Merge branch 'ylassoued/feat-request' of github.com:ylassoued/python-sdk into ylassoued/feat-request

Author: Yassine Lassoued

README.md

@@ -357,7 +357,7 @@ You can mount the SSE server to an existing ASGI server using the `sse_app` meth
 
 ```python
 from starlette.applications import Starlette
-from starlette.routes import Mount, Host
+from starlette.routing import Mount, Host
 from mcp.server.fastmcp import FastMCP
 
 

src/mcp/client/stdio.py src/mcp/client/stdio/__init__.pysrc/mcp/client/stdio.py renamed to src/mcp/client/stdio/__init__.py

@@ -12,6 +12,12 @@
 
 import mcp.types as types
 
+from .win32 import (
+    create_windows_process,
+    get_windows_executable_command,
+    terminate_windows_process,
+)
+
 # Environment variables to inherit by default
 DEFAULT_INHERITED_ENV_VARS = (
     [
@@ -101,14 +107,18 @@ async def stdio_client(server: StdioServerParameters, errlog: TextIO = sys.stder
     read_stream_writer, read_stream = anyio.create_memory_object_stream(0)
     write_stream, write_stream_reader = anyio.create_memory_object_stream(0)
 
-    process = await anyio.open_process(
-        [server.command, *server.args],
+    command = _get_executable_command(server.command)
+
+    # Open process with stderr piped for capture
+    process = await _create_platform_compatible_process(
+        command=command,
+        args=server.args,
         env=(
             {**get_default_environment(), **server.env}
             if server.env is not None
             else get_default_environment()
         ),
-        stderr=errlog,
+        errlog=errlog,
         cwd=server.cwd,
     )
 
@@ -159,4 +169,48 @@ async def stdin_writer():
     ):
         tg.start_soon(stdout_reader)
         tg.start_soon(stdin_writer)
-        yield read_stream, write_stream
+        try:
+            yield read_stream, write_stream
+        finally:
+            # Clean up process to prevent any dangling orphaned processes
+            if sys.platform == "win32":
+                await terminate_windows_process(process)
+            else:
+                process.terminate()
+
+
+def _get_executable_command(command: str) -> str:
+    """
+    Get the correct executable command normalized for the current platform.
+
+    Args:
+        command: Base command (e.g., 'uvx', 'npx')
+
+    Returns:
+        str: Platform-appropriate command
+    """
+    if sys.platform == "win32":
+        return get_windows_executable_command(command)
+    else:
+        return command
+
+
+async def _create_platform_compatible_process(
+    command: str,
+    args: list[str],
+    env: dict[str, str] | None = None,
+    errlog: TextIO = sys.stderr,
+    cwd: Path | str | None = None,
+):
+    """
+    Creates a subprocess in a platform-compatible way.
+    Returns a process handle.
+    """
+    if sys.platform == "win32":
+        process = await create_windows_process(command, args, env, errlog, cwd)
+    else:
+        process = await anyio.open_process(
+            [command, *args], env=env, stderr=errlog, cwd=cwd
+        )
+
+    return process

src/mcp/client/stdio/win32.py

@@ -0,0 +1,109 @@
+"""
+Windows-specific functionality for stdio client operations.
+"""
+
+import shutil
+import subprocess
+import sys
+from pathlib import Path
+from typing import TextIO
+
+import anyio
+from anyio.abc import Process
+
+
+def get_windows_executable_command(command: str) -> str:
+    """
+    Get the correct executable command normalized for Windows.
+
+    On Windows, commands might exist with specific extensions (.exe, .cmd, etc.)
+    that need to be located for proper execution.
+
+    Args:
+        command: Base command (e.g., 'uvx', 'npx')
+
+    Returns:
+        str: Windows-appropriate command path
+    """
+    try:
+        # First check if command exists in PATH as-is
+        if command_path := shutil.which(command):
+            return command_path
+
+        # Check for Windows-specific extensions
+        for ext in [".cmd", ".bat", ".exe", ".ps1"]:
+            ext_version = f"{command}{ext}"
+            if ext_path := shutil.which(ext_version):
+                return ext_path
+
+        # For regular commands or if we couldn't find special versions
+        return command
+    except OSError:
+        # Handle file system errors during path resolution
+        # (permissions, broken symlinks, etc.)
+        return command
+
+
+async def create_windows_process(
+    command: str,
+    args: list[str],
+    env: dict[str, str] | None = None,
+    errlog: TextIO = sys.stderr,
+    cwd: Path | str | None = None,
+):
+    """
+    Creates a subprocess in a Windows-compatible way.
+
+    Windows processes need special handling for console windows and
+    process creation flags.
+
+    Args:
+        command: The command to execute
+        args: Command line arguments
+        env: Environment variables
+        errlog: Where to send stderr output
+        cwd: Working directory for the process
+
+    Returns:
+        A process handle
+    """
+    try:
