Set bit 11 of the zip header flags in minizip if UTF-8.

The bit is set if the file name contains valid UTF-8 and there is
at least one code of two or more bytes. If there is a comment,
then the comment has to pass the same test for bit 11 to be set.

Author: madler

contrib/minizip/zip.c

@@ -1247,6 +1247,46 @@ local int Write_LocalFileHeader(zip64_internal* zi, const char* filename, uInt s
   return err;
 }
 
+// Return the length of the UTF-8 code at str[0..len-1] in [1..4], or negative
+// if there is no valid UTF-8 code there. If negative, it is minus the number
+// of bytes examined in order to determine it was bad. Or if minus the return
+// code is one less than len, then at least one more byte than provided would
+// be needed to complete the code.
+local inline int utf8len(unsigned char const *str, size_t len) {
+    return
+        len == 0 ? -1 :                         // empty input
+        str[0] < 0x80 ? 1 :                     // good one-byte
+        str[0] < 0xc0 ? -1 :                    // bad first byte
+        len < 2 || (str[1] >> 6) != 2 ? -2 :    // missing or bad second byte
+        str[0] < 0xc2 ? -2 :                    // overlong code
+        str[0] < 0xe0 ? 2 :                     // good two-byte
+        len < 3 || (str[2] >> 6) != 2 ? -3 :    // missing or bad third byte
+        str[0] == 0xe0 && str[1] < 0xa0 ? -3 :  // overlong code
+        str[0] < 0xf0 ? 3 :                     // good three-byte
+        len < 4 || (str[3] >> 6) != 2 ? -4 :    // missing or bad fourth byte
+        str[0] == 0xf0 && str[1] < 0x90 ? -4 :  // overlong code
+        str[0] < 0xf4 ||
+        (str[0] == 0xf4 && str[1] < 0x90) ? 4 : // good four-byte
+        -4;                                     // code > 0x10ffff
+}
+
+// Return true if str[0..len-1] is valid UTF-8 *and* it contains at least one
+// code of two or more bytes. This is used to determine whether or not to set
+// bit 11 in the zip header flags.
+local int isutf8(char const *str, size_t len) {
+    int utf8 = 0;
+    while (len) {
+        int code = utf8len((unsigned char const *)str, len);
+        if (code < 0)
+            return 0;
+        if (code > 1)
+            utf8 = 1;
+        str += code;
+        len -= code;
+    }
+    return utf8;
+}
+
 /*
  NOTE.
  When writing RAW the ZIP64 extended information in extrafield_local and extrafield_global needs to be stripped
@@ -1333,6 +1373,9 @@ extern int ZEXPORT zipOpenNewFileInZip4_64(zipFile file, const char* filename, c
       zi->ci.flag |= 6;
     if (password != NULL)
       zi->ci.flag |= 1;
+    if (isutf8(filename, size_filename) &&
+        (size_comment == 0 || isutf8(comment, size_comment)))
+      zi->ci.flag |= (1 << 11);
 
     zi->ci.crc32 = 0;
     zi->ci.method = method;