gl/base64.c

   1 /* base64.c -- Encode binary data using printable characters.
   2    Copyright (C) 1999, 2000, 2001, 2004, 2005, 2006 Free Software
   3    Foundation, Inc.
   4
   5    This program is free software; you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 2, or (at your option)
   8    any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program; if not, write to the Free Software Foundation,
  17    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
  18
  19 /* Written by Simon Josefsson.  Partially adapted from GNU MailUtils
  20  * (mailbox/filter_trans.c, as of 2004-11-28).  Improved by review
  21  * from Paul Eggert, Bruno Haible, and Stepan Kasal.
  22  *
  23  * See also RFC 3548 <http://www.ietf.org/rfc/rfc3548.txt>.
  24  *
  25  * Be careful with error checking.  Here is how you would typically
  26  * use these functions:
  27  *
  28  * bool ok = base64_decode_alloc (in, inlen, &out, &outlen);
  29  * if (!ok)
  30  *   FAIL: input was not valid base64
  31  * if (out == NULL)
  32  *   FAIL: memory allocation error
  33  * OK: data in OUT/OUTLEN
  34  *
  35  * size_t outlen = base64_encode_alloc (in, inlen, &out);
  36  * if (out == NULL && outlen == 0 && inlen != 0)
  37  *   FAIL: input too long
  38  * if (out == NULL)
  39  *   FAIL: memory allocation error
  40  * OK: data in OUT/OUTLEN.
  41  *
  42  */
  43
  44 #ifdef HAVE_CONFIG_H
  45 # include <config.h>
  46 #endif
  47
  48 /* Get prototype. */
  49 #include "base64.h"
  50
  51 /* Get malloc. */
  52 #include <stdlib.h>
  53
  54 /* Get UCHAR_MAX. */
  55 #include <limits.h>
  56
  57 /* C89 compliant way to cast 'char' to 'unsigned char'. */
  58 static inline unsigned char
  59 to_uchar (char ch)
  60 {
  61   return ch;
  62 }
  63
  64 /* Base64 encode IN array of size INLEN into OUT array of size OUTLEN.
  65    If OUTLEN is less than BASE64_LENGTH(INLEN), write as many bytes as
  66    possible.  If OUTLEN is larger than BASE64_LENGTH(INLEN), also zero
  67    terminate the output buffer. */
  68 void
  69 base64_encode (const char *restrict in, size_t inlen,
  70                char *restrict out, size_t outlen)
  71 {
  72   static const char b64str[64] =
  73     "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
  74
  75   while (inlen && outlen)
  76     {
  77       *out++ = b64str[(to_uchar (in[0]) >> 2) & 0x3f];
  78       if (!--outlen)
  79         break;
  80       *out++ = b64str[((to_uchar (in[0]) << 4)
  81                        + (--inlen ? to_uchar (in[1]) >> 4 : 0))
  82                       & 0x3f];
  83       if (!--outlen)
  84         break;
  85       *out++ =
  86         (inlen
  87          ? b64str[((to_uchar (in[1]) << 2)
  88                    + (--inlen ? to_uchar (in[2]) >> 6 : 0))
  89                   & 0x3f]
  90          : '=');
  91       if (!--outlen)
  92         break;
  93       *out++ = inlen ? b64str[to_uchar (in[2]) & 0x3f] : '=';
  94       if (!--outlen)
  95         break;
  96       if (inlen)
  97         inlen--;
  98       if (inlen)
  99         in += 3;
 100     }
 101
 102   if (outlen)
 103     *out = '\0';
 104 }
 105
 106 /* Allocate a buffer and store zero terminated base64 encoded data
 107    from array IN of size INLEN, returning BASE64_LENGTH(INLEN), i.e.,
 108    the length of the encoded data, excluding the terminating zero.  On
 109    return, the OUT variable will hold a pointer to newly allocated
 110    memory that must be deallocated by the caller.  If output string
 111    length would overflow, 0 is returned and OUT is set to NULL.  If
 112    memory allocation failed, OUT is set to NULL, and the return value
 113    indicates length of the requested memory block, i.e.,
 114    BASE64_LENGTH(inlen) + 1. */
 115 size_t
 116 base64_encode_alloc (const char *in, size_t inlen, char **out)
 117 {
 118   size_t outlen = 1 + BASE64_LENGTH (inlen);
 119
 120   /* Check for overflow in outlen computation.
 121    *
 122    * If there is no overflow, outlen >= inlen.
 123    *
 124    * If the operation (inlen + 2) overflows then it yields at most +1, so
 125    * outlen is 0.
