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Skip the copy in writeRbsp when a frame needs no escaping - #2184
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Find the escape points first, return the input when there are none, and otherwise copy the runs between them with Uint8Array.set. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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size-limit report 📦
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1egoman
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Oct 25, 2026
| * Returns `data_in` itself when nothing needs escaping, which is the case for almost | ||
| * every encrypted frame. Callers must not mutate the result in place. | ||
| */ | ||
| export function writeRbsp(data_in: NonSharedUint8Array): NonSharedUint8Array { |
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nitpick: data_in should probably be dataIn?
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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The E2EE worker calls
writeRbspon every encrypted H.264 and H.265 frame on the sender. It adds emulation prevention bytes so that the ciphertext never contains a start code. Today the function pushes every byte into a JS array and then copies that array into aUint8Array. On a 500 KB keyframe this takes about 2.2 ms, but AES-GCM takes about 0.09 ms. We found this while working on #2181.Change
writeRbspscans the input once and records each index that needs an emulation prevention byte. If there are none, it returns the input unchanged. This is the case for almost every encrypted frame, because random ciphertext rarely has two zeros followed by a byte<= 3. If there are escapes, it allocates the output once and copies the runs between the escapes withUint8Array.set. The output and the wire format do not change.parseRbspdoes not change, because the receiver calls it only afterneedsRbspUnescapingfinds an escape.Verified
npx vitest run src/e2eepasses. The newsrc/e2ee/utils.test.tschecks known escaped sequences: no escape, one escape, runs of zeros, and trailing zeros. It also checks that the function returns the same instance when nothing needs escaping.🤖 Generated with Claude Code