max / makenotwork

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1	//! stdio MCP transport: newline-delimited JSON-RPC over stdin/stdout.
2	//!
3	//! This is the transport an MCP client like Claude Code uses when it launches
4	//! the server as a subprocess (`claude mcp add <name> -- <binary> --stdio`).
5	//! One JSON-RPC message per line in on stdin, one per line out on stdout.
6	//! Anything the process wants to log must go to stderr — stdout is the
7	//! protocol channel and any stray byte there corrupts the stream.
8	//!
9	//! Reuses the same [`dispatch`](super::dispatch) as the HTTP server, so both
10	//! transports expose an identical tool surface and capability gate.
11
12	use serde_json::Value;
13	use tokio::io::{AsyncBufReadExt, AsyncWriteExt, BufReader};
14
15	use super::ServeConfig;
16	use super::protocol::{JsonRpcResponse, codes};
17	use crate::error::Result;
18	use crate::tool::ToolRegistry;
19
20	/// Serve the registry over stdio until stdin reaches EOF (the client closed the
21	/// pipe). Blocks for the lifetime of the connection.
22	pub async fn serve(registry: ToolRegistry, config: ServeConfig) -> Result<()> {
23	let mut lines = BufReader::new(tokio::io::stdin()).lines();
24	let mut stdout = tokio::io::stdout();
25
26	while let Some(line) = lines.next_line().await? {
27	let line = line.trim();
28	if line.is_empty() {
29	continue;
30	}
31	let response = match serde_json::from_str(line) {
32	Ok(req) => {
33	// stdio has no session, so subscriptions and cancellation are
34	// unavailable here; the resource read surface still works.
35	super::dispatch(
36	&registry,
37	config.resources.as_ref(),
38	config.projection,
39	config.grants.as_ref(),
40	None,
41	req,
42	)
43	.await
44	}
45	Err(e) => Some(JsonRpcResponse::err(
46	Value::Null,
47	codes::PARSE_ERROR,
48	e.to_string(),
49	)),
50	};
51	// Notifications (`dispatch` returned `None`) carry no reply.
52	if let Some(response) = response {
53	let mut buf = serde_json::to_vec(&response)?;
54	buf.push(b'\n');
55	stdout.write_all(&buf).await?;
56	stdout.flush().await?;
57	}
58	}
59	Ok(())
60	}
61