docker.yml

name: Docker image

# Builds and publishes the public Buzz relay image as ghcr.io/block/buzz.
#
# Strategy: each architecture builds on its native runner (ubuntu-24.04 for
# amd64, ubuntu-24.04-arm for arm64), pushes to GHCR by digest, then a final
# job stitches the per-arch digests into a single multi-arch manifest.
# This avoids QEMU emulation (~10× slower for Rust) at zero cost on free
# GitHub-hosted runners.
#
# Triggers:
#   - push to main         → :main + :sha-<7>
#   - push tags v*.*.*     → :latest + :{version} + :{major}.{minor} + :{major}
#   - pull_request         → build only (no push), cache stays warm
#   - workflow_dispatch    → manual canary

on:
  push:
    branches: [main]
    tags: ["v[0-9]*"]
  pull_request:
    paths:
      - "Dockerfile"
      - ".dockerignore"
      - ".github/workflows/docker.yml"
      - "Cargo.toml"
      - "Cargo.lock"
      - "rust-toolchain.toml"
      - "crates/**"
      - "web/**"
      - "package.json"
      - "pnpm-lock.yaml"
      - "pnpm-workspace.yaml"
      - "patches/**"
  workflow_dispatch:

# One image build per ref; cancel superseded PR builds, but never cancel
# tag/main builds (publishing must not be aborted mid-flight).
concurrency:
  group: docker-${{ github.workflow }}-${{ github.ref }}
  cancel-in-progress: ${{ github.ref_type == 'branch' && github.event_name == 'pull_request' }}

permissions: {}

env:
  # Single source of truth for the image name. Set GHCR_IMAGE as a repo
  # variable to override (e.g., for forks that want to push to their own
  # namespace without forking this file).
  IMAGE_NAME: ${{ vars.GHCR_IMAGE != '' && vars.GHCR_IMAGE || 'ghcr.io/block/buzz' }}

jobs:
  build:
    name: Build (${{ matrix.platform }})
    runs-on: ${{ matrix.runner }}
    timeout-minutes: 60
    permissions:
      contents: read
      packages: write    # push to GHCR
      id-token: write    # OIDC for build provenance attestation
      attestations: write
    strategy:
      fail-fast: false
      matrix:
        include:
          - platform: linux/amd64
            runner: ubuntu-24.04
            arch: amd64
          - platform: linux/arm64
            runner: ubuntu-24.04-arm
            arch: arm64

    outputs:
      # Used downstream by `merge` to stitch the manifest.
      version: ${{ steps.meta.outputs.version }}

    steps:
      - name: Checkout
        uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10  # v6
        with:
          persist-credentials: false

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@d7f5e7f509e45cec5c76c4d5afdd7de93d0b3df5  # v4.1.0
        with:
          # Default parallelism of 4 OOMs the 7GB GitHub runner during Rust
          # compiles (see moby/buildkit#3969). Vaultwarden hit this; we will
          # too without the cap.
          buildkitd-config-inline: |
            [worker.oci]
              max-parallelism = 2

      - name: Log in to GHCR
        # Skip on pull_request from forks — no GHCR creds, build-only.
        if: github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name == github.repository
        uses: docker/login-action@650006c6eb7dba73a995cc03b0b2d7f5ca915bee  # v4.2.0
        with:
          registry: ghcr.io
          username: ${{ github.repository_owner }}
          password: ${{ secrets.GITHUB_TOKEN }}

      - name: Extract metadata
        id: meta
        uses: docker/metadata-action@80c7e94dd9b9319bd5eb7a0e0fe9291e23a2a2e9  # v6.1.0
        with:
          images: ${{ env.IMAGE_NAME }}
          # Tag matrix — every main commit gets sha-<7>, releases get full
          # semver family. Pull requests get nothing (push: false below).
          tags: |
            type=ref,event=branch
            type=sha,prefix=sha-,format=short
            type=semver,pattern={{version}}
            type=semver,pattern={{major}}.{{minor}}
            type=semver,pattern={{major}}
            type=raw,value=latest,enable={{is_default_branch}}
          labels: |
            org.opencontainers.image.title=Buzz
            org.opencontainers.image.description=WebSocket relay server for the Buzz communications platform
            org.opencontainers.image.licenses=Apache-2.0

