1/* base64.c -- Encode binary data using printable characters.
2 Copyright (C) 1999-2001, 2004-2006, 2009-2012 Free Software Foundation, Inc.
3
4 This program is free software; you can redistribute it and/or modify
5 it under the terms of the GNU Lesser General Public License as published by
6 the Free Software Foundation; either version 2.1, or (at your option)
7 any later version.
8
9 This program is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 GNU Lesser General Public License for more details.
13
14 You should have received a copy of the GNU Lesser General Public License
15 along with this program; if not, see <http://www.gnu.org/licenses/>. */
16
17/* Written by Simon Josefsson. Partially adapted from GNU MailUtils
18 * (mailbox/filter_trans.c, as of 2004-11-28). Improved by review
19 * from Paul Eggert, Bruno Haible, and Stepan Kasal.
20 *
21 * See also RFC 4648 <http://www.ietf.org/rfc/rfc4648.txt>.
22 *
23 * Be careful with error checking. Here is how you would typically
24 * use these functions:
25 *
26 * bool ok = base64_decode_alloc (in, inlen, &out, &outlen);
27 * if (!ok)
28 * FAIL: input was not valid base64
29 * if (out == NULL)
30 * FAIL: memory allocation error
31 * OK: data in OUT/OUTLEN
32 *
33 * size_t outlen = base64_encode_alloc (in, inlen, &out);
34 * if (out == NULL && outlen == 0 && inlen != 0)
35 * FAIL: input too long
36 * if (out == NULL)
37 * FAIL: memory allocation error
38 * OK: data in OUT/OUTLEN.
39 *
40 */
41
42#include <config.h>
43
44/* Get prototype. */
45#include "base64.h"
46
47/* Get malloc. */
48#include <stdlib.h>
49
50/* Get UCHAR_MAX. */
51#include <limits.h>
52
53#include <string.h>
54
55/* C89 compliant way to cast 'char' to 'unsigned char'. */
56static inline unsigned char
57to_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. */
66static void
67base64_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. */
113size_t
114base64_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
221static 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. */
297bool
298isbase64 (char ch)
299{
300 return uchar_in_range (to_uchar (ch)) && 0 <= b64[to_uchar (ch)];
301}
302
303/* Initialize decode-context buffer, CTX. */
304void
305base64_decode_ctx_init (struct base64_decode_context *ctx)
306{
307 ctx->i = 0;
308}
309
310/* If CTX->i is 0 or 4, there are four or more bytes in [*IN..IN_END), and
311 none of those four is a newline, then return *IN. Otherwise, copy up to
312 4 - CTX->i non-newline bytes from that range into CTX->buf, starting at
313 index CTX->i and setting CTX->i to reflect the number of bytes copied,
314 and return CTX->buf. In either case, advance *IN to point to the byte
315 after the last one processed, and set *N_NON_NEWLINE to the number of
316 verified non-newline bytes accessible through the returned pointer. */
317static inline char *
318get_4 (struct base64_decode_context *ctx,
319 char const *restrict *in, char const *restrict in_end,
320 size_t *n_non_newline)
321{
322 if (ctx->i == 4)
323 ctx->i = 0;
324
325 if (ctx->i == 0)
326 {
327 char const *t = *in;
328 if (4 <= in_end - *in && memchr (t, '\n', 4) == NULL)
329 {
330 /* This is the common case: no newline. */
331 *in += 4;
332 *n_non_newline = 4;
333 return (char *) t;
334 }
335 }
336
337 {
338 /* Copy non-newline bytes into BUF. */
339 char const *p = *in;
340 while (p < in_end)
341 {
342 char c = *p++;
343 if (c != '\n')
344 {
345 ctx->buf[ctx->i++] = c;
346 if (ctx->i == 4)
347 break;
348 }
349 }
350
351 *in = p;
352 *n_non_newline = ctx->i;
353 return ctx->buf;
354 }
355}
356
357#define return_false \
358 do \
359 { \
360 *outp = out; \
361 return false; \
362 } \
363 while (false)
364
365/* Decode up to four bytes of base64-encoded data, IN, of length INLEN
366 into the output buffer, *OUT, of size *OUTLEN bytes. Return true if
367 decoding is successful, false otherwise. If *OUTLEN is too small,
368 as many bytes as possible are written to *OUT. On return, advance
369 *OUT to point to the byte after the last one written, and decrement
370 *OUTLEN to reflect the number of bytes remaining in *OUT. */
371static inline bool
372decode_4 (char const *restrict in, size_t inlen,
373 char *restrict *outp, size_t *outleft)
374{
375 char *out = *outp;
376 if (inlen < 2)
377 return false;
378
379 if (!isbase64 (in[0]) || !isbase64 (in[1]))
380 return false;
381
382 if (*outleft)
383 {
384 *out++ = ((b64[to_uchar (in[0])] << 2)
385 | (b64[to_uchar (in[1])] >> 4));
386 --*outleft;
387 }
388
389 if (inlen == 2)
390 return_false;
391
392 if (in[2] == '=')
393 {
394 if (inlen != 4)
395 return_false;
396
397 if (in[3] != '=')
398 return_false;
399 }
400 else
401 {
402 if (!isbase64 (in[2]))
403 return_false;
404
405 if (*outleft)
406 {
407 *out++ = (((b64[to_uchar (in[1])] << 4) & 0xf0)
408 | (b64[to_uchar (in[2])] >> 2));
409 --*outleft;
410 }
411
412 if (inlen == 3)
413 return_false;
414
415 if (in[3] == '=')
416 {
417 if (inlen != 4)
418 return_false;
419 }
420 else
421 {
422 if (!isbase64 (in[3]))
423 return_false;
424
425 if (*outleft)
426 {
427 *out++ = (((b64[to_uchar (in[2])] << 6) & 0xc0)
428 | b64[to_uchar (in[3])]);
429 --*outleft;
430 }
431 }
432 }
433
434 *outp = out;
435 return true;
436}
437
438/* Decode base64-encoded input array IN of length INLEN to output array
439 OUT that can hold *OUTLEN bytes. The input data may be interspersed
440 with newlines. Return true if decoding was successful, i.e. if the
441 input was valid base64 data, false otherwise. If *OUTLEN is too
442 small, as many bytes as possible will be written to OUT. On return,
443 *OUTLEN holds the length of decoded bytes in OUT. Note that as soon
444 as any non-alphabet, non-newline character is encountered, decoding
445 is stopped and false is returned. If INLEN is zero, then process
446 only whatever data is stored in CTX.
