Express 源码解析

var express = require('express')
var app = express()
app.use ...
app.get ...
app.listen ...

/**
 * Expose `createApplication()`.
 */

var proto = require('./application');

exports = module.exports = createApplication;

/**
 * Create an express application.
 *
 * @return {Function}
 * @api public
 */

function createApplication() {
  var app = function(req, res, next) {
    app.handle(req, res, next);
  };

  mixin(app, EventEmitter.prototype, false);
  mixin(app, proto, false);

  // expose the prototype that will get set on requests
  app.request = Object.create(req, {
    app: { configurable: true, enumerable: true, writable: true, value: app }
  })

  // expose the prototype that will get set on responses
  app.response = Object.create(res, {
    app: { configurable: true, enumerable: true, writable: true, value: app }
  })

  app.init();
  return app;
}

app.listen = function listen() {
  var server = http.createServer(this);
  return server.listen.apply(server, arguments);
};

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

  // default path to '/'
  // disambiguate app.use([fn])
  if (typeof fn !== 'function') {
    var arg = fn;

    while (Array.isArray(arg) && arg.length !== 0) {
      arg = arg[0];
    }

    // first arg is the path
    if (typeof arg !== 'function') {
      offset = 1;
      path = fn;
    }
  }

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

  if (fns.length === 0) {
    throw new TypeError('app.use() requires a middleware function')
  }

  // setup router
  this.lazyrouter();
  var router = this._router;

  fns.forEach(function (fn) {
    // non-express app
    if (!fn || !fn.handle || !fn.set) {
      return router.use(path, fn);
    }

    debug('.use app under %s', path);
    fn.mountpath = path;
    fn.parent = this;

    // restore .app property on req and res
    router.use(path, function mounted_app(req, res, next) {
      var orig = req.app;
      fn.handle(req, res, function (err) {
        setPrototypeOf(req, orig.request)
        setPrototypeOf(res, orig.response)
        next(err);
      });
    });

    // mounted an app
    fn.emit('mount', this);
  }, this);

  return this;
};

app.lazyrouter = function lazyrouter() {
  if (!this._router) {
    this._router = new Router({
      caseSensitive: this.enabled('case sensitive routing'),
      strict: this.enabled('strict routing')
    });

    this._router.use(query(this.get('query parser fn')));
    this._router.use(middleware.init(this));
  }
};

app.route = function route(path) {
  this.lazyrouter();
  return this._router.route(path);
};

/**
 * Delegate `.VERB(...)` calls to `router.VERB(...)`.
 */

methods.forEach(function(method){
  app[method] = function(path){
    if (method === 'get' && arguments.length === 1) {
      // app.get(setting)
      return this.set(path);
    }

    this.lazyrouter();

    var route = this._router.route(path);
    route[method].apply(route, slice.call(arguments, 1));
    return this;
  };
});

var proto = module.exports = function(options) {
  var opts = options || {};

  function router(req, res, next) {
    router.handle(req, res, next);
  }

  // mixin Router class functions
  setPrototypeOf(router, proto)

  router.params = {};
  router._params = [];
  router.caseSensitive = opts.caseSensitive;
  router.mergeParams = opts.mergeParams;
  router.strict = opts.strict;
  router.stack = [];

  return router;
};

// find next matching layer
var layer;
var match;
var route;

while (match !== true && idx < stack.length) {
  layer = stack[idx++];
  match = matchLayer(layer, path);
  route = layer.route;

  if (typeof match !== 'boolean') {
    // hold on to layerError
    layerError = layerError || match;
  }

  if (match !== true) {
    continue;
  }

  if (!route) {
    // process non-route handlers normally
    continue;
  }

  if (layerError) {
    // routes do not match with a pending error
    match = false;
    continue;
  }

  var method = req.method;
  var has_method = route._handles_method(method);

  // build up automatic options response
  if (!has_method && method === 'OPTIONS') {
    appendMethods(options, route._options());
  }

