Add fixes and tests for GOAWAY

 - Ensure that the GOAWAY exception is fired within each child channel's event
   loop to ensure correct ordering

 - Fix off-by-one error in MultiplexedChannelRecord

 - Add tests using a minimal H2 endpoint implementation

 - Remove test-server module since it's no longer needed

Author: dagnir

.changes/next-release/bugfix-NettyNIOHTTPClient-cb2d4c6.json

@@ -0,0 +1,5 @@
+{
+    "type": "bugfix",
+    "category": "Netty NIO HTTP Client",
+    "description": "Better handle `GOAWAY` messages from the remote endpoint."
+}

http-clients/netty-nio-client/pom.xml

@@ -97,12 +97,6 @@
         </dependency>
 
         <!--Test Dependencies-->
-        <dependency>
-            <groupId>software.amazon.awssdk</groupId>
-            <artifactId>test-server</artifactId>
-            <version>${awsjavasdk.version}</version>
-            <scope>test</scope>
-        </dependency>
         <dependency>
             <groupId>com.github.tomakehurst</groupId>
             <artifactId>wiremock</artifactId>

http-clients/netty-nio-client/src/main/java/software/amazon/awssdk/http/nio/netty/internal/http2/MultiplexedChannelRecord.java

@@ -103,14 +103,12 @@ MultiplexedChannelRecord acquire(Promise<Channel> channelPromise) {
      * streams newer than the last-stream-id on the go-away frame.
      */
     public void goAway(Http2GoAwayFrame frame) {
-        System.out.println("Got GOAWAY: " + frame);
         this.goAway = true;
-        doInEventLoop(connection.eventLoop(), () -> {
-            GoAwayException exception = new GoAwayException(frame.errorCode(), frame.content());
-            childChannels.entrySet().stream()
-                         .filter(c -> c.getValue().stream().id() > frame.lastStreamId())
-                         .forEach(c -> shutdownChildChannel(c.getValue(), exception));
-        });
+        GoAwayException exception = new GoAwayException(frame.errorCode(), frame.content());
+        childChannels.entrySet().stream()
+                     .map(Map.Entry::getValue)
+                     .filter(cc -> cc.stream().id() > frame.lastStreamId())
+                     .forEach(cc -> cc.eventLoop().execute(() -> shutdownChildChannel(cc, exception)));
     }
 
     /**
@@ -141,7 +139,7 @@ private void createChildChannel(Promise<Channel> channelPromise) {
     }
 
     private void createChildChannel0(Promise<Channel> channelPromise) {
-        if (availableStreams() <= 0) {
+        if (goAway) {
             channelPromise.tryFailure(new IOException("No streams are available on this connection."));
         } else {
             // Once protocol future is notified then parent pipeline is configured and ready to go