koa-router源码学习

源码架构图

调用链路-routes()

HTTP请求调用流程

Usage

const Koa = require('koa');
const Router = require('koa-router');

const app = new Koa();
const router = new Router();

router.get('/', async (ctx, next) => {
  console.log('index');
  ctx.body = 'index';
});

app.use(router.routes()).use(router.allowedMethods());

app.listen(3000);

Router

function Router(opts) {
  if (!(this instanceof Router)) {
    return new Router(opts);
  }

  this.opts = opts || {};
  this.methods = this.opts.methods || [
    'HEAD',
    'OPTIONS',
    'GET',
    'PUT',
    'PATCH',
    'POST',
    'DELETE'
  ];

    // 存放router.param方法指定的参数的中间件
  this.params = {};
  // 存放layer实例
  this.stack = [];
};

Layer

function Layer(path, methods, middleware, opts) {
  this.opts = opts || {};
  this.name = this.opts.name || null;
  this.methods = [];
  // 存放path路径参数的一些属性，eg: /test/:str => { name: str, prefix: '/' ....}
  this.paramNames = [];
  // 存放该路由的中间件
  this.stack = Array.isArray(middleware) ? middleware : [middleware];

  methods.forEach(function(method) {
    var l = this.methods.push(method.toUpperCase());
    // 如果支持get请求，一并支持head请求
    if (this.methods[l-1] === 'GET') {
      this.methods.unshift('HEAD');
    }
  }, this);

  // ensure middleware is a function
  this.stack.forEach(function(fn) {
    var type = (typeof fn);
    if (type !== 'function') {
      throw new Error(
        methods.toString() + " `" + (this.opts.name || path) +"`: `middleware` "
        + "must be a function, not `" + type + "`"
      );
    }
  }, this);

  this.path = path;
  // 将路由转为正则表达式
  this.regexp = pathToRegExp(path, this.paramNames, this.opts);

  debug('defined route %s %s', this.methods, this.opts.prefix + this.path);
};

给Router实例挂载HTTP方法

/**
 * Create `router.verb()` methods, where *verb* is one of the HTTP verbs such
 * as `router.get()` or `router.post()`.
 *
 * Match URL patterns to callback functions or controller actions using `router.verb()`,
 * where **verb** is one of the HTTP verbs such as `router.get()` or `router.post()`.
 *
 * Additionaly, `router.all()` can be used to match against all methods.
 *
 * ```javascript
 * router
 *   .get('/', (ctx, next) => {
 *     ctx.body = 'Hello World!';
 *   })
 *   .post('/users', (ctx, next) => {
 *     // ...
 *   })
 *   .put('/users/:id', (ctx, next) => {
 *     // ...
 *   })
 *   .del('/users/:id', (ctx, next) => {
 *     // ...
 *   })
 *   .all('/users/:id', (ctx, next) => {
 *     // ...
 *   });
 * ```
 *
 * When a route is matched, its path is available at `ctx._matchedRoute` and if named,
 * the name is available at `ctx._matchedRouteName`
 *
 * Route paths will be translated to regular expressions using
 * [path-to-regexp](https://github.com/pillarjs/path-to-regexp).
 *
 * Query strings will not be considered when matching requests.
 *
 * #### Named routes
 *
 * Routes can optionally have names. This allows generation of URLs and easy
 * renaming of URLs during development.
 *
 * ```javascript
 * router.get('user', '/users/:id', (ctx, next) => {
 *  // ...
 * });
 *
 * router.url('user', 3);
 * // => "/users/3"
 * ```
 *
 * #### Multiple middleware
 *
 * Multiple middleware may be given:
 *
 * ```javascript
 * router.get(
 *   '/users/:id',
 *   (ctx, next) => {
 *     return User.findOne(ctx.params.id).then(function(user) {
 *       ctx.user = user;
 *       next();
 *     });
 *   },
 *   ctx => {
 *     console.log(ctx.user);
 *     // => { id: 17, name: "Alex" }
 *   }
 * );
 * ```
 *
 * ### Nested routers
 *
 * Nesting routers is supported:
 *
 * ```javascript
 * var forums = new Router();
 * var posts = new Router();
 *
 * posts.get('/', (ctx, next) => {...});
 * posts.get('/:pid', (ctx, next) => {...});
 * forums.use('/forums/:fid/posts', posts.routes(), posts.allowedMethods());
 *
 * // responds to "/forums/123/posts" and "/forums/123/posts/123"
 * app.use(forums.routes());
 * ```
 *
 * #### Router prefixes
 *
 * Route paths can be prefixed at the router level:
 *
 * ```javascript
 * var router = new Router({
 *   prefix: '/users'
 * });
 *
 * router.get('/', ...); // responds to "/users"
 * router.get('/:id', ...); // responds to "/users/:id"
 * ```
 *
 * #### URL parameters
 *
 * Named route parameters are captured and added to `ctx.params`.
 *
 * ```javascript
 * router.get('/:category/:title', (ctx, next) => {
 *   console.log(ctx.params);
 *   // => { category: 'programming', title: 'how-to-node' }
 * });
 * ```
 *
 * The [path-to-regexp](https://github.com/pillarjs/path-to-regexp) module is
 * used to convert paths to regular expressions.
 *
 * @name get|put|post|patch|delete|del
 * @memberof module:koa-router.prototype
 * @param {String} path
 * @param {Function=} middleware route middleware(s)
 * @param {Function} callback route callback
 * @returns {Router}
 */
var methods = require('methods');

