ci(docker): portable multi-arch image, unprivileged runtime, GHCR publish

.github/workflows/docker.yml

@@ -0,0 +1,122 @@
+name: Docker
+
+on:
+  push:
+    branches: [main]
+    tags: ['v*']
+  workflow_dispatch:
+
+# Native per-arch runners instead of QEMU: build-std + fat LTO is far too slow
+# under emulation. Each arch builds in parallel, pushed by digest, then merged
+# into one multi-arch manifest.
+concurrency:
+  group: docker-${{ github.ref }}
+  cancel-in-progress: true
+
+env:
+  REGISTRY: ghcr.io
+  IMAGE_NAME: ${{ github.repository }}
+
+jobs:
+  build:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - platform: linux/amd64
+            runner: ubuntu-latest
+          - platform: linux/arm64
+            runner: ubuntu-24.04-arm
+    runs-on: ${{ matrix.runner }}
+    permissions:
+      contents: read
+      packages: write
+    steps:
+      - name: Prepare platform pair
+        run: |
+          platform=${{ matrix.platform }}
+          echo "PLATFORM_PAIR=${platform//\//-}" >> "$GITHUB_ENV"
+
+      - uses: actions/checkout@v6
+
+      - id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+
+      - uses: docker/setup-buildx-action@v3
+
+      - uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - id: build
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          platforms: ${{ matrix.platform }}
+          labels: ${{ steps.meta.outputs.labels }}
+          # Per-arch cache scope so the two matrix legs never clobber each other.
+          cache-from: type=gha,scope=${{ env.PLATFORM_PAIR }}
+          cache-to: type=gha,mode=max,scope=${{ env.PLATFORM_PAIR }}
+          outputs: type=image,name=${{ env.REGISTRY }}/${{ env.IMAGE_NAME }},push-by-digest=true,name-canonical=true,push=true
+
+      - name: Export digest
+        run: |
+          mkdir -p "${{ runner.temp }}/digests"
+          digest="${{ steps.build.outputs.digest }}"
+          touch "${{ runner.temp }}/digests/${digest#sha256:}"
+
+      - name: Upload digest
+        uses: actions/upload-artifact@v4
+        with:
+          name: digests-${{ env.PLATFORM_PAIR }}
+          path: ${{ runner.temp }}/digests/*
+          if-no-files-found: error
+          retention-days: 1
+
+  merge:
+    runs-on: ubuntu-latest
+    needs: [build]
+    permissions:
+      contents: read
+      packages: write
+    steps:
+      - name: Download digests
+        uses: actions/download-artifact@v4
+        with:
+          path: ${{ runner.temp }}/digests
+          pattern: digests-*
+          merge-multiple: true
+
+      - uses: docker/setup-buildx-action@v3
+
+      - id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+          tags: |
+            type=ref,event=branch
+            type=ref,event=tag
+            type=semver,pattern={{version}}
+            type=sha
+            type=raw,value=latest,enable={{is_default_branch}}
+
+      - uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Create manifest list and push
+        working-directory: ${{ runner.temp }}/digests
+        run: |
+          docker buildx imagetools create $(jq -cr '.tags | map("-t " + .) | join(" ")' <<< "$DOCKER_METADATA_OUTPUT_JSON") \
+            $(printf '${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}@sha256:%s ' *)
+        env:
+          DOCKER_METADATA_OUTPUT_JSON: ${{ steps.meta.outputs.json }}
+
+      - name: Inspect
+        run: docker buildx imagetools inspect ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:${{ steps.meta.outputs.version }}

Dockerfile

@@ -7,7 +7,9 @@
 # Build:  docker build -t whatsapp-rust .
 # Run:    docker run -v whatsapp-data:/data whatsapp-rust
 #
-# The /data volume persists the SQLite database across restarts.
+# The /data volume persists the SQLite database across restarts. The image runs
+# unprivileged (uid 65532); use a named volume (as below) so it inherits that
+# ownership and stays writable — a host bind mount would need matching ownership.
 # Pass --phone <number> for pair code auth:
 #   docker run -v whatsapp-data:/data whatsapp-rust --phone 15551234567
 
@@ -33,7 +35,11 @@ FROM chef AS builder
 # (measured: -666 KiB, -5.6% .text). Nightly-only, which this image already
 # pins via rust-toolchain.toml; with fat LTO the historical inlining downside
 # does not apply since LTO sees all bitcode anyway.
-ENV RUSTFLAGS="-C target-cpu=native -Zshare-generics=y"
+# No -C target-cpu: a published image must run on any host of its arch, so we
+# keep the portable musl baseline instead of pinning the build machine's CPU
+# (target-cpu=native would risk SIGILL on older/different hosts and is
+# meaningless under emulated cross-arch builds).
+ENV RUSTFLAGS="-Zshare-generics=y"
 
 # build-std recompiles std with the release profile so it participates in fat
 # LTO and dead-code elimination instead of linking the prebuilt rustup std
@@ -47,19 +53,29 @@ ENV CARGO_UNSTABLE_BUILD_STD="std,panic_abort"
 # chef stage's copy at /; the nightly-only RUSTFLAGS above depends on it.
 COPY rust-toolchain.toml .
 COPY --from=planner /app/recipe.json recipe.json
-# build-std demands an explicit --target; use the image's own host triple so
-# multi-arch builds (e.g. buildx linux/arm64) keep producing native binaries
-# exactly like the implicit-target build did.
+# build-std demands an explicit --target; derive the image's own host triple so
+# buildx per-arch builds (linux/amd64, linux/arm64) each target their own arch.
 RUN rustc -vV | sed -n 's/^host: //p' > /rust-target && test -s /rust-target
-RUN cargo chef cook --release --recipe-path recipe.json --target "$(cat /rust-target)"
+# Cook with the same --example as the final build so the example's dev-deps
+# (env_logger, …) are cached here instead of recompiling after the source COPY.
+RUN cargo chef cook --release --recipe-path recipe.json --target "$(cat /rust-target)" --example demo
 COPY . .
 # The client lives in examples/demo.rs (the package no longer ships a bin); the
 # example artifact lands under release/examples/. Default features cover it.
 RUN cargo build --release --example demo --target "$(cat /rust-target)" \
     && cp "target/$(cat /rust-target)/release/examples/demo" /app/whatsapp-rust-bin
 
-# --- Runtime: static binary on empty image ---
+# Empty dirs to stage into the scratch image; the COPY --chown below grants them
+# to the unprivileged uid so /data (DB; a fresh named volume inherits the
+# ownership) and /tmp (SQLite temp files, absent on scratch) stay writable.
+RUN mkdir -p /newroot/data /newroot/tmp
+
+# --- Runtime: static binary on empty image, unprivileged ---
 FROM scratch
+COPY --from=builder --chown=65532:65532 /newroot/tmp /tmp
+COPY --from=builder --chown=65532:65532 /newroot/data /data
 COPY --from=builder /app/whatsapp-rust-bin /whatsapp-rust
+ENV TMPDIR=/tmp
 WORKDIR /data
+USER 65532:65532
 ENTRYPOINT ["/whatsapp-rust"]