chore: import upstream snapshot with attribution

tests/server/test_cancel_handling.py

@@ -0,0 +1,250 @@
+"""Test that cancelled requests don't cause double responses."""
+
+import anyio
+import pytest
+from mcp_types import (
+    CallToolRequest,
+    CallToolRequestParams,
+    CallToolResult,
+    CancelledNotification,
+    CancelledNotificationParams,
+    ClientCapabilities,
+    Implementation,
+    InitializeRequestParams,
+    JSONRPCNotification,
+    JSONRPCRequest,
+    ListToolsResult,
+    PaginatedRequestParams,
+    TextContent,
+    Tool,
+)
+from mcp_types.version import LATEST_HANDSHAKE_VERSION
+
+from mcp import Client
+from mcp.server import Server, ServerRequestContext
+from mcp.shared.exceptions import MCPError
+from mcp.shared.message import SessionMessage
+
+
+@pytest.mark.anyio
+async def test_server_remains_functional_after_cancel():
+    """Verify server can handle new requests after a cancellation."""
+
+    # Track tool calls
+    call_count = 0
+    ev_first_call = anyio.Event()
+    first_request_id = None
+
+    async def handle_list_tools(ctx: ServerRequestContext, params: PaginatedRequestParams | None) -> ListToolsResult:
+        return ListToolsResult(
+            tools=[
+                Tool(
+                    name="test_tool",
+                    description="Tool for testing",
+                    input_schema={"type": "object"},
+                )
+            ]
+        )
+
+    async def handle_call_tool(ctx: ServerRequestContext, params: CallToolRequestParams) -> CallToolResult:
+        nonlocal call_count, first_request_id
+        if params.name == "test_tool":
+            call_count += 1
+            if call_count == 1:
+                first_request_id = ctx.request_id
+                ev_first_call.set()
+                await anyio.sleep(5)  # First call is slow
+            return CallToolResult(content=[TextContent(type="text", text=f"Call number: {call_count}")])
+        raise ValueError(f"Unknown tool: {params.name}")  # pragma: no cover
+
+    server = Server("test-server", on_list_tools=handle_list_tools, on_call_tool=handle_call_tool)
+
+    async with Client(server, mode="legacy") as client:
+        # First request (will be cancelled)
+        async def first_request():
+            try:
+                await client.session.send_request(
+                    CallToolRequest(params=CallToolRequestParams(name="test_tool", arguments={})),
+                    CallToolResult,
+                )
+                pytest.fail("First request should have been cancelled")  # pragma: no cover
+            except MCPError:
+                pass  # Expected
+
+        # Start first request
+        async with anyio.create_task_group() as tg:
+            tg.start_soon(first_request)
+
+            # Wait for it to start
+            await ev_first_call.wait()
+
+            # Cancel it
+            assert first_request_id is not None
+            await client.session.send_notification(
+                CancelledNotification(
+                    params=CancelledNotificationParams(request_id=first_request_id, reason="Testing server recovery"),
+                )
+            )
+
+        # Second request (should work normally)
+        result = await client.call_tool("test_tool", {})
+
+        # Verify second request completed successfully
+        assert len(result.content) == 1
+        # Type narrowing for pyright
+        content = result.content[0]
+        assert content.type == "text"
+        assert isinstance(content, TextContent)
+        assert content.text == "Call number: 2"
+        assert call_count == 2
+
+
+@pytest.mark.anyio
+async def test_server_cancels_in_flight_handlers_on_transport_close():
+    """When the transport closes mid-request, server.run() must cancel in-flight
+    handlers rather than join on them.
+
+    Without the cancel, the task group waits for the handler, which then tries
+    to respond through a write stream that _receive_loop already closed,
+    raising ClosedResourceError and crashing server.run() with exit code 1.
+
+    This drives server.run() with raw memory streams because InMemoryTransport
+    wraps it in its own finally-cancel (_memory.py) which masks the bug.
