HTTP/2 Buffer Leak if UTF8 Conversion Fails

Motivation:
Http2CodecUtil uses ByteBufUtil.writeUtf8 but does not account for it
throwing an exception. If an exception is thrown because the format is
not valid UTF16 encoded UTF8 then the buffer will leak.

Modifications:
- Make sure the buffer is released if an exception is thrown
- Ensure call sites of the Http2CodecUtil.toByteBuf can tolerate and
  exception being thrown

Result:
No leak if exception data can not be converted to UTF8.

codec-http2/src/main/java/io/netty/handler/codec/http2/Http2CodecUtil.java

@@ -152,7 +152,15 @@ public final class Http2CodecUtil {
 
         // Create the debug message. `* 3` because UTF-8 max character consumes 3 bytes.
         ByteBuf debugData = ctx.alloc().buffer(cause.getMessage().length() * 3);
-        ByteBufUtil.writeUtf8(debugData, cause.getMessage());
+        boolean shouldRelease = true;
+        try {
+            ByteBufUtil.writeUtf8(debugData, cause.getMessage());
+            shouldRelease = false;
+        } finally {
+            if (shouldRelease) {
+                debugData.release();
+            }
+        }
         return debugData;
     }
 

codec-http2/src/main/java/io/netty/handler/codec/http2/Http2ConnectionHandler.java

@@ -16,6 +16,7 @@ package io.netty.handler.codec.http2;
 
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.ByteBufUtil;
+import io.netty.buffer.Unpooled;
 import io.netty.channel.ChannelFuture;
 import io.netty.channel.ChannelFutureListener;
 import io.netty.channel.ChannelHandlerContext;
@@ -705,7 +706,13 @@ public class Http2ConnectionHandler extends ByteToMessageDecoder implements Http
      */
     private ChannelFuture goAway(ChannelHandlerContext ctx, Http2Exception cause) {
         long errorCode = cause != null ? cause.error().code() : NO_ERROR.code();
-        ByteBuf debugData = Http2CodecUtil.toByteBuf(ctx, cause);
+        ByteBuf debugData = Unpooled.EMPTY_BUFFER;
+        try {
+            debugData = Http2CodecUtil.toByteBuf(ctx, cause);
+        } catch (Throwable t) {
+            // We must continue on to prevent our internal state from becoming corrupted but we log this exception.
+            logger.warn("caught exception while translating " + cause + " to ByteBuf", t);
+        }
         int lastKnownStream = connection().remote().lastStreamCreated();
         return goAway(ctx, lastKnownStream, errorCode, debugData, ctx.newPromise());
     }