utf8.c

   1 #include "git-compat-util.h"
   2 #include "strbuf.h"
   3 #include "utf8.h"
   4
   5 /* This code is originally from http://www.cl.cam.ac.uk/~mgk25/ucs/ */
   6
   7 struct interval {
   8   int first;
   9   int last;
  10 };
  11
  12 size_t display_mode_esc_sequence_len(const char *s)
  13 {
  14         const char *p = s;
  15         if (*p++ != '\033')
  16                 return 0;
  17         if (*p++ != '[')
  18                 return 0;
  19         while (isdigit(*p) || *p == ';')
  20                 p++;
  21         if (*p++ != 'm')
  22                 return 0;
  23         return p - s;
  24 }
  25
  26 /* auxiliary function for binary search in interval table */
  27 static int bisearch(ucs_char_t ucs, const struct interval *table, int max)
  28 {
  29         int min = 0;
  30         int mid;
  31
  32         if (ucs < table[0].first || ucs > table[max].last)
  33                 return 0;
  34         while (max >= min) {
  35                 mid = (min + max) / 2;
  36                 if (ucs > table[mid].last)
  37                         min = mid + 1;
  38                 else if (ucs < table[mid].first)
  39                         max = mid - 1;
  40                 else
  41                         return 1;
  42         }
  43
  44         return 0;
  45 }
  46
  47 /* The following two functions define the column width of an ISO 10646
  48  * character as follows:
  49  *
  50  *    - The null character (U+0000) has a column width of 0.
  51  *
  52  *    - Other C0/C1 control characters and DEL will lead to a return
  53  *      value of -1.
  54  *
  55  *    - Non-spacing and enclosing combining characters (general
  56  *      category code Mn or Me in the Unicode database) have a
  57  *      column width of 0.
  58  *
  59  *    - SOFT HYPHEN (U+00AD) has a column width of 1.
  60  *
  61  *    - Other format characters (general category code Cf in the Unicode
  62  *      database) and ZERO WIDTH SPACE (U+200B) have a column width of 0.
  63  *
  64  *    - Hangul Jamo medial vowels and final consonants (U+1160-U+11FF)
  65  *      have a column width of 0.
  66  *
  67  *    - Spacing characters in the East Asian Wide (W) or East Asian
  68  *      Full-width (F) category as defined in Unicode Technical
  69  *      Report #11 have a column width of 2.
  70  *
  71  *    - All remaining characters (including all printable
  72  *      ISO 8859-1 and WGL4 characters, Unicode control characters,
  73  *      etc.) have a column width of 1.
  74  *
  75  * This implementation assumes that ucs_char_t characters are encoded
  76  * in ISO 10646.
  77  */
  78
  79 static int git_wcwidth(ucs_char_t ch)
  80 {
  81         /*
  82          * Sorted list of non-overlapping intervals of non-spacing characters,
  83          * generated by
  84          *   "uniset +cat=Me +cat=Mn +cat=Cf -00AD +1160-11FF +200B c".
  85          */
  86         static const struct interval combining[] = {
  87                 { 0x0300, 0x0357 }, { 0x035D, 0x036F }, { 0x0483, 0x0486 },
  88                 { 0x0488, 0x0489 }, { 0x0591, 0x05A1 }, { 0x05A3, 0x05B9 },
  89                 { 0x05BB, 0x05BD }, { 0x05BF, 0x05BF }, { 0x05C1, 0x05C2 },
  90                 { 0x05C4, 0x05C4 }, { 0x0600, 0x0603 }, { 0x0610, 0x0615 },
  91                 { 0x064B, 0x0658 }, { 0x0670, 0x0670 }, { 0x06D6, 0x06E4 },
  92                 { 0x06E7, 0x06E8 }, { 0x06EA, 0x06ED }, { 0x070F, 0x070F },
