feat: add response converters to support multiple A2A client events

a2a/pom.xml

@@ -16,7 +16,7 @@
   <properties>
     <java.version>17</java.version>
     <maven.compiler.release>${java.version}</maven.compiler.release>
-    <a2a.sdk.version>0.3.0.Beta1</a2a.sdk.version>
+    <a2a.sdk.version>0.3.2.Final</a2a.sdk.version>
     <google.adk.version>${project.version}</google.adk.version>
     <guava.version>33.0.0-jre</guava.version>
     <jackson.version>2.19.0</jackson.version>
@@ -89,6 +89,11 @@
       <artifactId>a2a-java-sdk-http-client</artifactId>
       <version>${a2a.sdk.version}</version>
     </dependency>
+    <dependency>
+      <groupId>io.github.a2asdk</groupId>
+      <artifactId>a2a-java-sdk-client</artifactId>
+      <version>${a2a.sdk.version}</version>
+    </dependency>
     <dependency>
       <groupId>junit</groupId>
       <artifactId>junit</artifactId>

a2a/src/main/java/com/google/adk/a2a/RemoteA2AAgent.java

@@ -1,7 +1,6 @@
 package com.google.adk.a2a;
 
 import static com.google.common.base.Strings.isNullOrEmpty;
-import static com.google.common.base.Strings.nullToEmpty;
 
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.google.adk.a2a.converters.EventConverter;
@@ -10,16 +9,13 @@
 import com.google.adk.agents.Callbacks;
 import com.google.adk.agents.InvocationContext;
 import com.google.adk.events.Event;
+import com.google.common.collect.ImmutableMap;
 import com.google.common.io.Resources;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import io.a2a.spec.AgentCard;
-import io.a2a.spec.EventKind;
 import io.a2a.spec.Message;
 import io.a2a.spec.MessageSendParams;
 import io.a2a.spec.SendMessageRequest;
-import io.a2a.spec.SendMessageResponse;
-import io.a2a.spec.Task;
-import io.a2a.spec.TaskStatus;
 import io.reactivex.rxjava3.core.Flowable;
 import java.io.IOException;
 import java.net.URL;
@@ -258,7 +254,7 @@ protected Flowable<Event> runAsyncImpl(InvocationContext invocationContext) {
     Message a2aMessage = new Message.Builder(originalMessage).contextId(sessionId).build();
 
     Map<String, Object> metadata =
-        originalMessage.getMetadata() == null ? Map.of() : originalMessage.getMetadata();
+        originalMessage.getMetadata() == null ? ImmutableMap.of() : originalMessage.getMetadata();
 
     MessageSendParams params = new MessageSendParams(a2aMessage, null, metadata);
     SendMessageRequest request = new SendMessageRequest(invocationContext.invocationId(), params);
@@ -268,7 +264,6 @@ protected Flowable<Event> runAsyncImpl(InvocationContext invocationContext) {
         .sendMessage(request)
         .flatMap(
             response -> {
-              String responseContextId = extractContextId(response);
               List<Event> events =
                   ResponseConverter.sendMessageResponseToEvents(
                       response,
@@ -296,34 +291,6 @@ protected Flowable<Event> runLiveImpl(InvocationContext invocationContext) {
         "_run_live_impl for " + getClass() + " via A2A is not implemented.");
   }
 
-  private static String extractContextId(SendMessageResponse response) {
-    if (response == null) {
-      return "";
-    }
-
-    EventKind result = response.getResult();
-    if (result instanceof Message message) {
-      String contextId = nullToEmpty(message.getContextId());
-      if (!contextId.isEmpty()) {
-        return contextId;
-      }
-    }
-    if (result instanceof Task task) {
-      String contextId = nullToEmpty(task.getContextId());
-      if (!contextId.isEmpty()) {
-        return contextId;
-      }
-      TaskStatus status = task.getStatus();
-      if (status != null && status.message() != null) {
-        String statusContext = nullToEmpty(status.message().getContextId());
-        if (!statusContext.isEmpty()) {
-          return statusContext;
-        }
-      }
-    }
-    return "";
-  }
-
   /** Exception thrown when the agent card cannot be resolved. */
   public static class AgentCardResolutionError extends RuntimeException {
     public AgentCardResolutionError(String message) {
@@ -335,17 +302,6 @@ public AgentCardResolutionError(String message, Throwable cause) {
     }
   }
 
