1 /* base64.c -- Encode binary data using printable characters.
2 Copyright (C) 1999-2001, 2004-2006, 2009-2023 Free Software Foundation, Inc.
3
4 This file is free software: you can redistribute it and/or modify
5 it under the terms of the GNU Lesser General Public License as
6 published by the Free Software Foundation; either version 2.1 of the
7 License, or (at your option) any later version.
8
9 This file 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 <https://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 <https://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 * idx_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 imalloc. */
48 #include <ialloc.h>
49
50 #include <intprops.h>
51
52 /* Get UCHAR_MAX. */
53 #include <limits.h>
54
55 #include <string.h>
56
57 /* Convert 'char' to 'unsigned char' without casting. */
58 static unsigned char
59 to_uchar (char ch)
60 {
61 return ch;
62 }
63
64 static const char b64c[64] =
65 "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
66
67 /* Base64 encode IN array of size INLEN into OUT array. OUT needs
68 to be of length >= BASE64_LENGTH(INLEN), and INLEN needs to be
69 a multiple of 3. */
70 static void
71 base64_encode_fast (const char *restrict in, idx_t inlen, char *restrict out)
72 {
73 while (inlen)
74 {
75 *out++ = b64c[(to_uchar (in[0]) >> 2) & 0x3f];
76 *out++ = b64c[((to_uchar (in[0]) << 4) + (to_uchar (in[1]) >> 4)) & 0x3f];
77 *out++ = b64c[((to_uchar (in[1]) << 2) + (to_uchar (in[2]) >> 6)) & 0x3f];
78 *out++ = b64c[to_uchar (in[2]) & 0x3f];
79
80 inlen -= 3;
81 in += 3;
82 }
83 }
84
85 /* Base64 encode IN array of size INLEN into OUT array of size OUTLEN.
86 If OUTLEN is less than BASE64_LENGTH(INLEN), write as many bytes as
87 possible. If OUTLEN is larger than BASE64_LENGTH(INLEN), also zero
88 terminate the output buffer. */
89 void
90 base64_encode (const char *restrict in, idx_t inlen,
91 char *restrict out, idx_t outlen)
92 {
93 /* Note this outlen constraint can be enforced at compile time.
94 I.E. that the output buffer is exactly large enough to hold
95 the encoded inlen bytes. The inlen constraints (of corresponding
96 to outlen, and being a multiple of 3) can change at runtime
97 at the end of input. However the common case when reading
98 large inputs is to have both constraints satisfied, so we depend
99 on both in base_encode_fast(). */
100 if (outlen % 4 == 0 && inlen == (outlen >> 2) * 3)
101 {
102 base64_encode_fast (in, inlen, out);
103 return;
104 }
105
106 while (inlen && outlen)
107 {
108 *out++ = b64c[(to_uchar (in[0]) >> 2) & 0x3f];
109 if (!--outlen)
110 break;
111 *out++ = b64c[((to_uchar (in[0]) << 4)
112 + (--inlen ? to_uchar (in[1]) >> 4 : 0))
113 & 0x3f];
114 if (!--outlen)
115 break;
116 *out++ =
117 (inlen
118 ? b64c[((to_uchar (in[1]) << 2)
119 + (--inlen ? to_uchar (in[2]) >> 6 : 0))
120 & 0x3f]
121 : '=');
122 if (!--outlen)
123 break;
124 *out++ = inlen ? b64c[to_uchar (in[2]) & 0x3f] : '=';
125 if (!--outlen)
126 break;
127 if (inlen)
128 inlen--;
129 if (inlen)
130 in += 3;
131 }
132
133 if (outlen)
134 *out = '\0';
135 }
136
137 /* Allocate a buffer and store zero terminated base64 encoded data
138 from array IN of size INLEN, returning BASE64_LENGTH(INLEN), i.e.,
139 the length of the encoded data, excluding the terminating zero. On
140 return, the OUT variable will hold a pointer to newly allocated
141 memory that must be deallocated by the caller. If output string
142 length would overflow, 0 is returned and OUT is set to NULL. If
143 memory allocation failed, OUT is set to NULL, and the return value
144 indicates length of the requested memory block, i.e.,
145 BASE64_LENGTH(inlen) + 1. */
146 idx_t
147 base64_encode_alloc (const char *in, idx_t inlen, char **out)
148 {
149 /* Check for overflow in outlen computation.
