Parse the font file to determine the correct type/subtype, rather than relying on the (often incorrect) data in the font dictionary

[Snuffleupagus]

The current font type/subtype detection code is quite inconsistent/unwieldy. In some cases it will simply assume that the font dictionary is correct, in others it will somewhat "arbitrarily" check the actual font file (more of these cases have been added over the years to fix specific bugs).

As is evident from e.g. issue #9949, the font type/subtype detection code is continuing to cause issues. In an attempt to get rid of these hacks once and for all, this patch instead re-factors the type/subtype detection to always parse the font file.

Please note that, as far as I can tell, we still appear to need to rely on the composite font detection based on the font dictionary. However, even if the composite/non-composite detection would get it wrong, that shouldn't really matter too much given that there's basically only two different code-paths (for "TrueType-like" vs "Type1-like" fonts).

This PR provides a complete fix for issue #9949, in addition to the generally useful workaround implemented by PR #9958. Furthermore, this PR also ought to prevent any future font type/subtype detection bugs too.

[Snuffleupagus]

Since I've not run any tests locally, I suppose that this could all fail spectacularly :-)

/botio test

[pdfjsbot]

From: Bot.io (Linux m4)

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Live output at: http://54.67.70.0:8877/f0223b1439add40/output.txt

[pdfjsbot]

From: Bot.io (Windows)

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Received

Command cmd_test from @Snuffleupagus received. Current queue size: 0

Live output at: http://54.215.176.217:8877/31cfe6bf0474055/output.txt

[pdfjsbot]

From: Bot.io (Windows)

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Failed

Full output at http://54.215.176.217:8877/31cfe6bf0474055/output.txt

Total script time: 28.26 mins

• Font tests: Passed
• Unit tests: Passed
• Regression tests: FAILED

Image differences available at: http://54.215.176.217:8877/31cfe6bf0474055/reftest-analyzer.html#web=eq.log

[pdfjsbot]

From: Bot.io (Linux m4)

---

Failed

Full output at http://54.67.70.0:8877/f0223b1439add40/output.txt

Total script time: 35.84 mins

• Font tests: Passed
• Unit tests: Passed
• Regression tests: FAILED

Image differences available at: http://54.67.70.0:8877/f0223b1439add40/reftest-analyzer.html#web=eq.log

[Snuffleupagus]

The failures should hopefully all be caused by a pre-existing existing, since the isTrueTypeFile helper function wasn't able to detect certain Mac fonts.

/botio test

[pdfjsbot]

From: Bot.io (Linux m4)

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Live output at: http://54.67.70.0:8877/fa6d144f1ee0ca8/output.txt

[pdfjsbot]

From: Bot.io (Windows)

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Received

Command cmd_test from @Snuffleupagus received. Current queue size: 0

Live output at: http://54.215.176.217:8877/1e43c45a6f0fe7c/output.txt

[pdfjsbot]

From: Bot.io (Windows)

---

Success

Full output at http://54.215.176.217:8877/1e43c45a6f0fe7c/output.txt

Total script time: 28.13 mins

• Font tests: Passed
• Unit tests: Passed
• Regression tests: Passed

[pdfjsbot]

From: Bot.io (Linux m4)

---

Success

Full output at http://54.67.70.0:8877/fa6d144f1ee0ca8/output.txt

Total script time: 36.04 mins

• Font tests: Passed
• Unit tests: Passed
• Regression tests: Passed

[Snuffleupagus]

/botio test

[pdfjsbot]

From: Bot.io (Linux m4)

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Command cmd_test from @Snuffleupagus received. Current queue size: 0

Live output at: http://54.67.70.0:8877/475437f1133487f/output.txt

[pdfjsbot]

From: Bot.io (Windows)

---

Received

Command cmd_test from @Snuffleupagus received. Current queue size: 0

Live output at: http://54.215.176.217:8877/f121e937e602f73/output.txt

[pdfjsbot]

From: Bot.io (Windows)

---

Success

Full output at http://54.215.176.217:8877/f121e937e602f73/output.txt

Total script time: 28.22 mins

• Font tests: Passed
• Unit tests: Passed
• Regression tests: Passed

[pdfjsbot]

From: Bot.io (Linux m4)

---

Success

Full output at http://54.67.70.0:8877/475437f1133487f/output.txt

Total script time: 35.44 mins

• Font tests: Passed
• Unit tests: Passed
• Regression tests: Passed

[timvandermeij]

/botio-linux preview

[pdfjsbot]

From: Bot.io (Linux m4)

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Live output at: http://54.67.70.0:8877/a981105c1fd19e7/output.txt

[pdfjsbot]

From: Bot.io (Linux m4)

---

Success

Full output at http://54.67.70.0:8877/a981105c1fd19e7/output.txt

Total script time: 6.91 mins

Published

• Viewer: http://54.67.70.0:8877/a981105c1fd19e7/web/viewer.html

[timvandermeij]

Thank you for improving this; much more readable this way and I verified that it fixes the issue too.

[brendandahl]

Another possibility is doing something like tx and peek into the file:

https://github.com/adobe-type-tools/afdko/blob/d9f9d28ac6959d7c12858c28a8a488e63e3dd174/c/tx/source/tx.c#L6767

[Snuffleupagus]

Another possibility is doing something like tx and peek into the file:

But... that's what this PR does :-)

The newly added getFontFileType function will "peek" into the font files themselves to determine their actual types, by making use of these existing helper functions:

pdf.js/src/core/fonts.js

Lines 656 to 700 in c8ee633

	function isTrueTypeFile(file) {
	var header = file.peekBytes(4);
	return (readUint32(header, 0) === 0x00010000 ||
	bytesToString(header) === 'true');
	}
	function isTrueTypeCollectionFile(file) {
	let header = file.peekBytes(4);
	return bytesToString(header) === 'ttcf';
	}
	function isOpenTypeFile(file) {
	var header = file.peekBytes(4);
	return bytesToString(header) === 'OTTO';
	}
	function isType1File(file) {
	var header = file.peekBytes(2);
	// All Type1 font programs must begin with the comment '%!' (0x25 + 0x21).
	if (header[0] === 0x25 && header[1] === 0x21) {
	return true;
	}
	// ... obviously some fonts violate that part of the specification,
	// please refer to the comment in |Type1Font| below.
	if (header[0] === 0x80 && header[1] === 0x01) { // pfb file header.
	return true;
	}
	return false;
	}
	/**
	* Compared to other font formats, the header in CFF files is not constant
	* but contains version numbers. To reduce the possibility of misclassifying
	* font files as CFF, it's recommended to check for other font formats first.
	*/
	function isCFFFile(file) {
	const header = file.peekBytes(4);
	if (/* major version, [1, 255] */ header[0] >= 1 &&
	/* minor version, [0, 255]; header[1] */
	/* header size, [0, 255]; header[2] */
	/* offset(0) size, [1, 4] */ (header[3] >= 1 && header[3] <= 4)) {
	return true;
	}
	return false;
	}

[brendandahl]

Hah, okay, I was lazy and didn't look into what all the is<SomeType> method did. I assumed we were just looking at the font dictionary.