W3C home > Mailing lists > Public > whatwg@whatwg.org > November 2014

[whatwg] Feedback wanted on integrating fetch request/response and streams

From: Domenic Denicola <d@domenic.me>
Date: Wed, 5 Nov 2014 10:01:04 +0000
To: WHAT Working Group Mailing List <whatwg@whatwg.org>
Message-ID: <1b7daf84ccd541acad00e15aacf70535@CY1PR0501MB1369.namprd05.prod.outlook.com>
Cc: Yutaka Hirano <yhirano@chromium.org>
In https://github.com/yutakahirano/fetch-with-streams Yutaka, Anne, and I are working on how to integrate the fetch API with streams. The general pattern we want is that for both request and response objects their creator is given a writable stream to write body content to, using [the revealing constructor pattern][1]. (That way, for requests or responses created by the browser, developers can only read---not write---the bodies; for requests/responses created by the developer, the developer can do both.)

The current fetch API when initializing with non-streaming bodies is roughly:

```js
var req = new Request("http://example.com", {
  method: "POST",
  body: '{ "json": "here" }' // or blob or FormData or ...
});

var res = new Response('{ "json": "here" }' /* or blob or FormData or ... */, {
  status: 201,
  headers: { 'Content-Type': 'application/json' }
});
```

Note how in both cases the "most important" value is given an unlabeled position as the first argument: requests are "about" URLs, and responses are "about" bodies.

Our current thought for streams integration is to overload the "body" position for each of these with a function that takes a writable stream:

```js
var req = new Request("http://example.com", {
  method: "POST",
  body(stream) {
    stream.write(myArrayBuffer);
    stream.close();
  }
});

var res = new Response(
  stream => {
    someCSVStream.pipeThrough(new CSVToJsonTransform()).pipeTo(stream);
  },
  {
    status: 201,
    headers: { 'Content-Type': 'application/json' }
  }
);
```

Do we think this is good? Any other ideas?

Personally I find the overloads weird, especially since they behave completely differently when passing a string versus passing a function. But after thinking through this for a while I didn't have any better ideas that worked for both requests and responses.
 
[1]: https://blog.domenic.me/the-revealing-constructor-pattern/
Received on Wednesday, 5 November 2014 10:01:33 UTC

This archive was generated by hypermail 2.3.1 : Monday, 13 April 2015 23:09:32 UTC