methods.forEach(function (method) {
  Router.prototype[method] = function (name, path, middleware) {
    var middleware;

        // 如果指定了路由name属性
    if (typeof path === 'string' || path instanceof RegExp) {
      middleware = Array.prototype.slice.call(arguments, 2);
    } else {
      middleware = Array.prototype.slice.call(arguments, 1);
      path = name;
      name = null;
    }

        // 路由注册
    this.register(path, [method], middleware, {
      name: name
    });

    return this;
  };
});

Router.prototype.register

/**
 * Create and register a route.
 *
 * @param {String} path Path string.
 * @param {Array.<String>} methods Array of HTTP verbs.
 * @param {Function} middleware Multiple middleware also accepted.
 * @returns {Layer}
 * @private
 */
Router.prototype.register = function (path, methods, middleware, opts) {
  opts = opts || {};

  var router = this;
  // layer实例数组，初始为空数组
  var stack = this.stack;

  // support array of paths
  if (Array.isArray(path)) {
      // 如果是多路径，递归注册路由
    path.forEach(function (p) {
      router.register.call(router, p, methods, middleware, opts);
    });

    return this;
  }

  // create route
  var route = new Layer(path, methods, middleware, {
    end: opts.end === false ? opts.end : true,
    name: opts.name,
    sensitive: opts.sensitive || this.opts.sensitive || false,
    strict: opts.strict || this.opts.strict || false,
    prefix: opts.prefix || this.opts.prefix || "",
    ignoreCaptures: opts.ignoreCaptures
  });

    // 设置前置路由
  if (this.opts.prefix) {
    route.setPrefix(this.opts.prefix);
  }

  // add parameter middleware
  Object.keys(this.params).forEach(function (param) {
      // 将router中this.params维护的参数中间件挂载到layer实例中
    route.param(param, this.params[param]);
  }, this);

    // 所有layer实例存放在router的stack属性中
  stack.push(route);

  return route;
};

Router.prototype.match

/**
 * Match given `path` and return corresponding routes.
 *
 * @param {String} path
 * @param {String} method
 * @returns {Object.<path, pathAndMethod>} returns layers that matched path and
 * path and method.
 * @private
 */
Router.prototype.match = function (path, method) {
    // layer实例组成的数组
  var layers = this.stack;
  var layer;
  var matched = {
    path: [],
    pathAndMethod: [],
    route: false
  };

  for (var len = layers.length, i = 0; i < len; i++) {
    layer = layers[i];

    debug('test %s %s', layer.path, layer.regexp);

        // 1.匹配路由
    if (layer.match(path)) {
      matched.path.push(layer);

