83 lines
2.9 KiB
Markdown
83 lines
2.9 KiB
Markdown
# Custom WebRTC for Rosetta Android (Audio E2EE Timestamp)
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This setup builds a custom `libwebrtc.aar` for Android and patches audio E2EE so
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`FrameEncryptor/FrameDecryptor` receive non-empty `additional_data` with RTP timestamp bytes.
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## Why
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Stock `io.github.webrtc-sdk:android:125.6422.07` can call audio frame encryptor with empty
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`additional_data` (`ad=0`), so nonce derivation based on timestamp is unavailable.
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Desktop uses frame timestamp for nonce. This patch aligns Android with that approach by passing
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an 8-byte big-endian timestamp payload in `additional_data` (absolute RTP timestamp,
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including sender start offset):
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- bytes `0..3` = `0`
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- bytes `4..7` = RTP timestamp (big-endian)
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## Files
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- `build_custom_webrtc.sh` — reproducible build script
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- `patches/0001-audio-e2ee-pass-rtp-timestamp-as-additional-data.patch` — WebRTC patch
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- `patches/0002-android-build-on-mac-host.patch` — allows Android target build on macOS host
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- `patches/0003-macos-host-java-ijar.patch` — enables host tools (`ijar`/`jdk`) on macOS
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- `patches/0004-macos-linker-missing-L-dirs.patch` — skips invalid host `-L...` paths for lld
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- `patches/0005-macos-server-utils-socket.patch` — handles macOS socket errno in Android Java compile helper
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## Build
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Recommended on Linux (macOS is supported via additional patches in this folder).
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Bootstrap `depot_tools` first:
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```bash
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cd /path/to/rosetta-android/tools/webrtc-custom
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./bootstrap_depot_tools.sh
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```
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Then run:
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```bash
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cd /path/to/rosetta-android/tools/webrtc-custom
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./build_custom_webrtc.sh
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```
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Optional env vars:
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- `WEBRTC_ROOT` — checkout root (default: `$HOME/webrtc_android`)
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- `WEBRTC_SRC` — direct path to `src/`
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- `WEBRTC_BRANCH` — default `branch-heads/6422`
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- `WEBRTC_TAG` — use a specific tag/commit instead of branch
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- `OUT_AAR` — output AAR path (default: `app/libs/libwebrtc-custom.aar`)
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- `SYNC_JOBS` — `gclient sync` jobs (default: `1`, safer for googlesource limits)
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- `SYNC_RETRIES` — sync retry attempts (default: `8`)
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- `SYNC_RETRY_BASE_SEC` — base retry delay in seconds (default: `20`)
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- `MAC_ANDROID_NDK_ROOT` — local Android NDK path on macOS (default: `~/Library/Android/sdk/ndk/27.1.12297006`)
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## Troubleshooting (HTTP 429 / RESOURCE_EXHAUSTED)
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If build fails with:
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- `The requested URL returned error: 429`
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- `RESOURCE_EXHAUSTED`
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- `Short term server-time rate limit exceeded`
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run with conservative sync settings:
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```bash
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SYNC_JOBS=1 SYNC_RETRIES=12 SYNC_RETRY_BASE_SEC=30 ./build_custom_webrtc.sh
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```
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The script now retries `fetch`, `git fetch`, and `gclient sync` with backoff.
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## Integration in app
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`app/build.gradle.kts` already prefers local `app/libs/libwebrtc-custom.aar` if present.
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If file exists, Maven WebRTC dependency is not used.
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## Maintenance policy
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- Keep patch small and isolated to `audio/channel_send.cc` + `audio/channel_receive.cc`.
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- Pin WebRTC branch/tag for releases.
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- Rebuild AAR on version bumps and verify `e2ee_diag.txt` shows `ad=8` (or non-zero).
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