fix: Require channel configuration for gRPC

Author: fjuma

client/transport/grpc/src/main/java/io/a2a/client/transport/grpc/GrpcTransportProvider.java

@@ -7,10 +7,10 @@
 import io.a2a.client.config.ClientTransportConfig;
 import io.a2a.client.transport.spi.ClientTransport;
 import io.a2a.client.transport.spi.ClientTransportProvider;
+import io.a2a.spec.A2AClientException;
 import io.a2a.spec.AgentCard;
 import io.a2a.spec.TransportProtocol;
 import io.grpc.Channel;
-import io.grpc.ManagedChannelBuilder;
 
 /**
  * Provider for gRPC transport implementation.
@@ -19,21 +19,18 @@ public class GrpcTransportProvider implements ClientTransportProvider {
 
     @Override
     public ClientTransport create(ClientConfig clientConfig, AgentCard agentCard,
-                                  String agentUrl, List<ClientCallInterceptor> interceptors) {
+                                  String agentUrl, List<ClientCallInterceptor> interceptors) throws A2AClientException {
         // not making use of the interceptors for gRPC for now
-        Channel channel;
         List<ClientTransportConfig> clientTransportConfigs = clientConfig.getClientTransportConfigs();
         if (clientTransportConfigs != null) {
             for (ClientTransportConfig clientTransportConfig : clientTransportConfigs) {
                 if (clientTransportConfig instanceof GrpcTransportConfig grpcTransportConfig) {
-                    channel = grpcTransportConfig.getChannelFactory().apply(agentUrl);
+                    Channel channel = grpcTransportConfig.getChannelFactory().apply(agentUrl);
                     return new GrpcTransport(channel, agentCard);
                 }
             }
         }
-        // no channel factory configured
-        channel = ManagedChannelBuilder.forTarget(agentUrl).build();
-        return new GrpcTransport(channel, agentCard);
+        throw new A2AClientException("Missing required GrpcTransportConfig");
     }
 
     @Override

client/transport/jsonrpc/src/main/java/io/a2a/client/transport/jsonrpc/JSONRPCTransportProvider.java

@@ -8,14 +8,15 @@
 import io.a2a.client.http.A2AHttpClient;
 import io.a2a.client.transport.spi.ClientTransport;
 import io.a2a.client.transport.spi.ClientTransportProvider;
+import io.a2a.spec.A2AClientException;
 import io.a2a.spec.AgentCard;
 import io.a2a.spec.TransportProtocol;
 
 public class JSONRPCTransportProvider implements ClientTransportProvider {
 
     @Override
     public ClientTransport create(ClientConfig clientConfig, AgentCard agentCard,
-                                  String agentUrl, List<ClientCallInterceptor> interceptors) {
+                                  String agentUrl, List<ClientCallInterceptor> interceptors) throws A2AClientException {
         A2AHttpClient httpClient = null;
         List<ClientTransportConfig> clientTransportConfigs = clientConfig.getClientTransportConfigs();
         if (clientTransportConfigs != null) {

client/transport/spi/src/main/java/io/a2a/client/transport/spi/ClientTransportProvider.java

@@ -4,6 +4,7 @@
 
 import io.a2a.client.config.ClientCallInterceptor;
 import io.a2a.client.config.ClientConfig;
+import io.a2a.spec.A2AClientException;
 import io.a2a.spec.AgentCard;
 
 /**
@@ -19,9 +20,10 @@ public interface ClientTransportProvider {
      * @param agentUrl the remote agent's URL
      * @param interceptors the optional interceptors to use for a client call (may be {@code null})
      * @return the client transport
+     * @throws io.a2a.spec.A2AClientException if an error occurs trying to create the client
      */
     ClientTransport create(ClientConfig clientConfig, AgentCard agentCard,
-                           String agentUrl, List<ClientCallInterceptor> interceptors);
+                           String agentUrl, List<ClientCallInterceptor> interceptors) throws A2AClientException;
 
     /**
      * Get the name of the client transport.

reference/grpc/src/test/java/io/a2a/server/grpc/quarkus/QuarkusA2AGrpcTest.java

@@ -1,12 +1,24 @@
 package io.a2a.server.grpc.quarkus;
 
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.TimeUnit;
+
+import io.a2a.client.config.ClientTransportConfig;
+import io.a2a.client.transport.grpc.GrpcTransportConfig;
 import io.a2a.server.apps.common.AbstractA2AServerTest;
 import io.a2a.spec.TransportProtocol;
+import io.grpc.ManagedChannel;
+import io.grpc.ManagedChannelBuilder;
 import io.quarkus.test.junit.QuarkusTest;
 
+import org.junit.jupiter.api.AfterAll;
+
 @QuarkusTest
 public class QuarkusA2AGrpcTest extends AbstractA2AServerTest {
 
+    private static ManagedChannel channel;
+
     public QuarkusA2AGrpcTest() {
         super(8081); // HTTP server port for utility endpoints
     }
@@ -20,4 +32,25 @@ protected String getTransportProtocol() {
     protected String getTransportUrl() {
         return "localhost:9001"; // gRPC server runs on port 9001
     }
+
+    @Override
+    protected List<ClientTransportConfig> getClientTransportConfigs() {
+        List<ClientTransportConfig> transportConfigs = new ArrayList<>();
+        transportConfigs.add(new GrpcTransportConfig(
+                target -> {
+                    channel = ManagedChannelBuilder.forTarget(target).usePlaintext().build();
+                    return channel;
+                }));
+        return transportConfigs;
+    }
+
+    @AfterAll
+    public static void closeChannel() {
+        channel.shutdownNow();
+        try {
+            channel.awaitTermination(10, TimeUnit.SECONDS);
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+        }
+    }
 }

tests/server-common/src/test/java/io/a2a/server/apps/common/AbstractA2AServerTest.java

@@ -134,6 +134,13 @@ protected AbstractA2AServerTest(int serverPort) {
      */
     protected abstract String getTransportUrl();
 
+    /**
+     * Get the transport configs to use for this test.
+     */
+    protected List<ClientTransportConfig> getClientTransportConfigs() {
+        return new ArrayList<>();
+    }
+
     @Test
     public void testTaskStoreMethodsSanityTest() throws Exception {
         Task task = new Task.Builder(MINIMAL_TASK).id("abcde").build();
@@ -1144,14 +1151,7 @@ private ClientConfig createClientConfig(boolean streaming) {
                 .setAcceptedOutputModes(List.of("text"));
 
         // Set transport-specific configuration
-        List<ClientTransportConfig> transportConfigs = new ArrayList<>();
-        if (TransportProtocol.JSONRPC.asString().equals(getTransportProtocol())) {
-            transportConfigs.add(new JSONRPCTransportConfig(new JdkA2AHttpClient()));
-        } else if (TransportProtocol.GRPC.asString().equals(getTransportProtocol())) {
-            // For gRPC, use a function that creates a channel with plaintext communication
-            transportConfigs.add(new GrpcTransportConfig(
-                target -> ManagedChannelBuilder.forTarget(target).usePlaintext().build()));
-        }
+        List<ClientTransportConfig> transportConfigs = getClientTransportConfigs();
 
         if (!transportConfigs.isEmpty()) {
             builder.setClientTransportConfigs(transportConfigs);