refactor: Refactor McpSessionManager to support custom transport builders

core/src/main/java/com/google/adk/tools/mcp/DefaultMcpTransportBuilder.java

@@ -0,0 +1,46 @@
+package com.google.adk.tools.mcp;
+
+import com.google.common.collect.ImmutableMap;
+import io.modelcontextprotocol.client.transport.HttpClientSseClientTransport;
+import io.modelcontextprotocol.client.transport.ServerParameters;
+import io.modelcontextprotocol.client.transport.StdioClientTransport;
+import io.modelcontextprotocol.spec.McpClientTransport;
+import java.util.Collection;
+import java.util.Optional;
+
+/**
+ * The default builder for creating MCP client transports. Supports StdioClientTransport based on
+ * {@link ServerParameters} and the standard HttpClientSseClientTransport based on {@link
+ * SseServerParameters}.
+ */
+public class DefaultMcpTransportBuilder implements McpTransportBuilder {
+
+  @Override
+  public McpClientTransport build(Object connectionParams) {
+    if (connectionParams instanceof ServerParameters serverParameters) {
+      return new StdioClientTransport(serverParameters);
+    } else if (connectionParams instanceof SseServerParameters sseServerParams) {
+      return HttpClientSseClientTransport.builder(sseServerParams.url())
+          .sseEndpoint("sse")
+          .customizeRequest(
+              builder ->
+                  Optional.ofNullable(sseServerParams.headers())
+                      .map(ImmutableMap::entrySet)
+                      .stream()
+                      .flatMap(Collection::stream)
+                      .forEach(
+                          entry ->
+                              builder.header(
+                                  entry.getKey(),
+                                  Optional.ofNullable(entry.getValue())
+                                      .map(Object::toString)
+                                      .orElse(""))))
+          .build();
+    } else {
+      throw new IllegalArgumentException(
+          "DefaultMcpTransportBuilder supports only ServerParameters or SseServerParameters, but"
+              + " got "
+              + connectionParams.getClass().getName());
+    }
+  }
+}

core/src/main/java/com/google/adk/tools/mcp/McpSessionManager.java

@@ -16,27 +16,20 @@
 
 package com.google.adk.tools.mcp;
 
-import com.google.common.collect.ImmutableMap;
 import io.modelcontextprotocol.client.McpClient;
 import io.modelcontextprotocol.client.McpSyncClient;
-import io.modelcontextprotocol.client.transport.HttpClientSseClientTransport;
-import io.modelcontextprotocol.client.transport.ServerParameters;
-import io.modelcontextprotocol.client.transport.StdioClientTransport;
 import io.modelcontextprotocol.spec.McpClientTransport;
 import io.modelcontextprotocol.spec.McpSchema.ClientCapabilities;
 import io.modelcontextprotocol.spec.McpSchema.InitializeResult;
+import java.time.Duration;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import java.time.Duration;
-import java.util.Collection;
-import java.util.Optional;
-
 /**
  * Manages MCP client sessions.
  *
  * <p>This class provides methods for creating and initializing MCP client sessions, handling
- * different connection parameters (Stdio and SSE).
+ * different connection parameters and transport builders.
  */
 // TODO(b/413489523): Implement this class.
 public class McpSessionManager {
@@ -53,31 +46,21 @@ public McpSyncClient createSession() {
   }
 
   public static McpSyncClient initializeSession(Object connectionParams) {
-    McpClientTransport transport;
-    if (connectionParams instanceof ServerParameters serverParameters) {
-      transport = new StdioClientTransport(serverParameters);
-    } else if (connectionParams instanceof SseServerParameters sseServerParams) {
-        transport = HttpClientSseClientTransport.builder(sseServerParams.url())
-                .sseEndpoint("sse")
-                .customizeRequest(builder ->
-                        Optional.ofNullable(sseServerParams.headers())
-                                .map(ImmutableMap::entrySet)
-                                .stream().flatMap(Collection::stream)
-                                .forEach(entry ->
-                                        builder.header(
-                                                entry.getKey(),
-                                                Optional.ofNullable(entry.getValue())
-                                                        .map(Object::toString)
-                                                        .orElse("")
-                                        )
-                                )
-                )
-                .build();
-    } else {
-      throw new IllegalArgumentException(
-          "Connection parameters must be either ServerParameters or SseServerParameters, but got "
-              + connectionParams.getClass().getName());
-    }
+    McpClientTransport transport = new DefaultMcpTransportBuilder().build(connectionParams);
+    McpSyncClient client =
+        McpClient.sync(transport)
+            .requestTimeout(Duration.ofSeconds(10))
+            .capabilities(ClientCapabilities.builder().build())
+            .build();
+    InitializeResult initResult = client.initialize();
+    logger.debug("Initialize Client Result: {}", initResult);
+    return client;
+  }
+
+  public static McpSyncClient initializeSession(
+      Object connectionParams, McpTransportBuilder transportBuilder) {
+    McpClientTransport transport = transportBuilder.build(connectionParams);
+
     McpSyncClient client =
         McpClient.sync(transport)
             .requestTimeout(Duration.ofSeconds(10))

core/src/main/java/com/google/adk/tools/mcp/McpTransportBuilder.java

@@ -0,0 +1,20 @@
+package com.google.adk.tools.mcp;
+
+import io.modelcontextprotocol.spec.McpClientTransport;
+
+/**
+ * Interface for building McpClientTransport instances. Implementations of this interface are
+ * responsible for constructing concrete McpClientTransport objects based on the provided connection
+ * parameters.
+ */
+public interface McpTransportBuilder {
+  /**
+   * Builds an McpClientTransport based on the provided connection parameters.
+   *
+   * @param connectionParams The parameters required to configure the transport. The type of this
+   *     object determines the type of transport built.
+   * @return An instance of McpClientTransport.
+   * @throws IllegalArgumentException if the connectionParams are not supported or invalid.
+   */
+  McpClientTransport build(Object connectionParams);
+}