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Improve WebM detection #486

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Sep 1, 2021
Merged

Improve WebM detection #486

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3 changes: 2 additions & 1 deletion core.js
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Original file line number Diff line number Diff line change
Expand Up @@ -736,7 +736,8 @@ async function _fromTokenizer(tokenizer) {
while (children > 0) {
const element = await readElement();
if (element.id === 0x42_82) {
return tokenizer.readToken(new Token.StringType(element.len, 'utf-8')); // Return DocType
const rawValue = await tokenizer.readToken(new Token.StringType(element.len, 'utf-8'));
return rawValue.replace(/\00.*$/g, ''); // Return DocType
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Does it document the maximum amount of null characters there could be? Would be nice to have a limit in place so it wouldn't hang on faulty files that has too many null characters.

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There is no maximum, it's used as a kind of padding.
The maximum length is of the string read is already terminated by element.len.

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@Borewit Borewit Aug 31, 2021 •
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Ah you mean check element.len? The length can exceed the JavaScript number length and is encoded a specific way (VINT examples).
At that point the assumption is already it is EBML and starts to consume the tokenizer
and iterate through the EBML elements.
You could say, the docType must be a relative short value, but then we already matched 0x1A, 0x45, 0xDF, 0xA3 & 0x42_82. Extremely unlikely we hit that point without the format being EBML.

}

await tokenizer.ignore(element.len); // ignore payload
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Binary file added fixture/fixture-null.webm
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3 changes: 3 additions & 0 deletions test.js
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Expand Up @@ -203,6 +203,9 @@ const names = {
'fixture-fast-web', // PDF saved from Adobe Illustrator, using the default "[Illustrator Default"] preset, but enabling "Optimize for Fast Web View"
'fixture-printed', // PDF printed from Adobe Illustrator, but with a PDF printer.
],
webm: [
'fixture-null', // EBML DocType with trailing null character
],
};

// Define an entry here only if the file type has potential
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