67 lines
2.5 KiB
Python
67 lines
2.5 KiB
Python
"""Proxy ``FastMCP`` servers for user-declared external MCPs (``stdio``/``http``).
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Both flavours end up as a ``FastMCPProxy`` instance, built via
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``fastmcp.server.create_proxy``. The proxy lazily opens the underlying
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client transport when the first MCP request arrives, so we don't pay
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for connections that nothing routes to. From the aggregator app's
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point of view a proxy is indistinguishable from a regular ``FastMCP``
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namespace — same ``http_app`` surface, same mount semantics.
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"""
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from __future__ import annotations
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from typing import TYPE_CHECKING
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from fastmcp import Client
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from fastmcp.client.transports import StdioTransport, StreamableHttpTransport
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from fastmcp.server import create_proxy
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from beaver_gateway.mcp.lenient import LenientStdioTransport
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if TYPE_CHECKING:
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from fastmcp import FastMCP
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from fastmcp.client.transports.base import ClientTransport
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from beaver_gateway.mcp.types import HttpMcp, StdioMcp
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def build_stdio_proxy(spec: StdioMcp) -> FastMCP:
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"""Wrap a stdio subprocess MCP into a mountable ``FastMCPProxy``.
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``spec.command`` is a non-empty tuple; the first element is the
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executable and the rest are CLI args. ``StdioTransport`` keeps the
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subprocess alive across calls. When ``spec.lenient`` is set we
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swap in :class:`LenientStdioTransport`, which silently drops
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non-JSON-RPC stdout lines instead of forwarding them as exceptions
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(lets us ingest MCPs that print ``Processing...`` chatter on stdout
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without leaking warnings to downstream UIs).
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"""
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if not spec.command:
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msg = f"stdio MCP {spec.name!r} has empty command"
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raise ValueError(msg)
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command, *args = spec.command
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cwd = str(spec.cwd) if spec.cwd is not None else None
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transport: ClientTransport
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if spec.lenient:
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transport = LenientStdioTransport(
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command=command, args=list(args), env=spec.env, cwd=cwd
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)
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else:
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transport = StdioTransport(
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command=command, args=list(args), env=spec.env, cwd=cwd
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)
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return create_proxy(Client(transport, name=spec.name))
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def build_http_proxy(spec: HttpMcp) -> FastMCP:
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"""Wrap a remote streamable-HTTP MCP into a mountable ``FastMCPProxy``.
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``spec.headers`` are folded into the upstream client; pass per-call
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auth (e.g. ``X-Api-Key``) here rather than as ``auth`` when the
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upstream rejects Bearer headers.
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"""
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transport = StreamableHttpTransport(
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url=spec.url, auth=spec.auth, headers=spec.headers
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)
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return create_proxy(Client(transport, name=spec.name))
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