backported improvements from development branch, bumped golang version to current stable

Dockerfile

@@ -1,4 +1,4 @@
-ARG GOVERSION="1.15.2"
+ARG GOVERSION="1.15.6"
 
 FROM golang:${GOVERSION}-alpine AS buildenv
 
@@ -10,22 +10,27 @@ ENV TEA_VERSION="${VERSION}"
 ARG CGO_ENABLED="0"
 ARG GOOS="linux"
 
+ARG BUILD_DATE
+
 WORKDIR $GOPATH/src
 
 RUN	apk add --quiet --no-cache git && \
 	git config --global advice.detachedHead false && \
-	if [ "${TEA_VERSION}" == "development" ]; \
-		then \
-			export TEA_VERSION="development-$(git ls-remote -q ${REPO} HEAD | cut -c-7)"; \
-		else \
-			export BRANCH_MODIFIER="-b v${TEA_VERSION}"; \
-	fi && \
-	git clone --single-branch ${REPO} ${BRANCH_MODIFIER} . && \
+	git clone --single-branch ${REPO} -b v${TEA_VERSION} . && \
 	go get -v . && \
 	go build -v -a -ldflags "-X main.Version=${TEA_VERSION}" -o /tea .
 
 FROM scratch
-LABEL maintainer="Tamás Gérczei <tamas@gerczei.eu>"
+ARG BUILD_DATE
+ARG VERSION
+LABEL org.opencontainers.image.title="Gitea - Git with a cup of tea"
+LABEL org.opencontainers.image.description="A command line tool to interact with Gitea servers"
+LABEL org.opencontainers.image.version="${VERSION}"
+LABEL org.opencontainers.image.url="https://gitea.com/gitea/tea"
+LABEL org.opencontainers.image.authors="Tamás Gérczei <tamas@gerczei.eu>"
+LABEL org.opencontainers.image.created="${BUILD_DATE}"
+LABEL org.opencontainers.image.source="https://github.com/tgerczei/conteaner"
+LABEL org.opencontainers.image.vendor="Gérczei Tamás E.V."
 COPY --from=buildenv /tea /
 ENV HOME="/app"
 ENTRYPOINT ["/tea"]

hooks/build

@@ -0,0 +1,2 @@
+#!/bin/sh
+docker build --build-arg BUILD_DATE=$(date -u +%Y-%m-%dT%H:%M:%SZ) -t $IMAGE_NAME .