Add a gRPC interceptor for getting client addresses

service/src/main/java/org/whispersystems/textsecuregcm/grpc/RemoteAddressInterceptor.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2023 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.whispersystems.textsecuregcm.grpc;
+
+import io.grpc.Context;
+import io.grpc.Contexts;
+import io.grpc.Grpc;
+import io.grpc.Metadata;
+import io.grpc.ServerCall;
+import io.grpc.ServerCallHandler;
+import io.grpc.ServerInterceptor;
+import java.net.SocketAddress;
+
+public class RemoteAddressInterceptor implements ServerInterceptor {
+
+  @Override
+  public <ReqT, RespT> ServerCall.Listener<ReqT> interceptCall(final ServerCall<ReqT, RespT> serverCall,
+      final Metadata headers,
+      final ServerCallHandler<ReqT, RespT> next) {
+
+    // Note: the specific implementation for getting a remote client address may change depending on the client
+    // connection strategy. The important thing is that the remote address wind up in the context for the current
+    // call so it can be retrieved by `RemoteAddressUtil`.
+    final SocketAddress remoteAddress = serverCall.getAttributes().get(Grpc.TRANSPORT_ATTR_REMOTE_ADDR);
+
+    return Contexts.interceptCall(
+        Context.current().withValue(RemoteAddressUtil.REMOTE_ADDRESS_CONTEXT_KEY, remoteAddress),
+        serverCall, headers, next);
+  }
+}

service/src/main/java/org/whispersystems/textsecuregcm/grpc/RemoteAddressUtil.java

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2023 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.whispersystems.textsecuregcm.grpc;
+
+import io.grpc.Context;
+import java.net.SocketAddress;
+
+public class RemoteAddressUtil {
+
+  static final Context.Key<SocketAddress> REMOTE_ADDRESS_CONTEXT_KEY = Context.key("remote-address");
+
+  /**
+   * Returns the socket address of the remote client in the current gRPC request context.
+   *
+   * @return the socket address of the remote client
+   */
+  public static SocketAddress getRemoteAddress() {
+    return REMOTE_ADDRESS_CONTEXT_KEY.get();
+  }
+}

service/src/test/java/org/whispersystems/textsecuregcm/grpc/MockRemoteAddressInterceptor.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2023 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.whispersystems.textsecuregcm.grpc;
+
+import io.grpc.Context;
+import io.grpc.Contexts;
+import io.grpc.Metadata;
+import io.grpc.ServerCall;
+import io.grpc.ServerCallHandler;
+import io.grpc.ServerInterceptor;
+import java.net.SocketAddress;
+import javax.annotation.Nullable;
+
+public class MockRemoteAddressInterceptor implements ServerInterceptor {
+
+  @Nullable
+  private SocketAddress remoteAddress;
+
+  public void setRemoteAddress(@Nullable final SocketAddress remoteAddress) {
+    this.remoteAddress = remoteAddress;
+  }
+
+  @Override
+  public <ReqT, RespT> ServerCall.Listener<ReqT> interceptCall(final ServerCall<ReqT, RespT> serverCall,
+      final Metadata headers,
+      final ServerCallHandler<ReqT, RespT> next) {
+
+    return remoteAddress != null
+        ? next.startCall(serverCall, headers)
+        : Contexts.interceptCall(
+            Context.current().withValue(RemoteAddressUtil.REMOTE_ADDRESS_CONTEXT_KEY, remoteAddress),
+            serverCall, headers, next);
+  }
+}