unsloth/studio/backend/core/inference/mcp_client.py

# SPDX-License-Identifier: AGPL-3.0-only
# Copyright 2026-present the Unsloth AI Inc. team. All rights reserved. See /studio/LICENSE.AGPL-3.0

from __future__ import annotations

import asyncio
import json
import os
import shlex
import sys
from typing import Any, Optional

from loggers import get_logger

logger = get_logger(__name__)

MCP_TOOL_PREFIX = "mcp__"

_oauth_token_store = None


def is_stdio(address: str) -> bool:
    """A non-HTTP address is a local stdio command, e.g.
    'npx -y @modelcontextprotocol/server-filesystem /path'."""
    return not address.strip().lower().startswith(("http://", "https://"))


def _split_windows_command_line(address: str) -> list[str]:
    """Parse a Windows command line using the same backslash/quote rules that
    subprocess.list2cmdline() writes. This keeps trailing backslashes before a
    closing quote from being doubled in the resulting argv."""
    parts: list[str] = []
    current: list[str] = []
    in_quotes = False
    backslashes = 0
    arg_started = False
    i = 0

    while i < len(address):
        ch = address[i]
        if ch == "\\":
            backslashes += 1
            i += 1
            continue
        if ch == '"':
            current.extend("\\" * (backslashes // 2))
            if backslashes % 2:
                current.append('"')
            else:
                in_quotes = not in_quotes
            arg_started = True
            backslashes = 0
            i += 1
            continue
        if ch.isspace() and not in_quotes:
            if backslashes:
                current.extend("\\" * backslashes)
                arg_started = True
                backslashes = 0
            if arg_started or current:
                parts.append("".join(current))
                current = []
                arg_started = False
            i += 1
            while i < len(address) and address[i].isspace():
                i += 1
            continue
        if backslashes:
            current.extend("\\" * backslashes)
            arg_started = True
            backslashes = 0
        current.append(ch)
        arg_started = True
        i += 1

    if backslashes:
        current.extend("\\" * backslashes)
        arg_started = True
    if in_quotes:
        raise ValueError("No closing quotation")
    if arg_started or current:
        parts.append("".join(current))
    return parts


def parse_stdio_command(address: str) -> list[str]:
    """Split a stdio command line into argv. Shared by route validation and the
    transport so both agree on quoting (notably Windows backslash paths)."""
    posix = sys.platform != "win32"
    if posix:
        return shlex.split(address, posix = posix)
    if address.lstrip().startswith("'"):
        raise ValueError("Single-quoted executables are not supported on Windows")
    return _split_windows_command_line(address)


def join_stdio_command(parts: list[str]) -> str:
    """Inverse of parse_stdio_command: join argv into a single command string
    that parse_stdio_command() splits back into ``parts`` on this platform.
    Config files (issue #5936) carry structured command + args; storage holds
    one string in the url field. Windows uses list2cmdline so spaced/backslash
    paths round-trip through the posix=False quote-strip; posix uses shlex."""
    if sys.platform == "win32":
        import subprocess
        return subprocess.list2cmdline(parts)
    return shlex.join(parts)


def stdio_mcp_enabled() -> bool:
    """stdio MCP servers spawn local processes as the backend user (bypassing the
    sandbox), so allowed only when the host is the user's own machine. The Tauri
    app sets UNSLOTH_STUDIO_ALLOW_STDIO_MCP=1; localhost/self-hosted users can opt
    in with the same var. Off for Colab and any network (0.0.0.0) bind."""
    return os.environ.get("UNSLOTH_STUDIO_ALLOW_STDIO_MCP") == "1"


# Probe timeouts for discovering a server's tool list. OAuth needs minutes for
# first-connect/expired-token browser sign-in; stdio allows for first-run
# package download (e.g. `npx -y ...`); HTTP fails fast.
_HTTP_PROBE_TIMEOUT = 8.0
_OAUTH_PROBE_TIMEOUT = 305.0
_STDIO_PROBE_TIMEOUT = 60.0


def probe_timeout(address: str, use_oauth: bool) -> float:
    if use_oauth:
        return _OAUTH_PROBE_TIMEOUT
    return _STDIO_PROBE_TIMEOUT if is_stdio(address) else _HTTP_PROBE_TIMEOUT


def parse_server_headers(server: dict) -> Optional[dict]:
    """Parsed headers_json. For stdio servers this dict is the process env
    instead of HTTP headers (see _client)."""
    raw = server.get("headers_json")
    if not raw:
        return None
    try:
        parsed = json.loads(raw)
    except (json.JSONDecodeError, ValueError):
        return None
    return parsed if isinstance(parsed, dict) else None


def _oauth_store():
    global _oauth_token_store
    if _oauth_token_store is None:
        from key_value.aio._utils.sanitization import AlwaysHashStrategy
        from key_value.aio.stores.filetree import FileTreeStore
        from utils.paths.storage_roots import ensure_dir, studio_root

