mcp-omnienv-nix

#!/usr/bin/env python3 """mcp-omnienv-nix: MCP server for Nix-backed polyglot ephemeral envs.""" from __future__ import annotations import json import re import subprocess from dataclasses import dataclass from typing import Iterable, List from fastmcp import FastMCP mcp = FastMCP("mcp-omnienv-nix") @dataclass(frozen=True) class LanguageProfile: label: str base_packages: List[str] SUPPORTED_LANGUAGES: dict[str, LanguageProfile] = { # Interpreted runtimes where we can build an env via withPackages. "python": LanguageProfile(label="Python 3.13", base_packages=["python313"]), "ruby": LanguageProfile(label="Ruby 3.3", base_packages=["ruby_3_3"]), "r": LanguageProfile(label="R", base_packages=["R"]), "lua": LanguageProfile(label="Lua 5.4", base_packages=["lua5_4"]), } _PACKAGE_RE = re.compile(r"^[a-zA-Z0-9+_.-]+$") def _validate_packages(pkgs: Iterable[str]) -> list[str]: validated: list[str] = [] for pkg in pkgs: pkg = pkg.strip() if not pkg: continue if not _PACKAGE_RE.match(pkg): raise ValueError(f"Invalid package name: {pkg}") validated.append(pkg) return validated def _nix_shell_command(lang: str, packages: list[str], command: str) -> list[str]: if lang not in SUPPORTED_LANGUAGES: raise ValueError(f"Unsupported language '{lang}'. Supported: {', '.join(SUPPORTED_LANGUAGES)}") profile = SUPPORTED_LANGUAGES[lang] # Import nixpkgs via flake to avoid relying on NIX_PATH. pkgs_expr = 'import (builtins.getFlake "nixpkgs") {}' if lang == "python": extra_expr = " ".join([f"ps.{p}" for p in packages]) expr = ( f"let pkgs = {pkgs_expr}; in pkgs.{profile.base_packages[0]}.withPackages (ps: [ {extra_expr} ])" ) elif lang == "ruby": extras = " ".join([f"ps.{p}" for p in packages]) expr = f"let pkgs = {pkgs_expr}; in pkgs.{profile.base_packages[0]}.withPackages (ps: [ {extras} ])" elif lang == "r": extras = " ".join([f"ps.{p}" for p in packages]) expr = f"let pkgs = {pkgs_expr}; in pkgs.rWrapper.override {{ packages = ps: [ {extras} ]; }}" elif lang == "lua": extras = " ".join([f"ps.{p}" for p in packages]) expr = f"let pkgs = {pkgs_expr}; in pkgs.lua5_4.withPackages (ps: [ {extras} ])" else: # Should not happen because of the guard above. raise ValueError(f"Unsupported language '{lang}'") return [ "nix", "shell", "--extra-experimental-features", "nix-command flakes", "--impure", "--expr", expr, "--command", "bash", "-lc", command, ] def _run(cmd: list[str], timeout: int = 120) -> dict[str, str | int]: proc = subprocess.run( cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True, timeout=timeout, ) return { "exit_code": proc.returncode, "stdout": proc.stdout, "stderr": proc.stderr, } @mcp.tool() def list_languages() -> str: """List supported languages and their base Nix packages.""" lines = [] for key, profile in SUPPORTED_LANGUAGES.items(): base = ", ".join(profile.base_packages) lines.append(f"- {key}: {profile.label} (base: {base})") return "\n".join(lines) def run_in_env_impl( language: str, command: str, extra_packages: list[str] | None = None, timeout_seconds: int = 120 ) -> str: """Run a shell command in a disposable Nix shell for the chosen language.""" extras = _validate_packages(extra_packages or []) cmd = _nix_shell_command(language.lower(), extras, command) result = _run(cmd, timeout=timeout_seconds) return json.dumps(result, indent=2) # Expose as MCP tool while keeping a plain callable for tests and reuse. run_in_env = mcp.tool()(run_in_env_impl) def main() -> None: mcp.run() if __name__ == "__main__": main()