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llmx/codex-rs/mcp-server/src/lib.rs

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//! Prototype MCP server.
#![deny(clippy::print_stdout, clippy::print_stderr)]
use std::io::Result as IoResult;
use mcp_types::JSONRPCMessage;
use tokio::io::AsyncBufReadExt;
use tokio::io::AsyncWriteExt;
use tokio::io::BufReader;
use tokio::io::{self};
use tokio::sync::mpsc;
use tracing::debug;
use tracing::error;
use tracing::info;
mod codex_tool_config;
mod codex_tool_runner;
mod message_processor;
use crate::message_processor::MessageProcessor;
/// Size of the bounded channels used to communicate between tasks. The value
/// is a balance between throughput and memory usage 128 messages should be
/// plenty for an interactive CLI.
const CHANNEL_CAPACITY: usize = 128;
pub async fn run_main() -> IoResult<()> {
// Install a simple subscriber so `tracing` output is visible. Users can
// control the log level with `RUST_LOG`.
tracing_subscriber::fmt()
.with_writer(std::io::stderr)
.init();
// Set up channels.
let (incoming_tx, mut incoming_rx) = mpsc::channel::<JSONRPCMessage>(CHANNEL_CAPACITY);
let (outgoing_tx, mut outgoing_rx) = mpsc::channel::<JSONRPCMessage>(CHANNEL_CAPACITY);
// Task: read from stdin, push to `incoming_tx`.
let stdin_reader_handle = tokio::spawn({
let incoming_tx = incoming_tx.clone();
async move {
let stdin = io::stdin();
let reader = BufReader::new(stdin);
let mut lines = reader.lines();
while let Some(line) = lines.next_line().await.unwrap_or_default() {
match serde_json::from_str::<JSONRPCMessage>(&line) {
Ok(msg) => {
if incoming_tx.send(msg).await.is_err() {
// Receiver gone nothing left to do.
break;
}
}
Err(e) => error!("Failed to deserialize JSONRPCMessage: {e}"),
}
}
debug!("stdin reader finished (EOF)");
}
});
// Task: process incoming messages.
let processor_handle = tokio::spawn({
let mut processor = MessageProcessor::new(outgoing_tx.clone());
async move {
while let Some(msg) = incoming_rx.recv().await {
match msg {
JSONRPCMessage::Request(r) => processor.process_request(r),
JSONRPCMessage::Response(r) => processor.process_response(r),
JSONRPCMessage::Notification(n) => processor.process_notification(n),
JSONRPCMessage::BatchRequest(b) => processor.process_batch_request(b),
JSONRPCMessage::Error(e) => processor.process_error(e),
JSONRPCMessage::BatchResponse(b) => processor.process_batch_response(b),
}
}
info!("processor task exited (channel closed)");
}
});
// Task: write outgoing messages to stdout.
let stdout_writer_handle = tokio::spawn(async move {
let mut stdout = io::stdout();
while let Some(msg) = outgoing_rx.recv().await {
match serde_json::to_string(&msg) {
Ok(json) => {
if let Err(e) = stdout.write_all(json.as_bytes()).await {
error!("Failed to write to stdout: {e}");
break;
}
if let Err(e) = stdout.write_all(b"\n").await {
error!("Failed to write newline to stdout: {e}");
break;
}
if let Err(e) = stdout.flush().await {
error!("Failed to flush stdout: {e}");
break;
}
}
Err(e) => error!("Failed to serialize JSONRPCMessage: {e}"),
}
}
info!("stdout writer exited (channel closed)");
});
// Wait for all tasks to finish. The typical exit path is the stdin reader
// hitting EOF which, once it drops `incoming_tx`, propagates shutdown to
// the processor and then to the stdout task.
let _ = tokio::join!(stdin_reader_handle, processor_handle, stdout_writer_handle);
Ok(())
}