+        # Try with Windows-specific flags to hide console window
+        process = await anyio.open_process(
+            [command, *args],
+            env=env,
+            # Ensure we don't create console windows for each process
+            creationflags=subprocess.CREATE_NO_WINDOW  # type: ignore
+            if hasattr(subprocess, "CREATE_NO_WINDOW")
+            else 0,
+            stderr=errlog,
+            cwd=cwd,
+        )
+        return process
+    except Exception:
+        # Don't raise, let's try to create the process without creation flags
+        process = await anyio.open_process(
+            [command, *args], env=env, stderr=errlog, cwd=cwd
+        )
+        return process
+
+
+async def terminate_windows_process(process: Process):
+    """
+    Terminate a Windows process.
+
+    Note: On Windows, terminating a process with process.terminate() doesn't
+    always guarantee immediate process termination.
+    So we give it 2s to exit, or we call process.kill()
+    which sends a SIGKILL equivalent signal.
+
+    Args:
+        process: The process to terminate
+    """
+    try:
+        process.terminate()
+        with anyio.fail_after(2.0):
+            await process.wait()
+    except TimeoutError:
+        # Force kill if it doesn't terminate
+        process.kill()

src/mcp/server/lowlevel/server.py

@@ -304,7 +304,7 @@ def create_content(data: str | bytes, mime_type: str | None):
 
                             return types.BlobResourceContents(
                                 uri=req.params.uri,
-                                blob=base64.urlsafe_b64encode(data).decode(),
+                                blob=base64.b64encode(data).decode(),
                                 mimeType=mime_type or "application/octet-stream",
                             )
 

tests/issues/test_342_base64_encoding.py

@@ -0,0 +1,89 @@
+"""Test for base64 encoding issue in MCP server.
+
+This test demonstrates the issue in server.py where the server uses
+urlsafe_b64encode but the BlobResourceContents validator expects standard
+base64 encoding.
+
+The test should FAIL before fixing server.py to use b64encode instead of
+urlsafe_b64encode.
+After the fix, the test should PASS.
+"""
+
+import base64
+from typing import cast
+
+import pytest
+from pydantic import AnyUrl
+
+from mcp.server.lowlevel.helper_types import ReadResourceContents
+from mcp.server.lowlevel.server import Server
+from mcp.types import (
+    BlobResourceContents,
+    ReadResourceRequest,
+    ReadResourceRequestParams,
+    ReadResourceResult,
+    ServerResult,
+)
+
+
+@pytest.mark.anyio
+async def test_server_base64_encoding_issue():
+    """Tests that server response can be validated by BlobResourceContents.
+
+    This test will:
+    1. Set up a server that returns binary data
+    2. Extract the base64-encoded blob from the server's response
+    3. Verify the encoded data can be properly validated by BlobResourceContents
+
+    BEFORE FIX: The test will fail because server uses urlsafe_b64encode
+    AFTER FIX: The test will pass because server uses standard b64encode
+    """
+    server = Server("test")
+
+    # Create binary data that will definitely result in + and / characters
+    # when encoded with standard base64
+    binary_data = bytes([x for x in range(255)] * 4)
+
+    # Register a resource handler that returns our test data
+    @server.read_resource()
+    async def read_resource(uri: AnyUrl) -> list[ReadResourceContents]:
+        return [
+            ReadResourceContents(
+                content=binary_data, mime_type="application/octet-stream"
+            )
+        ]
+
+    # Get the handler directly from the server
+    handler = server.request_handlers[ReadResourceRequest]
+
+    # Create a request
+    request = ReadResourceRequest(
+        method="resources/read",
+        params=ReadResourceRequestParams(uri=AnyUrl("test://resource")),
+    )
+
+    # Call the handler to get the response
+    result: ServerResult = await handler(request)
+
+    # After (fixed code):
+    read_result: ReadResourceResult = cast(ReadResourceResult, result.root)
+    blob_content = read_result.contents[0]
+
+    # First verify our test data actually produces different encodings
+    urlsafe_b64 = base64.urlsafe_b64encode(binary_data).decode()
+    standard_b64 = base64.b64encode(binary_data).decode()
+    assert urlsafe_b64 != standard_b64, "Test data doesn't demonstrate"
+    " encoding difference"
+
+    # Now validate the server's output with BlobResourceContents.model_validate
+    # Before the fix: This should fail with "Invalid base64" because server
+    # uses urlsafe_b64encode
+    # After the fix: This should pass because server will use standard b64encode
+    model_dict = blob_content.model_dump()
+
+    # Direct validation - this will fail before fix, pass after fix
+    blob_model = BlobResourceContents.model_validate(model_dict)
+
+    # Verify we can decode the data back correctly
+    decoded = base64.b64decode(blob_model.blob)
+    assert decoded == binary_data