 126    *
 127    * If the multiplication overflows, we lose at least half of the
 128    * correct value, so the result is < ((inlen + 2) / 3) * 2, which is
 129    * less than (inlen + 2) * 0.66667, which is less than inlen as soon as
 130    * (inlen > 4).
 131    */
 132   if (inlen > outlen)
 133     {
 134       *out = NULL;
 135       return 0;
 136     }
 137
 138   *out = malloc (outlen);
 139   if (!*out)
 140     return outlen;
 141
 142   base64_encode (in, inlen, *out, outlen);
 143
 144   return outlen - 1;
 145 }
 146
 147 /* With this approach this file works independent of the charset used
 148    (think EBCDIC).  However, it does assume that the characters in the
 149    Base64 alphabet (A-Za-z0-9+/) are encoded in 0..255.  POSIX
 150    1003.1-2001 require that char and unsigned char are 8-bit
 151    quantities, though, taking care of that problem.  But this may be a
 152    potential problem on non-POSIX C99 platforms.
 153
 154    IBM C V6 for AIX mishandles "#define B64(x) ...'x'...", so use "_"
 155    as the formal parameter rather than "x".  */
 156 #define B64(_)                                  \
 157   ((_) == 'A' ? 0                               \
 158    : (_) == 'B' ? 1                             \
 159    : (_) == 'C' ? 2                             \
 160    : (_) == 'D' ? 3                             \
 161    : (_) == 'E' ? 4                             \
 162    : (_) == 'F' ? 5                             \
 163    : (_) == 'G' ? 6                             \
 164    : (_) == 'H' ? 7                             \
 165    : (_) == 'I' ? 8                             \
 166    : (_) == 'J' ? 9                             \
 167    : (_) == 'K' ? 10                            \
 168    : (_) == 'L' ? 11                            \
 169    : (_) == 'M' ? 12                            \
 170    : (_) == 'N' ? 13                            \
 171    : (_) == 'O' ? 14                            \
 172    : (_) == 'P' ? 15                            \
 173    : (_) == 'Q' ? 16                            \
 174    : (_) == 'R' ? 17                            \
 175    : (_) == 'S' ? 18                            \
 176    : (_) == 'T' ? 19                            \
 177    : (_) == 'U' ? 20                            \
 178    : (_) == 'V' ? 21                            \
 179    : (_) == 'W' ? 22                            \
 180    : (_) == 'X' ? 23                            \
 181    : (_) == 'Y' ? 24                            \
 182    : (_) == 'Z' ? 25                            \
 183    : (_) == 'a' ? 26                            \
 184    : (_) == 'b' ? 27                            \
 185    : (_) == 'c' ? 28                            \
 186    : (_) == 'd' ? 29                            \
 187    : (_) == 'e' ? 30                            \
 188    : (_) == 'f' ? 31                            \
 189    : (_) == 'g' ? 32                            \
 190    : (_) == 'h' ? 33                            \
 191    : (_) == 'i' ? 34                            \
 192    : (_) == 'j' ? 35                            \
 193    : (_) == 'k' ? 36                            \
 194    : (_) == 'l' ? 37                            \
 195    : (_) == 'm' ? 38                            \
 196    : (_) == 'n' ? 39                            \
 197    : (_) == 'o' ? 40                            \
 198    : (_) == 'p' ? 41                            \
 199    : (_) == 'q' ? 42                            \
 200    : (_) == 'r' ? 43                            \
 201    : (_) == 's' ? 44                            \
 202    : (_) == 't' ? 45                            \
 203    : (_) == 'u' ? 46                            \
 204    : (_) == 'v' ? 47                            \
 205    : (_) == 'w' ? 48                            \
 206    : (_) == 'x' ? 49                            \
 207    : (_) == 'y' ? 50                            \
 208    : (_) == 'z' ? 51                            \
 209    : (_) == '0' ? 52                            \
 210    : (_) == '1' ? 53                            \
