Filesystem MCP Server

Instructions

Implementation Reference

• src/mcp-server/tools/readFile/readFileLogic.ts:31-56 (handler)

  Core handler function that resolves the file path using serverState.resolvePath and reads the file content with comprehensive error handling for not found, directories, and I/O errors.

  export const readFileLogic = async (input: ReadFileInput, context: RequestContext): Promise<ReadFileOutput> => {
    const { path: requestedPath } = input;
  
    // Resolve the path using serverState (handles relative/absolute logic and sanitization)
    // This will throw McpError if a relative path is given without a default set.
    const absolutePath = serverState.resolvePath(requestedPath, context);
  
    try {
      // Read the file content using the resolved absolute path
      const content = await fs.readFile(absolutePath, 'utf8');
      return { content };
    } catch (error: any) {
      // Handle specific file system errors
      // Handle specific file system errors using the resolved absolutePath in messages
      if (error.code === 'ENOENT') {
        // Use NOT_FOUND error code
        throw new McpError(BaseErrorCode.NOT_FOUND, `File not found at resolved path: ${absolutePath}`, { ...context, requestedPath, resolvedPath: absolutePath, originalError: error });
      }
      if (error.code === 'EISDIR') {
         // Use VALIDATION_ERROR
         throw new McpError(BaseErrorCode.VALIDATION_ERROR, `Resolved path is a directory, not a file: ${absolutePath}`, { ...context, requestedPath, resolvedPath: absolutePath, originalError: error });
      }
      // Handle other potential I/O errors using INTERNAL_ERROR
      throw new McpError(BaseErrorCode.INTERNAL_ERROR, `Failed to read file: ${error.message || 'Unknown I/O error'}`, { ...context, originalError: error });
    }
  };

• src/mcp-server/tools/readFile/readFileLogic.ts:10-21 (schema)

  Zod input schema for read_file tool parameters, TypeScript input/output types.

  export const ReadFileInputSchema = z.object({
    path: z.string().min(1, 'Path cannot be empty')
      .describe('The path to the file to read. Can be relative or absolute. If relative, it resolves against the path set by `set_filesystem_default`. If absolute, it is used directly. If relative and no default is set, an error occurs.'),
  });
  
  // Define the TypeScript type for the input
  export type ReadFileInput = z.infer<typeof ReadFileInputSchema>;
  
  // Define the TypeScript type for the output
  export interface ReadFileOutput {
    content: string;
  }

• src/mcp-server/tools/readFile/registration.ts:22-52 (registration)

  Registers the 'read_file' MCP tool with description, input schema shape, and async handler function that invokes readFileLogic and formats the MCP response.

  server.tool(
    'read_file', // Tool name
    'Reads the entire content of a specified file as UTF-8 text. Accepts relative or absolute paths. Relative paths are resolved against the session default set by `set_filesystem_default`.', // Updated Description
    ReadFileInputSchema.shape, // Pass the schema shape, not the object instance
    async (params, extra) => { // Correct handler signature: params and extra
      // Cast params to the correct type within the handler for type safety
      const typedParams = params as ReadFileInput;
      // Create a new context for this specific tool execution
      // We might potentially use `extra.requestId` if available and needed for tracing, but let's keep it simple for now.
      const callContext = requestContextService.createRequestContext({ operation: 'ReadFileToolExecution', parentId: registrationContext.requestId });
      logger.info(`Executing 'read_file' tool for path: ${typedParams.path}`, callContext);
  
      // ErrorHandler will catch McpErrors thrown by readFileLogic and format them
      const result = await ErrorHandler.tryCatch(
        () => readFileLogic(typedParams, callContext), // Use typedParams
        {
          operation: 'readFileLogic',
          context: callContext,
          input: typedParams, // Input is automatically sanitized by ErrorHandler for logging
          errorCode: BaseErrorCode.INTERNAL_ERROR // Default error if unexpected failure
        }
      );
  
      logger.info(`Successfully read file: ${typedParams.path}`, callContext); // Use typedParams
  
      // Format the successful response
      return {
        content: [{ type: 'text', text: result.content }],
      };
    }
  );

• src/mcp-server/server.ts:81-92 (registration)

  Calls registerReadFileTool(server) as part of the Promise.all for registering all filesystem tools during server initialization.

  const registrationPromises = [
    registerReadFileTool(server),
    registerSetFilesystemDefaultTool(server),
    registerWriteFileTool(server),
    registerUpdateFileTool(server),
    registerListFilesTool(server),
    registerDeleteFileTool(server),
    registerDeleteDirectoryTool(server),
    registerCreateDirectoryTool(server),
    registerMovePathTool(server),
    registerCopyPathTool(server)
  ];