1 /* base64.c -- Encode binary data using printable characters.
2 Copyright (C) 1999, 2000, 2001, 2004, 2005, 2006 Free Software
3 Foundation, Inc.
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.
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.
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. */
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 */
44 #include <config.h>
46 /* Get prototype. */
47 #include "base64.h"
49 /* Get malloc. */
50 #include <stdlib.h>
52 /* Get UCHAR_MAX. */
53 #include <limits.h>
55 #include <string.h>
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 }
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+/";
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 }
102 if (outlen)
103 *out = '\0';
104 }
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);
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 }
138 *out = malloc (outlen);
139 if (!*out)
140 return outlen;
142 base64_encode (in, inlen, *out, outlen);
144 return outlen - 1;
145 }
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.
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)
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 };
290 #if UCHAR_MAX == 255
291 # define uchar_in_range(c) true
292 #else
293 # define uchar_in_range(c) ((c) <= 255)
294 #endif
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 }
305 /* Initialize decode-context buffer, CTX. */
306 void
307 base64_decode_ctx_init (struct base64_decode_context *ctx)
308 {
309 ctx->i = 0;
310 }
312 /* If CTX->i is 0 or 4, there are four or more bytes in [*IN..IN_END), and
313 none of those four is a newline, then return *IN. Otherwise, copy up to
314 4 - CTX->i non-newline bytes from that range into CTX->buf, starting at
315 index CTX->i and setting CTX->i to reflect the number of bytes copied,
316 and return CTX->buf. In either case, advance *IN to point to the byte
317 after the last one processed, and set *N_NON_NEWLINE to the number of
318 verified non-newline bytes accessible through the returned pointer. */
319 static inline char *
320 get_4 (struct base64_decode_context *ctx,
321 char const *restrict *in, char const *restrict in_end,
322 size_t *n_non_newline)
323 {
324 if (ctx->i == 4)
325 ctx->i = 0;
327 if (ctx->i == 0)
328 {
329 char const *t = *in;
330 if (4 <= in_end - *in && memchr (t, '\n', 4) == NULL)
331 {
332 /* This is the common case: no newline. */
333 *in += 4;
334 *n_non_newline = 4;
335 return (char *) t;
336 }
337 }
339 {
340 /* Copy non-newline bytes into BUF. */
341 char const *p = *in;
342 while (p < in_end)
343 {
344 char c = *p++;
345 if (c != '\n')
346 {
347 ctx->buf[ctx->i++] = c;
348 if (ctx->i == 4)
349 break;
350 }
351 }
353 *in = p;
354 *n_non_newline = ctx->i;
355 return ctx->buf;
356 }
357 }
359 #define return_false \
360 do \
361 { \
362 *outp = out; \
363 return false; \
364 } \
365 while (false)
367 /* Decode up to four bytes of base64-encoded data, IN, of length INLEN
368 into the output buffer, *OUT, of size *OUTLEN bytes. Return true if
369 decoding is successful, false otherwise. If *OUTLEN is too small,
370 as many bytes as possible are written to *OUT. On return, advance
371 *OUT to point to the byte after the last one written, and decrement
372 *OUTLEN to reflect the number of bytes remaining in *OUT. */
373 static inline bool
374 decode_4 (char const *restrict in, size_t inlen,
375 char *restrict *outp, size_t *outleft)
376 {
377 char *out = *outp;
378 if (inlen < 2)
379 return false;
381 if (!isbase64 (in[0]) || !isbase64 (in[1]))
382 return false;
384 if (*outleft)
385 {
386 *out++ = ((b64[to_uchar (in[0])] << 2)
387 | (b64[to_uchar (in[1])] >> 4));
388 --*outleft;
389 }
391 if (inlen == 2)
392 return_false;
394 if (in[2] == '=')
395 {
396 if (inlen != 4)
397 return_false;
399 if (in[3] != '=')
400 return_false;
401 }
402 else
403 {
404 if (!isbase64 (in[2]))
405 return_false;
407 if (*outleft)
408 {
409 *out++ = (((b64[to_uchar (in[1])] << 4) & 0xf0)
410 | (b64[to_uchar (in[2])] >> 2));
411 --*outleft;
412 }
414 if (inlen == 3)
415 return_false;
417 if (in[3] == '=')
418 {
419 if (inlen != 4)
420 return_false;
421 }
422 else
423 {
424 if (!isbase64 (in[3]))
425 return_false;
427 if (*outleft)
428 {
429 *out++ = (((b64[to_uchar (in[2])] << 6) & 0xc0)
430 | b64[to_uchar (in[3])]);
431 --*outleft;
432 }
433 }
434 }
436 *outp = out;
437 return true;
438 }
440 /* Decode base64-encoded input array IN of length INLEN to output array
441 OUT that can hold *OUTLEN bytes. The input data may be interspersed
442 with newlines. Return true if decoding was successful, i.e. if the
443 input was valid base64 data, false otherwise. If *OUTLEN is too
444 small, as many bytes as possible will be written to OUT. On return,
445 *OUTLEN holds the length of decoded bytes in OUT. Note that as soon
446 as any non-alphabet, non-newline character is encountered, decoding
447 is stopped and false is returned. If INLEN is zero, then process
448 only whatever data is stored in CTX.
