Fixed byte buffer leak in Netty4 request handler

If creating the REST request throws an exception (for example, because
of invalid headers), we leak the request due to failure to release the
buffer (which would otherwise happen after replying on the
channel). This commit addresses this leak by handling the failure case.

Relates #27222

Author: original-brownbear

modules/transport-netty4/src/main/java/org/elasticsearch/http/netty4/Netty4HttpRequestHandler.java

@@ -64,7 +64,15 @@ protected void channelRead0(ChannelHandlerContext ctx, Object msg) throws Except
                         Unpooled.copiedBuffer(request.content()),
                         request.headers(),
                         request.trailingHeaders());
-        final Netty4HttpRequest httpRequest = new Netty4HttpRequest(serverTransport.xContentRegistry, copy, ctx.channel());
+        final Netty4HttpRequest httpRequest;
+        try {
+            httpRequest = new Netty4HttpRequest(serverTransport.xContentRegistry, copy, ctx.channel());
+        } catch (Exception ex) {
+            if (pipelinedRequest != null) {
+                pipelinedRequest.release();
+            }
+            throw ex;
+        }
         final Netty4HttpChannel channel =
                 new Netty4HttpChannel(serverTransport, httpRequest, pipelinedRequest, detailedErrorsEnabled, threadContext);