Infinitty Control

infinitty Control Socket

infinitty exposes one Unix socket per pane. Any script can read the live screen and type into the terminal — no screen-scraping, no ANSI parsing. Implementation: Sources/infinitty/ControlServer.swift.

Choosing an interface

Same engine, three front doors — use the highest one available:

1. MCP tools (infinitty_*) — if tools like infinitty_todos, infinitty_run, infinitty_screen, infinitty_send, infinitty_surface, infinitty_new_tab are loaded in the session, prefer them over raw sockets. Structured arguments (no shell quoting or hand-built JSON) and the cleanest transcript for the user. Registered by this repo's .mcp.json; the server binary ships at /Applications/Infinitty.app/Contents/MacOS/infinitty-mcp.
2. App socket — /tmp/infinitty-app-<pid>.sock (newest instance symlinked at /tmp/infinitty-current.sock, or $INFINITTY_APP_SOCKET when spawned by infinitty). Multi-pane commands take a pane id: list, run <id> <cmd>, todos <id> [json], surface <id> <json>, new-tab [dir], new-window [dir], split <id>, focus <id>, subscribe.
3. Pane socket — $INFINITTY_SOCKET, the id-less per-pane protocol below. Always available from inside a pane's shell; the fallback when MCP isn't loaded.

MCP tools map 1:1 onto socket commands (infinitty_todos ⇄ todos, infinitty_send ⇄ send/send-line, infinitty_run ⇄ run), so every recipe below works through either door. The wait-for-prompt rule applies to all three.

When running as an agent inside an Infinitty terminal, call infinitty_channel_self with action=context at the start of every user turn. Its result is authoritative for whether this pane is connected, your unique participant identity, Channel name, peers, roles, work, and recent messages. Use infinitty_channel_post for messages intended for those peers. Never infer membership from environment variables or supply an author/Channel ID: the pane socket binds both server-side.

MCP-owned registration lifetime is process-bound. Forced client termination is reaped by the host, and cleanup from an older MCP process cannot clear a newer registration in the same pane. Raw socket clients own their explicit channel-unregister lifecycle.

Socket discovery

• Inside the shell infinitty spawned: $INFINITTY_SOCKET (exported, mode 0600).
• From outside: /tmp/infinitty-<PID>-<N>.sock — PID is the infinitty process, N counts panes. ls /tmp/infinitty-*.sock and pick; ping each to find live ones.

Protocol

One command per connection. Send the command, newline-terminated; read the response until EOF (socket closes after the body). Responses always end with \n. Writes return ok; failures return a line starting with error:.

Bounded responses: every response is hard-capped at 256 KiB. Oversized bodies are truncated from the front and prefixed with a [truncated: showing last N bytes] line — page with history N instead of requesting everything. Connections have a 5s read/write deadline and each client is served on its own thread, so a stalled client cannot block others.

printf 'screen\n' | nc -U "$INFINITTY_SOCKET"

import socket
def infinitty(cmd, path):
    s = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
    s.connect(path)
    s.sendall(cmd.encode() + b"\n")
    data = b""
    while chunk := s.recv(65536):
        data += chunk
    s.close()
    return data.decode()

Commands

* Requires OSC 133 shell integration (below); otherwise returns error: no completed command (enable OSC 133 shell integration).

Gotchas:

• A newline in send text terminates the command — one line per connection; use send-line for return, multiple connections for multiple lines.
• Trailing whitespace on the request is trimmed; leading spaces after send are preserved.
• send/send-line write raw bytes to the PTY, so control bytes work — see ESC below.

The wait-for-prompt rule

Never sleep blindly. Always poll screen for the text that proves the terminal is ready (a prompt, an app's UI, expected output) before sending keys or reading results. Keys sent early go to the wrong program; exit-code/last-output read early return the previous command's values.

wait_for() {  # wait_for PATTERN [TIMEOUT_S]
  local t=${2:-10} start=$SECONDS
  until printf 'screen\n' | nc -U "$INFINITTY_SOCKET" | grep -q "$1"; do
    (( SECONDS - start >= t )) && return 1
    sleep 0.2
  done
}

Driving TUI apps (vim example)

Send keys with send, poll screen between steps. ESC and other control bytes go through printf escapes:

S="$INFINITTY_SOCKET"
printf 'send-line vim /tmp/demo.txt\n' | nc -U "$S"
wait_for 'demo.txt'                              # vim is up
printf 'send i\n' | nc -U "$S"                   # insert mode
printf 'send hello from infinitty\n' | nc -U "$S"
printf 'send \033\n' | nc -U "$S"                # raw ESC byte back to normal mode
printf 'send-line :wq\n' | nc -U "$S"
wait_for '%%'                                    # shell prompt is back

Same pattern for any TUI: htop (send q to quit), REPLs (send-line expressions, poll for the result), fzf, lazygit.

Automated test recipe

Launch, poll, assert on screen text and exit code, report PASS/FAIL:

#!/bin/zsh
S="$INFINITTY_SOCKET"
tt() { printf '%s\n' "$1" | nc -U "$S"; }
fail() { echo "FAIL: $1"; tt screen; exit 1 }

tt 'send-line ./myapp --version'
wait_for 'myapp 2\.' 10        || fail "version banner not shown"
wait_for '%%' 5                || fail "prompt did not return"
[[ $(tt exit-code) == 0 ]]     || fail "exit code $(tt exit-code)"
tt last-output | grep -q 2.1.0 || fail "wrong version in output"
echo PASS

Assert on screen for UI state, last-output for exact command output, exit-code for success — always after wait_for confirms the command finished (prompt visible again).

OSC 133 shell integration

last-output, last-command, and exit-code need semantic prompt markers. Enable once:

echo 'source /path/to/infinitty/shell-integration/infinitty.zsh' >> ~/.zshrc

infinitty tracks the markers (prompt start, input start, output start, exit) by absolute line number, so "the last command's output" is an exact O(1) lookup — not a heuristic. Without integration those three commands return error:; screen/history always work.

Background control (no focus stealing)

Socket commands (send, send-line, screen, run) write straight to the pty and read the cell grid — they NEVER require infinitty to be focused or frontmost. You can drive a pane while the user types in another app.

• Launch without stealing focus: open -g -a Infinitty or INFINITTY_NO_ACTIVATE=1.
• Agent-created panes (new-tab / new-window on the app socket) appear without taking keyboard focus. Only the explicit focus <pane> command brings a pane forward — use it only when the user asked to see it.
• toggle-quick-terminal shows or hides the persistent quick-terminal panel. It is intentionally user-visible; invoke it only when the user asks.

Rendered markdown

With markdown-render = auto in the config, a completed command whose output looks like markdown is auto-rendered through glow in place (guarded: skips interactive/alt-screen apps, non-markdown output, and anything large). Off by default; agents can rely on plain cmd | glow regardless.