rule.alloc(), i, false, false, true, Unpooled.EMPTY_BUFFER, Unpooled.EMPTY_BUFFER);
+
+      RaceTestUtils.race(
+          () -> {
+            rule.connection.addToReceivedBuffer(payloadFrame.copy());
+            rule.connection.addToReceivedBuffer(payloadFrame.copy());
+            rule.connection.addToReceivedBuffer(payloadFrame);
+          },
+          () -> {
+            assertSubscriber.request(1);
+            assertSubscriber.request(1);
+            assertSubscriber.request(1);
+          });
+
+      Assertions.assertThat(rule.connection.getSent()).allMatch(ByteBuf::release);
+
+      Assertions.assertThat(rule.socket.isDisposed()).isFalse();
+
+      assertSubscriber.values().forEach(ReferenceCountUtil::safeRelease);
+      assertSubscriber.assertNoError();
+
+      rule.connection.clearSendReceiveBuffers();
+      rule.assertHasNoLeaks();
+    }
+  }
+
   public static class ClientSocketRule extends AbstractSocketRule<RSocketRequester> {
     @Override
     protected RSocketRequester newRSocket() {