  93                 { 0x0711, 0x0711 }, { 0x0730, 0x074A }, { 0x07A6, 0x07B0 },
  94                 { 0x0901, 0x0902 }, { 0x093C, 0x093C }, { 0x0941, 0x0948 },
  95                 { 0x094D, 0x094D }, { 0x0951, 0x0954 }, { 0x0962, 0x0963 },
  96                 { 0x0981, 0x0981 }, { 0x09BC, 0x09BC }, { 0x09C1, 0x09C4 },
  97                 { 0x09CD, 0x09CD }, { 0x09E2, 0x09E3 }, { 0x0A01, 0x0A02 },
  98                 { 0x0A3C, 0x0A3C }, { 0x0A41, 0x0A42 }, { 0x0A47, 0x0A48 },
  99                 { 0x0A4B, 0x0A4D }, { 0x0A70, 0x0A71 }, { 0x0A81, 0x0A82 },
 100                 { 0x0ABC, 0x0ABC }, { 0x0AC1, 0x0AC5 }, { 0x0AC7, 0x0AC8 },
 101                 { 0x0ACD, 0x0ACD }, { 0x0AE2, 0x0AE3 }, { 0x0B01, 0x0B01 },
 102                 { 0x0B3C, 0x0B3C }, { 0x0B3F, 0x0B3F }, { 0x0B41, 0x0B43 },
 103                 { 0x0B4D, 0x0B4D }, { 0x0B56, 0x0B56 }, { 0x0B82, 0x0B82 },
 104                 { 0x0BC0, 0x0BC0 }, { 0x0BCD, 0x0BCD }, { 0x0C3E, 0x0C40 },
 105                 { 0x0C46, 0x0C48 }, { 0x0C4A, 0x0C4D }, { 0x0C55, 0x0C56 },
 106                 { 0x0CBC, 0x0CBC }, { 0x0CBF, 0x0CBF }, { 0x0CC6, 0x0CC6 },
 107                 { 0x0CCC, 0x0CCD }, { 0x0D41, 0x0D43 }, { 0x0D4D, 0x0D4D },
 108                 { 0x0DCA, 0x0DCA }, { 0x0DD2, 0x0DD4 }, { 0x0DD6, 0x0DD6 },
 109                 { 0x0E31, 0x0E31 }, { 0x0E34, 0x0E3A }, { 0x0E47, 0x0E4E },
 110                 { 0x0EB1, 0x0EB1 }, { 0x0EB4, 0x0EB9 }, { 0x0EBB, 0x0EBC },
 111                 { 0x0EC8, 0x0ECD }, { 0x0F18, 0x0F19 }, { 0x0F35, 0x0F35 },
 112                 { 0x0F37, 0x0F37 }, { 0x0F39, 0x0F39 }, { 0x0F71, 0x0F7E },
 113                 { 0x0F80, 0x0F84 }, { 0x0F86, 0x0F87 }, { 0x0F90, 0x0F97 },
 114                 { 0x0F99, 0x0FBC }, { 0x0FC6, 0x0FC6 }, { 0x102D, 0x1030 },
 115                 { 0x1032, 0x1032 }, { 0x1036, 0x1037 }, { 0x1039, 0x1039 },
 116                 { 0x1058, 0x1059 }, { 0x1160, 0x11FF }, { 0x1712, 0x1714 },
 117                 { 0x1732, 0x1734 }, { 0x1752, 0x1753 }, { 0x1772, 0x1773 },
 118                 { 0x17B4, 0x17B5 }, { 0x17B7, 0x17BD }, { 0x17C6, 0x17C6 },
 119                 { 0x17C9, 0x17D3 }, { 0x17DD, 0x17DD }, { 0x180B, 0x180D },
 120                 { 0x18A9, 0x18A9 }, { 0x1920, 0x1922 }, { 0x1927, 0x1928 },
 121                 { 0x1932, 0x1932 }, { 0x1939, 0x193B }, { 0x200B, 0x200F },
 122                 { 0x202A, 0x202E }, { 0x2060, 0x2063 }, { 0x206A, 0x206F },
 123                 { 0x20D0, 0x20EA }, { 0x302A, 0x302F }, { 0x3099, 0x309A },
 124                 { 0xFB1E, 0xFB1E }, { 0xFE00, 0xFE0F }, { 0xFE20, 0xFE23 },
 125                 { 0xFEFF, 0xFEFF }, { 0xFFF9, 0xFFFB }, { 0x1D167, 0x1D169 },
 126                 { 0x1D173, 0x1D182 }, { 0x1D185, 0x1D18B },
 127                 { 0x1D1AA, 0x1D1AD }, { 0xE0001, 0xE0001 },
 128                 { 0xE0020, 0xE007F }, { 0xE0100, 0xE01EF }
 129         };
 130
 131         /* test for 8-bit control characters */
 132         if (ch == 0)
 133                 return 0;
 134         if (ch < 32 || (ch >= 0x7f && ch < 0xa0))
 135                 return -1;
 136
 137         /* binary search in table of non-spacing characters */
 138         if (bisearch(ch, combining, sizeof(combining)
 139                                 / sizeof(struct interval) - 1))
 140                 return 0;
 141
 142         /*
 143          * If we arrive here, ch is neither a combining nor a C0/C1
 144          * control character.