-  /** Exception thrown when the A2A client encounters an error. */
-  public static class A2AClientError extends RuntimeException {
-    public A2AClientError(String message) {
-      super(message);
-    }
-
-    public A2AClientError(String message, Throwable cause) {
-      super(message, cause);
-    }
-  }
-
   /** Exception thrown when a type error occurs. */
   public static class TypeError extends RuntimeException {
     public TypeError(String message) {

a2a/src/main/java/com/google/adk/a2a/common/A2AClientError.java

@@ -0,0 +1,12 @@
+package com.google.adk.a2a.common;
+
+/** Exception thrown when the A2A client encounters an error. */
+public class A2AClientError extends RuntimeException {
+  public A2AClientError(String message) {
+    super(message);
+  }
+
+  public A2AClientError(String message, Throwable cause) {
+    super(message, cause);
+  }
+}

a2a/src/main/java/com/google/adk/a2a/converters/EventConverter.java

@@ -24,6 +24,14 @@ public final class EventConverter {
 
   private EventConverter() {}
 
+  /**
+   * Aggregation mode for converting events to A2A messages.
+   *
+   * <p>AS_IS: Parts are aggregated as-is.
+   *
+   * <p>EXTERNAL_HANDOFF: Parts are aggregated as-is, except for function responses, which are
+   * converted to text parts with the function name and response map.
+   */
   public enum AggregationMode {
     AS_IS,
     EXTERNAL_HANDOFF

a2a/src/main/java/com/google/adk/a2a/converters/PartConverter.java

@@ -1,7 +1,10 @@
 package com.google.adk.a2a.converters;
 
+import static java.util.stream.Collectors.toCollection;
+
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.google.common.collect.ImmutableMap;
 import com.google.genai.types.Blob;
 import com.google.genai.types.FileData;
 import com.google.genai.types.FunctionCall;
@@ -13,8 +16,10 @@
 import io.a2a.spec.FileWithBytes;
 import io.a2a.spec.FileWithUri;
 import io.a2a.spec.TextPart;
+import java.util.ArrayList;
 import java.util.Base64;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 import org.slf4j.Logger;
@@ -60,6 +65,13 @@ public static Optional<com.google.genai.types.Part> toGenaiPart(io.a2a.spec.Part
     return Optional.empty();
   }
 
+  public static List<com.google.genai.types.Part> toGenaiParts(List<io.a2a.spec.Part<?>> a2aParts) {
+    return a2aParts.stream()
+        .map(PartConverter::toGenaiPart)
+        .flatMap(Optional::stream)
+        .collect(toCollection(ArrayList::new));
+  }
+
   /**
    * Convert a Google GenAI Part to an A2A Part.
    *
@@ -129,8 +141,8 @@ private static Optional<com.google.genai.types.Part> convertDataPartToGenAiPart(
 
     String metadataType = metadata.getOrDefault(A2A_DATA_PART_METADATA_TYPE_KEY, "").toString();
 
-    if (data.containsKey("name") && data.containsKey("args")
-        || A2A_DATA_PART_METADATA_TYPE_FUNCTION_CALL.equals(metadataType)) {
+    if ((data.containsKey("name") && data.containsKey("args"))
+        || metadataType.equals(A2A_DATA_PART_METADATA_TYPE_FUNCTION_CALL)) {
       String functionName = String.valueOf(data.getOrDefault("name", ""));
       String functionId = String.valueOf(data.getOrDefault("id", ""));
       Map<String, Object> args = coerceToMap(data.get("args"));
@@ -141,8 +153,8 @@ private static Optional<com.google.genai.types.Part> convertDataPartToGenAiPart(
               .build());
     }
 
-    if (data.containsKey("name") && data.containsKey("response")
-        || A2A_DATA_PART_METADATA_TYPE_FUNCTION_RESPONSE.equals(metadataType)) {
+    if ((data.containsKey("name") && data.containsKey("response"))
+        || metadataType.equals(A2A_DATA_PART_METADATA_TYPE_FUNCTION_RESPONSE)) {
       String functionName = String.valueOf(data.getOrDefault("name", ""));
       String functionId = String.valueOf(data.getOrDefault("id", ""));
       Map<String, Object> response = coerceToMap(data.get("response"));
@@ -175,10 +187,10 @@ private static Optional<DataPart> createDataPartFromFunctionCall(FunctionCall fu
     Map<String, Object> data = new HashMap<>();
     data.put("name", functionCall.name().orElse(""));
     data.put("id", functionCall.id().orElse(""));
-    data.put("args", functionCall.args().orElse(Map.of()));
+    data.put("args", functionCall.args().orElse(ImmutableMap.of()));
 
