javascript - 如何为 express.static 模拟 http.ServerResponse 和 http.IncomingMessage

Question

我在测试自己的路由处理程序时没有遇到任何问题，但在这种情况下，我想测试 express 的静态处理程序。我终其一生都无法弄清楚它为什么会挂起。显然，我缺少一些回调或需要发出一些事件。

我尽量做最小的例子。

var events = require('events');
var express = require('express');
var stream = require('stream');
var util = require('util');

function MockResponse(callback) {
  stream.Writable.call(this);
  this.headers = {};
  this.statusCode = -1;
  this.body = undefined;

  this.setHeader = function(key, value) {
    this.headers[key] = value;
  }.bind(this);

  this.on('finish', function() {
    console.log("finished response");
    callback();
  });
};

util.inherits(MockResponse, stream.Writable);

MockResponse.prototype._write = function(chunk, encoding, done) {
  if (this.body === undefined) {
    this.body = "";
  }
  this.body += chunk.toString(encoding !== 'buffer' ? encoding : undefined);
  done();
};

function createRequest(req) {
  var emitter = new events.EventEmitter();
  req.on = emitter.on.bind(emitter);
  req.once = emitter.once.bind(emitter);
  req.addListener = emitter.addListener.bind(emitter);
  req.emit = emitter.emit.bind(emitter);
  return req;
};

describe('test', function() {

  var app;

  before(function() {
    app = express();
    app.use(express.static(__dirname));
  });

  it('gets test.js', function(done) {

    var req = createRequest({
        url: "http://foo.com/test.js",
        method: 'GET',
        headers: {
        },
    });
    var res = new MockResponse(responseDone);
    app(req, res);

    function responseDone() {
      console.log("done");
      done();
    }

  });

});

设置，

mkdir foo
cd foo
mkdir test
cat > test/test.js   # copy and paste code above
^D
npm install express
npm install mocha
node node_modules/mocha/bin/mocha --recursive

它只是超时。

我错过了什么？

我还尝试将请求设为可读流。没有变化

var events = require('events');
var express = require('express');
var stream = require('stream');
var util = require('util');

function MockResponse(callback) {
  stream.Writable.call(this);
  this.headers = {};
  this.statusCode = -1;
  this.body = undefined;

  this.setHeader = function(key, value) {
    this.headers[key] = value;
  }.bind(this);

  this.on('finish', function() {
    console.log("finished response");
    callback();
  });
};

util.inherits(MockResponse, stream.Writable);

MockResponse.prototype._write = function(chunk, encoding, done) {
  if (this.body === undefined) {
    this.body = "";
  }
  this.body += chunk.toString(encoding !== 'buffer' ? encoding : undefined);
  done();
};

function MockMessage(req) {
  stream.Readable.call(this);
  var self = this;
  Object.keys(req).forEach(function(key) {
    self[key] = req[key];
  });
}

util.inherits(MockMessage, stream.Readable);

MockMessage.prototype._read = function() {
  this.push(null);
};


describe('test', function() {

  var app;

  before(function() {
    app = express();
    app.use(express.static(__dirname));
  });

  it('gets test.js', function(done) {

    var req = new MockMessage({
        url: "http://foo.com/test.js",
        method: 'GET',
        headers: {
        },
    });
    var res = new MockResponse(responseDone);
    app(req, res);

    function responseDone() {
      console.log("done");
      done();
    }

  });

});

我还在挖掘。查看静态服务器内部，我看到它通过调用 fs.createReadStream 创建了一个可读流。它确实有效

var s = fs.createReadStream(filename);
s.pipe(res);

所以试着让我自己工作就好了

  it('test stream', function(done) {
    var s = fs.createReadStream(__dirname + "/test.js");
    var res = new MockResponse(responseDone);
    s.pipe(res);

    function responseDone() {
      console.log("done");
      done();
    }    
  });

我认为这可能与快速等待输入流完成有关，但似乎也不是这样。如果我使用带有响应的模拟输入流，它就可以正常工作

  it('test msg->res', function(done) {
    var req = new MockMessage({});
    var res = new MockResponse(responseDone);
    req.pipe(res);

    function responseDone() {
      console.log("done");
      done();
    }    
  });

任何我可能缺少的见解都会有所帮助

注意:虽然对第 3 方模拟库的建议表示赞赏，但我仍然非常想了解自己缺少什么。即使我最终切换到某个库，我仍然想知道为什么这不起作用。

Answer 1

我发现了两个导致 finish 回调无法执行的问题。

1. serve-static 使用 send 模块，该模块用于从路径创建文件读取流并将其通过管道传输到 res 对象。但是该模块使用 on-finished 模块检查响应对象中的 finished 属性是否设置为 false，否则 destroys the file readstream .所以文件流永远没有机会发出数据事件。

2. express initialization覆盖响应对象原型(prototype)。所以像 end() 这样的默认流方法被 http 响应原型(prototype)覆盖:

   exports.init = function(app){
     return function expressInit(req, res, next){
       ...
       res.__proto__ = app.response;
       ..
     };
   };
   

   为了防止这种情况，我在静态中间件之前添加了另一个中间件，以将其重置回 MockResponse 原型(prototype):

   app.use(function(req, res, next){
     res.__proto__ = MockResponse.prototype; //change it back to MockResponse prototype
     next();
   });
   

以下是使其与 MockResponse 一起使用所做的更改:

...
function MockResponse(callback) {
  ...
  this.finished = false; // so `on-finished` module doesn't emit finish event prematurely

  //required because of 'send' module
  this.getHeader = function(key) {
    return this.headers[key];
  }.bind(this);
  ...
};

...
describe('test', function() {

  var app;

  before(function() {
    app = express();

    //another middleware to reset the res object
    app.use(function(req, res, next){
      res.__proto__ = MockResponse.prototype;
      next();
    });

    app.use(express.static(__dirname));
  });

  ...

});

编辑:

正如@gman 所指出的，可以使用直接属性而不是原型(prototype)方法。在这种情况下，不需要额外的中间件来覆盖原型(prototype):

function MockResponse(callback) {
  ...
  this.finished = false; // so `on-finished` module doesn't emit finish event prematurely

  //required because of 'send' module
  this.getHeader = function(key) {
     return this.headers[key];
  }.bind(this);

  ...

  //using direct property for _write, write, end - since all these are changed when prototype is changed
  this._write = function(chunk, encoding, done) {
    if (this.body === undefined) {
      this.body = "";
    }
    this.body += chunk.toString(encoding !== 'buffer' ? encoding : undefined);
    done();
  };

  this.write = stream.Writable.prototype.write;
  this.end = stream.Writable.prototype.end;

};