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fix(core): read WebP VP8X canvas height from the correct byte offset #5194

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Merged
wenshao merged 2 commits into from
Jun 18, 2026
Merged

fix(core): read WebP VP8X canvas height from the correct byte offset #5194

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1f8e96c
fix(core): read WebP VP8X canvas height from the correct byte offset
he-yufeng Jun 16, 2026
09c53bb
docs(core): document WebP dimension byte offsets
he-yufeng Jun 17, 2026
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25 changes: 25 additions & 0 deletions packages/core/src/utils/request-tokenizer/imageTokenizer.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -102,6 +102,31 @@ describe('ImageTokenizer', () => {
});
});

describe('WebP dimension extraction', () => {
it('should extract canvas dimensions from VP8X', async () => {
const width = 100;
const height = 80;

const buf = Buffer.alloc(30);
buf.write('RIFF', 0, 'ascii');
buf.writeUInt32LE(22, 4);
buf.write('WEBP', 8, 'ascii');
buf.write('VP8X', 12, 'ascii');
buf.writeUInt32LE(10, 16); // VP8X chunk size
buf.writeUInt8(0, 20); // flags
buf.writeUIntLE(width - 1, 24, 3); // canvas width minus one (24-bit LE)
buf.writeUIntLE(height - 1, 27, 3); // canvas height minus one (24-bit LE)

const metadata = await tokenizer.extractImageMetadata(
buf.toString('base64'),
'image/webp',
);

expect(metadata.width).toBe(width);
expect(metadata.height).toBe(height);
});
});

describe('batch processing', () => {
it('should process multiple images serially', async () => {
const pngBase64 =
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7 changes: 5 additions & 2 deletions packages/core/src/utils/request-tokenizer/imageTokenizer.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -213,17 +213,20 @@ export class ImageTokenizer {
const format = buffer.subarray(12, 16).toString('ascii');

if (format === 'VP8 ') {
// Lossy: 14-bit width/height at bytes 26-27 and 28-29 (little-endian)
const width = buffer.readUInt16LE(26) & 0x3fff;
const height = buffer.readUInt16LE(28) & 0x3fff;
return { width, height };
} else if (format === 'VP8L') {
// Lossless: 14-bit (width-1) then (height-1) packed from byte 21 (little-endian)
const bits = buffer.readUInt32LE(21);
const width = (bits & 0x3fff) + 1;
const height = ((bits >> 14) & 0x3fff) + 1;
return { width, height };
} else if (format === 'VP8X') {
const width = (buffer.readUInt32LE(24) & 0xffffff) + 1;
const height = (buffer.readUInt32LE(26) & 0xffffff) + 1;
// Extended: 24-bit (canvas width-1) at bytes 24-26 and (height-1) at bytes 27-29 (little-endian)
const width = buffer.readUIntLE(24, 3) + 1;
const height = buffer.readUIntLE(27, 3) + 1;

@doudouOUC doudouOUC Jun 16, 2026

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[Suggestion] The byte offsets 24 and 27 are undocumented magic numbers. The surrounding codebase has an established convention: extractPngDimensions documents "Width/height at bytes 16-19 and 20-23", and extractJpegDimensions documents "Dimensions at offset +5 (height) and +7 (width)". The VP8X branch is the only format parser without such documentation.

The bug this PR fixes was precisely caused by a wrong offset (26 instead of 27) — the absence of a spec-reference comment makes this code fragile against future edits.

Suggested change
const height = buffer.readUIntLE(27, 3) + 1;
} else if (format === 'VP8X') {
// VP8X extended format: canvas dimensions are 24-bit LE values
// stored as (dimension - 1). Width at bytes 24-26, height at 27-29.
const width = buffer.readUIntLE(24, 3) + 1;
const height = buffer.readUIntLE(27, 3) + 1;
return { width, height };

— qwen3.7-max via Qwen Code /review

return { width, height };
}

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