            // 2.匹配http请求方法
      if (layer.methods.length === 0 || ~layer.methods.indexOf(method)) {
        matched.pathAndMethod.push(layer);
        // 3.指定了http请求方法，判定为路由匹配成功
        if (layer.methods.length) matched.route = true;
      }
    }
  }

  return matched;
};

Router.prototype.routes

/**
 * Returns router middleware which dispatches a route matching the request.
 *
 * @returns {Function}
 */
Router.prototype.routes = Router.prototype.middleware = function () {
  var router = this;

  var dispatch = function dispatch(ctx, next) {
    debug('%s %s', ctx.method, ctx.path);

        // 请求路由
    var path = router.opts.routerPath || ctx.routerPath || ctx.path;
    // 将注册路由和请求的路由进行匹配
    var matched = router.match(path, ctx.method);
    var layerChain, layer, i;

    if (ctx.matched) {
      ctx.matched.push.apply(ctx.matched, matched.path);
    } else {
      ctx.matched = matched.path;
    }

    ctx.router = router;

        // route属性是三次匹配的结果，表示最终是否匹配成功
    if (!matched.route) return next();

        // 同时满足路由匹配和http请求方法的layer数组
    var matchedLayers = matched.pathAndMethod
    // 匹配多个路由时认为最后一个是匹配有效的路由
    var mostSpecificLayer = matchedLayers[matchedLayers.length - 1]
    ctx._matchedRoute = mostSpecificLayer.path;
    if (mostSpecificLayer.name) {
      ctx._matchedRouteName = mostSpecificLayer.name;
    }

        // 将匹配的路由reduce为一个数组
    layerChain = matchedLayers.reduce(function(memo, layer) {
        // 执行注册路由中间件之前，对context中的一些参数进行设置
      memo.push(function(ctx, next) {
          // :path/XXX 捕获的路径
        ctx.captures = layer.captures(path, ctx.captures);
        // 捕获的路径上的参数, { key: value }
        ctx.params = layer.params(path, ctx.captures, ctx.params);
        // 路由名称
        ctx.routerName = layer.name;
        return next();
      });
      // 返回路由中间件的数组
      return memo.concat(layer.stack);
    }, []);

        // 处理为promise对象
    return compose(layerChain)(ctx, next);
  };

  dispatch.router = this;

  return dispatch;
};

Router.prototype.allowedMethod

/**
 * Returns separate middleware for responding to `OPTIONS` requests with
 * an `Allow` header containing the allowed methods, as well as responding
 * with `405 Method Not Allowed` and `501 Not Implemented` as appropriate.
 *
 * @example
 *
 * ```javascript
 * var Koa = require('koa');
 * var Router = require('koa-router');
 *
 * var app = new Koa();
 * var router = new Router();
 *
 * app.use(router.routes());
 * app.use(router.allowedMethods());
 * ```
 *
 * **Example with [Boom](https://github.com/hapijs/boom)**
 *
 * ```javascript
 * var Koa = require('koa');
 * var Router = require('koa-router');
 * var Boom = require('boom');
 *
 * var app = new Koa();
 * var router = new Router();
 *
 * app.use(router.routes());
 * app.use(router.allowedMethods({
 *   throw: true,
 *   notImplemented: () => new Boom.notImplemented(),
 *   methodNotAllowed: () => new Boom.methodNotAllowed()
 * }));
 * ```
 *
 * @param {Object=} options
 * @param {Boolean=} options.throw throw error instead of setting status and header
 * @param {Function=} options.notImplemented throw the returned value in place of the default NotImplemented error
 * @param {Function=} options.methodNotAllowed throw the returned value in place of the default MethodNotAllowed error
 * @returns {Function}
 */
Router.prototype.allowedMethods = function (options) {
  options = options || {};
  var implemented = this.methods;

  return function allowedMethods(ctx, next) {
      // 所有中间件执行完之后执行allowedMethod方法
    return next().then(function() {
      var allowed = {};

            // 没有响应状态码或者响应了404
      if (!ctx.status || ctx.status === 404) {
          // 在match方法中，匹配的路由的layer实例对象组成的数组
        ctx.matched.forEach(function (route) {
          route.methods.forEach(function (method) {
              // 把匹配的路由的http方法保存起来，认为是允许的http请求方法
            allowed[method] = method;
          });
        });

        var allowedArr = Object.keys(allowed);

