Pull request: all: switch to SOURCE_DATE_EPOCH for source date

Closes #4221.

Squashed commit of the following:

commit c84a5699280cf4c0b1c2ed034a44f05ffc74d30d
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Tue Feb 1 21:13:30 2022 +0300

    all: switch to SOURCE_DATE_EPOCH for source date

scripts/README.md

@@ -90,14 +90,15 @@ Required environment:
  ###  `go-build.sh`: Build The Backend
 
 Optional environment:
- *  `BUILD_TIME`: If set, overrides the build time information.  Useful for
-    reproducible builds.
  *  `GOARM`: ARM processor options for the Go compiler.
  *  `GOMIPS`: ARM processor options for the Go compiler.
  *  `GO`: set an alternative name for the Go compiler.
  *  `OUT`: output binary name.
  *  `PARALLELISM`: set the maximum number of concurrently run build commands
     (that is, compiler, linker, etc.).
+ *  `SOURCE_DATE_EPOCH`: the [standardized][repr] environment variable for the
+    Unix epoch time of the latest commit in the repository.  If set, overrides
+    the default obtained from Git.  Useful for reproducible builds.
  *  `VERBOSE`: verbosity level.  `1` shows every command that is run and every
     Go package that is processed.  `2` also shows subcommands and environment.
     The default value is `0`, don't be verbose.
@@ -107,6 +108,8 @@ Optional environment:
 Required environment:
  *  `CHANNEL`: release channel, see above.
 
+[repr]: https://reproducible-builds.org/docs/source-date-epoch/
+
 
 
  ###  `go-deps.sh`: Install Backend Dependencies

scripts/make/Dockerfile

@@ -5,22 +5,26 @@ FROM alpine:3.13
 ARG BUILD_DATE
 ARG VERSION
 ARG VCS_REF
-LABEL maintainer="AdGuard Team <devteam@adguard.com>" \
-  org.opencontainers.image.created=$BUILD_DATE \
-  org.opencontainers.image.url="https://adguard.com/adguard-home.html" \
-  org.opencontainers.image.source="https://github.com/AdguardTeam/AdGuardHome" \
-  org.opencontainers.image.version=$VERSION \
-  org.opencontainers.image.revision=$VCS_REF \
-  org.opencontainers.image.vendor="AdGuard" \
-  org.opencontainers.image.title="AdGuard Home" \
-  org.opencontainers.image.description="Network-wide ads & trackers blocking DNS server" \
-  org.opencontainers.image.licenses="GPL-3.0"
+
+LABEL\
+	maintainer="AdGuard Team <devteam@adguard.com>" \
+	org.opencontainers.image.authors="AdGuard Team <devteam@adguard.com>" \
+	org.opencontainers.image.created=$BUILD_DATE \
+	org.opencontainers.image.description="Network-wide ads & trackers blocking DNS server" \
+	org.opencontainers.image.documentation="https://github.com/AdguardTeam/AdGuardHome/wiki/" \
+	org.opencontainers.image.licenses="GPL-3.0" \
+	org.opencontainers.image.revision=$VCS_REF \
+	org.opencontainers.image.source="https://github.com/AdguardTeam/AdGuardHome" \
+	org.opencontainers.image.title="AdGuard Home" \
+	org.opencontainers.image.url="https://adguard.com/en/adguard-home/overview.html" \
+	org.opencontainers.image.vendor="AdGuard" \
+	org.opencontainers.image.version=$VERSION
 
 # Update certificates.
 RUN apk --no-cache --update add ca-certificates libcap tzdata && \
-    rm -rf /var/cache/apk/* && \
-    mkdir -p /opt/adguardhome/conf /opt/adguardhome/work && \
-    chown -R nobody: /opt/adguardhome
+	rm -rf /var/cache/apk/* && \
+	mkdir -p /opt/adguardhome/conf /opt/adguardhome/work && \
+	chown -R nobody: /opt/adguardhome
 
 ARG DIST_DIR
 ARG TARGETARCH

scripts/make/go-build.sh

@@ -65,9 +65,9 @@ then
 fi
 readonly version
 
-# Set date and time of the current build unless already set.
-buildtime="${BUILD_TIME:-$( date -u +%FT%TZ%z )}"
-readonly buildtime
+# Set date and time of the latest commit unless already set.
+committime="${SOURCE_DATE_EPOCH:-$( git log -1 --pretty=%ct )}"
+readonly committime
 
 # Set the linker flags accordingly: set the release channel and the current
 # version as well as goarm and gomips variable values, if the variables are set
@@ -78,7 +78,7 @@ readonly version_pkg
 ldflags="-s -w"
 ldflags="${ldflags} -X ${version_pkg}.version=${version}"
 ldflags="${ldflags} -X ${version_pkg}.channel=${channel}"
-ldflags="${ldflags} -X ${version_pkg}.buildtime=${buildtime}"
+ldflags="${ldflags} -X ${version_pkg}.committime=${committime}"
 if [ "${GOARM:-}" != '' ]
 then
 	ldflags="${ldflags} -X ${version_pkg}.goarm=${GOARM}"

scripts/make/version.sh

@@ -86,6 +86,7 @@ in
 	# minor release.  If the current commit is the new minor release,
 	# num_commits_since_minor is zero.
 	num_commits_since_minor="$( git rev-list "${last_minor_zero}..HEAD" | wc -l )"
+
 	# The output of darwin's implementation of wc needs to be trimmed from
 	# redundant spaces.
 	num_commits_since_minor="$( echo "$num_commits_since_minor" | tr -d '[:space:]' )"