150 Treat negative INLEN as overflow, for better compatibility with
151 pre-2021-08-27 API, which used size_t. */
152 idx_t in_over_3 = inlen / 3 + (inlen % 3 != 0), outlen;
153 if (! INT_MULTIPLY_OK (in_over_3, 4, &outlen) || inlen < 0)
154 {
155 *out = NULL;
156 return 0;
157 }
158 outlen++;
159
160 *out = imalloc (outlen);
161 if (!*out)
162 return outlen;
163
164 base64_encode (in, inlen, *out, outlen);
165
166 return outlen - 1;
167 }
168
169 /* With this approach this file works independent of the charset used
170 (think EBCDIC). However, it does assume that the characters in the
171 Base64 alphabet (A-Za-z0-9+/) are encoded in 0..255. POSIX
172 1003.1-2001 require that char and unsigned char are 8-bit
173 quantities, though, taking care of that problem. But this may be a
174 potential problem on non-POSIX C99 platforms.
175
176 IBM C V6 for AIX mishandles "#define B64(x) ...'x'...", so use "_"
177 as the formal parameter rather than "x". */
178 #define B64(_) \
179 ((_) == 'A' ? 0 \
180 : (_) == 'B' ? 1 \
181 : (_) == 'C' ? 2 \
182 : (_) == 'D' ? 3 \
183 : (_) == 'E' ? 4 \
184 : (_) == 'F' ? 5 \
185 : (_) == 'G' ? 6 \
186 : (_) == 'H' ? 7 \
187 : (_) == 'I' ? 8 \
188 : (_) == 'J' ? 9 \
189 : (_) == 'K' ? 10 \
190 : (_) == 'L' ? 11 \
191 : (_) == 'M' ? 12 \
192 : (_) == 'N' ? 13 \
193 : (_) == 'O' ? 14 \
194 : (_) == 'P' ? 15 \
195 : (_) == 'Q' ? 16 \
196 : (_) == 'R' ? 17 \
197 : (_) == 'S' ? 18 \
198 : (_) == 'T' ? 19 \
199 : (_) == 'U' ? 20 \
200 : (_) == 'V' ? 21 \
201 : (_) == 'W' ? 22 \
202 : (_) == 'X' ? 23 \
203 : (_) == 'Y' ? 24 \
204 : (_) == 'Z' ? 25 \
205 : (_) == 'a' ? 26 \
206 : (_) == 'b' ? 27 \
207 : (_) == 'c' ? 28 \
208 : (_) == 'd' ? 29 \
209 : (_) == 'e' ? 30 \
210 : (_) == 'f' ? 31 \
211 : (_) == 'g' ? 32 \
212 : (_) == 'h' ? 33 \
213 : (_) == 'i' ? 34 \
214 : (_) == 'j' ? 35 \
215 : (_) == 'k' ? 36 \
216 : (_) == 'l' ? 37 \
217 : (_) == 'm' ? 38 \
218 : (_) == 'n' ? 39 \
219 : (_) == 'o' ? 40 \
220 : (_) == 'p' ? 41 \
221 : (_) == 'q' ? 42 \
222 : (_) == 'r' ? 43 \
223 : (_) == 's' ? 44 \
224 : (_) == 't' ? 45 \
225 : (_) == 'u' ? 46 \
226 : (_) == 'v' ? 47 \
227 : (_) == 'w' ? 48 \
228 : (_) == 'x' ? 49 \
229 : (_) == 'y' ? 50 \
230 : (_) == 'z' ? 51 \
231 : (_) == '0' ? 52 \
232 : (_) == '1' ? 53 \
233 : (_) == '2' ? 54 \
234 : (_) == '3' ? 55 \
235 : (_) == '4' ? 56 \
236 : (_) == '5' ? 57 \
237 : (_) == '6' ? 58 \
238 : (_) == '7' ? 59 \
239 : (_) == '8' ? 60 \
240 : (_) == '9' ? 61 \
241 : (_) == '+' ? 62 \
242 : (_) == '/' ? 63 \
243 : -1)
244
245 static const signed char b64[0x100] = {
246 B64 (0), B64 (1), B64 (2), B64 (3),
247 B64 (4), B64 (5), B64 (6), B64 (7),
248 B64 (8), B64 (9), B64 (10), B64 (11),
249 B64 (12), B64 (13), B64 (14), B64 (15),
250 B64 (16), B64 (17), B64 (18), B64 (19),
251 B64 (20), B64 (21), B64 (22), B64 (23),
252 B64 (24), B64 (25), B64 (26), B64 (27),
253 B64 (28), B64 (29), B64 (30), B64 (31),
254 B64 (32), B64 (33), B64 (34), B64 (35),
255 B64 (36), B64 (37), B64 (38), B64 (39),
256 B64 (40), B64 (41), B64 (42), B64 (43),
257 B64 (44), B64 (45), B64 (46), B64 (47),
258 B64 (48), B64 (49), B64 (50), B64 (51),
259 B64 (52), B64 (53), B64 (54), B64 (55),
260 B64 (56), B64 (57), B64 (58), B64 (59),