        # Hash keys/collections — fastmcp uses raw URLs as keys, and FileTreeStore
        # would treat the "://" as nested directories.
        _oauth_token_store = FileTreeStore(
            data_directory = ensure_dir(studio_root() / "mcp-oauth-tokens"),
            key_sanitization_strategy = AlwaysHashStrategy(),
            collection_sanitization_strategy = AlwaysHashStrategy(),
        )
    return _oauth_token_store


async def clear_oauth_tokens_async(url: str) -> None:
    """Drop any persisted OAuth tokens for ``url``. fastmcp keys tokens by MCP
    URL, so on server delete / URL change / OAuth disable we must clear them, else
    re-registering the same URL reuses the old account's token. Best-effort: store
    / OAuth failures must not 500 the delete / update route."""
    try:
        from fastmcp.client.auth import OAuth
        auth = OAuth(mcp_url = url, token_storage = _oauth_store())
        await auth.token_storage_adapter.clear()
    except Exception as exc:  # noqa: BLE001
        # Cleanup is best-effort; the row delete still wins.
        logger.warning("Failed to clear OAuth tokens for %s: %s", url, exc)


def _client(
    url: str,
    headers: Optional[dict],
    use_oauth: bool = False,
):
    from fastmcp import Client

    if is_stdio(url):
        # Belt-and-suspenders: never spawn unless stdio is enabled on this host.
        if not stdio_mcp_enabled():
            raise PermissionError("stdio MCP servers are disabled on this host")
        from fastmcp.client.transports import StdioTransport

        parts = parse_stdio_command(url)
        if not parts:
            raise ValueError(f"Empty stdio command: {url!r}")
        # env vars ride the headers field (merged over the SDK default env).
        # keep_alive=False tears the subprocess down so a one-shot call leaves no orphan.
        return Client(
            StdioTransport(
                command = parts[0],
                args = parts[1:],
                env = headers or None,
                keep_alive = False,
            )
        )

    from fastmcp.client.transports import SSETransport, StreamableHttpTransport
    from fastmcp.mcp_config import infer_transport_type_from_url

    auth = None
    if use_oauth:
        from fastmcp.client.auth import OAuth
        auth = OAuth(mcp_url = url, token_storage = _oauth_store())

    transport_cls = (
        SSETransport if infer_transport_type_from_url(url) == "sse" else StreamableHttpTransport
    )
    return Client(transport_cls(url = url, headers = headers or None, auth = auth))


async def list_tools_async(
    url: str,
    headers: Optional[dict] = None,
    timeout: float = 5.0,
    use_oauth: bool = False,
) -> list[dict]:
    async def _fetch() -> list[dict]:
        async with _client(url, headers, use_oauth) as client:
            tools = await client.list_tools()
        return [t.model_dump(exclude_none = True) for t in tools]

    return await asyncio.wait_for(_fetch(), timeout = timeout)


def _flatten_result(result: Any) -> str:
    parts = []
    for block in getattr(result, "content", None) or []:
        text = getattr(block, "text", None)
        if text:
            parts.append(str(text))
    body = "\n".join(parts)
    if not body:
        structured = getattr(result, "structured_content", None)
        body = str(structured) if structured is not None else ""

    if getattr(result, "is_error", False):
        # "Error: " prefix triggers tool_call_parser's TOOL_ERROR_PREFIXES nudge.
        return f"Error: {body}" if body else "Error: tool returned no content"
    return body


def call_tool_sync(
    url: str,
    headers: Optional[dict],
    name: str,
    args: dict,
    timeout: Optional[float] = 300.0,
    use_oauth: bool = False,
    cancel_event = None,
) -> str:
    """Synchronously call an MCP tool.

    ``cancel_event``: optional ``threading.Event``. When set, the in-flight call is
    cancelled and a cancellation Error returned. Polled alongside the tool call via
    ``asyncio.wait`` so a /cancel POST interrupts even mid-network-read.
    """

    async def _call() -> Any:
        async with _client(url, headers, use_oauth) as client:
            return await client.call_tool(name, args)

    async def _watch_cancel() -> None:
        # 50 ms cadence keeps cancellation responsive without busy-looping;
        # matches routes/inference.py's cancel watcher cadence.
        while cancel_event is not None and not cancel_event.is_set():
            await asyncio.sleep(0.05)

    async def _race() -> Any:
        # Check cancellation before spawning the call task so a pre-set event
        # short-circuits before opening the transport / HTTP connection.
        if cancel_event is not None and cancel_event.is_set():
            raise _MCPCancelled
        call_task = asyncio.create_task(_call())
        if cancel_event is None:
            return await asyncio.wait_for(call_task, timeout = timeout)
        watch_task = asyncio.create_task(_watch_cancel())
        try:
            done, pending = await asyncio.wait(
                {call_task, watch_task},
                timeout = timeout,
                return_when = asyncio.FIRST_COMPLETED,
            )
        finally:
            for t in (call_task, watch_task):
                if not t.done():
                    t.cancel()
        if not done:
            raise asyncio.TimeoutError
        if call_task in done:
            return call_task.result()
        raise _MCPCancelled

    try:
        result = asyncio.run(_race())
    except _MCPCancelled:
        return f"Error: MCP tool '{name}' cancelled"
    except asyncio.TimeoutError:
        return f"Error: MCP tool '{name}' timed out after {timeout:g}s"
    except Exception as exc:
        logger.exception("MCP call_tool failed for %s: %s", name, exc)
        return f"Error: MCP tool '{name}' failed: {exc}"

    return _flatten_result(result)


class _MCPCancelled(Exception):
    """Internal sentinel raised when cancel_event fires before the tool returns."""