Report version in registry binary

We've added support to the registry command to report the current version of
the distribution package. The version package is generated with a shell script
that gets the latest tag and add "+unknown". This allows builds from "go get"
and "go install" to have a rough version number. Generated periodically, it
will provide a decent indication of what code built the binary. For more
accurate versioning, one can build with the "binaries" make target. Linker
flags are used to replace the version string with the actual current tag at
build time.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

cmd/registry/main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"flag"
 	"fmt"
+	"io"
 	"net/http"
 	_ "net/http/pprof"
 	"os"
@@ -19,12 +20,24 @@ import (
 	_ "github.com/docker/distribution/storagedriver/filesystem"
 	_ "github.com/docker/distribution/storagedriver/inmemory"
 	_ "github.com/docker/distribution/storagedriver/s3"
+	"github.com/docker/distribution/version"
 )
 
+var showVersion bool
+
+func init() {
+	flag.BoolVar(&showVersion, "version", false, "show the version and exit")
+}
+
 func main() {
 	flag.Usage = usage
 	flag.Parse()
 
+	if showVersion {
+		printVersion(os.Stdout)
+		return
+	}
+
 	config, err := resolveConfiguration()
 	if err != nil {
 		fatalf("configuration error: %v", err)
@@ -46,6 +59,10 @@ func usage() {
 	flag.PrintDefaults()
 }
 
+func printVersion(w io.Writer) {
+	fmt.Fprintln(w, os.Args[0], version.Package, version.Version)
+}
+
 func fatalf(format string, args ...interface{}) {
 	fmt.Fprintf(os.Stderr, format+"\n", args...)
 	usage()