Max Isbey
98bd125ddd
The 2026-07-28 protocol did not work over stdio: subscriptions/listen was hard-refused, a legacy initialize arriving during an in-flight modern request was accepted and re-locked the connection, and a peer cancel produced a trailing "Request cancelled" frame. All three share one root cause: the connection's era was derived from which requests had completed instead of being decided once, in wire order, from how the client opened the connection. Replace serve_dual_era_loop and serve_loop with a single serve_stream driver that decides the era synchronously in the dispatcher's read loop, before the request body is spawned. initialize (or any envelope-less request) opens the legacy era, an enveloped request opens the modern era, server/discover is answered without pinning, and a stray leading notification opens nothing. A conflicting era claim on a committed connection is refused (-32022 or -32600) rather than silently switching. Cancel silence is structural: each request answers through a one-shot channel whose write target becomes a powerless void on a peer cancel, so there is no cancelled-check at any write site. The generic JSON-RPC dispatcher loses the code-0 cancel frame, the code-0 str(exc) catch-all, and the inline_methods knob, and documents that handlers are invoked synchronously in receive order with the returned awaitable as the body. Add a Posture enum (DUAL default, LEGACY_ONLY, MODERN_ONLY) on the Server and MCPServer constructors, honoured by the stream driver and the streamable-HTTP manager alike. Server.run(read, write) now stands alone, Server.lifespan() is a bound context manager, and serve_listener / newline_json_transport / close_subscriptions() give a straightforward path for custom transports. See docs/migration.md for the full list of observable changes.
MCP Simple Resource
A simple MCP server that exposes sample text files as resources.
Usage
Start the server using either stdio (default) or Streamable HTTP transport:
# Using stdio transport (default)
uv run mcp-simple-resource
# Using Streamable HTTP transport on custom port
uv run mcp-simple-resource --transport streamable-http --port 8000
The server exposes some basic text file resources that can be read by clients.
Example
Using the MCP client, you can retrieve resources like this using the STDIO transport:
import asyncio
from pydantic import AnyUrl
from mcp.client.session import ClientSession
from mcp.client.stdio import StdioServerParameters, stdio_client
async def main():
async with stdio_client(
StdioServerParameters(command="uv", args=["run", "mcp-simple-resource"])
) as (read, write):
async with ClientSession(read, write) as session:
await session.initialize()
# List available resources
resources = await session.list_resources()
print(resources)
# Get a specific resource
resource = await session.read_resource(AnyUrl("file:///greeting.txt"))
print(resource)
asyncio.run(main())