Support for http request injection propagation to tools

src/mcp/server/lowlevel/server.py

@@ -85,7 +85,7 @@ async def main():
 from mcp.server.stdio import stdio_server as stdio_server
 from mcp.shared.context import RequestContext
 from mcp.shared.exceptions import McpError
-from mcp.shared.message import SessionMessage
+from mcp.shared.message import ServerMessageMetadata, SessionMessage
 from mcp.shared.session import RequestResponder
 
 logger = logging.getLogger(__name__)
@@ -215,7 +215,9 @@ def get_capabilities(
         )
 
     @property
-    def request_context(self) -> RequestContext[ServerSession, LifespanResultT]:
+    def request_context(
+        self,
+    ) -> RequestContext[ServerSession, LifespanResultT]:
         """If called outside of a request context, this will raise a LookupError."""
         return request_ctx.get()
 
@@ -555,6 +557,13 @@ async def _handle_request(
 
             token = None
             try:
+                # Extract request context from message metadata
+                request_data = None
+                if message.message_metadata is not None and isinstance(
+                    message.message_metadata, ServerMessageMetadata
+                ):
+                    request_data = message.message_metadata.request_context
+
                 # Set our global state that can be retrieved via
                 # app.get_request_context()
                 token = request_ctx.set(
@@ -563,6 +572,7 @@ async def _handle_request(
                         message.request_meta,
                         session,
                         lifespan_context,
+                        request=request_data,
                     )
                 )
                 response = await handler(req)

src/mcp/server/sse.py

@@ -52,7 +52,8 @@ async def handle_sse(request):
 from starlette.types import Receive, Scope, Send
 
 import mcp.types as types
-from mcp.shared.message import SessionMessage
+from mcp.shared.message import ServerMessageMetadata, SessionMessage
+from mcp.types import RequestData
 
 logger = logging.getLogger(__name__)
 
@@ -203,7 +204,19 @@ async def handle_post_message(
             await writer.send(err)
             return
 
-        session_message = SessionMessage(message)
+        # Extract request headers and other context
+        request_context: RequestData = {
+            "headers": dict(request.headers),
+            "method": request.method,
+            "url": str(request.url),
+            "client": request.client,
+            "path_params": request.path_params,
+            "query_params": dict(request.query_params),
+        }
+
+        # Create session message with request context
+        metadata = ServerMessageMetadata(request_context=request_context)
+        session_message = SessionMessage(message, metadata=metadata)
         logger.debug(f"Sending session message to writer: {session_message}")
         response = Response("Accepted", status_code=202)
         await response(scope, receive, send)

src/mcp/shared/context.py

@@ -4,7 +4,7 @@
 from typing_extensions import TypeVar
 
 from mcp.shared.session import BaseSession
-from mcp.types import RequestId, RequestParams
+from mcp.types import RequestData, RequestId, RequestParams
 
 SessionT = TypeVar("SessionT", bound=BaseSession[Any, Any, Any, Any, Any])
 LifespanContextT = TypeVar("LifespanContextT")
@@ -16,3 +16,4 @@ class RequestContext(Generic[SessionT, LifespanContextT]):
     meta: RequestParams.Meta | None
     session: SessionT
     lifespan_context: LifespanContextT
+    request: RequestData | None = None

src/mcp/shared/message.py

@@ -8,7 +8,7 @@
 from collections.abc import Awaitable, Callable
 from dataclasses import dataclass
 
-from mcp.types import JSONRPCMessage, RequestId
+from mcp.types import JSONRPCMessage, RequestData, RequestId
 
 ResumptionToken = str
 
@@ -30,6 +30,8 @@ class ServerMessageMetadata:
     """Metadata specific to server messages."""
 
     related_request_id: RequestId | None = None
+    # Request-specific context (e.g., headers, auth info)
+    request_context: RequestData | None = None
 
 
 MessageMetadata = ClientMessageMetadata | ServerMessageMetadata | None

src/mcp/shared/session.py

@@ -80,10 +80,12 @@ def __init__(
             ReceiveNotificationT
         ]""",
         on_complete: Callable[["RequestResponder[ReceiveRequestT, SendResultT]"], Any],
+        message_metadata: MessageMetadata = None,
     ) -> None:
         self.request_id = request_id
         self.request_meta = request_meta
         self.request = request
+        self.message_metadata = message_metadata
         self._session = session
         self._completed = False
         self._cancel_scope = anyio.CancelScope()
@@ -364,6 +366,7 @@ async def _receive_loop(self) -> None:
                         request=validated_request,
                         session=self,
                         on_complete=lambda r: self._in_flight.pop(r.request_id, None),
+                        message_metadata=message.metadata,
                     )
 
                     self._in_flight[responder.request_id] = responder

src/mcp/types.py

@@ -36,6 +36,8 @@
 Role = Literal["user", "assistant"]
 RequestId = str | int
 AnyFunction: TypeAlias = Callable[..., Any]
+# Http request-specific data (e.g., headers, auth info)
+RequestData = dict[str, Any]
 
 
 class RequestParams(BaseModel):

tests/server/fastmcp/test_integration.py

@@ -5,6 +5,7 @@
 including with and without authentication.
 """
 
