API Changes

• Static methods in Builders that always throw are now annotated @DoNotCall. This annotation can be noticed by ErrorProne and inform you of a mistake at compile time instead of runtime. This applies to static methods like InProcessServerBuilder.forPort(int) which are inherited from base classes like ServerBuilder/ManagedChannelBuilder yet are a bug if used.
• api, core: Support zero copy into protobuf. New APIs have been added to support the custom implementation of a zero-copy Protobuf deserialization marshaller. The HasByteBuffer API exposes ByteBuffers underlying the InputStream being passed to the Marshaller and the Detachable API allows custom Marshaller to take over the ownership of buffers for performing delayed deserialization.
• NettyChannelBuilder supports SocketAddress with ChannelCredentials.

Bug Fixes

• netty: Remove Maven pom.properties from netty-shaded jar. The properties don’t add much value and mainly confuse tools in a shaded jar.
• netty-shaded: Modify the shading operation to transform native-image resources so they correctly reference shaded class names (#7540)
• xds: Shut down the scheduledExecutorService in the CertificateProvider when it is shutdown.
• xds: Close the SslContexrProviderSupplier when a CDS LoadBalancer is shut down to prevent leakage.
• xds, grpclb: Use a standalone Context for control plane RPCs. The existing behavior of implicitly using the Context in ThreadLocal can cause control plane RPCs to be cancelled prematurely, in cases the data plane RPC is made within a gRPC service to another service. To avoid being impacted by data plane RPC lifecycle, the fix creates standalone Context for control plane RPCs.
• xds: cluster_resolver LB policy should wait until all clusters are resolved before propagating endpoints to child LB policy. Previously, the cluster_resolver LB policy propagated partially resolved results (endpoints for a subset of clusters) to its child LB policy, which can cause RPCs to be sent to less favored clusters before endpoints of more favored clusters are discovered.
• xds: use load assignment endpoint address in Cluster as the DNS hostname for LOGICAL_DNS. The LOGICAL_DNS concept was misunderstood previously. Instead of using the channel authority, the hostname should be given by Cluster resource in CDS responses.
• grpclb: skip fallback if the LB is already in fallback mode. An invariant check for gRPCLB LB policy’s internal state introduced by #8035 is broken in case the LB policy is in fallback mode while receiving an address update without remote balancer addresses. The fix mitigated the temporal invariant violation.

New Features

• compiler: Add support for ppc64le on RHEL8.

Dependencies

• Protobuf upgraded to 3.17.2
• We now use custom Gradle logic to determine if Maven’s requireUpperBoundDeps would fail for our published artifacts instead of Gradle’s failOnVersionConflict. This means we now make use of fewer dependency exclusions (#8238). failOnVersionConflict has similar behavior to dependencyConvergence but we previously lacked a more precise tool to detect cases where Maven would downgrade dependencies. We strongly encourage all Maven users to use Maven Enforcer’s requireUpperBoundDeps and continue to discourage using dependencyConvergence

Acknowledgements

@lepistone Leonardo Pistone
@shirodkara Amit Shirodkar
@cfredri4