+    """
+    handler_started = anyio.Event()
+    handler_cancelled = anyio.Event()
+    server_run_returned = anyio.Event()
+
+    async def handle_call_tool(ctx: ServerRequestContext, params: CallToolRequestParams) -> CallToolResult:
+        handler_started.set()
+        try:
+            await anyio.sleep_forever()
+        finally:
+            handler_cancelled.set()
+        # unreachable: sleep_forever only exits via cancellation
+        raise AssertionError  # pragma: no cover
+
+    server = Server("test", on_call_tool=handle_call_tool)
+
+    to_server, server_read = anyio.create_memory_object_stream[SessionMessage | Exception](10)
+    server_write, from_server = anyio.create_memory_object_stream[SessionMessage](10)
+
+    async def run_server():
+        await server.run(server_read, server_write, server.create_initialization_options())
+        server_run_returned.set()
+
+    init_req = JSONRPCRequest(
+        jsonrpc="2.0",
+        id=1,
+        method="initialize",
+        params=InitializeRequestParams(
+            protocol_version=LATEST_HANDSHAKE_VERSION,
+            capabilities=ClientCapabilities(),
+            client_info=Implementation(name="test", version="1.0"),
+        ).model_dump(by_alias=True, mode="json", exclude_none=True),
+    )
+    initialized = JSONRPCNotification(jsonrpc="2.0", method="notifications/initialized")
+    call_req = JSONRPCRequest(
+        jsonrpc="2.0",
+        id=2,
+        method="tools/call",
+        params=CallToolRequestParams(name="slow", arguments={}).model_dump(by_alias=True, mode="json"),
+    )
+
+    with anyio.fail_after(5):
+        async with anyio.create_task_group() as tg, to_server, server_read, server_write, from_server:
+            tg.start_soon(run_server)
+
+            await to_server.send(SessionMessage(init_req))
+            await from_server.receive()  # init response
+            await to_server.send(SessionMessage(initialized))
+            await to_server.send(SessionMessage(call_req))
+
+            await handler_started.wait()
+
+            # Close the server's input stream — this is what stdin EOF does.
+            # server.run()'s incoming_messages loop ends, finally-cancel fires,
+            # handler gets CancelledError, server.run() returns.
+            await to_server.aclose()
+
+            await server_run_returned.wait()
+
+    assert handler_cancelled.is_set()
+
+
+@pytest.mark.anyio
+async def test_server_handles_transport_close_with_pending_server_to_client_requests():
+    """When the transport closes while handlers are blocked on server→client
+    requests (sampling, roots, elicitation), server.run() must still exit cleanly.
+
+    Two bugs covered:
+      1. _receive_loop's finally iterates _response_streams with await checkpoints
+         inside; the woken handler's send_request finally pops from that dict
+         before the next __next__() — RuntimeError: dictionary changed size.
+      2. The woken handler's MCPError is caught in _handle_request, which falls
+         through to respond() against a write stream _receive_loop already closed.
+    """
+    handlers_started = 0
+    both_started = anyio.Event()
+    server_run_returned = anyio.Event()
+
+    async def handle_call_tool(ctx: ServerRequestContext, params: CallToolRequestParams) -> CallToolResult:
+        nonlocal handlers_started
+        handlers_started += 1
+        if handlers_started == 2:
+            both_started.set()
+        # Blocks on send_request waiting for a client response that never comes.
+        # _receive_loop's finally will wake this with CONNECTION_CLOSED.
+        await ctx.session.list_roots()  # pyright: ignore[reportDeprecated]
+        raise AssertionError  # pragma: no cover
+
+    server = Server("test", on_call_tool=handle_call_tool)
+
+    to_server, server_read = anyio.create_memory_object_stream[SessionMessage | Exception](10)
+    server_write, from_server = anyio.create_memory_object_stream[SessionMessage](10)
+
+    async def run_server():
+        await server.run(server_read, server_write, server.create_initialization_options())
+        server_run_returned.set()
+
+    init_req = JSONRPCRequest(
+        jsonrpc="2.0",
+        id=1,
+        method="initialize",
+        params=InitializeRequestParams(
+            protocol_version=LATEST_HANDSHAKE_VERSION,
+            capabilities=ClientCapabilities(),
+            client_info=Implementation(name="test", version="1.0"),
+        ).model_dump(by_alias=True, mode="json", exclude_none=True),
+    )
+    initialized = JSONRPCNotification(jsonrpc="2.0", method="notifications/initialized")
+
+    with anyio.fail_after(5):
+        async with anyio.create_task_group() as tg, to_server, server_read, server_write, from_server:
+            tg.start_soon(run_server)
+
+            await to_server.send(SessionMessage(init_req))
+            await from_server.receive()  # init response
+            await to_server.send(SessionMessage(initialized))
+
+            # Two tool calls → two handlers → two _response_streams entries.
+            for rid in (2, 3):
+                call_req = JSONRPCRequest(
+                    jsonrpc="2.0",
+                    id=rid,
+                    method="tools/call",
+                    params=CallToolRequestParams(name="t", arguments={}).model_dump(by_alias=True, mode="json"),
+                )
+                await to_server.send(SessionMessage(call_req))
+
+            await both_started.wait()
+            # Drain the two roots/list requests so send_request's _write_stream.send()
+            # completes and both handlers are parked at response_stream_reader.receive().
+            await from_server.receive()
+            await from_server.receive()
+
+            await to_server.aclose()
+
+            # Without the fixes: RuntimeError (dict mutation) or ClosedResourceError
+            # (respond after write-stream close) escapes run_server and this hangs.
+            await server_run_returned.wait()