Enable "read with streaming" test in test/unit/network_spec.js

[Rob--W]

The "read with streaming" test looks like this:

pdf.js/test/unit/network_spec.js

Lines 67 to 77 in a4cc85f

	it('read with streaming', function(done) {
	var userAgent = window.navigator.userAgent;
	// The test is valid for FF only: the XHR has support of the
	// 'moz-chunked-array' response type.
	// TODO enable for other browsers, e.g. when fetch/streams API is supported.
	var m = /Mozilla\/5.0.*?rv:(\d+).*? Gecko/.exec(userAgent);
	if (!m || m[1] < 9) {
	expect(true).toEqual(true);
	done();
	return;
	}

There are two issues here:

• Lines 74 - 76 should use pending('Streaming not supported by user agent'); instead of an incorrect done() call.
• With Adds fetch stream logic for networking part of PDF.js #8768, it seems that the test can be enabled for other browsers (Chrome).

@yurydelendik Can the test be enabled for other browsers?

[yurydelendik]

Can the test be enabled for other browsers?

Yes. I don't see why not.

[aryanshar]

Hi. I would like to solve this issue. Please assign me this. And also, please guide me how do i move forward in contributing more to this repository !

[Rob--W]

@aryanshar That's fast, I was still typing the motivation for the good-beginner-bug label. Here it goes:

This bug consist of two parts. The first part is fully explained in the original report.

For the second part, we need to update the if condition to logic along the lines of "if (!isFirefoxWithMozChunkedEncodingSupport && !isFetchWithStreamSupport)` (choose shorter but understandable variable if you wish). The first variable name is based on the current content of the if-statement (by the way, that has a flaw too. If Firefox 90 becomes available, the condition is incorrect). The second variable should indicate whether ReadableStream is supported (see e.g. cd95b42).

[kushagra189]

Is the issue still up? I would like to solve if it is.
PS: Noob here.

[timvandermeij]

There is a PR above, but there was no response since 24 October. You're welcome to use that PR, and in particular the comments there, as inspiration to create a new PR so we can hopefully merge it soon.

[JavierPons]

Hi there!
Do you need help for a "beginners" :p Can you explain more concretely where do you need help? I see that this issue is for @kushagra189. Do you have an other one where I can participate?

[choilmto]

Under the section titled "Browser compatibility", there is a summary of native browser support across desktop and mobile platforms. What does 'streaming response body' refer to, and is it relevant to our needs? Under whatwg's streams standard, a readable stream is a class that uses chunks...is that what line 70 in the code cited above refers to?

As an aside, instead of checking for browser support of fetch() by looking at the user-agent header for information on the browser version, can we do something like expect('fetch' in window).toBe(true);?

[Rob--W]

@choilmto I have updated the MDN pages to be more clear. Take another look if you want to get a better understanding.

Line 70 in the above code refers to the non-standard way of obtaining a response stream in Firefox, via the xhr.responseType = "moz-chunked-arraybuffer" (where xhr is a XMLHttpRequest instance) (so the comment has a typo, "array" should be "arraybuffer").

As an aside, instead of checking for browser support of fetch()

fetch support does not equate support for streaming responses (see the note at the end of #6126 (comment)). Checking for existence of ReadableStream would be sufficient though (this was also done in the proposed pull request at #9050).

The user agent line is still necessary; Alternatively, feature detection can be used, as shown at:

pdf.js/src/display/network.js

Lines 55 to 72 in edaf4b3

	var supportsMozChunked =
	typeof PDFJSDev !== 'undefined' && PDFJSDev.test('CHROME') ? false :
	(function supportsMozChunkedClosure() {
	try {
	var x = new XMLHttpRequest();
	// Firefox 37- required .open() to be called before setting responseType.
	// https://bugzilla.mozilla.org/show_bug.cgi?id=707484
	// Even though the URL is not visited, .open() could fail if the URL is
	// blocked, e.g. via the connect-src CSP directive or the NoScript addon.
	// When this error occurs, this feature detection method will mistakenly
	// report that moz-chunked-arraybuffer is not supported in Firefox 37-.
	x.open('GET', globalScope.location.href);
	x.responseType = 'moz-chunked-arraybuffer';
	return x.responseType === 'moz-chunked-arraybuffer';
	} catch (e) {
	return false;
	}
	})();

[manmeet0307]

Hi. I would like to solve this issue. Please assign me this. And also, please guide me how do i move forward in contributing more to this repository !

[s1iqbal]

Resolved!