feat: add multi-architecture support for Docker build (#536)

Author: realskyrin

Diff for: docker/latest/Dockerfile.standalone

@@ -1,18 +1,21 @@
 ARG VER_GOLANG=1.17.6-alpine3.15
 ARG VER_ALPINE=3.15
 
-FROM "doocs/md:latest-assets" AS assets
+FROM --platform=$BUILDPLATFORM "doocs/md:latest-assets" AS assets
 
-FROM "golang:$VER_GOLANG" AS gobuilder
+FROM --platform=$BUILDPLATFORM "golang:$VER_GOLANG" AS gobuilder
+ARG TARGETARCH
+ARG TARGETOS
 COPY --from=assets /app/* /app/assets/
-COPY server/main.go /app
+COPY docker/latest/server/main.go /app
 RUN apk add git bash gcc musl-dev upx
 WORKDIR /app
+ENV GOOS=$TARGETOS GOARCH=$TARGETARCH
 RUN go build -ldflags "-w -s" -o md main.go && \
     apk add upx && \
-    upx -9 -o md.minify md
+    if [ "$TARGETARCH" = "amd64" ]; then upx -9 -o md.minify md; else cp md md.minify; fi
 
-FROM "alpine:$VER_ALPINE"
+FROM --platform=$TARGETPLATFORM "alpine:$VER_ALPINE"
 LABEL MAINTAINER="ylb<[email protected]>"
 COPY --from=gobuilder /app/md.minify /bin/md
 EXPOSE 80