add version package

Added version info to binary.
Added the go version dependency to read executable info.
Original version package from 654e10aaab/version

pkg/version/version.go

@@ -0,0 +1,94 @@
+/*
+	Package version provides utilities for displaying version information about a Go application.
+	To use this package, a program would set the package variables at build time, using the
+	-ldflags go build flag.
+	Example:
+		go build -ldflags "-X micromdm.io/v2/pkg/version.version=1.0.0"
+	Available values and defaults to use with ldflags:
+		version   = "unknown"
+		branch    = "unknown"
+		revision  = "unknown"
+		buildDate = "unknown"
+		buildUser = "unknown"
+		appName   = "unknown"
+*/
+package version
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"os"
+
+	goversion "rsc.io/goversion/version"
+)
+
+var (
+	version   = "unknown"
+	branch    = "unknown"
+	revision  = "unknown"
+	buildDate = "unknown"
+	buildUser = "unknown"
+	appName   = "micromdm"
+)
+
+// Info holds version and build info about the program.
+type Info struct {
+	Version   string `json:"version"`
+	Branch    string `json:"branch"`
+	Revision  string `json:"revision"`
+	BuildDate string `json:"build_date"`
+	BuildUser string `json:"build_user"`
+}
+
+// Version returns a struct with the current version information.
+func Version() Info {
+	return Info{
+		Version:   version,
+		Branch:    branch,
+		Revision:  revision,
+		BuildDate: buildDate,
+		BuildUser: buildUser,
+	}
+}
+
+// Print outputs the app name and version string.
+func Print() {
+	v := Version()
+	fmt.Printf("%s version %s\n", appName, v.Version)
+}
+
+// PrintFull outputs the app name and detailed version information.
+func PrintFull() error {
+	v := Version()
+	fmt.Printf("%s - version %s\n", appName, v.Version)
+	fmt.Printf("branch: \t%s\n", v.Branch)
+	fmt.Printf("revision: \t%s\n", v.Revision)
+	fmt.Printf("build date: \t%s\n", v.BuildDate)
+	fmt.Printf("build user: \t%s\n", v.BuildUser)
+
+	binary, err := os.Executable()
+	if err != nil {
+		return err
+	}
+
+	binVersion, err := goversion.ReadExe(binary)
+	if err != nil {
+		return err
+	}
+	fmt.Printf("go release: \t%s\n", binVersion.Release)
+	fmt.Println()
+	fmt.Println(binVersion.ModuleInfo)
+	return nil
+}
+
+// Handler provides an HTTP Handler which returns JSON formatted version info.
+func Handler() http.Handler {
+	v := Version()
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json; charset=utf-8")
+		enc := json.NewEncoder(w)
+		enc.SetIndent("", "  ")
+		enc.Encode(v)
+	})
+}