+import json
 import multiprocessing
 import socket
 import time
@@ -13,13 +14,15 @@
 import pytest
 import uvicorn
 from pydantic import AnyUrl
+from starlette.applications import Starlette
 
 import mcp.types as types
 from mcp.client.session import ClientSession
 from mcp.client.sse import sse_client
 from mcp.client.streamable_http import streamablehttp_client
 from mcp.server.fastmcp import FastMCP
 from mcp.server.fastmcp.resources import FunctionResource
+from mcp.server.fastmcp.server import Context
 from mcp.shared.context import RequestContext
 from mcp.types import (
     CreateMessageRequestParams,
@@ -78,8 +81,6 @@ def stateless_http_server_url(stateless_http_server_port: int) -> str:
 # Create a function to make the FastMCP server app
 def make_fastmcp_app():
     """Create a FastMCP server without auth settings."""
-    from starlette.applications import Starlette
-
     mcp = FastMCP(name="NoAuthServer")
 
     # Add a simple tool
@@ -198,8 +199,6 @@ def complex_prompt(user_query: str, context: str = "general") -> str:
 
 def make_everything_fastmcp_app():
     """Create a comprehensive FastMCP server with SSE transport."""
-    from starlette.applications import Starlette
-
     mcp = make_everything_fastmcp()
     # Create the SSE app
     app: Starlette = mcp.sse_app()
@@ -208,7 +207,6 @@ def make_everything_fastmcp_app():
 
 def make_fastmcp_streamable_http_app():
     """Create a FastMCP server with StreamableHTTP transport."""
-    from starlette.applications import Starlette
 
     mcp = FastMCP(name="NoAuthServer")
 
@@ -225,8 +223,6 @@ def echo(message: str) -> str:
 
 def make_everything_fastmcp_streamable_http_app():
     """Create a comprehensive FastMCP server with StreamableHTTP transport."""
-    from starlette.applications import Starlette
-
     # Create a new instance with different name for HTTP transport
     mcp = make_everything_fastmcp()
     # We can't change the name after creation, so we'll use the same name
@@ -237,7 +233,6 @@ def make_everything_fastmcp_streamable_http_app():
 
 def make_fastmcp_stateless_http_app():
     """Create a FastMCP server with stateless StreamableHTTP transport."""
-    from starlette.applications import Starlette
 
     mcp = FastMCP(name="StatelessServer", stateless_http=True)
 
@@ -435,6 +430,181 @@ async def test_fastmcp_without_auth(server: None, server_url: str) -> None:
             assert tool_result.content[0].text == "Echo: hello"
 
