Request Path Resolution

/**
 * Function to resolve request path before proxying
 * @param {object} req - Express request object
 * @returns {string|Promise<string>} The resolved path including query parameters
 */
proxyReqPathResolver: (req) => string | Promise<string>;

const proxy = require('express-http-proxy');

// Simple path modification
app.use('/api', proxy('localhost:8080', {
  proxyReqPathResolver: function (req) {
    // Replace '/api' with '/v1'
    return req.url.replace('/api', '/v1');
  }
}));

// Query parameter handling
app.use('/search', proxy('search.example.com', {
  proxyReqPathResolver: function (req) {
    const parts = req.url.split('?');
    const queryString = parts[1];
    const updatedPath = parts[0].replace(/test/, 'prod');
    return updatedPath + (queryString ? '?' + queryString : '');
  }
}));

/**
 * Promise-based path resolver for async operations
 * @param {object} req - Express request object
 * @returns {Promise<string>} Promise resolving to the final path
 */
proxyReqPathResolver: (req) => Promise<string>;

// Async path resolution
app.use('/dynamic', proxy('api.example.com', {
  proxyReqPathResolver: function(req) {
    return new Promise((resolve, reject) => {
      // Simulate async lookup (database, cache, etc.)
      setTimeout(() => {
        const userId = req.headers['x-user-id'];
        const resolvedPath = `/users/${userId}${req.url}`;
        resolve(resolvedPath);
      }, 100);
    });
  }
}));

// Database-driven path resolution
app.use('/tenant', proxy('multi-tenant.example.com', {
  proxyReqPathResolver: async function(req) {
    const tenantId = req.headers['x-tenant-id'];
    const tenant = await db.getTenant(tenantId);
    return `/${tenant.subdomain}${req.url}`;
  }
}));

/**
 * Complex path resolver with URL construction
 * @param {object} req - Express request object with full URL context
 * @returns {string} Constructed path with proper encoding
 */
proxyReqPathResolver: (req) => string;

// Advanced URL construction
app.use('/forward', proxy('backend.example.com', {
  proxyReqPathResolver: function(req) {
    const url = new URL(req.url, 'http://dummy');
    
    // Add API version to path
    const pathSegments = url.pathname.split('/').filter(Boolean);
    pathSegments.unshift('v2', 'api');
    
    // Modify query parameters
    url.searchParams.set('source', 'proxy');
    url.searchParams.set('timestamp', Date.now().toString());
    
    return '/' + pathSegments.join('/') + url.search;
  }
}));

/**
 * @deprecated Use proxyReqPathResolver instead
 */
forwardPath?: (req) => string;

/**
 * @deprecated Use proxyReqPathResolver instead
 */
forwardPathAsync?: (req, callback) => void;