Multi-architecture, runnable Docker image

Dockerfile

@@ -1,20 +1,65 @@
-FROM golang:1.16
+# Single source stage
+FROM    --platform=$BUILDPLATFORM golang:1.16   as fetcher
 
-RUN apt-get update -yy && \
-    apt-get install -yy \
-        autoconf \
-        libtool \
-        portaudio19-dev
+# Bring the source in
+COPY    . "$GOPATH"/src/github.com/albanseurat/goplay2
+WORKDIR "$GOPATH"/src/github.com/albanseurat/goplay2
 
-COPY . /go/src/github.com/albanseurat/goplay2/
-WORKDIR /go/src/github.com/albanseurat/goplay2/
-RUN GOOS=linux make
+# Patch source to be able to link dynamically as debian packages do not provide static version of libfdk
+RUN      sed -Ei 's/-l:libfdk-aac.a/-lfdk-aac/' ./codec/aac.go
+
+# Actual cross-compiling image, per target platform
+FROM    --platform=$BUILDPLATFORM fetcher       as builder
+
+ARG     TARGETOS
+ARG     TARGETARCH
+ARG     TARGETVARIANT
+
+ENV     GOOS=$TARGETOS
+ENV     GOARCH=$TARGETARCH
+ENV     CGO_ENABLED=1
+
+RUN     sed -Ei 's/main$/main non-free/g' /etc/apt/sources.list; \
+        DEB_TARGET_ARCH="$(echo "$TARGETARCH$TARGETVARIANT" | sed -e "s/^armv6$/armel/" -e "s/^armv7$/armhf/" -e "s/^ppc64le$/ppc64el/" -e "s/^386$/i386/")"; \
+        dpkg --add-architecture "$DEB_TARGET_ARCH"; \
+        apt-get update; \
+        apt-get install -qq --no-install-recommends \
+            autoconf \
+            libtool \
+            crossbuild-essential-"$DEB_TARGET_ARCH" \
+            libfdk-aac1:"$DEB_TARGET_ARCH" \
+            libfdk-aac-dev:"$DEB_TARGET_ARCH" \
+            portaudio19-dev:"$DEB_TARGET_ARCH"
+
+RUN     eval "$(dpkg-architecture -A "$(echo "$TARGETARCH$TARGETVARIANT" | sed -e "s/^armv6$/armel/" -e "s/^armv7$/armhf/" -e "s/^ppc64le$/ppc64el/" -e "s/^386$/i386/")")"; \
+        export CC="${DEB_TARGET_GNU_TYPE}-gcc"; \
+        export CXX="${DEB_TARGET_GNU_TYPE}-g++"; \
+        export GOARM="$(printf "%s" "$TARGETVARIANT" | tr -d v)"; \
+        go build -trimpath -buildmode=pie -tags "netgo osusergo cgo" -ldflags "-s -w" -o /dist/goplay2 .
+
+# Runtime image
+FROM    debian:buster
+
+RUN     sed -Ei 's/main$/main non-free/g' /etc/apt/sources.list; \
+        apt-get update; \
+        apt-get install -qq --no-install-recommends \
+            libportaudio2 \
+            pulseaudio-utils \
+            libfdk-aac1; \
+        apt-get -qq autoremove      && \
+        apt-get -qq clean           && \
+        rm -rf /var/lib/apt/lists/* && \
+        rm -rf /tmp/*               && \
+        rm -rf /var/tmp/*
 
-FROM debian:jessie
-RUN apt-get update -yy && \
-    apt-get install -yy libportaudio2
 WORKDIR /opt
-COPY --from=0 /go/src/github.com/albanseurat/goplay2/goplay2 .
-CMD ["/opt/goplay2"]
 
+RUN     adduser --system --no-create-home --home /nonexistent --gecos "in dockerfile user" --uid 1000 goplay
+RUN     chown 1000 /opt
+
+COPY    --from=builder --chown=1000:root /dist/goplay2 .
+RUN     setcap 'cap_net_bind_service+ep' ./goplay2
+
+USER    goplay
 
+CMD     ["/opt/goplay2"]

README.MD

@@ -81,24 +81,53 @@ brew install portaudio fdk-aac go
 
 ### Docker image
 
-You can build the image to test Linux build and that the service run properly 
+You can build and run the image to quickly test goplay, though this is experimental right now and comes with caveats.
 
 * Build the image
 
+The following platforms are supported: linux/amd64, linux/arm64, linux/arm/v7.
+Other platforms should also build.
+
+You can build with docker directly:
 ```shell
-docker build -t albanseurat/goplay2:latest .
+docker build --platform=linux/amd64 -t you/goplay2 .
 ```
 
+Or with buildctl / buildkit if you want to assemble a multi-arch image.
+
 * Run the container
 
+This image currently does not provide a way to run pulseaudio inside the container itself, and pulseaudio is expected 
+to be available and running on the host for this to work.
+
+On debian variants, this is typically as simple as:
+```
+sudo apt-get install pulseaudio
+pulseaudio --start
+```
+
+To then run the container
 ```shell
-docker run -p 7000:7000 -it albanseurat/goplay2:latest
+export STATION_NAME="GoplaySpeaker"
+
+mkdir -p "$(pwd)/$STATION_NAME"
+
+docker run \
+	--rm \
+	--name goplay \
+	--volume "$(pwd)/$STATION_NAME":/opt/"$STATION_NAME" \
+	--volume /run/user/1000/pulse/native:/pulse \
+	--env PULSE_SERVER=/pulse \
+	--net host \
+	--cap-drop=ALL \
+	--cap-add=NET_BIND_SERVICE \
+	--read-only \
+	you/goplay2 ./goplay2 -n "$STATION_NAME"
 ```
 
-#### Acknowledgments  
+Note that mDNS by design will only work with networking mode "host" (recommended for beginners) or (mac/ip)vlan.
 
-* Docker build is intended to test building the program on Linux platform
-* Bonjour/mDns implementation needs to be changed to allow exposing airplay service outside docker container
+#### Acknowledgments  
 
 ## Run