      - name: Build and push by digest
        id: build
        uses: docker/build-push-action@f9f3042f7e2789586610d6e8b85c8f03e5195baf  # v7.2.0
        with:
          context: .
          file: ./Dockerfile
          platforms: ${{ matrix.platform }}
          labels: ${{ steps.meta.outputs.labels }}
          # Push by digest, not by tag — the merge job assembles the tags
          # into one multi-arch manifest. This is what makes the native-arm
          # matrix possible.
          outputs: type=image,name=${{ env.IMAGE_NAME }},push-by-digest=true,name-canonical=true,push=${{ github.event_name != 'pull_request' }}
          cache-from: |
            type=registry,ref=${{ env.IMAGE_NAME }}-buildcache:${{ matrix.arch }}
          cache-to: |
            ${{ (github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name == github.repository) && format('type=registry,ref={0}-buildcache:{1},mode=max,compression=zstd', env.IMAGE_NAME, matrix.arch) || '' }}

      - name: Export digest
        if: github.event_name != 'pull_request'
        env:
          DIGEST: ${{ steps.build.outputs.digest }}
        run: |
          mkdir -p /tmp/digests
          touch "/tmp/digests/${DIGEST#sha256:}"

      - name: Upload digest
        if: github.event_name != 'pull_request'
        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a  # v7.0.1
        with:
          name: digests-${{ matrix.arch }}
          path: /tmp/digests/*
          if-no-files-found: error
          retention-days: 1

  merge:
    name: Merge multi-arch manifest
    if: github.event_name != 'pull_request'
    runs-on: ubuntu-24.04
    needs: build
    timeout-minutes: 15
    permissions:
      contents: read
      packages: write    # push the merged manifest
      id-token: write    # OIDC for provenance attestation on the manifest
      attestations: write

    steps:
      - name: Download all per-arch digests
        uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c  # v8.0.1
        with:
          path: /tmp/digests
          pattern: digests-*
          merge-multiple: true

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@d7f5e7f509e45cec5c76c4d5afdd7de93d0b3df5  # v4.1.0

      - name: Log in to GHCR
        uses: docker/login-action@650006c6eb7dba73a995cc03b0b2d7f5ca915bee  # v4.2.0
        with:
          registry: ghcr.io
          username: ${{ github.repository_owner }}
          password: ${{ secrets.GITHUB_TOKEN }}

      - name: Extract metadata
        id: meta
        uses: docker/metadata-action@80c7e94dd9b9319bd5eb7a0e0fe9291e23a2a2e9  # v6.1.0
        with:
          images: ${{ env.IMAGE_NAME }}
          tags: |
            type=ref,event=branch
            type=sha,prefix=sha-,format=short
            type=semver,pattern={{version}}
            type=semver,pattern={{major}}.{{minor}}
            type=semver,pattern={{major}}
            type=raw,value=latest,enable={{is_default_branch}}

      - name: Create and push manifest list
        id: manifest
        working-directory: /tmp/digests
        env:
          IMAGE_NAME: ${{ env.IMAGE_NAME }}
          META_TAGS: ${{ steps.meta.outputs.tags }}
        run: |
          set -euo pipefail
          # Build -t flags from the metadata-action output.
          tags=()
          while IFS= read -r tag; do
            [ -n "$tag" ] && tags+=("-t" "$tag")
          done <<< "$META_TAGS"

          # Build the digest refs from the per-arch artifacts.
          digests=()
          for digest in *; do
            digests+=("${IMAGE_NAME}@sha256:${digest}")
          done

          docker buildx imagetools create "${tags[@]}" "${digests[@]}"

          # Capture the merged manifest digest for the attestation step.
          first_tag=$(echo "$META_TAGS" | head -n1)
          merged_digest=$(docker buildx imagetools inspect "$first_tag" \
            --format '{{json .Manifest}}' | jq -r '.digest')
          echo "digest=${merged_digest}" >> "$GITHUB_OUTPUT"

      - name: Attest provenance for the merged image
        # Sigstore-signed in-toto attestation, verifiable with:
        #   gh attestation verify oci://ghcr.io/block/buzz:<tag> --owner block
        uses: actions/attest-build-provenance@a2bbfa25375fe432b6a289bc6b6cd05ecd0c4c32  # v4.1.0
        with:
          subject-name: ${{ env.IMAGE_NAME }}
          subject-digest: ${{ steps.manifest.outputs.digest }}
          push-to-registry: true

      - name: Summary
        env:
          IMAGE_NAME: ${{ env.IMAGE_NAME }}
          MERGED_DIGEST: ${{ steps.manifest.outputs.digest }}
          META_TAGS: ${{ steps.meta.outputs.tags }}
        run: |
          {
            echo "### Published \`${IMAGE_NAME}\`"
            echo
            echo "**Digest:** \`${MERGED_DIGEST}\`"
            echo
            echo "**Tags:**"
            echo '```'
            echo "${META_TAGS}"
            echo '```'
            echo
            echo "Verify provenance:"
            echo '```'
            echo "gh attestation verify oci://${IMAGE_NAME}@${MERGED_DIGEST} --owner block"
            echo '```'
          } >> "$GITHUB_STEP_SUMMARY"