 145          */
 146
 147         return 1 +
 148                 (ch >= 0x1100 &&
 149                     /* Hangul Jamo init. consonants */
 150                  (ch <= 0x115f ||
 151                   ch == 0x2329 || ch == 0x232a ||
 152                   /* CJK ... Yi */
 153                   (ch >= 0x2e80 && ch <= 0xa4cf &&
 154                    ch != 0x303f) ||
 155                   /* Hangul Syllables */
 156                   (ch >= 0xac00 && ch <= 0xd7a3) ||
 157                   /* CJK Compatibility Ideographs */
 158                   (ch >= 0xf900 && ch <= 0xfaff) ||
 159                   /* CJK Compatibility Forms */
 160                   (ch >= 0xfe30 && ch <= 0xfe6f) ||
 161                   /* Fullwidth Forms */
 162                   (ch >= 0xff00 && ch <= 0xff60) ||
 163                   (ch >= 0xffe0 && ch <= 0xffe6) ||
 164                   (ch >= 0x20000 && ch <= 0x2fffd) ||
 165                   (ch >= 0x30000 && ch <= 0x3fffd)));
 166 }
 167
 168 /*
 169  * Pick one ucs character starting from the location *start points at,
 170  * and return it, while updating the *start pointer to point at the
 171  * end of that character.  When remainder_p is not NULL, the location
 172  * holds the number of bytes remaining in the string that we are allowed
 173  * to pick from.  Otherwise we are allowed to pick up to the NUL that
 174  * would eventually appear in the string.  *remainder_p is also reduced
 175  * by the number of bytes we have consumed.
 176  *
 177  * If the string was not a valid UTF-8, *start pointer is set to NULL
 178  * and the return value is undefined.
 179  */
 180 static ucs_char_t pick_one_utf8_char(const char **start, size_t *remainder_p)
 181 {
 182         unsigned char *s = (unsigned char *)*start;
 183         ucs_char_t ch;
 184         size_t remainder, incr;
 185
 186         /*
 187          * A caller that assumes NUL terminated text can choose
 188          * not to bother with the remainder length.  We will
 189          * stop at the first NUL.
 190          */
 191         remainder = (remainder_p ? *remainder_p : 999);
 192
 193         if (remainder < 1) {
 194                 goto invalid;
 195         } else if (*s < 0x80) {
 196                 /* 0xxxxxxx */
 197                 ch = *s;
 198                 incr = 1;
 199         } else if ((s[0] & 0xe0) == 0xc0) {
 200                 /* 110XXXXx 10xxxxxx */
 201                 if (remainder < 2 ||
 202                     (s[1] & 0xc0) != 0x80 ||
 203                     (s[0] & 0xfe) == 0xc0)
 204                         goto invalid;
 205                 ch = ((s[0] & 0x1f) << 6) | (s[1] & 0x3f);
 206                 incr = 2;
 207         } else if ((s[0] & 0xf0) == 0xe0) {
 208                 /* 1110XXXX 10Xxxxxx 10xxxxxx */
 209                 if (remainder < 3 ||
 210                     (s[1] & 0xc0) != 0x80 ||
 211                     (s[2] & 0xc0) != 0x80 ||
 212                     /* overlong? */
 213                     (s[0] == 0xe0 && (s[1] & 0xe0) == 0x80) ||
 214                     /* surrogate? */
 215                     (s[0] == 0xed && (s[1] & 0xe0) == 0xa0) ||
 216                     /* U+FFFE or U+FFFF? */
 217                     (s[0] == 0xef && s[1] == 0xbf &&
 218                      (s[2] & 0xfe) == 0xbe))
 219                         goto invalid;
 220                 ch = ((s[0] & 0x0f) << 12) |
 221                         ((s[1] & 0x3f) << 6) | (s[2] & 0x3f);
 222                 incr = 3;
 223         } else if ((s[0] & 0xf8) == 0xf0) {
 224                 /* 11110XXX 10XXxxxx 10xxxxxx 10xxxxxx */
 225                 if (remainder < 4 ||
 226                     (s[1] & 0xc0) != 0x80 ||
 227                     (s[2] & 0xc0) != 0x80 ||
 228                     (s[3] & 0xc0) != 0x80 ||
 229                     /* overlong? */
 230                     (s[0] == 0xf0 && (s[1] & 0xf0) == 0x80) ||
 231                     /* > U+10FFFF? */
 232                     (s[0] == 0xf4 && s[1] > 0x8f) || s[0] > 0xf4)
 233                         goto invalid;
 234                 ch = ((s[0] & 0x07) << 18) | ((s[1] & 0x3f) << 12) |
 235                         ((s[2] & 0x3f) << 6) | (s[3] & 0x3f);
 236                 incr = 4;
 237         } else {
 238 invalid:
 239                 *start = NULL;
 240                 return 0;
 241         }
 242
 243         *start += incr;
 244         if (remainder_p)
 245                 *remainder_p = remainder - incr;
 246         return ch;
 247 }
 248
 249 /*
 250  * This function returns the number of columns occupied by the character
 251  * pointed to by the variable start. The pointer is updated to point at
 252  * the next character. When remainder_p is not NULL, it points at the
 253  * location that stores the number of remaining bytes we can use to pick
 254  * a character (see pick_one_utf8_char() above).
