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Maja Wichrowska 119a547a31 Prevent idle Windows MCP pipes from blocking unrelated I/O (#59726 )

## Why

Idle reads from local MCP servers on Windows can occupy Tokio's blocking threads and delay unrelated filesystem operations.

## What changed

Use IOCP-backed named pipes for local MCP server stdin, stdout, and stderr on Windows. Connect child endpoints before launch, restrict pipe access to the owner and SYSTEM, and reject remote clients. Preserve the shared legacy and modern protocol framing.

## Testing

Add Windows regression tests to verify that idle MCP reads leave blocking I/O available in both protocol modes and that child output handles support querying the pipe mode.

GitOrigin-RevId: ca39b940a54427a2cd7bab5291011b0b09143b3f

2026-11-05 19:46:31 +00:00

src

Prevent idle Windows MCP pipes from blocking unrelated I/O (#59726 )

2026-11-05 19:46:31 +00:00

tests

Use descriptor-safe helpers for executable test fixtures (#50018 )

2026-10-01 15:57:03 +00:00

BUILD.bazel

…

Cargo.toml

Use descriptor-safe helpers for executable test fixtures (#50018 )

2026-10-01 15:57:03 +00:00

README.md

Prefer just test over cargo test in docs (#23910 )

2026-05-22 16:58:14 +00:00

README.md

codex-utils-pty

Lightweight helpers for spawning interactive processes either under a PTY (pseudo terminal) or regular pipes. The public API is minimal and mirrors both backends so callers can switch based on their needs (e.g., enabling or disabling TTY).

API surface

spawn_pty_process(program, args, cwd, env, arg0, size) → SpawnedProcess
spawn_pipe_process(program, args, cwd, env, arg0) → SpawnedProcess
spawn_pipe_process_no_stdin(program, args, cwd, env, arg0) → SpawnedProcess
combine_output_receivers(stdout_rx, stderr_rx) → broadcast::Receiver<Vec<u8>>
conpty_supported() → bool (Windows only; always true elsewhere)
TerminalSize { rows, cols } selects PTY dimensions in character cells.
ProcessHandle exposes:
- writer_sender() → mpsc::Sender<Vec<u8>> (stdin)
- resize(TerminalSize)
- close_stdin()
- has_exited(), exit_code(), terminate()
SpawnedProcess bundles session, stdout_rx, stderr_rx, and exit_rx (oneshot exit code).

Usage examples

use std::collections::HashMap;
use std::path::Path;
use codex_utils_pty::combine_output_receivers;
use codex_utils_pty::spawn_pty_process;
use codex_utils_pty::TerminalSize;

# tokio_test::block_on(async {
let env_map: HashMap<String, String> = std::env::vars().collect();
let spawned = spawn_pty_process(
    "bash",
    &["-lc".into(), "echo hello".into()],
    Path::new("."),
    &env_map,
    &None,
    TerminalSize::default(),
).await?;

let writer = spawned.session.writer_sender();
writer.send(b"exit\n".to_vec()).await?;

// Collect output until the process exits.
let mut output_rx = combine_output_receivers(spawned.stdout_rx, spawned.stderr_rx);
let mut collected = Vec::new();
while let Ok(chunk) = output_rx.try_recv() {
    collected.extend_from_slice(&chunk);
}
let exit_code = spawned.exit_rx.await.unwrap_or(-1);
# let _ = (collected, exit_code);
# anyhow::Ok(())
# });

Swap in spawn_pipe_process for a non-TTY subprocess; the rest of the API stays the same. Use spawn_pipe_process_no_stdin to force stdin closed (commands that read stdin will see EOF immediately).

Tests

Unit tests live in src/lib.rs and cover both backends (PTY Python REPL and pipe-based stdin roundtrip). Run with:

just test -p codex-utils-pty --no-capture