                // 如果该方法在router实例的methods中不存在
        if (!~implemented.indexOf(ctx.method)) {
            // 如果在初始化router时配置了throw属性为true
          if (options.throw) {
            var notImplementedThrowable;
            if (typeof options.notImplemented === 'function') {
                // 指定了报错函数
              notImplementedThrowable = options.notImplemented(); // set whatever the user returns from their function
            } else {
                // 没有指定则抛出http异常
              notImplementedThrowable = new HttpError.NotImplemented();
            }
            throw notImplementedThrowable;
          } else {
              // 没有配置throw则响应501
            ctx.status = 501;
            // 设置响应头中的allow字段，返回允许的http方法
            ctx.set('Allow', allowedArr.join(', '));
          }
        } else if (allowedArr.length) {
          if (ctx.method === 'OPTIONS') {
              // 如果是OPTIONS请求，则认为是请求成功，响应200，并根据OPTIONS请求约定返回允许的http方法
            ctx.status = 200;
            ctx.body = '';
            ctx.set('Allow', allowedArr.join(', '));
          } else if (!allowed[ctx.method]) {
              // 如果请求方法在router实例的methods中存在，但是在匹配的路由中该http方法不存在
            if (options.throw) {
              var notAllowedThrowable;
              if (typeof options.methodNotAllowed === 'function') {
                notAllowedThrowable = options.methodNotAllowed(); // set whatever the user returns from their function
              } else {
                notAllowedThrowable = new HttpError.MethodNotAllowed();
              }
              throw notAllowedThrowable;
            } else {
                // 响应405 http请求方法错误
              ctx.status = 405;
              ctx.set('Allow', allowedArr.join(', '));
            }
          }
        }
      }
    });
  };
};

Router.prototype.use

/**
 * Use given middleware.
 *
 * Middleware run in the order they are defined by `.use()`. They are invoked
 * sequentially, requests start at the first middleware and work their way
 * "down" the middleware stack.
 *
 * @example
 *
 * ```javascript
 * // session middleware will run before authorize
 * router
 *   .use(session())
 *   .use(authorize());
 *
 * // use middleware only with given path
 * router.use('/users', userAuth());
 *
 * // or with an array of paths
 * router.use(['/users', '/admin'], userAuth());
 *
 * app.use(router.routes());
 * ```
 *
 * @param {String=} path
 * @param {Function} middleware
 * @param {Function=} ...
 * @returns {Router}
 */
Router.prototype.use = function () {
  var router = this;
  var middleware = Array.prototype.slice.call(arguments);
  var path;

  // support array of paths
  // 如果第一个参数是一个数组，且数组中元素为字符串
  if (Array.isArray(middleware[0]) && typeof middleware[0][0] === 'string') {
      // 递归调用use方法
    middleware[0].forEach(function (p) {
      router.use.apply(router, [p].concat(middleware.slice(1)));
    });

    return this;
  }

  var hasPath = typeof middleware[0] === 'string';
  if (hasPath) {
    path = middleware.shift();
  }

  middleware.forEach(function (m) {
      // 如果这个中间件是由router.routes()方法返回的dispatch中间件，即这是一个嵌套的路由
    if (m.router) {
        // 遍历router.stack属性中所有的layer
      m.router.stack.forEach(function (nestedLayer) {
          // 被嵌套的路由需要以父路由path为前缀
        if (path) nestedLayer.setPrefix(path);
        // 如果父路由有指定前缀，被嵌套的路由需要把这个前缀再加上
        if (router.opts.prefix) nestedLayer.setPrefix(router.opts.prefix);
        router.stack.push(nestedLayer);
      });

      if (router.params) {
        Object.keys(router.params).forEach(function (key) {
          m.router.param(key, router.params[key]);
        });
      }
    } else {
      router.register(path || '(.*)', [], m, { end: false, ignoreCaptures: !hasPath });
    }
  });

  return this;
};