 255  */
 256 int utf8_width(const char **start, size_t *remainder_p)
 257 {
 258         ucs_char_t ch = pick_one_utf8_char(start, remainder_p);
 259         if (!*start)
 260                 return 0;
 261         return git_wcwidth(ch);
 262 }
 263
 264 /*
 265  * Returns the total number of columns required by a null-terminated
 266  * string, assuming that the string is utf8.  Returns strlen() instead
 267  * if the string does not look like a valid utf8 string.
 268  */
 269 int utf8_strnwidth(const char *string, int len, int skip_ansi)
 270 {
 271         int width = 0;
 272         const char *orig = string;
 273
 274         if (len == -1)
 275                 len = strlen(string);
 276         while (string && string < orig + len) {
 277                 int skip;
 278                 while (skip_ansi &&
 279                        (skip = display_mode_esc_sequence_len(string)) != 0)
 280                         string += skip;
 281                 width += utf8_width(&string, NULL);
 282         }
 283         return string ? width : len;
 284 }
 285
 286 int utf8_strwidth(const char *string)
 287 {
 288         return utf8_strnwidth(string, -1, 0);
 289 }
 290
 291 int is_utf8(const char *text)
 292 {
 293         while (*text) {
 294                 if (*text == '\n' || *text == '\t' || *text == '\r') {
 295                         text++;
 296                         continue;
 297                 }
 298                 utf8_width(&text, NULL);
 299                 if (!text)
 300                         return 0;
 301         }
 302         return 1;
 303 }
 304
 305 static void strbuf_addchars(struct strbuf *sb, int c, size_t n)
 306 {
 307         strbuf_grow(sb, n);
 308         memset(sb->buf + sb->len, c, n);
 309         strbuf_setlen(sb, sb->len + n);
 310 }
 311
 312 static void strbuf_add_indented_text(struct strbuf *buf, const char *text,
 313                                      int indent, int indent2)
 314 {
 315         if (indent < 0)
 316                 indent = 0;
 317         while (*text) {
 318                 const char *eol = strchrnul(text, '\n');
 319                 if (*eol == '\n')
 320                         eol++;
 321                 strbuf_addchars(buf, ' ', indent);
 322                 strbuf_add(buf, text, eol - text);
 323                 text = eol;
 324                 indent = indent2;
 325         }
 326 }
 327
 328 /*
 329  * Wrap the text, if necessary. The variable indent is the indent for the
 330  * first line, indent2 is the indent for all other lines.
 331  * If indent is negative, assume that already -indent columns have been
 332  * consumed (and no extra indent is necessary for the first line).
