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fix(media): add hasBinaryAudioMagic + audio skip in extractFileBlocks

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Combines two complementary defenses against audio misidentification:

1. Skip audio kind early in extractFileBlocks() to avoid unnecessary
   buffer reads (original fix from #4235)
2. Add hasBinaryAudioMagic() to detect OGG/MP3 by magic bytes, preventing
   looksLikeUtf8Text() false positives (approach from #3904)

Together these provide defense-in-depth: the kind check handles the
common case efficiently, while magic bytes catch edge cases where
attachment kind resolution fails.

Fixes #1989
This commit is contained in:
nullrunner 2026-01-30 00:01:03 +01:00
parent 67bbacb3b7
commit 586cf569fd
1 changed files with 47 additions and 1 deletions
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48
src/media-understanding/apply.ts
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@ -162,6 +162,48 @@ function looksLikeUtf8Text(buffer?: Buffer): boolean {
return printable / total > 0.85;
}
/**
* Detects binary audio/video formats by magic bytes (file signatures).
*
* OGG files (used by Telegram voice messages as OGG Opus) have ASCII-heavy
* headers that can pass looksLikeUtf8Text() due to Vorbis/Opus comment metadata
* containing printable strings. This causes them to be misidentified as text.
*
* Magic bytes provide authoritative format detection independent of MIME type
* or file extension, following established file format specifications.
*
* References:
* - OGG container: RFC 3533 (https://datatracker.ietf.org/doc/html/rfc3533)
* Section 6: "OggS" capture pattern at byte offset 0
* - MP3 ID3v2: id3.org spec (https://id3.org/id3v2.4.0-structure)
* Section 3.1: "ID3" identifier at file start
*
* @see https://github.com/moltbot/moltbot/issues/1989
*/
function hasBinaryAudioMagic(buffer?: Buffer): boolean {
if (!buffer || buffer.length < 4) return false;
// OGG container format: "OggS" signature (RFC 3533 Section 6)
// Covers OGG Vorbis, OGG Opus (Telegram voice), OGG Theora, etc.
if (
buffer[0] === 0x4f && // 'O'
buffer[1] === 0x67 && // 'g'
buffer[2] === 0x67 && // 'g'
buffer[3] === 0x53 // 'S'
) {
return true;
}
// MP3 with ID3v2 tag: "ID3" signature (id3.org spec Section 3.1)
// ID3v2 tags can contain large amounts of ASCII text (lyrics, comments)
if (
buffer[0] === 0x49 && // 'I'
buffer[1] === 0x44 && // 'D'
buffer[2] === 0x33 // '3'
) {
return true;
}
return false;
}
function decodeTextSample(buffer?: Buffer): string {
if (!buffer || buffer.length === 0) return "";
const sample = buffer.subarray(0, Math.min(buffer.length, 8192));
@ -242,7 +284,11 @@ async function extractFileBlocks(params: {
const forcedTextMimeResolved = forcedTextMime ?? resolveTextMimeFromName(nameHint ?? "");
const utf16Charset = resolveUtf16Charset(bufferResult?.buffer);
const textSample = decodeTextSample(bufferResult?.buffer);
const textLike = Boolean(utf16Charset) || looksLikeUtf8Text(bufferResult?.buffer);
// Check if content looks like text, but exclude files with known binary audio magic bytes
// OGG files can pass looksLikeUtf8Text() due to ASCII-heavy headers (>85% printable)
const textLike =
(Boolean(utf16Charset) || looksLikeUtf8Text(bufferResult?.buffer)) &&
!hasBinaryAudioMagic(bufferResult?.buffer);
if (!forcedTextMimeResolved && kind === "audio" && !textLike) {
continue;
}