test: interaction-model end-to-end suite with a requirements manifest (#2691)

tests/interaction/transports/test_stdio.py

@@ -0,0 +1,143 @@
+"""The stdio transport: one subprocess end-to-end test and one in-process framing test.
+
+Everything else in the suite runs in a single process; the subprocess test exists to prove the same
+client↔server round trip works over the stdio transport's real boundary (a child process whose
+stdin/stdout carry one newline-delimited JSON-RPC message per line). The server lives in
+`_stdio_server.py` and is launched via `python -m` so subprocess coverage measurement applies.
+
+The framing test drives `stdio_server` in-process by passing it injected text streams instead of the
+real stdin/stdout, so the raw lines the transport writes can be asserted directly without a process
+boundary.
+
+stdio is deliberately not a leg of the `connect`-fixture matrix: spawning a subprocess per test
+would be slow, and the matrix already proves transport-agnosticism over three in-process
+transports. Process-lifecycle edge cases (escalation to terminate/kill, parse errors) are covered by
+`tests/client/test_stdio.py` and stay deferred here.
+"""
+
+import io
+import json
+import os
+import sys
+import tempfile
+from pathlib import Path
+
+import anyio
+import pytest
+from inline_snapshot import snapshot
+
+from mcp.client.client import Client
+from mcp.client.stdio import StdioServerParameters, stdio_client
+from mcp.server.stdio import stdio_server
+from mcp.shared.message import SessionMessage
+from mcp.types import (
+    CallToolResult,
+    JSONRPCNotification,
+    JSONRPCRequest,
+    JSONRPCResponse,
+    LoggingMessageNotificationParams,
+    TextContent,
+)
+from mcp.types.jsonrpc import jsonrpc_message_adapter
+from tests.interaction._connect import initialize_body
+from tests.interaction._requirements import requirement
+from tests.interaction.transports import _stdio_server
+
+pytestmark = pytest.mark.anyio
+
+_REPO_ROOT = Path(__file__).parents[3]
+
+
+@requirement("transport:stdio")
+@requirement("transport:stdio:clean-shutdown")
+@requirement("transport:stdio:stderr-passthrough")
+async def test_tool_call_and_notification_round_trip_over_a_stdio_subprocess() -> None:
+    """A Client connected over stdio initializes, calls a tool with arguments, receives the
+    server's log notification before the call returns, and the server exits when the transport
+    closes its stdin."""
+    received: list[LoggingMessageNotificationParams] = []
+
+    async def collect(params: LoggingMessageNotificationParams) -> None:
+        received.append(params)
+
+    with tempfile.TemporaryFile(mode="w+") as errlog:
+        transport = stdio_client(
+            StdioServerParameters(
+                command=sys.executable,
+                args=["-m", _stdio_server.__name__],
+                cwd=str(_REPO_ROOT),
+                # stdio_client deliberately filters the inherited environment to a safe minimum,
+                # which drops the variables coverage.py's subprocess support uses; pass them through
+                # so the server module is measured. Empty when not running under coverage.
+                env={key: value for key, value in os.environ.items() if key.startswith("COVERAGE_")},
+            ),
+            errlog=errlog,
+        )
+
+        with anyio.fail_after(10):
+            async with Client(transport, logging_callback=collect) as client:
+                assert client.initialize_result.server_info.name == "stdio-echo"
+                result = await client.call_tool("echo", {"text": "across\nprocesses"})
+
+        errlog.seek(0)
+        captured_stderr = errlog.read()
+
+    assert result == snapshot(CallToolResult(content=[TextContent(text="across\nprocesses")]))
+    # stdio carries one ordered server→client stream, so the same notification-before-response
+    # guarantee holds here as for the in-memory transport.
+    assert received == snapshot(
+        [LoggingMessageNotificationParams(level="info", logger="echo", data="echoing across\nprocesses")]
+    )
+    # The server writes this line only after its run loop returns, which happens when stdin closes:
+    # seeing it proves the process exited on its own rather than via the transport's terminate
+    # escalation, without a timing-based assertion. The capture itself proves stderr passthrough:
+    # the transport routes the child's stderr to the caller's `errlog` without consuming it.
+    assert captured_stderr == snapshot("stdio-echo: clean exit\n")
+
+
+@requirement("transport:stdio:stream-purity")
+@requirement("transport:stdio:no-embedded-newlines")
+async def test_stdio_server_writes_one_jsonrpc_message_per_line() -> None:
+    """Everything `stdio_server` writes is a valid JSON-RPC message on its own line, and nothing else.
+
+    The transport's stdin/stdout parameters are public, so the test injects in-process text streams
+    instead of the real process handles and drives the read/write streams directly: a JSON-RPC line on
+    stdin is parsed and delivered, and every message sent on the write stream appears as exactly one
+    newline-terminated line whose payload newlines are JSON-escaped. This proves the transport's own
+    framing; it does not guard `sys.stdout` against handler code that prints to it directly (see the
+    divergence on `transport:stdio:stream-purity`).
+    """
+    captured = io.StringIO()
+    sent_line = json.dumps(initialize_body(request_id=1)) + "\n"
+
+    with anyio.fail_after(5):
+        async with (
+            stdio_server(stdin=anyio.wrap_file(io.StringIO(sent_line)), stdout=anyio.wrap_file(captured)) as (
+                read_stream,
+                write_stream,
+            ),
+            read_stream,
+            write_stream,
+        ):
+            received = await read_stream.receive()
+            assert isinstance(received, SessionMessage)
+            assert isinstance(received.message, JSONRPCRequest)
+            assert received.message.method == "initialize"
+
+            response = JSONRPCResponse(jsonrpc="2.0", id=1, result={"text": "line\nbreak"})
+            notification = JSONRPCNotification(
+                jsonrpc="2.0", method="notifications/message", params={"level": "info", "data": "two\nlines"}
+            )
+            await write_stream.send(SessionMessage(response))
+            await write_stream.send(SessionMessage(notification))
+
+    output = captured.getvalue()
+    assert output.endswith("\n")
+    lines = output.removesuffix("\n").split("\n")
+    assert len(lines) == 2
+    messages = [jsonrpc_message_adapter.validate_json(line) for line in lines]
+    assert [type(message).__name__ for message in messages] == snapshot(["JSONRPCResponse", "JSONRPCNotification"])
+    # The newline inside the payload is JSON-escaped on the wire, not a literal newline that would
+    # break the one-message-per-line framing.
+    assert r"line\nbreak" in lines[0]
+    assert r"two\nlines" in lines[1]