450 Initially, CTX must have been initialized via base64_decode_ctx_init.
451 Subsequent calls to this function must reuse whatever state is recorded
452 in that buffer. It is necessary for when a quadruple of base64 input
453 bytes spans two input buffers.
455 If CTX is NULL then newlines are treated as garbage and the input
456 buffer is processed as a unit. */
458 bool
459 base64_decode_ctx (struct base64_decode_context *ctx,
460 const char *restrict in, size_t inlen,
461 char *restrict out, size_t *outlen)
462 {
463 size_t outleft = *outlen;
464 bool ignore_newlines = ctx != NULL;
465 bool flush_ctx = false;
466 unsigned int ctx_i = 0;
468 if (ignore_newlines)
469 {
470 ctx_i = ctx->i;
471 flush_ctx = inlen == 0;
472 }
475 while (true)
476 {
477 size_t outleft_save = outleft;
478 if (ctx_i == 0 && !flush_ctx)
479 {
480 while (true)
481 {
482 /* Save a copy of outleft, in case we need to re-parse this
483 block of four bytes. */
484 outleft_save = outleft;
485 if (!decode_4 (in, inlen, &out, &outleft))
486 break;
488 in += 4;
489 inlen -= 4;
490 }
491 }
493 if (inlen == 0 && !flush_ctx)
494 break;
496 /* Handle the common case of 72-byte wrapped lines.
497 This also handles any other multiple-of-4-byte wrapping. */
498 if (inlen && *in == '\n' && ignore_newlines)
499 {
500 ++in;
501 --inlen;
502 continue;
503 }
505 /* Restore OUT and OUTLEFT. */
506 out -= outleft_save - outleft;
507 outleft = outleft_save;
509 {
510 char const *in_end = in + inlen;
511 char const *non_nl;
513 if (ignore_newlines)
514 non_nl = get_4 (ctx, &in, in_end, &inlen);
515 else
516 non_nl = in; /* Might have nl in this case. */
518 /* If the input is empty or consists solely of newlines (0 non-newlines),
519 then we're done. Likewise if there are fewer than 4 bytes when not
520 flushing context and not treating newlines as garbage. */
521 if (inlen == 0 || (inlen < 4 && !flush_ctx && ignore_newlines))
522 {
523 inlen = 0;
524 break;
525 }
526 if (!decode_4 (non_nl, inlen, &out, &outleft))
527 break;
529 inlen = in_end - in;
530 }
531 }
533 *outlen -= outleft;
535 return inlen == 0;
536 }
538 /* Allocate an output buffer in *OUT, and decode the base64 encoded
539 data stored in IN of size INLEN to the *OUT buffer. On return, the
540 size of the decoded data is stored in *OUTLEN. OUTLEN may be NULL,
541 if the caller is not interested in the decoded length. *OUT may be
542 NULL to indicate an out of memory error, in which case *OUTLEN
543 contains the size of the memory block needed. The function returns
544 true on successful decoding and memory allocation errors. (Use the
545 *OUT and *OUTLEN parameters to differentiate between successful
546 decoding and memory error.) The function returns false if the
547 input was invalid, in which case *OUT is NULL and *OUTLEN is
548 undefined. */
549 bool
550 base64_decode_alloc_ctx (struct base64_decode_context *ctx,
551 const char *in, size_t inlen, char **out,
552 size_t *outlen)
553 {
554 /* This may allocate a few bytes too many, depending on input,
555 but it's not worth the extra CPU time to compute the exact size.
556 The exact size is 3 * inlen / 4, minus 1 if the input ends
557 with "=" and minus another 1 if the input ends with "==".
558 Dividing before multiplying avoids the possibility of overflow. */
559 size_t needlen = 3 * (inlen / 4) + 2;
561 *out = malloc (needlen);
562 if (!*out)
563 return true;
565 if (!base64_decode_ctx (ctx, in, inlen, *out, &needlen))
566 {
567 free (*out);
568 *out = NULL;
569 return false;
570 }
572 if (outlen)
573 *outlen = needlen;
575 return true;
576 }