MCP TypeScript SDK (V2)
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    Interface Transport

    Describes the minimal contract for an MCP transport that a client or server can communicate over.

    interface Transport {
        onclose?: () => void;
        onerror?: (error: Error) => void;
        onmessage?: <T extends JSONRPCMessage>(
            message: T,
            extra?: MessageExtraInfo,
        ) => void;
        sessionId?: string;
        setProtocolVersion?: (version: string) => void;
        setSupportedProtocolVersions?: (versions: string[]) => void;
        close(): Promise<void>;
        send(
            message: JSONRPCMessage,
            options?: TransportSendOptions,
        ): Promise<void>;
        start(): Promise<void>;
    }

    Implemented by

    Index

    Properties

    onclose? onerror? onmessage? sessionId? setProtocolVersion? setSupportedProtocolVersions?

    Methods

    close send start

    Properties

    onclose?: () => void

    Callback for when the connection is closed for any reason.

    This should be invoked when close() is called as well.

    onerror?: (error: Error) => void

    Callback for when an error occurs.

    Note that errors are not necessarily fatal; they are used for reporting any kind of exceptional condition out of band.

    onmessage?: <T extends JSONRPCMessage>(
        message: T,
        extra?: MessageExtraInfo,
    ) => void

    Callback for when a message (request or response) is received over the connection.

    Includes the request and authInfo if the transport is authenticated.

    The request can be used to get the original request information (headers, etc.)

    sessionId?: string

    The session ID generated for this connection.

    setProtocolVersion?: (version: string) => void

    Sets the protocol version used for the connection (called when the initialize response is received).

    setSupportedProtocolVersions?: (versions: string[]) => void

    Sets the supported protocol versions for header validation (called during connect). This allows the server to pass its supported versions to the transport.

    Methods

    • Starts processing messages on the transport, including any connection steps that might need to be taken.

      This method should only be called after callbacks are installed, or else messages may be lost.

      NOTE: This method should not be called explicitly when using Client or Server classes, as they will implicitly call start().

      Returns Promise<void>

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