Build the DirectAudio relay from source

The relay helper shipped as a prebuilt libdirectaudiorelay.so with no source in the
repo. Its source (The412Banner/directaudio @ 3548a4a, the commit the bundled driver
names in version.txt) now lives in tools/directaudio-relay, unmodified, and CI and
build_local.sh compile it into jniLibs the way proot is built. It shares
da_relay_proto.h with the PulseAudio sink, which is byte-identical to its own copy.

.github/workflows/build-aaudio-sink.yml

@@ -6,6 +6,7 @@ on:
   push:
     paths:
       - 'tools/aaudio-sink/**'
+      - 'tools/directaudio-relay/**'
       - '.github/workflows/build-aaudio-sink.yml'
   workflow_dispatch:
 
@@ -25,6 +26,7 @@ jobs:
           set -euo pipefail
           export NDK="${ANDROID_NDK_LATEST_HOME:-${ANDROID_NDK_HOME:-$ANDROID_NDK_ROOT}}"
           tools/aaudio-sink/build.sh "$PWD/pa13" "$PWD/out"
+          tools/directaudio-relay/build.sh "$PWD/out"
       - uses: actions/upload-artifact@v4
         with:
           name: audio-sink-modules

.github/workflows/build.yml

@@ -325,6 +325,11 @@ jobs:
           mv pulseaudio.tzst app/src/main/assets/pulseaudio.tzst
           tar --use-compress-program=unzstd -tf app/src/main/assets/pulseaudio.tzst | grep -c '\.so$'
           rm -rf pa-bundle sink-out
+      - name: Build the DirectAudio relay
+        run: |
+          set -euo pipefail
+          export NDK="${ANDROID_NDK_LATEST_HOME:-${ANDROID_NDK_HOME:-$ANDROID_NDK_ROOT}}"
+          tools/directaudio-relay/build.sh app/src/main/jniLibs/arm64-v8a
 
       - name: Cache proot
         id: proot

.gitignore

@@ -14,6 +14,7 @@ app/src/main/assets/linuxfs/
 app/src/main/jniLibs/arm64-v8a/libproot.so
 app/src/main/jniLibs/arm64-v8a/.proot-inputs
 app/src/main/jniLibs/arm64-v8a/libproot-loader.so
+app/src/main/jniLibs/arm64-v8a/libdirectaudiorelay.so
 app/src/main/assets/droiddeck-esync/
 
 # Kotlin compiler session files (build-tool state, never source).

tools/build_local.sh

@@ -301,6 +301,7 @@ fi
 
 sink_output="${staging_dir}/sink-out"
 "${repo_root}/tools/aaudio-sink/build.sh" "${pa_source}" "${sink_output}"
+"${repo_root}/tools/directaudio-relay/build.sh" "${repo_root}/app/src/main/jniLibs/arm64-v8a"
 # proot is rebuilt only when its sources (source.env, the patches, the build script) changed since
 # the libraries in jniLibs were built.
 proot_out="${repo_root}/app/src/main/jniLibs/arm64-v8a"

tools/directaudio-relay/build.sh

@@ -0,0 +1,40 @@
+#!/usr/bin/env bash
+set -euo pipefail
+OUTDIR=$1
+mkdir -p "$OUTDIR"
+: "${NDK:?set NDK to the Android NDK root}"
+API=28
+HERE=$(cd "$(dirname "$0")" && pwd)
+REPO=$(cd "$HERE/../.." && pwd)
+case "$(uname -s):$(uname -m)" in
+  Darwin:arm64) NDK_HOST=darwin-arm64 ;;
+  Darwin:x86_64) NDK_HOST=darwin-x86_64 ;;
+  Linux:x86_64) NDK_HOST=linux-x86_64 ;;
+  Linux:aarch64|Linux:arm64) NDK_HOST=linux-aarch64 ;;
+  *) echo "Unsupported build host: $(uname -s) $(uname -m)" >&2; exit 1 ;;
+esac
+TOOLCHAIN="$NDK/toolchains/llvm/prebuilt/$NDK_HOST/bin"
+if [[ ! -d "$TOOLCHAIN" && "$NDK_HOST" == darwin-arm64 && -d "$NDK/toolchains/llvm/prebuilt/darwin-x86_64/bin" ]]; then
+  TOOLCHAIN="$NDK/toolchains/llvm/prebuilt/darwin-x86_64/bin"
+fi
+if [[ ! -d "$TOOLCHAIN" && "$NDK_HOST" == linux-aarch64 && -d "$NDK/toolchains/llvm/prebuilt/linux-x86_64/bin" ]]; then
+  TOOLCHAIN="$NDK/toolchains/llvm/prebuilt/linux-x86_64/bin"
+fi
+CC="$TOOLCHAIN/aarch64-linux-android${API}-clang"
+if [[ ! -x "$CC" ]]; then
+  echo "Android NDK toolchain not found at $TOOLCHAIN" >&2
+  exit 1
+fi
+OUT="$OUTDIR/libdirectaudiorelay.so"
+"$CC" -O2 -Wall -Wextra -Wno-unused-parameter -Wno-sign-compare -fPIE -pie -Wl,-z,max-page-size=16384 \
+    -I"$REPO/tools/aaudio-sink" \
+    -o "$OUT" "$HERE/directaudio-relay.c" -laaudio -llog
+"$TOOLCHAIN/llvm-strip" --strip-unneeded "$OUT"
+NEEDED=$("$TOOLCHAIN/llvm-readelf" -d "$OUT" | sed -n 's/.*NEEDED.*\[\(.*\)\]/\1/p' | tr '\n' ' ')
+echo "$(basename "$OUT") NEEDED: $NEEDED"
+for lib in $NEEDED; do
+  case $lib in libaaudio.so|liblog.so|libc.so|libm.so|libdl.so) ;;
+  *) echo "ERROR: unexpected dependency $lib"; exit 1 ;;
+  esac
+done
+ls -l "$OUT"