 333  */
 334 void strbuf_add_wrapped_text(struct strbuf *buf,
 335                 const char *text, int indent1, int indent2, int width)
 336 {
 337         int indent, w, assume_utf8 = 1;
 338         const char *bol, *space, *start = text;
 339         size_t orig_len = buf->len;
 340
 341         if (width <= 0) {
 342                 strbuf_add_indented_text(buf, text, indent1, indent2);
 343                 return;
 344         }
 345
 346 retry:
 347         bol = text;
 348         w = indent = indent1;
 349         space = NULL;
 350         if (indent < 0) {
 351                 w = -indent;
 352                 space = text;
 353         }
 354
 355         for (;;) {
 356                 char c;
 357                 size_t skip;
 358
 359                 while ((skip = display_mode_esc_sequence_len(text)))
 360                         text += skip;
 361
 362                 c = *text;
 363                 if (!c || isspace(c)) {
 364                         if (w <= width || !space) {
 365                                 const char *start = bol;
 366                                 if (!c && text == start)
 367                                         return;
 368                                 if (space)
 369                                         start = space;
 370                                 else
 371                                         strbuf_addchars(buf, ' ', indent);
 372                                 strbuf_add(buf, start, text - start);
 373                                 if (!c)
 374                                         return;
 375                                 space = text;
 376                                 if (c == '\t')
 377                                         w |= 0x07;
 378                                 else if (c == '\n') {
 379                                         space++;
 380                                         if (*space == '\n') {
 381                                                 strbuf_addch(buf, '\n');
 382                                                 goto new_line;
 383                                         }
 384                                         else if (!isalnum(*space))
 385                                                 goto new_line;
 386                                         else
 387                                                 strbuf_addch(buf, ' ');
 388                                 }
 389                                 w++;
 390                                 text++;
 391                         }
 392                         else {
 393 new_line:
 394                                 strbuf_addch(buf, '\n');
 395                                 text = bol = space + isspace(*space);
 396                                 space = NULL;
 397                                 w = indent = indent2;
 398                         }
 399                         continue;
 400                 }
 401                 if (assume_utf8) {
 402                         w += utf8_width(&text, NULL);
 403                         if (!text) {
 404                                 assume_utf8 = 0;
 405                                 text = start;
 406                                 strbuf_setlen(buf, orig_len);
 407                                 goto retry;
 408                         }
 409                 } else {
 410                         w++;
 411                         text++;
 412                 }
 413         }
 414 }
 415
 416 void strbuf_add_wrapped_bytes(struct strbuf *buf, const char *data, int len,
 417                              int indent, int indent2, int width)
 418 {
 419         char *tmp = xstrndup(data, len);
 420         strbuf_add_wrapped_text(buf, tmp, indent, indent2, width);
 421         free(tmp);
 422 }
 423
 424 void strbuf_utf8_replace(struct strbuf *sb_src, int pos, int width,
 425                          const char *subst)
 426 {
 427         struct strbuf sb_dst = STRBUF_INIT;
 428         char *src = sb_src->buf;
 429         char *end = src + sb_src->len;
 430         char *dst;
 431         int w = 0, subst_len = 0;
 432
 433         if (subst)
 434                 subst_len = strlen(subst);
 435         strbuf_grow(&sb_dst, sb_src->len + subst_len);
 436         dst = sb_dst.buf;
 437
 438         while (src < end) {
 439                 char *old;
 440                 size_t n;
 441
 442                 while ((n = display_mode_esc_sequence_len(src))) {
 443                         memcpy(dst, src, n);
 444                         src += n;
 445                         dst += n;
 446                 }
 447
 448                 old = src;
 449                 n = utf8_width((const char**)&src, NULL);
 450                 if (!src)       /* broken utf-8, do nothing */
 451                         return;
 452                 if (n && w >= pos && w < pos + width) {
 453                         if (subst) {
 454                                 memcpy(dst, subst, subst_len);
 455                                 dst += subst_len;
 456                                 subst = NULL;
 457                         }
 458                         w += n;
 459                         continue;
 460                 }
 461                 memcpy(dst, old, src - old);
 462                 dst += src - old;
 463                 w += n;
 464         }
 465         strbuf_setlen(&sb_dst, dst - sb_dst.buf);
 466         strbuf_swap(sb_src, &sb_dst);
 467         strbuf_release(&sb_dst);
 468 }
 469
 470 int is_encoding_utf8(const char *name)
 471 {
 472         if (!name)
 473                 return 1;
 474         if (!strcasecmp(name, "utf-8") || !strcasecmp(name, "utf8"))
 475                 return 1;
 476         return 0;
 477 }
 478
 479 int same_encoding(const char *src, const char *dst)
 480 {
 481         if (is_encoding_utf8(src) && is_encoding_utf8(dst))
 482                 return 1;
 483         return !strcasecmp(src, dst);
 484 }
 485
 486 /*
 487  * Wrapper for fprintf and returns the total number of columns required
 488  * for the printed string, assuming that the string is utf8.
 489  */
 490 int utf8_fprintf(FILE *stream, const char *format, ...)
 491 {
 492         struct strbuf buf = STRBUF_INIT;
 493         va_list arg;
 494         int columns;
 495
 496         va_start(arg, format);
 497         strbuf_vaddf(&buf, format, arg);
 498         va_end(arg);
 499
 500         columns = fputs(buf.buf, stream);
 501         if (0 <= columns) /* keep the error from the I/O */
 502                 columns = utf8_strwidth(buf.buf);
 503         strbuf_release(&buf);
 504         return columns;
 505 }
 506
 507 /*
 508  * Given a buffer and its encoding, return it re-encoded
 509  * with iconv.  If the conversion fails, returns NULL.
