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LibWeb: Implement OfflineAudioContext #224

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Lubrsi opened this issue Jun 20, 2024 · 1 comment
Open

LibWeb: Implement OfflineAudioContext #224

Lubrsi opened this issue Jun 20, 2024 · 1 comment
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enhancement New feature or request reduction of web content Issue has a simplified reduction based on real-world web content. web compatibility

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@Lubrsi
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Lubrsi commented Jun 20, 2024

Required by Cloudflare Turnstile's fingerprinting. It checks for the existence of OfflineAudioContext and, if that doesn't exist, webkitOfflineAudioContext. If neither exist, it returns from the AudioContext fingerprinting test but fails to progress the challenge runner to the next test, causing it to indefinitely lock-up. (Side note, this seems to be a bug in the challenge runner, as it progresses the runner for other things not existing such as fetch, which arrived to the web platform after OfflineAudioContext)

Reduced from Turnstile:

<!DOCTYPE html>
<html>
<head>
</head>
<body>
<div id="challenge-stage"></div>
<script>
    function sha256Hash(stringToHash) {
        const encodedString = new TextEncoder().encode(stringToHash);
        return crypto.subtle.digest("SHA-256", encodedString).then((value) => {
            const valueAsArray = Array.from(new Uint8Array(value));
            const arrayAsHex = valueAsArray.map(num => num.toString(16).padStart(2, '0'));
            return arrayAsHex.join("");
        });
    }

    const audioContext = new OfflineAudioContext(1, 5000, 44100);

    const oscillator = audioContext.createOscillator();
    oscillator.type = "triangle";
    oscillator.frequency.value = 9998.123456;

    const dynamicsCompressor = audioContext.createDynamicsCompressor();
    dynamicsCompressor.threshold.value = -52;
    dynamicsCompressor.knee.value = 40;
    dynamicsCompressor.ratio.value = 12;
    dynamicsCompressor.attack.value = 0.0001;
    dynamicsCompressor.release.value = 0.25;

    oscillator.connect(dynamicsCompressor);

    dynamicsCompressor.connect(audioContext.destination);

    oscillator.start();
    audioContext.oncomplete = function (ev) {
        const data = ev.renderedBuffer.getChannelData(0);
        if (data && data.length > 0) {
            const joinedValues = data.join("|");
            sha256Hash(joinedValues).then(fingerprint => {
                document.getElementById("challenge-stage").innerText = `AudioContext fingerprint: ${fingerprint}`
            });
        }
    };

    audioContext.startRendering();
</script>
</body>
</html>
@Lubrsi Lubrsi added enhancement New feature or request reduction of web content Issue has a simplified reduction based on real-world web content. web compatibility labels Jun 20, 2024
This was referenced Jun 20, 2024
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@carlosjeurissen
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In Safari Lockdown mode, both OfflineAudioContext and AudioContext are undefined. So if the Cloudflare Turnstile's fingerprinting works fine in Safari Lockdown mode, the issue seems not be caused by the OfflineAudioContext.

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enhancement New feature or request reduction of web content Issue has a simplified reduction based on real-world web content. web compatibility
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@carlosjeurissen @Lubrsi