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Merge pull request #20969 from calixteman/fix_test_comparaison

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Strip private ancillary PNG chunks before comparing images in ref tests
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calixteman 2026-03-24 22:59:12 +01:00 committed by GitHub
commit ae70a5d123
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1 changed files with 36 additions and 1 deletions
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37
test/test.mjs
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@ -33,6 +33,38 @@ import { WebServer } from "./webserver.mjs";
const __dirname = import.meta.dirname;
// Strip private ancillary PNG chunks before comparing snapshots. Firefox adds
// a `deBG` chunk with a per-session unique ID to canvas.toDataURL("image/png")
// output, causing false failures when ref and test were captured in different
// browser sessions.
// For reference:
// https://searchfox.org/firefox-main/rev/1427c88632d1474d2653928745d78feca1a64ee0/image/encoders/png/nsPNGEncoder.cpp#367
function stripPrivatePngChunks(buf) {
const PNG_SIGNATURE = 8;
let pos = PNG_SIGNATURE;
const chunks = [];
const pre_chunk_data = 8; // len (4) + type (4)
const post_chunk_data = 4; // CRC
while (pos < buf.length) {
const len = buf.readUInt32BE(pos);
const type = buf.slice(pos + 4, pos + 8).toString("latin1");
const to_skip = pre_chunk_data + len + post_chunk_data;
// Keep critical chunks (uppercase first letter) and public ancillary
// chunks (uppercase second letter). Drop private ancillary chunks
// (lowercase second letter), e.g. "deBG" added by Firefox.
// See PNG specification for details on chunk types:
// https://www.libpng.org/pub/png/spec/1.2/PNG-Chunks.html#:~:text=4%2E3%2E,-Summary
if (
type[0] === type[0].toUpperCase() ||
type[1] === type[1].toUpperCase()
) {
chunks.push(buf.slice(pos, pos + to_skip));
}
pos += to_skip;
}
return Buffer.concat([buf.slice(0, PNG_SIGNATURE), ...chunks]);
}
function parseOptions() {
const { values } = parseArgs({
args: process.argv.slice(2),
@ -395,7 +427,9 @@ function checkEq(task, results, browser, masterMode) {
}
} else {
refSnapshot = fs.readFileSync(refPath);
eq = refSnapshot.toString("hex") === testSnapshot.toString("hex");
eq =
stripPrivatePngChunks(refSnapshot).toString("hex") ===
stripPrivatePngChunks(testSnapshot).toString("hex");
if (!eq) {
console.log(
"TEST-UNEXPECTED-FAIL | " +
@ -899,6 +933,7 @@ async function startBrowser({
"browser.ml.linkPreview.enabled": false,
"browser.tabs.groups.smart.enabled": false,
"browser.tabs.groups.smart.userEnabled": false,
"privacy.baselineFingerprintingProtection": false,
...extraPrefsFirefox,
};
}