NodeJS中间件如何从可写流中读取(http.ServerResponse) [英] NodeJS middleware how to read from a writable stream (http.ServerResponse)

问题描述

我正在开发由一组中间件和node-http-proxy模块组成的应用程序(使用Connect not Express )，也就是说，我有一系列中间件，例如:

I'm working on a app (using Connect not Express) composed of a set of middlewares plus node-http-proxy module, that is, I have a chain of middlewares like:

midA -> midB -> http-proxy -> midC 

在这种情况下，响应是由http-proxy编写的，该代理将请求代理到某个目标并返回内容.

In this scenario, the response is wrote by the http-proxy that proxies the request to some target and returns the content.

我想创建一个中间件(例如midB)充当缓存.这个想法是:

I would like to create a middleware (say midB) to act as a cache. The idea is:

• 如果缓存了url，则缓存中间件将写入响应，并避免继续使用Middleares链.
• 如果未缓存url，则缓存中间件将中间件链中的请求传递给位，要求读取要缓存的最终响应内容.

如何实现呢?还是有另一种方法?

How can achieve this? Or there is another approach?

欢呼

推荐答案

正在回答自己. 如果您有像function(req, res, next){..}这样的中间件，并且需要读取响应对象的内容.

Answering myself. If you have a middleware like function(req, res, next){..} and need to read the content of the response object.

在这种情况下，res是一个http.ServerResponse对象，这是一个可写流，其中链中的每个中间件都可以编写符合我们要返回的响应的内容.

In this case the res is a http.ServerResponse object, a writable stream where every middleware in the chain is allowed to write content that will conform the response we want to return.

在与http.request()进行请求时，不要混淆您得到的响应，这是一个http.IncomingMessage实际上是可读的流.

Do not confuse with the response you get when make a request with http.request(), that is a http.IncomingMessage which in fact is a readable stream.

我发现读取所有中间件写入响应的内容的方式是重新定义write方法:

The way I found to read the content all middlewares write to the response is redefining the write method:

var middleare = function(req, res, next) {

  var data = "";
  res._oldWrite = res.write;
  res.write = function(chunk, encoding, cb) {
    data += chunck;
    return res._oldWrite.call(res, chunck, encoding, cb);
  }

  ...
}

任何其他解决方案将不胜感激.

Any other solutions will be appreciated.

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