447
448 Initially, CTX must have been initialized via base64_decode_ctx_init.
449 Subsequent calls to this function must reuse whatever state is recorded
450 in that buffer. It is necessary for when a quadruple of base64 input
451 bytes spans two input buffers.
452
453 If CTX is NULL then newlines are treated as garbage and the input
454 buffer is processed as a unit. */
455
456bool
457base64_decode_ctx (struct base64_decode_context *ctx,
458 const char *restrict in, size_t inlen,
459 char *restrict out, size_t *outlen)
460{
461 size_t outleft = *outlen;
462 bool ignore_newlines = ctx != NULL;
463 bool flush_ctx = false;
464 unsigned int ctx_i = 0;
465
466 if (ignore_newlines)
467 {
468 ctx_i = ctx->i;
469 flush_ctx = inlen == 0;
470 }
471
472
473 while (true)
474 {
475 size_t outleft_save = outleft;
476 if (ctx_i == 0 && !flush_ctx)
477 {
478 while (true)
479 {
480 /* Save a copy of outleft, in case we need to re-parse this
481 block of four bytes. */
482 outleft_save = outleft;
483 if (!decode_4 (in, inlen, &out, &outleft))
484 break;
485
486 in += 4;
487 inlen -= 4;
488 }
489 }
490
491 if (inlen == 0 && !flush_ctx)
492 break;
493
494 /* Handle the common case of 72-byte wrapped lines.
495 This also handles any other multiple-of-4-byte wrapping. */
496 if (inlen && *in == '\n' && ignore_newlines)
497 {
498 ++in;
499 --inlen;
500 continue;
501 }
502
503 /* Restore OUT and OUTLEFT. */
504 out -= outleft_save - outleft;
505 outleft = outleft_save;
506
507 {
508 char const *in_end = in + inlen;
509 char const *non_nl;
510
511 if (ignore_newlines)
512 non_nl = get_4 (ctx, &in, in_end, &inlen);
513 else
514 non_nl = in; /* Might have nl in this case. */
515
516 /* If the input is empty or consists solely of newlines (0 non-newlines),
517 then we're done. Likewise if there are fewer than 4 bytes when not
518 flushing context and not treating newlines as garbage. */
519 if (inlen == 0 || (inlen < 4 && !flush_ctx && ignore_newlines))
520 {
521 inlen = 0;
522 break;
523 }
524 if (!decode_4 (non_nl, inlen, &out, &outleft))
525 break;
526
527 inlen = in_end - in;
528 }
529 }
530
531 *outlen -= outleft;
532
533 return inlen == 0;
534}
535
536/* Allocate an output buffer in *OUT, and decode the base64 encoded
537 data stored in IN of size INLEN to the *OUT buffer. On return, the
538 size of the decoded data is stored in *OUTLEN. OUTLEN may be NULL,
539 if the caller is not interested in the decoded length. *OUT may be
540 NULL to indicate an out of memory error, in which case *OUTLEN
541 contains the size of the memory block needed. The function returns
542 true on successful decoding and memory allocation errors. (Use the
543 *OUT and *OUTLEN parameters to differentiate between successful
544 decoding and memory error.) The function returns false if the
545 input was invalid, in which case *OUT is NULL and *OUTLEN is
546 undefined. */
547bool
548base64_decode_alloc_ctx (struct base64_decode_context *ctx,
549 const char *in, size_t inlen, char **out,
550 size_t *outlen)
551{
552 /* This may allocate a few bytes too many, depending on input,
553 but it's not worth the extra CPU time to compute the exact size.
554 The exact size is 3 * (inlen + (ctx ? ctx->i : 0)) / 4, minus 1 if the
555 input ends with "=" and minus another 1 if the input ends with "==".
556 Dividing before multiplying avoids the possibility of overflow. */
557 size_t needlen = 3 * (inlen / 4) + 3;
558
559 *out = malloc (needlen);
560 if (!*out)
561 return true;
562
563 if (!base64_decode_ctx (ctx, in, inlen, *out, &needlen))
564 {
565 free (*out);
566 *out = NULL;
567 return false;
568 }
569
570 if (outlen)
571 *outlen = needlen;
572
573 return true;
574}
575