netty: Increase HPACK encoder bucket count to 64

Increase the client and server HPACK encoder bucket counts from 16 to 64,
matching the new Netty default. On newer Netty versions, 64 buckets allow
encoder tables up to 4 KiB within the peer-advertised limit.

Use 64 instead of 128 as requested in review: the adjusted benchmark
shows comparable performance, while larger dynamic tables need further
improvements to Netty’s encoder. Advertised table sizes and the Netty
dependency version remain unchanged.

Co-Authored-By: Codex <noreply@openai.com>

Co-Authored-By: Xirp Agent (gpt-6.1-sol) <xirp-agent@users.noreply.ghe.spotify.net>

Author: petedmarsh

netty/src/main/java/io/grpc/netty/NettyClientHandler.java

@@ -175,8 +175,10 @@ static NettyClientHandler newHandler(
     Preconditions.checkArgument(maxHeaderListSize > 0, "maxHeaderListSize must be positive");
     Http2HeadersDecoder headersDecoder = new GrpcHttp2ClientHeadersDecoder(maxHeaderListSize);
     Http2FrameReader frameReader = new DefaultHttp2FrameReader(headersDecoder);
+    // TODO: Add support upstream in Netty for injecting a custom Http2HeadersEncoder subclass
+    // into Http2FrameCodecBuilder before migrating to that API.
     Http2HeadersEncoder encoder = new DefaultHttp2HeadersEncoder(
-        sensitivityDetector(neverIndexedMetadataKeys), false, 16, Integer.MAX_VALUE);
+        sensitivityDetector(neverIndexedMetadataKeys), false, 64, Integer.MAX_VALUE);
     Http2FrameWriter frameWriter = new DefaultHttp2FrameWriter(encoder);
     Http2Connection connection = new DefaultHttp2Connection(false);
     UniformStreamByteDistributor dist = new UniformStreamByteDistributor(connection);

netty/src/main/java/io/grpc/netty/NettyServerHandler.java

@@ -189,7 +189,7 @@ static NettyServerHandler newHandler(
     Http2HeadersEncoder encoder = new DefaultHttp2HeadersEncoder(
         NettyClientHandler.sensitivityDetector(neverIndexedMetadataKeys),
         false,
-        16,
+        64,
         Integer.MAX_VALUE);
     Http2FrameWriter frameWriter =
         new Http2OutboundFrameLogger(new DefaultHttp2FrameWriter(encoder), frameLogger);