Configuration

Configuration Management Skill

Overview

This skill provides guidance for implementing safe configuration file management including backup systems, atomic updates, and recovery mechanisms. For US-4 (MCP Uninstaller), this skill covers:

• Creating timestamped configuration backups
• Atomic JSON file updates
• Configuration validation
• Backup restoration and cleanup

Core Capabilities

• Atomic File Operations: Write-then-rename pattern for safe file updates
• Backup Management: Create, restore, and clean up timestamped backups
• JSON Manipulation: Safe parsing, modification, and validation of JSON config files
• Error Recovery: Automatic rollback on failures
• Metadata Tracking: Include metadata in backups for audit trail
• Cleanup Policies: Implement retention policies (e.g., keep last 10 backups)

Input Requirements

Required:

• Configuration file path
• Operation type (backup, update, restore)
• Backup directory path

Optional:

• Retention policy (number of backups to keep)
• Validation schema
• Metadata to include in backup

Output Format

Returns:

• Operation result (success/failure)
• Backup file path (for backup operations)
• Validation results
• Error messages if applicable

Dependencies

• fs-extra: Enhanced file system operations
• JSON schema validator (optional): For config validation
• TypeScript 5.x: For type-safe config handling

Workflow

Step 1: Define Configuration Interfaces

Create TypeScript interfaces for config structure:

// src/interfaces/config.interface.ts
export interface ClaudeConfig {
  mcpServers?: Record<string, MCPServerConfig>;
  [key: string]: any;
}

export interface MCPServerConfig {
  command: string;
  args?: string[];
  env?: Record<string, string>;
}

export interface BackupMetadata {
  timestamp: string;
  originalPath: string;
  reason: string;
  mcpName?: string;
}

Step 2: Implement Backup Service

Create backup with metadata:

// src/services/config-backup.ts
import * as fs from 'fs-extra';
import * as path from 'path';

export class ConfigBackup {
  private backupDir: string;
  private maxBackups: number;

  constructor(backupDir: string = '.claude/backups', maxBackups: number = 10) {
    this.backupDir = backupDir;
    this.maxBackups = maxBackups;
  }

  async createBackup(configPath: string, reason: string, mcpName?: string): Promise<string> {
    // Ensure backup directory exists
    await fs.ensureDir(this.backupDir);

    // Generate timestamp
    const timestamp = new Date().toISOString().replace(/[:.]/g, '-');
    const backupFileName = `config-backup-${timestamp}.json`;
    const backupPath = path.join(this.backupDir, backupFileName);

    // Read original config
    const config = await fs.readJson(configPath);

    // Create backup with metadata
    const backup = {
      metadata: {
        timestamp: new Date().toISOString(),
        originalPath: configPath,
        reason,
        mcpName
      },
      config
    };

    // Write backup atomically
    await this.atomicWrite(backupPath, JSON.stringify(backup, null, 2));

    // Verify backup
    if (!await fs.pathExists(backupPath)) {
      throw new Error('Backup verification failed');
    }

    // Clean up old backups
    await this.cleanupOldBackups();

    return backupPath;
  }

  private async atomicWrite(filePath: string, content: string): Promise<void> {
    const tempPath = `${filePath}.tmp`;
    await fs.writeFile(tempPath, content, 'utf-8');
    await fs.rename(tempPath, filePath);
  }

  private async cleanupOldBackups(): Promise<void> {
    const files = await fs.readdir(this.backupDir);
    const backupFiles = files
      .filter(f => f.startsWith('config-backup-'))
      .sort()
      .reverse();

    // Keep only the most recent maxBackups
    const filesToDelete = backupFiles.slice(this.maxBackups);
    for (const file of filesToDelete) {
      await fs.remove(path.join(this.backupDir, file));
    }
  }

  async restore(backupPath: string, targetPath: string): Promise<void> {
    const backup = await fs.readJson(backupPath);

    if (!backup.config) {
      throw new Error('Invalid backup file: missing config data');
    }

    // Write config atomically
    await this.atomicWrite(targetPath, JSON.stringify(backup.config, null, 2));
  }
}

Step 3: Implement Configuration Update

Update config with atomic operations:

// src/services/config-updater.ts
import * as fs from 'fs-extra';

export class ConfigUpdater {
  async removeMCPEntry(configPath: string, mcpName: string): Promise<void> {
    // Read config
    const config = await fs.readJson(configPath);

    // Remove MCP entry
    if (config.mcpServers && config.mcpServers[mcpName]) {
      delete config.mcpServers[mcpName];
    } else {
      throw new Error(`MCP "${mcpName}" not found in configuration`);
    }

    // Validate resulting config
    this.validateConfig(config);