 510  */
 511 #ifndef NO_ICONV
 512 #if defined(OLD_ICONV) || (defined(__sun__) && !defined(_XPG6))
 513         typedef const char * iconv_ibp;
 514 #else
 515         typedef char * iconv_ibp;
 516 #endif
 517 char *reencode_string_iconv(const char *in, size_t insz, iconv_t conv, int *outsz_p)
 518 {
 519         size_t outsz, outalloc;
 520         char *out, *outpos;
 521         iconv_ibp cp;
 522
 523         outsz = insz;
 524         outalloc = outsz + 1; /* for terminating NUL */
 525         out = xmalloc(outalloc);
 526         outpos = out;
 527         cp = (iconv_ibp)in;
 528
 529         while (1) {
 530                 size_t cnt = iconv(conv, &cp, &insz, &outpos, &outsz);
 531
 532                 if (cnt == -1) {
 533                         size_t sofar;
 534                         if (errno != E2BIG) {
 535                                 free(out);
 536                                 return NULL;
 537                         }
 538                         /* insz has remaining number of bytes.
 539                          * since we started outsz the same as insz,
 540                          * it is likely that insz is not enough for
 541                          * converting the rest.
 542                          */
 543                         sofar = outpos - out;
 544                         outalloc = sofar + insz * 2 + 32;
 545                         out = xrealloc(out, outalloc);
 546                         outpos = out + sofar;
 547                         outsz = outalloc - sofar - 1;
 548                 }
 549                 else {
 550                         *outpos = '\0';
 551                         if (outsz_p)
 552                                 *outsz_p = outpos - out;
 553                         break;
 554                 }
 555         }
 556         return out;
 557 }
 558
 559 char *reencode_string_len(const char *in, int insz,
 560                           const char *out_encoding, const char *in_encoding,
 561                           int *outsz)
 562 {
 563         iconv_t conv;
 564         char *out;
 565
 566         if (!in_encoding)
 567                 return NULL;
 568
 569         conv = iconv_open(out_encoding, in_encoding);
 570         if (conv == (iconv_t) -1) {
 571                 /*
 572                  * Some platforms do not have the variously spelled variants of
 573                  * UTF-8, so let's fall back to trying the most official
 574                  * spelling. We do so only as a fallback in case the platform
 575                  * does understand the user's spelling, but not our official
 576                  * one.
 577                  */
 578                 if (is_encoding_utf8(in_encoding))
 579                         in_encoding = "UTF-8";
 580                 if (is_encoding_utf8(out_encoding))
 581                         out_encoding = "UTF-8";
 582                 conv = iconv_open(out_encoding, in_encoding);
 583                 if (conv == (iconv_t) -1)
 584                         return NULL;
 585         }
 586
 587         out = reencode_string_iconv(in, insz, conv, outsz);
 588         iconv_close(conv);
 589         return out;
 590 }
 591 #endif
 592
 593 /*
 594  * Returns first character length in bytes for multi-byte `text` according to
 595  * `encoding`.
 596  *
 597  * - The `text` pointer is updated to point at the next character.
 598  * - When `remainder_p` is not NULL, on entry `*remainder_p` is how much bytes
 599  *   we can consume from text, and on exit `*remainder_p` is reduced by returned
 600  *   character length. Otherwise `text` is treated as limited by NUL.
 601  */
 602 int mbs_chrlen(const char **text, size_t *remainder_p, const char *encoding)
 603 {
 604         int chrlen;
 605         const char *p = *text;
 606         size_t r = (remainder_p ? *remainder_p : SIZE_MAX);
 607
 608         if (r < 1)
 609                 return 0;
 610
 611         if (is_encoding_utf8(encoding)) {
 612                 pick_one_utf8_char(&p, &r);
 613
 614                 chrlen = p ? (p - *text)
 615                            : 1 /* not valid UTF-8 -> raw byte sequence */;
 616         }
 617         else {
 618                 /*
 619                  * TODO use iconv to decode one char and obtain its chrlen
 620                  * for now, let's treat encodings != UTF-8 as one-byte
 621                  */
 622                 chrlen = 1;
 623         }
 624
 625         *text += chrlen;
 626         if (remainder_p)
 627                 *remainder_p -= chrlen;
 628
 629         return chrlen;
 630 }