  // don't even bother matching route
  if (!has_method && method !== 'HEAD') {
    match = false;
    continue;
  }
}

// no match
if (match !== true) {
  return done(layerError);
}

// store route for dispatch on change
if (route) {
  req.route = route;
}

function matchLayer(layer, path) {
  try {
    return layer.match(path);
  } catch (err) {
    return err;
  }
}

// create Router#VERB functions
methods.concat('all').forEach(function(method){
  proto[method] = function(path){
    var route = this.route(path)
    route[method].apply(route, slice.call(arguments, 1));
    return this;
  };
});

function Layer(path, options, fn) {
  if (!(this instanceof Layer)) {
    return new Layer(path, options, fn);
  }
  debug('new %o', path)
  var opts = options || {};
  this.handle = fn;
  this.name = fn.name || '<anonymous>';
  this.params = undefined;
  this.path = undefined;
  this.regexp = pathRegexp(path, this.keys = [], opts);
  // set fast path flags
  this.regexp.fast_star = path === '*'
  this.regexp.fast_slash = path === '/' && opts.end === false
}

Layer.prototype.handle_request = function handle(req, res, next) {
  var fn = this.handle;
	...
  try {
    fn(req, res, next);
  } catch (err) {
    next(err);
  }
};

proto.use = function use(fn) {
  ...
  var layer = new Layer(path, {
    sensitive: this.caseSensitive,
    strict: false,
    end: false
  }, fn);

  layer.route = undefined;

  this.stack.push(layer);

  return this;
};

  proto.route = function route(path) {
  var route = new Route(path);

  var layer = new Layer(path, {
    sensitive: this.caseSensitive,
    strict: this.strict,
    end: true
  }, route.dispatch.bind(route));

  layer.route = route;

  this.stack.push(layer);
  return route;
};

Route.prototype.dispatch = function dispatch(req, res, done) {
  ...
  req.route = this;

  next();

  function next(err) {
		...
    var layer = stack[idx++];
    
    if (err) {
      layer.handle_error(err, req, res, next);
    } else {
      layer.handle_request(req, res, next);
    }
  }
};

Route.prototype[method] = function(){
  var handles = flatten(slice.call(arguments));

  for (var i = 0; i < handles.length; i++) {
    var handle = handles[i];

    if (typeof handle !== 'function') {
      var type = toString.call(handle);
      var msg = 'Route.' + method + '() requires a callback function but got a ' + type
      throw new Error(msg);
    }

    debug('%s %o', method, this.path)

    var layer = Layer('/', {}, handle);
    layer.method = method;

    this.methods[method] = true;
    this.stack.push(layer);
  }

  return this;
};

var req = Object.create(http.IncomingMessage.prototype)

var res = Object.create(http.ServerResponse.prototype)

function stringify (value, replacer, spaces, escape) {
  var json = replacer || spaces
    ? JSON.stringify(value, replacer, spaces)
    : JSON.stringify(value);

  if (escape) {
    json = json.replace(/[<>&]/g, function (c) {
      switch (c.charCodeAt(0)) {
        case 0x3c:
          return '\\u003c'
        case 0x3e:
          return '\\u003e'
        case 0x26:
          return '\\u0026'
        default:
          return c
      }
    })
  }
  return json
}

if (!opts.root && !isAbsolute(path)) {
  throw new TypeError('path must be absolute or specify root to res.sendFile');
}

var file = send(req, path, opts);

  file.on('directory', ondirectory);
  file.on('end', onend);
  file.on('error', onerror);
  file.on('file', onfile);
  file.on('stream', onstream);
  onFinished(res, onfinish);

setImmediate(function () {
  ...
  if (done) return;
  done = true;
  callback();
});

  file.pipe(res);

// Set location header
address = this.location(address).get('Location');

res.location = function location(url) {
  var loc = url;

  // "back" is an alias for the referrer
  if (url === 'back') {
    loc = this.req.get('Referrer') || '/';
  }

  // set location
  return this.set('Location', encodeUrl(loc));
};