Added release build targets to makefile

Makefile

@@ -3,6 +3,9 @@
 # use go netcode instead of libc
 export CGO_ENABLED = 0
 
+# all release binaries to build by default
+RELEASE_BINARIES := restreamer-linux-amd64 restreamer-linux-386 restreamer-linux-arm restreamer-linux-arm64 restreamer-darwin-amd64 restreamer-windows-amd64.exe restreamer-windows-386.exe
+
 # always force a rebuild of the main binary
 .PHONY: all clean test fmt vendor docker restreamer
 
@@ -22,3 +25,35 @@ docker:
 
 restreamer:
 	go build ./cmd/restreamer
+
+# release builds - use docker to cross-compile to various architectures
+
+release: SHA256SUMS
+
+SHA256SUMS: $(RELEASE_BINARIES)
+	sha256sum $^ > $@
+
+restreamer-linux-amd64:
+	docker run -e GOOS=linux -e GOARCH=amd64 -e GOCACHE=/go/.cache -e CGO_ENABLED=0 -ti --rm --user $(shell id -u):$(shell id -g) -v $(shell pwd):/go/restreamer -w /go/restreamer golang:1 go build -o $@ ./cmd/restreamer
+
+restreamer-linux-386:
+	docker run -e GOOS=linux -e GOARCH=386 -e GOCACHE=/go/.cache -e CGO_ENABLED=0 -ti --rm --user $(shell id -u):$(shell id -g) -v $(shell pwd):/go/restreamer -w /go/restreamer golang:1 go build -o $@ ./cmd/restreamer
+
+restreamer-linux-arm:
+	docker run -e GOOS=linux -e GOARCH=arm -e GOCACHE=/go/.cache -e CGO_ENABLED=0 -ti --rm --user $(shell id -u):$(shell id -g) -v $(shell pwd):/go/restreamer -w /go/restreamer golang:1 go build -o $@ ./cmd/restreamer
+
+restreamer-linux-arm64:
+	docker run -e GOOS=linux -e GOARCH=arm64 -e GOCACHE=/go/.cache -e CGO_ENABLED=0 -ti --rm --user $(shell id -u):$(shell id -g) -v $(shell pwd):/go/restreamer -w /go/restreamer golang:1 go build -o $@ ./cmd/restreamer
+
+restreamer-darwin-amd64:
+	docker run -e GOOS=darwin -e GOARCH=amd64 -e GOCACHE=/go/.cache -e CGO_ENABLED=0 -ti --rm --user $(shell id -u):$(shell id -g) -v $(shell pwd):/go/restreamer -w /go/restreamer golang:1 go build -o $@ ./cmd/restreamer
+
+# cross-compling from linux to non-amd64 darwin doesn't seem to work, even with CGO_ENABLED=0
+restreamer-darwin-arm64:
+	docker run -e GOOS=darwin -e GOARCH=arm64 -e GOCACHE=/go/.cache -e CGO_ENABLED=0 -ti --rm --user $(shell id -u):$(shell id -g) -v $(shell pwd):/go/restreamer -w /go/restreamer golang:1 go build -o $@ ./cmd/restreamer
+
+restreamer-windows-amd64.exe:
+	docker run -e GOOS=windows -e GOARCH=amd64 -e GOCACHE=/go/.cache -e CGO_ENABLED=0 -ti --rm --user $(shell id -u):$(shell id -g) -v $(shell pwd):/go/restreamer -w /go/restreamer golang:1 go build -o $@ ./cmd/restreamer
+
+restreamer-windows-386.exe:
+	docker run -e GOOS=windows -e GOARCH=386 -e GOCACHE=/go/.cache -e CGO_ENABLED=0 -ti --rm --user $(shell id -u):$(shell id -g) -v $(shell pwd):/go/restreamer -w /go/restreamer golang:1 go build -o $@ ./cmd/restreamer