http-proxy-middleware/lib/path-rewriter.js

var _      = require('lodash');
var logger = require('./logger').getInstance();

module.exports = {
    create: createPathRewriter
};

/**
 * Create rewrite function, to cache parsed rewrite rules.
 *
 * @returns {function} Function to rewrite paths; This function should accept `path` (request.url) as parameter
 */
function createPathRewriter(rewriteConfig) {
    var rulesCache;

    if (!isValidRewriteConfig(rewriteConfig)) {
        return;
    }

    if (_.isFunction(rewriteConfig)) {
        var customRewriteFn = rewriteConfig;
        return customRewriteFn;
    } else {
        rulesCache = parsePathRewriteRules(rewriteConfig);
        return rewritePath;
    }

    function rewritePath(path) {
        var result = path;

        _.forEach(rulesCache, function(rule) {
            if (rule.regex.test(path)) {
                result = result.replace(rule.regex, rule.value);
                logger.debug('[HPM] Rewriting path from "%s" to "%s"', path, result);
                return false;
            }
        });

        return result;
    }
}

function isValidRewriteConfig(rewriteConfig) {
    if (_.isFunction(rewriteConfig)) {
        return true;
    } else if (!_.isEmpty(rewriteConfig) && _.isPlainObject(rewriteConfig)) {
        return true;
    } else if (_.isUndefined(rewriteConfig) ||
               _.isNull(rewriteConfig) ||
               _.isEqual(rewriteConfig, {})) {
        return false;
    } else {
        throw new Error('[HPM] Invalid pathRewrite config. Expecting object with pathRewrite config or a rewrite function');
    }
}

function parsePathRewriteRules(rewriteConfig) {
    var rules = [];

    if (_.isPlainObject(rewriteConfig)) {
        _.forIn(rewriteConfig, function(value, key) {
            rules.push({
                regex: new RegExp(key),
                value: rewriteConfig[key]
            });
            logger.info('[HPM] Proxy rewrite rule created: "%s" ~> "%s"', key, rewriteConfig[key]);
        });
    }

    return rules;
}