 
+def make_fastmcp_with_context_app():
+    """Create a FastMCP server that can access request context."""
+
+    mcp = FastMCP(name="ContextServer")
+
+    # Tool that echoes request headers
+    @mcp.tool(description="Echo request headers from context")
+    def echo_headers(ctx: Context) -> str:
+        """Returns the request headers as JSON."""
+        headers_info = {}
+        try:
+            if ctx.request_context.request:
+                headers_info = ctx.request_context.request.get("headers", {})
+        except Exception:
+            pass
+        return json.dumps(headers_info)
+
+    # Tool that returns full request context
+    @mcp.tool(description="Echo request context with custom data")
+    def echo_context(custom_request_id: str, ctx: Context) -> str:
+        """Returns request context including headers and custom data."""
+        context_data = {
+            "custom_request_id": custom_request_id,
+            "headers": {},
+            "method": None,
+            "url": None,
+        }
+        try:
+            if ctx.request_context.request:
+                context_data["headers"] = ctx.request_context.request.get("headers", {})
+                context_data["method"] = ctx.request_context.request.get("method")
+                context_data["url"] = ctx.request_context.request.get("url")
+        except Exception:
+            pass
+        return json.dumps(context_data)
+
+    # Create the SSE app
+    app: Starlette = mcp.sse_app()
+    return mcp, app
+
+
+def run_context_server(server_port: int) -> None:
+    """Run the context-aware FastMCP server."""
+    _, app = make_fastmcp_with_context_app()
+    server = uvicorn.Server(
+        config=uvicorn.Config(
+            app=app, host="127.0.0.1", port=server_port, log_level="error"
+        )
+    )
+    print(f"Starting context server on port {server_port}")
+    server.run()
+
+
+@pytest.fixture()
+def context_aware_server(server_port: int) -> Generator[None, None, None]:
+    """Start the context-aware server in a separate process."""
+    proc = multiprocessing.Process(
+        target=run_context_server, args=(server_port,), daemon=True
+    )
+    print("Starting context-aware server process")
+    proc.start()
+
+    # Wait for server to be running
+    max_attempts = 20
+    attempt = 0
+    print("Waiting for context-aware server to start")
+    while attempt < max_attempts:
+        try:
+            with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
+                s.connect(("127.0.0.1", server_port))
+                break
+        except ConnectionRefusedError:
+            time.sleep(0.1)
+            attempt += 1
+    else:
+        raise RuntimeError(
+            f"Context server failed to start after {max_attempts} attempts"
+        )
+
+    yield
+
+    print("Killing context-aware server")
+    proc.kill()
+    proc.join(timeout=2)
+    if proc.is_alive():
+        print("Context server process failed to terminate")
+
+
+@pytest.mark.anyio
+async def test_fast_mcp_with_request_context(
+    context_aware_server: None, server_url: str
+) -> None:
+    """Test that FastMCP properly propagates request context to tools."""
+    # Test with custom headers
+    custom_headers = {
+        "Authorization": "Bearer fastmcp-test-token",
+        "X-Custom-Header": "fastmcp-value",
+        "X-Request-Id": "req-123",
+    }
+
+    async with sse_client(server_url + "/sse", headers=custom_headers) as streams:
+        async with ClientSession(*streams) as session:
+            # Initialize the session
+            result = await session.initialize()
+            assert isinstance(result, InitializeResult)
+            assert result.serverInfo.name == "ContextServer"
+
+            # Test 1: Call tool that echoes headers
+            headers_result = await session.call_tool("echo_headers", {})
+            assert len(headers_result.content) == 1
+            assert isinstance(headers_result.content[0], TextContent)
+
+            headers_data = json.loads(headers_result.content[0].text)
+            assert headers_data.get("authorization") == "Bearer fastmcp-test-token"
+            assert headers_data.get("x-custom-header") == "fastmcp-value"
+            assert headers_data.get("x-request-id") == "req-123"
+
+            # Test 2: Call tool that returns full context
+            context_result = await session.call_tool(
+                "echo_context", {"custom_request_id": "test-123"}
+            )
+            assert len(context_result.content) == 1
+            assert isinstance(context_result.content[0], TextContent)
+
+            context_data = json.loads(context_result.content[0].text)
+            assert context_data["custom_request_id"] == "test-123"
+            assert (
+                context_data["headers"].get("authorization")
+                == "Bearer fastmcp-test-token"
+            )
+            assert context_data["method"] == "POST"  # SSE messages are POSTed
+            assert (
+                "/messages/" in context_data["url"]
+            )  # Should contain the messages endpoint
+
+
+@pytest.mark.anyio
+async def test_fast_mcp_request_context_isolation(
+    context_aware_server: None, server_url: str
+) -> None:
+    """Test that request contexts are isolated between different FastMCP clients."""
+    contexts = []
+
+    # Create multiple clients with different headers
+    for i in range(3):
+        headers = {
+            "Authorization": f"Bearer token-{i}",
+            "X-Request-Id": f"fastmcp-req-{i}",
+            "X-Custom-Value": f"value-{i}",
+        }
+
+        async with sse_client(server_url + "/sse", headers=headers) as streams:
+            async with ClientSession(*streams) as session:
+                await session.initialize()
+
+                # Call the tool that returns context
+                tool_result = await session.call_tool(
+                    "echo_context", {"custom_request_id": f"test-req-{i}"}
+                )
+
+                # Parse and store the result
+                assert len(tool_result.content) == 1
+                assert isinstance(tool_result.content[0], TextContent)
+                context_data = json.loads(tool_result.content[0].text)
+                contexts.append(context_data)
+
+    # Verify each request had its own isolated context
+    assert len(contexts) == 3
+    for i, ctx in enumerate(contexts):
+        assert ctx["custom_request_id"] == f"test-req-{i}"
+        assert ctx["headers"].get("authorization") == f"Bearer token-{i}"
+        assert ctx["headers"].get("x-request-id") == f"fastmcp-req-{i}"
+        assert ctx["headers"].get("x-custom-value") == f"value-{i}"
+
+
 @pytest.mark.anyio
 async def test_fastmcp_streamable_http(
     streamable_http_server: None, http_server_url: str