261 B64 (60), B64 (61), B64 (62), B64 (63),
262 B64 (64), B64 (65), B64 (66), B64 (67),
263 B64 (68), B64 (69), B64 (70), B64 (71),
264 B64 (72), B64 (73), B64 (74), B64 (75),
265 B64 (76), B64 (77), B64 (78), B64 (79),
266 B64 (80), B64 (81), B64 (82), B64 (83),
267 B64 (84), B64 (85), B64 (86), B64 (87),
268 B64 (88), B64 (89), B64 (90), B64 (91),
269 B64 (92), B64 (93), B64 (94), B64 (95),
270 B64 (96), B64 (97), B64 (98), B64 (99),
271 B64 (100), B64 (101), B64 (102), B64 (103),
272 B64 (104), B64 (105), B64 (106), B64 (107),
273 B64 (108), B64 (109), B64 (110), B64 (111),
274 B64 (112), B64 (113), B64 (114), B64 (115),
275 B64 (116), B64 (117), B64 (118), B64 (119),
276 B64 (120), B64 (121), B64 (122), B64 (123),
277 B64 (124), B64 (125), B64 (126), B64 (127),
278 B64 (128), B64 (129), B64 (130), B64 (131),
279 B64 (132), B64 (133), B64 (134), B64 (135),
280 B64 (136), B64 (137), B64 (138), B64 (139),
281 B64 (140), B64 (141), B64 (142), B64 (143),
282 B64 (144), B64 (145), B64 (146), B64 (147),
283 B64 (148), B64 (149), B64 (150), B64 (151),
284 B64 (152), B64 (153), B64 (154), B64 (155),
285 B64 (156), B64 (157), B64 (158), B64 (159),
286 B64 (160), B64 (161), B64 (162), B64 (163),
287 B64 (164), B64 (165), B64 (166), B64 (167),
288 B64 (168), B64 (169), B64 (170), B64 (171),
289 B64 (172), B64 (173), B64 (174), B64 (175),
290 B64 (176), B64 (177), B64 (178), B64 (179),
291 B64 (180), B64 (181), B64 (182), B64 (183),
292 B64 (184), B64 (185), B64 (186), B64 (187),
293 B64 (188), B64 (189), B64 (190), B64 (191),
294 B64 (192), B64 (193), B64 (194), B64 (195),
295 B64 (196), B64 (197), B64 (198), B64 (199),
296 B64 (200), B64 (201), B64 (202), B64 (203),
297 B64 (204), B64 (205), B64 (206), B64 (207),
298 B64 (208), B64 (209), B64 (210), B64 (211),
299 B64 (212), B64 (213), B64 (214), B64 (215),
300 B64 (216), B64 (217), B64 (218), B64 (219),
301 B64 (220), B64 (221), B64 (222), B64 (223),
302 B64 (224), B64 (225), B64 (226), B64 (227),
303 B64 (228), B64 (229), B64 (230), B64 (231),
304 B64 (232), B64 (233), B64 (234), B64 (235),
305 B64 (236), B64 (237), B64 (238), B64 (239),
306 B64 (240), B64 (241), B64 (242), B64 (243),
307 B64 (244), B64 (245), B64 (246), B64 (247),
308 B64 (248), B64 (249), B64 (250), B64 (251),
309 B64 (252), B64 (253), B64 (254), B64 (255)
310 };
311
312 #if UCHAR_MAX == 255
313 # define uchar_in_range(c) true
314 #else
315 # define uchar_in_range(c) ((c) <= 255)
316 #endif
317
318 /* Return true if CH is a character from the Base64 alphabet, and
319 false otherwise. Note that '=' is padding and not considered to be
320 part of the alphabet. */
321 bool
322 isbase64 (char ch)
323 {
324 return uchar_in_range (to_uchar (ch)) && 0 <= b64[to_uchar (ch)];
325 }
326
327 /* Initialize decode-context buffer, CTX. */
328 void
329 base64_decode_ctx_init (struct base64_decode_context *ctx)
330 {
331 ctx->i = 0;
332 }
333
334 /* If CTX->i is 0 or 4, there are four or more bytes in [*IN..IN_END), and
335 none of those four is a newline, then return *IN. Otherwise, copy up to
336 4 - CTX->i non-newline bytes from that range into CTX->buf, starting at
337 index CTX->i and setting CTX->i to reflect the number of bytes copied,
