Send Message to Extension

Instructions

Implementation Reference

• src/servers/mcp.ts:129-159 (registration)

  Registration of the 'skippr_send_to_extension' tool with the MCP server, defining input schema (extensionId, type, payload) and output schema (success, extensionId, message).

  // Extension communication tools
  mcpServer.registerTool(
    'skippr_send_to_extension',
    {
      title: 'Send Message to Extension',
      description: 'Sends a message to a specific browser extension by its ID',
      inputSchema: z.object({
        extensionId: z.string().describe('The extension ID to send the message to'),
        type: z.enum(['notification', 'command', 'data', 'status']).describe('Message type'),
        payload: z.any().describe('The message payload')
      }).shape,
      outputSchema: z.object({
        success: z.boolean(),
        extensionId: z.string(),
        message: z.string()
      }).shape
    },
    async (args) => {
      const message: z.infer<typeof ServerToClientMessageSchema> = {
        type: args.type,
        payload: args.payload
      };
      const success = sendToExtension(args.extensionId, message);
      const result = {
        success,
        extensionId: args.extensionId,
        message: success ? 'Message sent successfully' : 'Failed to send message (extension may be disconnected)'
      };
      return createStructuredResponse(result);
    }
  );

• src/servers/mcp.ts:146-158 (handler)

  Handler function that builds a ServerToClientMessage from args, calls sendToExtension(), and returns a structured response with success status.

  async (args) => {
    const message: z.infer<typeof ServerToClientMessageSchema> = {
      type: args.type,
      payload: args.payload
    };
    const success = sendToExtension(args.extensionId, message);
    const result = {
      success,
      extensionId: args.extensionId,
      message: success ? 'Message sent successfully' : 'Failed to send message (extension may be disconnected)'
    };
    return createStructuredResponse(result);
  }

• src/servers/websocket.ts:368-391 (helper)

  sendToExtension() helper function that looks up the extension's WebSocket connection from the clients map, adds timestamp/messageId, and sends the JSON message over the WebSocket.

  export function sendToExtension(extensionId: string, message: z.infer<typeof ServerToClientMessageSchema>): boolean {
    const client = clients.get(extensionId);
  
    if (!client) {
      return false;
    }
  
    if (client && client.ws.readyState === WebSocket.OPEN) {
      try {
        // Add timestamp and messageId if not present
        const serverMessage = {
          ...message,
          timestamp: message.timestamp ?? Date.now(),
          messageId: message.messageId ?? crypto.randomBytes(8).toString('hex')
        };
        client.ws.send(JSON.stringify(serverMessage));
        return true;
      } catch (error) {
        console.error(`[sendToExtension] Error sending message to extension ${extensionId}:`, error);
        return false;
      }
    }
    return false;
  }

• src/schemas/index.ts:131-165 (schema)

  ServerToClientMessageSchema - a discriminated union schema defining valid message types (notification, command, data, status, ping, pong) and their payloads, used to validate messages sent by the tool handler.

  export const ServerToClientMessageSchema = z.discriminatedUnion('type', [
    z.object({
      type: z.literal('notification'),
      payload: NotificationPayloadSchema,
      timestamp: z.number().optional(),
      messageId: z.string().optional(),
    }),
    z.object({
      type: z.literal('command'),
      payload: CommandPayloadSchema,
      timestamp: z.number().optional(),
      messageId: z.string().optional(),
    }),
    z.object({
      type: z.literal('data'),
      payload: DataPayloadSchema,
      timestamp: z.number().optional(),
      messageId: z.string().optional(),
    }),
    z.object({
      type: z.literal('status'),
      payload: StatusPayloadSchema,
      timestamp: z.number().optional(),
      messageId: z.string().optional(),
    }),
    z.object({
      type: z.literal('ping'),
      timestamp: z.number().optional(),
      messageId: z.string().optional(),
    }),
    z.object({
      type: z.literal('pong'),
      timestamp: z.number().optional(),
      messageId: z.string().optional(),
    }),