 211    : (_) == '2' ? 54                            \
 212    : (_) == '3' ? 55                            \
 213    : (_) == '4' ? 56                            \
 214    : (_) == '5' ? 57                            \
 215    : (_) == '6' ? 58                            \
 216    : (_) == '7' ? 59                            \
 217    : (_) == '8' ? 60                            \
 218    : (_) == '9' ? 61                            \
 219    : (_) == '+' ? 62                            \
 220    : (_) == '/' ? 63                            \
 221    : -1)
 222
 223 static const signed char b64[0x100] = {
 224   B64 (0), B64 (1), B64 (2), B64 (3),
 225   B64 (4), B64 (5), B64 (6), B64 (7),
 226   B64 (8), B64 (9), B64 (10), B64 (11),
 227   B64 (12), B64 (13), B64 (14), B64 (15),
 228   B64 (16), B64 (17), B64 (18), B64 (19),
 229   B64 (20), B64 (21), B64 (22), B64 (23),
 230   B64 (24), B64 (25), B64 (26), B64 (27),
 231   B64 (28), B64 (29), B64 (30), B64 (31),
 232   B64 (32), B64 (33), B64 (34), B64 (35),
 233   B64 (36), B64 (37), B64 (38), B64 (39),
 234   B64 (40), B64 (41), B64 (42), B64 (43),
 235   B64 (44), B64 (45), B64 (46), B64 (47),
 236   B64 (48), B64 (49), B64 (50), B64 (51),
 237   B64 (52), B64 (53), B64 (54), B64 (55),
 238   B64 (56), B64 (57), B64 (58), B64 (59),
 239   B64 (60), B64 (61), B64 (62), B64 (63),
 240   B64 (64), B64 (65), B64 (66), B64 (67),
 241   B64 (68), B64 (69), B64 (70), B64 (71),
 242   B64 (72), B64 (73), B64 (74), B64 (75),
 243   B64 (76), B64 (77), B64 (78), B64 (79),
 244   B64 (80), B64 (81), B64 (82), B64 (83),
 245   B64 (84), B64 (85), B64 (86), B64 (87),
 246   B64 (88), B64 (89), B64 (90), B64 (91),
 247   B64 (92), B64 (93), B64 (94), B64 (95),
 248   B64 (96), B64 (97), B64 (98), B64 (99),
 249   B64 (100), B64 (101), B64 (102), B64 (103),
 250   B64 (104), B64 (105), B64 (106), B64 (107),
 251   B64 (108), B64 (109), B64 (110), B64 (111),
 252   B64 (112), B64 (113), B64 (114), B64 (115),
 253   B64 (116), B64 (117), B64 (118), B64 (119),
 254   B64 (120), B64 (121), B64 (122), B64 (123),
 255   B64 (124), B64 (125), B64 (126), B64 (127),
 256   B64 (128), B64 (129), B64 (130), B64 (131),
 257   B64 (132), B64 (133), B64 (134), B64 (135),
 258   B64 (136), B64 (137), B64 (138), B64 (139),
 259   B64 (140), B64 (141), B64 (142), B64 (143),
 260   B64 (144), B64 (145), B64 (146), B64 (147),
 261   B64 (148), B64 (149), B64 (150), B64 (151),
 262   B64 (152), B64 (153), B64 (154), B64 (155),
 263   B64 (156), B64 (157), B64 (158), B64 (159),
 264   B64 (160), B64 (161), B64 (162), B64 (163),
 265   B64 (164), B64 (165), B64 (166), B64 (167),
 266   B64 (168), B64 (169), B64 (170), B64 (171),
 267   B64 (172), B64 (173), B64 (174), B64 (175),
 268   B64 (176), B64 (177), B64 (178), B64 (179),
 269   B64 (180), B64 (181), B64 (182), B64 (183),
 270   B64 (184), B64 (185), B64 (186), B64 (187),
 271   B64 (188), B64 (189), B64 (190), B64 (191),
 272   B64 (192), B64 (193), B64 (194), B64 (195),
 273   B64 (196), B64 (197), B64 (198), B64 (199),
 274   B64 (200), B64 (201), B64 (202), B64 (203),
 275   B64 (204), B64 (205), B64 (206), B64 (207),
 276   B64 (208), B64 (209), B64 (210), B64 (211),
 277   B64 (212), B64 (213), B64 (214), B64 (215),
 278   B64 (216), B64 (217), B64 (218), B64 (219),
 279   B64 (220), B64 (221), B64 (222), B64 (223),
 280   B64 (224), B64 (225), B64 (226), B64 (227),
 281   B64 (228), B64 (229), B64 (230), B64 (231),
 282   B64 (232), B64 (233), B64 (234), B64 (235),
 283   B64 (236), B64 (237), B64 (238), B64 (239),
 284   B64 (240), B64 (241), B64 (242), B64 (243),
 285   B64 (244), B64 (245), B64 (246), B64 (247),
 286   B64 (248), B64 (249), B64 (250), B64 (251),
 287   B64 (252), B64 (253), B64 (254), B64 (255)
 288 };
 289
 290 #if UCHAR_MAX == 255
 291 # define uchar_in_range(c) true
 292 #else
 293 # define uchar_in_range(c) ((c) <= 255)
 294 #endif
 295
 296 /* Return true if CH is a character from the Base64 alphabet, and
 297    false otherwise.  Note that '=' is padding and not considered to be
 298    part of the alphabet.  */
 299 bool
 300 isbase64 (char ch)
 301 {