    // Write atomically
    const tempPath = `${configPath}.tmp`;
    await fs.writeJson(tempPath, config, { spaces: 2 });
    await fs.rename(tempPath, configPath);

    // Verify write
    const written = await fs.readJson(configPath);
    if (JSON.stringify(written) !== JSON.stringify(config)) {
      throw new Error('Configuration verification failed');
    }
  }

  private validateConfig(config: any): void {
    // Basic validation
    if (typeof config !== 'object' || config === null) {
      throw new Error('Invalid config: must be an object');
    }

    // Validate mcpServers if present
    if (config.mcpServers) {
      if (typeof config.mcpServers !== 'object') {
        throw new Error('Invalid config: mcpServers must be an object');
      }

      for (const [name, server] of Object.entries(config.mcpServers)) {
        if (typeof server !== 'object' || server === null) {
          throw new Error(`Invalid config: mcpServers.${name} must be an object`);
        }
      }
    }
  }

  async updateWithRetry(configPath: string, mcpName: string, maxAttempts: number = 3): Promise<void> {
    let lastError: Error | null = null;

    for (let attempt = 1; attempt <= maxAttempts; attempt++) {
      try {
        await this.removeMCPEntry(configPath, mcpName);
        return; // Success
      } catch (error) {
        lastError = error instanceof Error ? error : new Error('Unknown error');

        if (error instanceof Error && error.message.includes('EBUSY')) {
          // File is locked, wait and retry
          await new Promise(resolve => setTimeout(resolve, 1000 * attempt));
        } else {
          // Non-retryable error
          throw error;
        }
      }
    }

    throw new Error(`Config update failed after ${maxAttempts} attempts: ${lastError?.message}`);
  }
}

Step 4: Integrate with Rollback

Support transaction-like operations:

// src/services/config-transaction.ts
export class ConfigTransaction {
  private backup: ConfigBackup;
  private updater: ConfigUpdater;
  private backupPath?: string;

  constructor() {
    this.backup = new ConfigBackup();
    this.updater = new ConfigUpdater();
  }

  async execute(configPath: string, mcpName: string): Promise<void> {
    try {
      // Step 1: Create backup
      this.backupPath = await this.backup.createBackup(
        configPath,
        `Removing MCP: ${mcpName}`,
        mcpName
      );

      // Step 2: Update config
      await this.updater.removeMCPEntry(configPath, mcpName);

    } catch (error) {
      // Rollback on error
      if (this.backupPath) {
        await this.backup.restore(this.backupPath, configPath);
      }
      throw error;
    }
  }

  async rollback(configPath: string): Promise<void> {
    if (!this.backupPath) {
      throw new Error('No backup available for rollback');
    }

    await this.backup.restore(this.backupPath, configPath);
  }
}

Example Usage

Example 1: Create Backup (TASK-4.2)

import { ConfigBackup } from './services/config-backup';

const backup = new ConfigBackup('.claude/backups', 10);

// Create backup before modifications
const backupPath = await backup.createBackup(
  '~/.claude/claude_desktop_config.json',
  'Pre-uninstall backup',
  'server-filesystem'
);

console.log(`Backup created: ${backupPath}`);

Example 2: Update Configuration (TASK-4.5)

import { ConfigUpdater } from './services/config-updater';

const updater = new ConfigUpdater();

// Remove MCP entry with retry logic
await updater.updateWithRetry(
  '~/.claude/claude_desktop_config.json',
  'server-filesystem',
  3 // max retries
);

console.log('MCP entry removed successfully');

Example 3: Transactional Update

import { ConfigTransaction } from './services/config-transaction';

const transaction = new ConfigTransaction();

try {
  // Execute with automatic backup
  await transaction.execute(
    '~/.claude/claude_desktop_config.json',
    'server-filesystem'
  );

  console.log('Configuration updated successfully');
} catch (error) {
  console.error('Update failed, rollback performed:', error);
}

Error Handling

File Locked Error

if (error.code === 'EBUSY' || error.code === 'EPERM') {
  throw new Error('Configuration file is locked. Close Claude Code and try again.');
}

Malformed JSON Error

try {
  const config = await fs.readJson(configPath);
} catch (error) {
  throw new Error(`Invalid JSON in config file: ${error.message}. Please fix manually or restore from backup.`);
}

Backup Restore Error

if (!await fs.pathExists(backupPath)) {
  throw new Error(`Backup file not found: ${backupPath}. Cannot perform rollback.`);
}

Integration Points

With API Services

• Backup service is used by configuration updater
• Both used by rollback mechanism

With Rollback Mechanism

• Provides backup/restore capabilities
• Supports transaction-like operations

With CLI Interface

• CLI orchestrates backup and update operations
• Displays backup paths and success messages

With Testing

• Mock file system for unit tests
• Test atomic operations and rollback