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PiperOrigin-RevId: 748777998

src/google/adk/tools/mcp_tool/mcp_session_manager.py

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+from contextlib import AsyncExitStack
+import functools
+import sys
+from typing import Any, TextIO
+import anyio
+from pydantic import BaseModel
+
+try:
+  from mcp import ClientSession, StdioServerParameters
+  from mcp.client.sse import sse_client
+  from mcp.client.stdio import stdio_client
+except ImportError as e:
+  import sys
+
+  if sys.version_info < (3, 10):
+    raise ImportError(
+        'MCP Tool requires Python 3.10 or above. Please upgrade your Python'
+        ' version.'
+    ) from e
+  else:
+    raise e
+
+
+class SseServerParams(BaseModel):
+  """Parameters for the MCP SSE connection.
+
+  See MCP SSE Client documentation for more details.
+  https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/client/sse.py
+  """
+
+  url: str
+  headers: dict[str, Any] | None = None
+  timeout: float = 5
+  sse_read_timeout: float = 60 * 5
+
+
+def retry_on_closed_resource(async_reinit_func_name: str):
+  """Decorator to automatically reinitialize session and retry action.
+
+  When MCP session was closed, the decorator will automatically recreate the
+  session and retry the action with the same parameters.
+
+  Note:
+  1. async_reinit_func_name is the name of the class member function that
+  reinitializes the MCP session.
+  2. Both the decorated function and the async_reinit_func_name must be async
+  functions.
+
+  Usage:
+  class MCPTool:
+    ...
+    async def create_session(self):
+      self.session = ...
+
+    @retry_on_closed_resource('create_session')
+    async def use_session(self):
+      await self.session.call_tool()
+
+  Args:
+    async_reinit_func_name: The name of the async function to recreate session.
+
+  Returns:
+    The decorated function.
+  """
+
+  def decorator(func):
+    @functools.wraps(
+        func
+    )  # Preserves original function metadata (name, docstring)
+    async def wrapper(self, *args, **kwargs):
+      try:
+        return await func(self, *args, **kwargs)
+      except anyio.ClosedResourceError:
+        try:
+          if hasattr(self, async_reinit_func_name) and callable(
+              getattr(self, async_reinit_func_name)
+          ):
+            async_init_fn = getattr(self, async_reinit_func_name)
+            await async_init_fn()
+          else:
+            raise ValueError(
+                f'Function {async_reinit_func_name} does not exist in decorated'
+                ' class. Please check the function name in'
+                ' retry_on_closed_resource decorator.'
+            )
+        except Exception as reinit_err:
+          raise RuntimeError(
+              f'Error reinitializing: {reinit_err}'
+          ) from reinit_err
+        return await func(self, *args, **kwargs)
+
+    return wrapper
+
+  return decorator
+
+
+class MCPSessionManager:
+  """Manages MCP client sessions.
+
+  This class provides methods for creating and initializing MCP client sessions,
+  handling different connection parameters (Stdio and SSE).
+  """
+
+  def __init__(
+      self,
+      connection_params: StdioServerParameters | SseServerParams,
+      exit_stack: AsyncExitStack,
+      errlog: TextIO = sys.stderr,
+  ) -> ClientSession:
+    """Initializes the MCP session manager.
+
+    Example usage:
+    ```
+    mcp_session_manager = MCPSessionManager(
+        connection_params=connection_params,
+        exit_stack=exit_stack,
+    )
+    session = await mcp_session_manager.create_session()
+    ```
+
+    Args:
+        connection_params: Parameters for the MCP connection (Stdio or SSE).
+        exit_stack: AsyncExitStack to manage the session lifecycle.
+        errlog: (Optional) TextIO stream for error logging. Use only for
+          initializing a local stdio MCP session.
+    """
+    self.connection_params = connection_params
+    self.exit_stack = exit_stack
+    self.errlog = errlog
+
+  async def create_session(self) -> ClientSession:
+    return await MCPSessionManager.initialize_session(
+        connection_params=self.connection_params,
+        exit_stack=self.exit_stack,
+        errlog=self.errlog,
+    )
+
+  @classmethod
+  async def initialize_session(
+      cls,
+      *,
+      connection_params: StdioServerParameters | SseServerParams,
+      exit_stack: AsyncExitStack,
+      errlog: TextIO = sys.stderr,
+  ) -> ClientSession:
+    """Initializes an MCP client session.
+
+    Args:
+        connection_params: Parameters for the MCP connection (Stdio or SSE).
+        exit_stack: AsyncExitStack to manage the session lifecycle.
+        errlog: (Optional) TextIO stream for error logging. Use only for
+          initializing a local stdio MCP session.
+
+    Returns:
+        ClientSession: The initialized MCP client session.
+    """
+    if isinstance(connection_params, StdioServerParameters):
+      client = stdio_client(server=connection_params, errlog=errlog)
+    elif isinstance(connection_params, SseServerParams):
+      client = sse_client(
+          url=connection_params.url,
+          headers=connection_params.headers,
+          timeout=connection_params.timeout,
+          sse_read_timeout=connection_params.sse_read_timeout,
+      )
+    else:
+      raise ValueError(
+          'Unable to initialize connection. Connection should be'
+          ' StdioServerParameters or SseServerParams, but got'
+          f' {connection_params}'
+      )
+
+    transports = await exit_stack.enter_async_context(client)
+    session = await exit_stack.enter_async_context(ClientSession(*transports))
+    await session.initialize()
+    return session