 302   return uchar_in_range (to_uchar (ch)) && 0 <= b64[to_uchar (ch)];
 303 }
 304
 305 /* Decode base64 encoded input array IN of length INLEN to output
 306    array OUT that can hold *OUTLEN bytes.  Return true if decoding was
 307    successful, i.e. if the input was valid base64 data, false
 308    otherwise.  If *OUTLEN is too small, as many bytes as possible will
 309    be written to OUT.  On return, *OUTLEN holds the length of decoded
 310    bytes in OUT.  Note that as soon as any non-alphabet characters are
 311    encountered, decoding is stopped and false is returned.  This means
 312    that, when applicable, you must remove any line terminators that is
 313    part of the data stream before calling this function.  */
 314 bool
 315 base64_decode (const char *restrict in, size_t inlen,
 316                char *restrict out, size_t *outlen)
 317 {
 318   size_t outleft = *outlen;
 319
 320   while (inlen >= 2)
 321     {
 322       if (!isbase64 (in[0]) || !isbase64 (in[1]))
 323         break;
 324
 325       if (outleft)
 326         {
 327           *out++ = ((b64[to_uchar (in[0])] << 2)
 328                     | (b64[to_uchar (in[1])] >> 4));
 329           outleft--;
 330         }
 331
 332       if (inlen == 2)
 333         break;
 334
 335       if (in[2] == '=')
 336         {
 337           if (inlen != 4)
 338             break;
 339
 340           if (in[3] != '=')
 341             break;
 342
 343         }
 344       else
 345         {
 346           if (!isbase64 (in[2]))
 347             break;
 348
 349           if (outleft)
 350             {
 351               *out++ = (((b64[to_uchar (in[1])] << 4) & 0xf0)
 352                         | (b64[to_uchar (in[2])] >> 2));
 353               outleft--;
 354             }
 355
 356           if (inlen == 3)
 357             break;
 358
 359           if (in[3] == '=')
 360             {
 361               if (inlen != 4)
 362                 break;
 363             }
 364           else
 365             {
 366               if (!isbase64 (in[3]))
 367                 break;
 368
 369               if (outleft)
 370                 {
 371                   *out++ = (((b64[to_uchar (in[2])] << 6) & 0xc0)
 372                             | b64[to_uchar (in[3])]);
 373                   outleft--;
 374                 }
 375             }
 376         }
 377
 378       in += 4;
 379       inlen -= 4;
 380     }
 381
 382   *outlen -= outleft;
 383
 384   if (inlen != 0)
 385     return false;
 386
 387   return true;
 388 }
 389
 390 /* Allocate an output buffer in *OUT, and decode the base64 encoded
 391    data stored in IN of size INLEN to the *OUT buffer.  On return, the
 392    size of the decoded data is stored in *OUTLEN.  OUTLEN may be NULL,
 393    if the caller is not interested in the decoded length.  *OUT may be
 394    NULL to indicate an out of memory error, in which case *OUTLEN
 395    contains the size of the memory block needed.  The function returns
 396    true on successful decoding and memory allocation errors.  (Use the
 397    *OUT and *OUTLEN parameters to differentiate between successful
 398    decoding and memory error.)  The function returns false if the
 399    input was invalid, in which case *OUT is NULL and *OUTLEN is
 400    undefined. */
 401 bool
 402 base64_decode_alloc (const char *in, size_t inlen, char **out,
 403                      size_t *outlen)
 404 {
 405   /* This may allocate a few bytes too much, depending on input,
 406      but it's not worth the extra CPU time to compute the exact amount.
 407      The exact amount is 3 * inlen / 4, minus 1 if the input ends
 408      with "=" and minus another 1 if the input ends with "==".
 409      Dividing before multiplying avoids the possibility of overflow.  */
 410   size_t needlen = 3 * (inlen / 4) + 2;
 411
 412   *out = malloc (needlen);
 413   if (!*out)
 414     return true;
 415
 416   if (!base64_decode (in, inlen, *out, &needlen))
 417     {
 418       free (*out);
 419       *out = NULL;
 420       return false;
 421     }
 422
 423   if (outlen)
 424     *outlen = needlen;
 425
 426   return true;
 427 }