SurfSense/surfsense_local/backend/modules/plugins/remote/mcp_client/session.py

"""A plugin's MCP server, listed through the official SDK's client over its transport.

SurfSense lists a plugin's tools itself, to connect it and to notice tools that change;
the agent's opencode calls them with its own client. Each listing opens its own SDK
client: the SDK's tasks must close in the task that opened them.
"""

from collections.abc import AsyncIterator, Awaitable, Callable
from contextlib import asynccontextmanager

import httpx2
from mcp.client.client import Client
from mcp.client.sse import sse_client
from mcp.client.streamable_http import streamable_http_client
from mcp.shared.exceptions import MCPError

from modules.plugins.remote.mcp_client.http_failure import refused, unreachable
from modules.plugins.remote.mcp_client.remote_tool import RemoteTool
from modules.plugins.remote.mcp_client.retries import retried
from modules.plugins.remote.mcp_client.scope_challenge import challenged_scopes
from modules.plugins.remote.mcp_client.sdk_errors import translated
from modules.plugins.remote.mcp_client.session_expired import SessionExpiredError
from modules.plugins.remote.mcp_client.transports import (
    SSE,
    STREAMABLE_HTTP,
    Transport,
)
from modules.plugins.remote.mcp_client.unwrapped import unwrapped


class McpSession:
    def __init__(
        self,
        url: str,
        headers: dict[str, str] | None = None,
        transport: Transport = STREAMABLE_HTTP,
    ) -> None:
        self._url = url
        self._headers = headers or {}
        self._transport = transport

    async def list_tools(self) -> list[RemoteTool]:
        return await retried(self._list_in_fresh_session)

    async def close(self) -> None:
        """Nothing stays open between listings."""

    async def _list_in_fresh_session(self) -> list[RemoteTool]:
        """List once more on a new session if the server forgot ours: it handled nothing."""
        try:
            return await self._list()
        except SessionExpiredError:
            return await self._list()

    async def _list(self) -> list[RemoteTool]:
        failed_status: list[int] = []
        reasons: list[str | None] = []
        scopes: list[list[str] | None] = []

        async def record_failure(response: httpx2.Response) -> None:
            if response.status_code >= 400:
                failed_status.append(response.status_code)
                reasons.append(await _refusal_reason(response))
                scopes.append(challenged_scopes(response))

        try:
            async with self._client(record_failure) as client:
                return await _every_page(client)
        except (MCPError, httpx2.TransportError, BaseExceptionGroup) as raised:
            error = unwrapped(raised)
            if isinstance(error, MCPError):
                status = failed_status[-1] if failed_status else None
                reason = reasons[-1] if reasons else None
                asked = scopes[-1] if scopes else None
                raise translated(error, status, reason, asked) from error
            if isinstance(error, httpx2.TransportError):
                raise unreachable(error) from error
            if isinstance(error, httpx2.HTTPStatusError):
                raise _stream_refused(error, reasons, scopes) from error
            raise
        except httpx2.HTTPStatusError as error:
            raise _stream_refused(error, reasons, scopes) from error

    @asynccontextmanager
    async def _client(
        self, on_response: Callable[[httpx2.Response], Awaitable[None]]
    ) -> AsyncIterator[Client]:
        hooks = {"response": [on_response]}
        if self._transport == SSE:

            def http_client(
                headers=None, timeout=None, auth=None
            ) -> httpx2.AsyncClient:
                return httpx2.AsyncClient(
                    headers=headers, timeout=timeout, auth=auth, event_hooks=hooks
                )

            # The SDK refuses an `endpoint` event on another origin, so a server cannot
            # point SurfSense at a host the user did not allow.
            transport = sse_client(
                self._url, headers=self._headers, httpx_client_factory=http_client
            )
            async with Client(transport) as client:
                yield client
            return
        async with (
            httpx2.AsyncClient(headers=self._headers, event_hooks=hooks) as http,
            Client(streamable_http_client(self._url, http_client=http)) as client,
        ):
            yield client


async def _refusal_reason(response: httpx2.Response) -> str | None:
    """A 401 or 403's `{"reason": ...}`, which SurfSense's plugin host sends; None otherwise."""
    if response.status_code not in (401, 403):
        return None
    await response.aread()
    try:
        reason = response.json().get("reason")
    except (ValueError, AttributeError):
        return None
    return reason if isinstance(reason, str) else None


async def _every_page(client: Client) -> list[RemoteTool]:
    tools: list[RemoteTool] = []
    cursor: str | None = None
    while True:
        page = await client.list_tools(cursor=cursor, cache_mode="bypass")
        tools += [
            RemoteTool.from_listing(tool.model_dump(by_alias=True, exclude_none=True))
            for tool in page.tools
        ]
        cursor = page.next_cursor
        if not cursor:
            return tools


def _stream_refused(
    error: httpx2.HTTPStatusError,
    reasons: list[str | None],
    scopes: list[list[str] | None],
) -> Exception:
    """The SSE client raises a refused stream as is: kept as the status it answered."""
    return refused(
        error.response.status_code,
        reasons[-1] if reasons else None,
        scopes[-1] if scopes else None,
    )