338 and return CTX->buf. In either case, advance *IN to point to the byte
339 after the last one processed, and set *N_NON_NEWLINE to the number of
340 verified non-newline bytes accessible through the returned pointer. */
341 static char *
342 get_4 (struct base64_decode_context *ctx,
343 char const *restrict *in, char const *restrict in_end,
344 idx_t *n_non_newline)
345 {
346 if (ctx->i == 4)
347 ctx->i = 0;
348
349 if (ctx->i == 0)
350 {
351 char const *t = *in;
352 if (4 <= in_end - *in && memchr (t, '\n', 4) == NULL)
353 {
354 /* This is the common case: no newline. */
355 *in += 4;
356 *n_non_newline = 4;
357 return (char *) t;
358 }
359 }
360
361 {
362 /* Copy non-newline bytes into BUF. */
363 char const *p = *in;
364 while (p < in_end)
365 {
366 char c = *p++;
367 if (c != '\n')
368 {
369 ctx->buf[ctx->i++] = c;
370 if (ctx->i == 4)
371 break;
372 }
373 }
374
375 *in = p;
376 *n_non_newline = ctx->i;
377 return ctx->buf;
378 }
379 }
380
381 #define return_false \
382 do \
383 { \
384 *outp = out; \
385 return false; \
386 } \
387 while (false)
388
389 /* Decode up to four bytes of base64-encoded data, IN, of length INLEN
390 into the output buffer, *OUT, of size *OUTLEN bytes. Return true if
391 decoding is successful, false otherwise. If *OUTLEN is too small,
392 as many bytes as possible are written to *OUT. On return, advance
393 *OUT to point to the byte after the last one written, and decrement
394 *OUTLEN to reflect the number of bytes remaining in *OUT. */
395 static bool
396 decode_4 (char const *restrict in, idx_t inlen,
397 char *restrict *outp, idx_t *outleft)
398 {
399 char *out = *outp;
400 if (inlen < 2)
401 return false;
402
403 if (!isbase64 (in[0]) || !isbase64 (in[1]))
404 return false;
405
406 if (*outleft)
407 {
408 *out++ = ((b64[to_uchar (in[0])] << 2)
409 | (b64[to_uchar (in[1])] >> 4));
410 --*outleft;
411 }
412
413 if (inlen == 2)
414 return_false;
415
416 if (in[2] == '=')
417 {
418 if (inlen != 4)
419 return_false;
420
421 if (in[3] != '=')
422 return_false;
423 }
424 else
425 {
426 if (!isbase64 (in[2]))
427 return_false;
428
429 if (*outleft)
430 {
431 *out++ = (((b64[to_uchar (in[1])] << 4) & 0xf0)
432 | (b64[to_uchar (in[2])] >> 2));
433 --*outleft;
434 }
435
436 if (inlen == 3)
437 return_false;
438
439 if (in[3] == '=')
440 {
441 if (inlen != 4)
442 return_false;
443 }
444 else
445 {
446 if (!isbase64 (in[3]))
447 return_false;
448
449 if (*outleft)
450 {
451 *out++ = (((b64[to_uchar (in[2])] << 6) & 0xc0)
452 | b64[to_uchar (in[3])]);
453 --*outleft;
454 }
455 }
456 }
457
458 *outp = out;
459 return true;
460 }
461
462 /* Decode base64-encoded input array IN of length INLEN to output array
463 OUT that can hold *OUTLEN bytes. The input data may be interspersed
464 with newlines. Return true if decoding was successful, i.e. if the
465 input was valid base64 data, false otherwise. If *OUTLEN is too
466 small, as many bytes as possible will be written to OUT. On return,
467 *OUTLEN holds the length of decoded bytes in OUT. Note that as soon
468 as any non-alphabet, non-newline character is encountered, decoding
469 is stopped and false is returned. If INLEN is zero, then process
470 only whatever data is stored in CTX.
