@modelcontextprotocol/sdk
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    Interface Transport

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

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

    Implemented by

    Index

    Properties

    onclose? onerror? onmessage? sessionId? setProtocolVersion?

    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?: (message: JSONRPCMessage, extra?: MessageExtraInfo) => void

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

    Includes the requestInfo and authInfo if the transport is authenticated.

    The requestInfo 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).

    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, Server, or Protocol classes, as they will implicitly call start().

      Returns Promise<void>

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