make: add target "docker-release"

"make docker-release tag=..." produces the same binaries regardless on
the platform and the installed Go version, because it uses Docker.

Author: starius

Makefile

@@ -38,10 +38,18 @@ endif
 
 DOCKER_TOOLS = docker run \
   --rm \
-  -v $(shell bash -c "go env GOCACHE || (mkdir -p /tmp/go-cache; echo /tmp/go-cache)"):/tmp/build/.cache \
-  -v $(shell bash -c "go env GOMODCACHE || (mkdir -p /tmp/go-modcache; echo /tmp/go-modcache)"):/tmp/build/.modcache \
+  -v $(shell bash -c "go env GOCACHE 2>/dev/null || (mkdir -p /tmp/go-cache; echo /tmp/go-cache)"):/tmp/build/.cache \
+  -v $(shell bash -c "go env GOMODCACHE 2>/dev/null || (mkdir -p /tmp/go-modcache; echo /tmp/go-modcache)"):/tmp/build/.modcache \
   -v $$(pwd):/build loop-tools
 
+DOCKER_RELEASE_BUILDER = docker run \
+  --rm \
+  -v $(shell bash -c "go env GOCACHE 2>/dev/null || (mkdir -p /tmp/go-cache; echo /tmp/go-cache)"):/tmp/build/.cache \
+  -v $(shell bash -c "go env GOMODCACHE 2>/dev/null || (mkdir -p /tmp/go-modcache; echo /tmp/go-modcache)"):/tmp/build/.modcache \
+  -v $$(pwd):/repo \
+  -e LOOPBUILDSYS='$(buildsys)' \
+  loop-release-builder
+
 GREEN := "\\033[0;32m"
 NC := "\\033[0m"
 define print
@@ -71,6 +79,13 @@ install:
 	$(GOINSTALL) -tags="${tags}" $(LDFLAGS) $(PKG)/cmd/loop
 	$(GOINSTALL) -tags="${tags}" $(LDFLAGS) $(PKG)/cmd/loopd
 
+# docker-release: Same as release.sh but within a docker container to support
+# reproducible builds on any platform.
+docker-release: docker-release-builder
+	@$(call print, "Building release binaries in docker.")
+	@if [ "$(tag)" = "" ]; then echo "Must specify tag=<commit_or_tag>!"; exit 1; fi
+	$(DOCKER_RELEASE_BUILDER) bash release.sh $(tag)
+
 rpc:
 	@$(call print, "Compiling protos.")
 	cd ./swapserverrpc; ./gen_protos_docker.sh
@@ -131,6 +146,10 @@ docker-tools:
 	@$(call print, "Building tools docker image.")
 	docker build -q -t loop-tools $(TOOLS_DIR)
 
+docker-release-builder:
+	@$(call print, "Building release builder docker image.")
+	docker build -q -t loop-release-builder -f release.Dockerfile .
+
 mod-tidy:
 	@$(call print, "Tidying modules.")
 	$(GOMOD) tidy

release.Dockerfile

@@ -0,0 +1,23 @@
+FROM golang:1.24.6
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    git ca-certificates zip gpg && rm -rf /var/lib/apt/lists/*
+
+# Add GPG key of Alex Bosworth to verify release tag signature.
+RUN gpg --keyserver keys.openpgp.org \
+    --recv-keys DE23E73BFA8A0AD5587D2FCDE80D2F3F311FD87E
+
+# Mark the repo directory safe for git. User ID may be different inside
+# Docker and Git might refuse to work without this setting.
+RUN git config --global --add safe.directory /repo
+RUN git config --global --add safe.directory /repo/.git
+
+# Set GO build time environment variables.
+ENV GOCACHE=/tmp/build/.cache \
+    GOMODCACHE=/tmp/build/.modcache
+
+# Create directories to which host's Go caches are mounted.
+RUN mkdir -p /tmp/build/.cache /tmp/build/.modcache \
+    && chmod -R 777 /tmp/build/
+
+WORKDIR /repo