feat(image): support tar.gz image (fanal#40)

utils/utils.go

@@ -2,6 +2,7 @@ package utils
 
 import (
 	"fmt"
+	"io"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -37,3 +38,13 @@ func IsCommandAvailable(name string) bool {
 	}
 	return true
 }
+
+func IsGzip(f *os.File) bool {
+	buf := make([]byte, 3)
+	n, _ := f.Read(buf)
+	defer f.Seek(0, io.SeekStart)
+	if n < 3 {
+		return false
+	}
+	return buf[0] == 0x1F && buf[1] == 0x8B && buf[2] == 0x8
+}