fixup func isBinary to handle CJK runes correctly

Former-commit-id: 880817e9e688f7126eb5e3010f5fc37110b28448 [formerly d44d541d75c625a474ca7c8f9adcc52e20ee69e0] [formerly fbbaf7b6a31ed09944700f1ffa98c0baca9ae0f3 [formerly 1c42539522]]
Former-commit-id: 2a647332f2d80741f7ac9cd4eccffbf8a0dd5348 [formerly ef7355350d4d1276911bcdd8b4aaaf1b82efe50c]
Former-commit-id: 7c6d116b6bda492cc9544dc4a46d95cd225c1b39

files/file.go

@@ -164,7 +164,7 @@ func (i *FileInfo) detectType(modify, saveContent bool) error {
 	case strings.HasPrefix(mimetype, "image"):
 		i.Type = "image"
 		return nil
-	case isBinary(string(buffer[:n])) || i.Size > 10*1024*1024: // 10 MB
+	case isBinary(buffer[:n], n) || i.Size > 10*1024*1024: // 10 MB
 		i.Type = "blob"
 		return nil
 	default:

files/utils.go

@@ -1,12 +1,46 @@
 package files
 
-func isBinary(content string) bool {
-	for _, b := range content {
-		// 65533 is the unknown char
+import (
+	"unicode/utf8"
+)
+
+func isBinary(content []byte, n int) bool {
+	maybeStr := string(content)
+	runeCnt := utf8.RuneCount(content)
+	runeIndex := 0
+	gotRuneErrCnt := 0
+	firstRuneErrIndex := -1
+
+	for _, b := range maybeStr {
 		// 8 and below are control chars (e.g. backspace, null, eof, etc)
-		if b <= 8 || b == 65533 {
+		if b <= 8 {
 			return true
 		}
+
+		// 0xFFFD(65533) is  the "error" Rune or "Unicode replacement character"
+		// see https://golang.org/pkg/unicode/utf8/#pkg-constants
+		if b == 0xFFFD {
+			//if it is not the last (utf8.UTFMax - x) rune
+			if runeCnt > utf8.UTFMax && runeIndex < runeCnt-utf8.UTFMax {
+				return true
+			} else {
+				//else it is the last (utf8.UTFMax - x) rune
+				//there maybe Vxxx, VVxx, VVVx, thus, we may got max 3 0xFFFD rune (asume V is the byte we got)
+				//for Chinese, it can only be Vxx, VVx, we may got max 2 0xFFFD rune
+				gotRuneErrCnt++
+
+				//mark the first time
+				if firstRuneErrIndex == -1 {
+					firstRuneErrIndex = runeIndex
+				}
+			}
+		}
+		runeIndex++
+	}
+
+	//if last (utf8.UTFMax - x ) rune has the "error" Rune, but not all
+	if firstRuneErrIndex != -1 && gotRuneErrCnt != runeCnt-firstRuneErrIndex {
+		return true
 	}
 	return false
 }