MCP Filesystem Server

Instructions

Implementation Reference

• src/utils/exec/index.ts:96-149 (handler)

  Primary handler function that performs command validation, executes the command using child_process.exec with timeout and cwd, captures stdout/stderr/exitCode, logs metrics.

  export async function executeCommand(
    args: z.infer<typeof ExecuteCommandArgsSchema>,
    _config: Config
  ): Promise<{ stdout: string; stderr: string; exitCode: number }> {
    const endMetric = metrics.startOperation('execute_command')
    try {
      await logger.debug(`Executing command: ${args.command}`, { args })
  
      // Validate the command for security
      validateCommand(args.command)
  
      // Set working directory or use current directory
      const options = {
        cwd: args.workingDir || process.cwd(),
        timeout: args.timeout,
        encoding: 'utf-8' as const,
      }
  
      try {
        // Execute the command
        const { stdout, stderr } = await exec(args.command, options)
        await logger.debug(`Command executed successfully: ${args.command}`, {
          stdout: stdout.substring(0, 100) + (stdout.length > 100 ? '...' : ''),
        })
  
        endMetric()
        return {
          stdout,
          stderr,
          exitCode: 0,
        }
      } catch (error: any) {
        // Handle command execution errors
        const stderr = error.stderr || ''
        const stdout = error.stdout || ''
        const exitCode = error.code || 1
  
        await logger.warn(`Command execution failed: ${args.command}`, {
          exitCode,
          stderr: stderr.substring(0, 100) + (stderr.length > 100 ? '...' : ''),
        })
  
        endMetric()
        return {
          stdout,
          stderr,
          exitCode,
        }
      }
    } catch (error) {
      metrics.recordError('execute_command')
      throw error
    }
  }

• src/utils/exec/index.ts:44-57 (schema)

  Zod schema defining the input parameters for the execute_command tool: command (required), workingDir (optional), timeout (optional, default 5000ms, max 30s), captureOutput (optional boolean).

   * Schema for execute_command arguments
   */
  export const ExecuteCommandArgsSchema = z.object({
    command: z.string().describe('The command to execute'),
    workingDir: z.string().optional().describe('Working directory for command execution'),
    timeout: z
      .number()
      .int()
      .positive()
      .max(30000)
      .default(5000)
      .describe('Maximum execution time in milliseconds (max 30s)'),
    captureOutput: z.boolean().default(true).describe('Whether to capture and return command output'),
  })

• src/index.ts:348-353 (registration)

  Tool registration in the list_tools response, defining name, description, and inputSchema converted from ExecuteCommandArgsSchema.

  name: 'execute_command',
  description:
    'Execute a system command with security restrictions. ' +
    'Validates commands for safety and provides detailed output. ' +
    'Limited to basic system operations with security checks.',
  inputSchema: zodToJsonSchema(ExecuteCommandArgsSchema) as ToolInput,

• src/index.ts:736-755 (handler)

  MCP call_tool dispatcher case for 'execute_command': parses args with schema, calls the executeCommand implementation, formats response with stdout/stderr/exitCode.

  case 'execute_command': {
    const parsed = ExecuteCommandArgsSchema.safeParse(a)
    if (!parsed.success) {
      throw new FileSystemError(`Invalid arguments for ${name}`, 'INVALID_ARGS', undefined, {
        errors: parsed.error.format(),
      })
    }
  
    const result = await executeCommand(parsed.data, config)
  
    endMetric()
    return {
      content: [
        {
          type: 'text',
          text: `Command execution completed with exit code: ${result.exitCode}\n\nSTDOUT:\n${result.stdout}\n\nSTDERR:\n${result.stderr}`,
        },
      ],
    }
  }

• src/utils/exec/index.ts:65-87 (helper)

  Helper function to validate command safety: checks against forbidden substrings and safe regex pattern, throws FileSystemError if unsafe.

  function validateCommand(command: string): boolean {
    // Check for forbidden commands
    if (FORBIDDEN_COMMANDS.some((forbidden) => command.includes(forbidden))) {
      throw new FileSystemError(
        `Command contains forbidden operations`,
        'FORBIDDEN_COMMAND',
        undefined,
        { command }
      )
    }
  
    // Validate command against safe pattern
    if (!SAFE_COMMAND_REGEX.test(command)) {
      throw new FileSystemError(
        `Command contains potentially unsafe characters`,
        'UNSAFE_COMMAND',
        undefined,
        { command }
      )
    }
  
    return true
  }