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