Add MatchingFormat function to archiver package and refactor main.go to use it.

archiver.go

@@ -31,6 +31,17 @@ func RegisterFormat(name string, format Archiver) {
 	SupportedFormats[name] = format
 }
 
+// MatchingFormat returns the first archive format that matches
+// the given file, or nil if there is no match
+func MatchingFormat(fpath string) Archiver {
+	for _, fmt := range SupportedFormats {
+		if fmt.Match(fpath) {
+			return fmt
+		}
+	}
+	return nil
+}
+
 func writeNewFile(fpath string, in io.Reader, fm os.FileMode) error {
 	err := os.MkdirAll(filepath.Dir(fpath), 0755)
 	if err != nil {

cmd/archiver/main.go

@@ -14,35 +14,32 @@ func main() {
 
 	cmd, filename := os.Args[1], os.Args[2]
 
-	for _, ff := range archiver.SupportedFormats {
-		if !ff.Match(filename) {
-			continue
-		}
-		var err error
-		switch cmd {
-		case "make":
-			if len(os.Args) < 4 {
-				fatal(usage)
-			}
-			err = ff.Make(filename, os.Args[3:])
-		case "open":
-			dest := ""
-			if len(os.Args) == 4 {
-				dest = os.Args[3]
-			} else if len(os.Args) > 4 {
-				fatal(usage)
-			}
-			err = ff.Open(filename, dest)
-		default:
+	ff := archiver.MatchingFormat(filename)
+	if ff == nil {
+		fatalf("%s: Unsupported file extension", filename)
+	}
+
+	var err error
+	switch cmd {
+	case "make":
+		if len(os.Args) < 4 {
 			fatal(usage)
 		}
-		if err != nil {
-			fatal(err)
+		err = ff.Make(filename, os.Args[3:])
+	case "open":
+		dest := ""
+		if len(os.Args) == 4 {
+			dest = os.Args[3]
+		} else if len(os.Args) > 4 {
+			fatal(usage)
 		}
-		return
+		err = ff.Open(filename, dest)
+	default:
+		fatal(usage)
+	}
+	if err != nil {
+		fatal(err)
 	}
-
-	fatalf("%s: Unsupported file extension", filename)
 }
 
 func fatal(v ...interface{}) {