Add a fetch option to allow wrappers

[valeriangalliat]

This way a wrapper library like fetch-cookie could transparently leverage node-fetch way of handling redirects without having to force { redirect: 'manual' } and re-implement the logic.

Instead, a wrapper could just pass the fetch option and point it to the wrapped function. And this would also allow wrappers to be combined as long as they also support being given the fetch option, e.g.:

function fetchCookie(url, opts) {
    return fetch(url, Object.assign({ fetch: fetchCookie }, opts));
}

[bitinn]

From what I see this saves you from duplicating code, basically allow you to hook into the redirection process which is where automate cookie handling is desired, true?

@TimothyGu I think this makes sense, just wondering if fetch option naming is the way to go. I think it solves #146 and #94, or at least make implementing them trivial to users.

[valeriangalliat]

From what I see this saves you from duplicating code, basically allow you to hook into the redirection process which is where automate cookie handling is desired, true?

Exactly. 👍

[ahmadnassri]

resolver instead of fetch would be my choice for naming.

[valeriangalliat]

I can rename it to resolver. Would that be fine @bitinn?

[bitinn]

@valeriangalliat I think resolver should do just fine, would you kindly add some comment, test and document for the change?

@TimothyGu what do you think, I do want this to happen, because it's one of the most discussed pain point of node-fetch. Given we are unlikely ever going to implement server-side cookies ourselves, we should make it easier for others to add this feature.

[valeriangalliat]

@bitinn I added comment, test and documentation for the resolver option. Does it looks good to you?

[TimothyGu]

For now this PR looks fine to me. On the long term, however, I envision a mechanism to have a "store" of Web interfaces including fetch, Promise, FormData, URL, Blob, URLSearchParams, CookieJar etc., that the users can pass in, and for node-fetch to use.

The approach I have on my mind is to exports an additional createFetch() function that allows users to bind specific available features. The traditional { fetch, Headers, Request, Response } API is created with createFetch() with a default set of available utilities (native Promise, etc.).

So to implement a fuller-featured isomorphic-fetch, something like this would work:

// isomorphic-fetch-node.js
import { URL, URLSearchParams } from 'url';

import { Blob } from 'file-api';
import { FormData } from 'form-data';
import { createFetch } from 'node-fetch';
import { CookieJar } from 'tough-cookie';

export createFetch({
  Blob,
  CookieJar,
  FormData,
  URL,
  URLSearchParams
});

// isomorphic-fetch-browser.js
import 'whatwg-fetch';
export { fetch, Headers, Request, Response };

And for traditional uses of the API can be extended:

import { Blob, readBlob } from 'file-api';
import createFetchCookie from 'fetch-cookie';
import originalFetch from 'node-fetch';

const fetch = createFetchCookie(originalFetch);

(async () => {
  const res = await fetch(url, {
    method: 'POST',
    body: 'abc',
    interfaces: {
      Blob,
      fetch // this line might not even be necessary
    }
  });
  const blob = await res.blob();
  const buf = await readBlob(blob);
  // Buffer.isBuffer(buf);
})();

[codecov-io]

Codecov Report

Merging #229 into master will decrease coverage by -1.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #229      +/-   ##
==========================================
- Coverage     100%   98.97%   -1.03%     
==========================================
  Files           6        6              
  Lines         383      392       +9     
  Branches      117      118       +1     
==========================================
+ Hits          383      388       +5     
- Misses          0        2       +2     
- Partials        0        2       +2

Impacted Files	Coverage Δ
src/index.js	97.33% <100%> (-2.67%)	❌
src/body.js	98.56% <0%> (-1.44%)	❌
src/response.js	100% <0%> (ø)	✅
src/headers.js	100% <0%> (ø)	✅
src/request.js	100% <0%> (ø)	✅

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[bitinn]

The approach I have on my mind is to exports an additional createFetch() function that allows users to bind specific available features.

I agree this would be the superior approach, but significant work needs to be done to support this modularize approach. Anyone up to the task?

(Also color me a bit wary of adding features most don't use)

[TimothyGu]

Closing, as we need a bit more time to figure out the best way to tackle this issue.