koa-router源码学习

摘要：源码架构图调用链路请求调用流程存放方法指定的参数的中间件存放实例存放路径参数的一些属性，存放该路由的中间件如果支持请求，一并支持请求将路由转为正则表达式给实例挂载方法如果指定了路由属性路由注册实例数组，初始为空数

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);

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 = [];
};

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);
};

/**
 * 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;
  };
});

/**
 * Create and register a route.
 *
 * @param {String} path Path string.
 * @param {Array.} 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;
};

/**
 * Match given `path` and return corresponding routes.
 *
 * @param {String} path
 * @param {String} method
 * @returns {Object.} 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;
};

/**
 * 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;
};

/**
 * 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(", "));
            }
          }
        }
      }
    });
  };
};

/**
 * 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;
};