-    Map<String, Object> metadata =
-        Map.of(A2A_DATA_PART_METADATA_TYPE_KEY, A2A_DATA_PART_METADATA_TYPE_FUNCTION_CALL);
+    ImmutableMap<String, Object> metadata =
+        ImmutableMap.of(A2A_DATA_PART_METADATA_TYPE_KEY, A2A_DATA_PART_METADATA_TYPE_FUNCTION_CALL);
 
     return Optional.of(new DataPart(data, metadata));
   }
@@ -194,10 +206,11 @@ private static Optional<DataPart> createDataPartFromFunctionResponse(
     Map<String, Object> data = new HashMap<>();
     data.put("name", functionResponse.name().orElse(""));
     data.put("id", functionResponse.id().orElse(""));
-    data.put("response", functionResponse.response().orElse(Map.of()));
+    data.put("response", functionResponse.response().orElse(ImmutableMap.of()));
 
-    Map<String, Object> metadata =
-        Map.of(A2A_DATA_PART_METADATA_TYPE_KEY, A2A_DATA_PART_METADATA_TYPE_FUNCTION_RESPONSE);
+    ImmutableMap<String, Object> metadata =
+        ImmutableMap.of(
+            A2A_DATA_PART_METADATA_TYPE_KEY, A2A_DATA_PART_METADATA_TYPE_FUNCTION_RESPONSE);
 
     return Optional.of(new DataPart(data, metadata));
   }

a2a/src/main/java/com/google/adk/a2a/converters/RequestConverter.java

@@ -2,6 +2,7 @@
 
 import com.google.adk.events.Event;
 import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableMap;
 import com.google.genai.types.Content;
 import io.a2a.spec.DataPart;
 import io.a2a.spec.Message;
@@ -159,16 +160,17 @@ public static ImmutableList<Event> convertAggregatedA2aMessageToAdkEvents(
 
   private static String extractAuthorFromMetadata(Part<?> a2aPart) {
     if (a2aPart instanceof DataPart dataPart) {
-      Map<String, Object> metadata = Optional.ofNullable(dataPart.getMetadata()).orElse(Map.of());
+      Map<String, Object> metadata =
+          Optional.ofNullable(dataPart.getMetadata()).orElse(ImmutableMap.of());
       String type =
           metadata.getOrDefault(PartConverter.A2A_DATA_PART_METADATA_TYPE_KEY, "").toString();
-      if (PartConverter.A2A_DATA_PART_METADATA_TYPE_FUNCTION_CALL.equals(type)) {
+      if (type.equals(PartConverter.A2A_DATA_PART_METADATA_TYPE_FUNCTION_CALL)) {
         return "model";
       }
-      if (PartConverter.A2A_DATA_PART_METADATA_TYPE_FUNCTION_RESPONSE.equals(type)) {
+      if (type.equals(PartConverter.A2A_DATA_PART_METADATA_TYPE_FUNCTION_RESPONSE)) {
         return "user";
       }
-      Map<String, Object> data = Optional.ofNullable(dataPart.getData()).orElse(Map.of());
+      Map<String, Object> data = Optional.ofNullable(dataPart.getData()).orElse(ImmutableMap.of());
       if (data.containsKey("args")) {
         return "model";
       }
@@ -193,14 +195,4 @@ private static Event createEvent(
         .timestamp(Instant.now().toEpochMilli())
         .build();
   }
-
-  /**
-   * Convert an A2A Part to a GenAI Part.
-   *
-   * @param a2aPart The A2A Part to convert.
-   * @return Optional containing the converted GenAI Part, or empty if conversion fails.
-   */
-  private static Optional<com.google.genai.types.Part> convertA2aPartToGenAiPart(Part<?> a2aPart) {
-    return PartConverter.toGenaiPart(a2aPart);
-  }
 }