add util func to get latest version tag

backend/app.go

@@ -16,8 +16,9 @@ import (
 )
 
 const (
-	AppName    = "supersonic"
-	configFile = "config.toml"
+	AppName          = "supersonic"
+	configFile       = "config.toml"
+	LatestReleaseURL = "https://github.com/dweymouth/supersonic/releases/latest"
 )
 
 var (

backend/util/util.go

@@ -2,8 +2,11 @@ package util
 
 import (
 	"io"
+	"log"
 	"math/rand"
+	"net/http"
 	"os"
+	"strings"
 	"time"
 )
 
@@ -37,3 +40,18 @@ func CopyFile(srcPath, dstPath string) error {
 	_, err = io.Copy(fout, fin)
 	return err
 }
+
+func LatestVersionTag(latestReleaseURL string) string {
+	resp, err := http.Head(latestReleaseURL)
+	if err != nil {
+		log.Printf("failed to check for newest version: %s", err.Error())
+		return ""
+	}
+	url := resp.Request.URL.String()
+	url = strings.TrimSuffix(url, "/")
+	idx := strings.LastIndex(url, "/")
+	if idx >= len(url)-1 {
+		return ""
+	}
+	return url[idx+1:]
+}