terimnated connections should propagate into response.body

[Gozala]

What is the purpose of this pull request?

• Documentation update
• Bug fix
• New feature
• Other, please explain: Test case for the bug report

What changes did you make? (provide an overview)

• Added a test case that illustrates the probem

Which issue (if any) does this pull request address?

#1055

Is there anything you'd like reviewers to know?

[tekwiz]

@Gozala Is this intended to be a draft pull request? I only see a failing test case for Node 12. Also, it appears that Node 14 is unaffected by this bug. Can you confirm?

[tekwiz]

@Gozala Nevermind my previous comment. I understand what this is for now. Thank you for the test case. I may have a solution for this in the works already, but I'll keep you posted.

[Gozala]

@tekwiz I did some investigation of this and I think the fix would require lifting this, up into the response.body itself:

node-fetch/src/body.js

Lines 218 to 230 in d016690

	if (body.readableEnded === true || body._readableState.ended === true) {
	try {
	if (accum.every(c => typeof c === 'string')) {
	return Buffer.from(accum.join(''));
	}
	return Buffer.concat(accum, accumBytes);
	} catch (error) {
	throw new FetchError(`Could not create Buffer from response body for ${data.url}: ${error.message}`, 'system', error);
	}
	} else {
	throw new FetchError(`Premature close of server response while trying to fetch ${data.url}`);
	}

However I was not sure what made sense here as I don't exactly understand rationale behind choosing to use node stream for response.body (as opposed to ReadableStream) & if propagating those errors was aligned with it.

[tekwiz]

This was merged with #1064.