Method discover

src/mcp/client/session.py:438–474

Probe `server/discover` and adopt the result. Sends a single `server/discover` proposing the newest modern protocol version. On `UNSUPPORTED_PROTOCOL_VERSION` (-32022) the server's `supported` list is intersected with `MODERN_PROTOCOL_VERSIONS` and the probe is retri

(self)

        return await self._dispatcher.send_raw_request(data["method"], data.get("params"), opts)

    async def discover(self) -> types.DiscoverResult:
        """Probe `server/discover` and adopt the result.

        Sends a single `server/discover` proposing the newest modern protocol
        version. On `UNSUPPORTED_PROTOCOL_VERSION` (-32022) the server's
        `supported` list is intersected with `MODERN_PROTOCOL_VERSIONS` and the
        probe is retried once at the highest mutual version. Any other error —
        including `METHOD_NOT_FOUND` (-32601) and `REQUEST_TIMEOUT` (-32001) —
        propagates; the legacy `initialize()` fallback is the caller's policy.

        Raises:
            MCPError: The server rejected `server/discover`, the probe timed
                out, or the -32022 retry found no mutual version / failed again.
            RuntimeError: `adopt()` found no mutual version in the returned
                `supported_versions`.
        """
        if self._discover_result is not None:
            return self._discover_result

        try:
            raw = await self.send_discover(LATEST_MODERN_VERSION)
        except MCPError as e:
            if e.code != UNSUPPORTED_PROTOCOL_VERSION:
                raise
            try:
                data = types.UnsupportedProtocolVersionErrorData.model_validate(e.error.data)
            except ValidationError:
                raise e from None
            # ordered oldest→newest via MODERN_PROTOCOL_VERSIONS
            mutual = [v for v in MODERN_PROTOCOL_VERSIONS if v in data.supported]
            if not mutual:
                raise
            raw = await self.send_discover(mutual[-1])

        result = types.DiscoverResult.model_validate(raw)
        self.adopt(result)
        return result

    @property
    def initialize_result(self) -> types.InitializeResult | None: