build: Build and publish Docker images for relay and discovery server (fixes #8691, fixes #8960)

This adds builds for the discovery and relay servers in the same manner
as Syncthing, so that Docker images are kept up to date with releases.

Inspired by and closes #8834.

Co-authored-by: Migelo <miha@filetki.si>

.github/workflows/build-syncthing.yaml

@@ -647,6 +647,19 @@ jobs:
     runs-on: ubuntu-latest
     if: github.event_name == 'push' && (github.ref == 'refs/heads/release' || github.ref == 'refs/heads/main' || startsWith(github.ref, 'refs/heads/release-'))
     environment: docker
+    strategy:
+      matrix:
+        pkg:
+          - syncthing
+          - strelaysrv
+          - stdiscosrv
+        include:
+          - pkg: syncthing
+            dockerfile: Dockerfile
+          - pkg: strelaysrv
+            dockerfile: Dockerfile.strelaysrv
+          - pkg: stdiscosrv
+            dockerfile: Dockerfile.stdiscosrv
     steps:
       - uses: actions/checkout@v3
         with:
@@ -663,13 +676,13 @@ jobs:
           path: |
             ~/.cache/go-build
             ~/go/pkg/mod
-          key: ${{ runner.os }}-go-${{ env.GO_VERSION }}-docker-${{ hashFiles('**/go.sum') }}
+          key: ${{ runner.os }}-go-${{ env.GO_VERSION }}-docker-${{ matrix.pkg }}-${{ hashFiles('**/go.sum') }}
 
       - name: Build binaries
         run: |
           for arch in arm64 amd64; do
-            go run build.go -goos linux -goarch "$arch" -no-upgrade build syncthing
-            mv syncthing syncthing-linux-"$arch"
+            go run build.go -goos linux -goarch "$arch" -no-upgrade build ${{ matrix.pkg }}
+            mv ${{ matrix.pkg }} ${{ matrix.pkg }}-linux-"$arch"
           done
         env:
           CGO_ENABLED: "0"
@@ -692,21 +705,21 @@ jobs:
             echo Release version, pushing to :latest and version tags
             major=${version%.*.*}
             minor=${version%.*}
-            tags=syncthing/syncthing:$version,syncthing/syncthing:$major,syncthing/syncthing:$minor,syncthing/syncthing:latest
+            tags=syncthing/${{ matrix.pkg }}:$version,syncthing/${{ matrix.pkg }}:$major,syncthing/${{ matrix.pkg }}:$minor,syncthing/${{ matrix.pkg }}:latest
           elif [[ $version == *-rc.@([0-9]|[0-9][0-9]) ]] ; then
             echo Release candidate, pushing to :rc
-            tags=syncthing/syncthing:rc
+            tags=syncthing/${{ matrix.pkg }}:rc
           else
             echo Development version, pushing to :edge
-            tags=syncthing/syncthing:edge
+            tags=syncthing/${{ matrix.pkg }}:edge
           fi
           echo "DOCKER_TAGS=$tags" >> $GITHUB_ENV
 
-      - name: Build and push syncthing
+      - name: Build and push Docker image
         uses: docker/build-push-action@v4
         with:
           context: .
-          file: ./Dockerfile
+          file: ${{ matrix.dockerfile }}
           platforms: linux/amd64,linux/arm64
           push: true
           tags: ${{ env.DOCKER_TAGS }}

Dockerfile.stdiscosrv

@@ -1,15 +1,20 @@
 ARG GOVERSION=latest
 FROM golang:$GOVERSION AS builder
+ARG BUILD_USER
+ARG BUILD_HOST
+ARG TARGETARCH
 
 WORKDIR /src
 COPY . .
 
 ENV CGO_ENABLED=0
-ENV BUILD_HOST=syncthing.net
-ENV BUILD_USER=docker
-RUN rm -f stdiscosrv && go run build.go -no-upgrade build stdiscosrv
+RUN if [ ! -f stdiscosrv-linux-$TARGETARCH ] ; then \
+    go run build.go -no-upgrade build stdiscosrv ; \
+    mv stdiscosrv stdiscosrv-linux-$TARGETARCH ; \
+  fi
 
 FROM alpine
+ARG TARGETARCH
 
 EXPOSE 19200 8443
 
@@ -17,7 +22,7 @@ VOLUME ["/var/stdiscosrv"]
 
 RUN apk add --no-cache ca-certificates su-exec
 
-COPY --from=builder /src/stdiscosrv /bin/stdiscosrv
+COPY --from=builder /src/stdiscosrv-linux-$TARGETARCH /bin/stdiscosrv
 COPY --from=builder /src/script/docker-entrypoint.sh /bin/entrypoint.sh
 
 ENV PUID=1000 PGID=1000 HOME=/var/stdiscosrv

Dockerfile.strelaysrv

@@ -1,15 +1,20 @@
 ARG GOVERSION=latest
 FROM golang:$GOVERSION AS builder
+ARG BUILD_USER
+ARG BUILD_HOST
+ARG TARGETARCH
 
 WORKDIR /src
 COPY . .
 
 ENV CGO_ENABLED=0
-ENV BUILD_HOST=syncthing.net
-ENV BUILD_USER=docker
-RUN rm -f strelaysrv && go run build.go -no-upgrade build strelaysrv
+RUN if [ ! -f strelaysrv-linux-$TARGETARCH ] ; then \
+    go run build.go -no-upgrade build strelaysrv ; \
+    mv strelaysrv strelaysrv-linux-$TARGETARCH ; \
+  fi
 
 FROM alpine
+ARG TARGETARCH
 
 EXPOSE 22067 22070
 
@@ -17,7 +22,7 @@ VOLUME ["/var/strelaysrv"]
 
 RUN apk add --no-cache ca-certificates su-exec
 
-COPY --from=builder /src/strelaysrv /bin/strelaysrv
+COPY --from=builder /src/strelaysrv-linux-$TARGETARCH /bin/strelaysrv
 COPY --from=builder /src/script/docker-entrypoint.sh /bin/entrypoint.sh
 
 ENV PUID=1000 PGID=1000 HOME=/var/strelaysrv