.6-浅析express源码之Router模块(2)-router.use

proto.use = function use(fn) {
    var offset = 0;
    var path = '/';

    if (typeof fn !== 'function') {
        var arg = fn;
        while (Array.isArray(arg) && arg.length !== 0) arg = arg[0];
        if (typeof arg !== 'function') {
            offset = 1;
            path = fn;
        }
    }

    var callbacks = flatten(slice.call(arguments, offset));

    if (callbacks.length === 0) throw new TypeError('Router.use() requires a middleware function')

    for (var i = 0; i < callbacks.length; i++) {
        var fn = callbacks[i];

        if (typeof fn !== 'function') throw new TypeError('Router.use() requires a middleware function but got a ' + gettype(fn))

        debug('use %o %s', path, fn.name || '<anonymous>');
        // 内部模块layer!
        var layer = new Layer(path, {
            sensitive: this.caseSensitive,
            strict: false,
            end: false
        }, fn);
        // 通过use方法生成的layer没有route值
        layer.route = undefined;
        // 初始化时定义的数组
        this.stack.push(layer);
    }

    return this;
};

function Layer(path, options, fn) {
    if (!(this instanceof Layer)) {
        return new Layer(path, options, fn);
    }

    debug('new %o', path)
    var opts = options || {};
    /**
     * layer.handle => 中间件函数
     * layer.name => 函数名
     * layer.regexp => 路径的正则
     */
    this.handle = fn;
    this.name = fn.name || '<anonymous>';
    this.params = undefined;
    this.path = undefined;
    this.regexp = pathRegexp(path, this.keys = [], opts);

    // 快速匹配标记
    this.regexp.fast_star = path === '*'
    this.regexp.fast_slash = path === '/' && opts.end === false
}

function pathtoRegexp(path, keys, options) {
    // ...

    // 字符串
    path = ('^' + path + (strict ? '' : path[path.length - 1] === '/' ? '?' : '/?'));
    // ...后面有很多replace

    // 数组
    if (Array.isArray(path)) {
        path = path.map(function(value) {
            return pathtoRegexp(value, keys, options).source;
        });
        // 使用|分割多个规则来进行多重匹配
        return new RegExp('(?:' + path.join('|') + ')', flags);
    }

    // 正则 比较简单的
    // var MATCHING_GROUP_REGEXP = /((?!?)/g;
    if (path instanceof RegExp) {
        // 匹配组
        while (m = MATCHING_GROUP_REGEXP.exec(path.source)) {
            keys.push({
                name: name++,
                optional: false,
                offset: m.index
            });
        }

        return path;
    }
}