response.write - 它是从可写流还是从http.ServerResponse调用write？

Question

I am new to node. In a setup like this

server.on('request', function(request, response) {
  // the same kind of magic happens here!
});

I presume response is an instance of http.ServerResponse . But one tutorial I read says: http.ServerResponse is WritableStream .

Now both writable stream and http.ServerResponse have write methods; here and here .

My question is when I call response.write which version of write gets called? One from http.ServerResponse or one from writable stream?

Answer 1

http.ServerResponse implements a version of the stream.Writable interface but does not inherit its actual implementation. So when you call response.write() you're calling http.ServerResponse.write() and not stream.Writable.write() .

Class: http.ServerResponse

The response implements, but does not inherit from, the Writable Stream interface.

Internally, the http.ServerResponse is actually an OutgoingMessage , which is a Stream , and that supplies write() . If you compare this against the stream.Writable.write() implementation, the way they going about writing the data is different.

I was also curious what benefits it gets in implementing writable stream if it uses its own write for example, etc? (From Comments below)

Without being part of the Node.js Foundation I can't speak to the motivation but, just from a design standpoint, implementing the stream.Writable interface provides familiar and common set of methods and events for developers to work with. Additionally, http.ServerResponse is writing to the connection socket (see OutgoingMessage._send() ) which isn't part of stream.Writable.write() implementation. Perhaps the below excerpt provides some insight into the thought process of the Foundation

Writable Streams

All Writable streams implement the interface defined by the stream.Writable class.

While specific instances of Writable streams may differ in various ways, all Writable streams follow the same fundamental usage pattern