471
472 Initially, CTX must have been initialized via base64_decode_ctx_init.
473 Subsequent calls to this function must reuse whatever state is recorded
474 in that buffer. It is necessary for when a quadruple of base64 input
475 bytes spans two input buffers.
476
477 If CTX is NULL then newlines are treated as garbage and the input
478 buffer is processed as a unit. */
479
480 bool
481 base64_decode_ctx (struct base64_decode_context *ctx,
482 const char *restrict in, idx_t inlen,
483 char *restrict out, idx_t *outlen)
484 {
485 idx_t outleft = *outlen;
486 bool ignore_newlines = ctx != NULL;
487 bool flush_ctx = false;
488 unsigned int ctx_i = 0;
489
490 if (ignore_newlines)
491 {
492 ctx_i = ctx->i;
493 flush_ctx = inlen == 0;
494 }
495
496
497 while (true)
498 {
499 idx_t outleft_save = outleft;
500 if (ctx_i == 0 && !flush_ctx)
501 {
502 while (true)
503 {
504 /* Save a copy of outleft, in case we need to re-parse this
505 block of four bytes. */
506 outleft_save = outleft;
507 if (!decode_4 (in, inlen, &out, &outleft))
508 break;
509
510 in += 4;
511 inlen -= 4;
512 }
513 }
514
515 if (inlen == 0 && !flush_ctx)
516 break;
517
518 /* Handle the common case of 72-byte wrapped lines.
519 This also handles any other multiple-of-4-byte wrapping. */
520 if (inlen && *in == '\n' && ignore_newlines)
521 {
522 ++in;
523 --inlen;
524 continue;
525 }
526
527 /* Restore OUT and OUTLEFT. */
528 out -= outleft_save - outleft;
529 outleft = outleft_save;
530
531 {
532 char const *in_end = in + inlen;
533 char const *non_nl;
534
535 if (ignore_newlines)
536 non_nl = get_4 (ctx, &in, in_end, &inlen);
537 else
538 non_nl = in; /* Might have nl in this case. */
539
540 /* If the input is empty or consists solely of newlines (0 non-newlines),
541 then we're done. Likewise if there are fewer than 4 bytes when not
542 flushing context and not treating newlines as garbage. */
543 if (inlen == 0 || (inlen < 4 && !flush_ctx && ignore_newlines))
544 {
545 inlen = 0;
546 break;
547 }
548 if (!decode_4 (non_nl, inlen, &out, &outleft))
549 break;
550
551 inlen = in_end - in;
552 }
553 }
554
555 *outlen -= outleft;
556
557 return inlen == 0;
558 }
559
560 /* Allocate an output buffer in *OUT, and decode the base64 encoded
561 data stored in IN of size INLEN to the *OUT buffer. On return, the
562 size of the decoded data is stored in *OUTLEN. OUTLEN may be NULL,
563 if the caller is not interested in the decoded length. *OUT may be
564 NULL to indicate an out of memory error, in which case *OUTLEN
565 contains the size of the memory block needed. The function returns
566 true on successful decoding and memory allocation errors. (Use the
567 *OUT and *OUTLEN parameters to differentiate between successful
568 decoding and memory error.) The function returns false if the
569 input was invalid, in which case *OUT is NULL and *OUTLEN is
570 undefined. */
571 bool
572 base64_decode_alloc_ctx (struct base64_decode_context *ctx,
573 const char *in, idx_t inlen, char **out,
574 idx_t *outlen)
575 {
576 /* This may allocate a few bytes too many, depending on input,
577 but it's not worth the extra CPU time to compute the exact size.
578 The exact size is 3 * (inlen + (ctx ? ctx->i : 0)) / 4, minus 1 if the
579 input ends with "=" and minus another 1 if the input ends with "==".
580 Shifting before multiplying avoids the possibility of overflow. */
581 idx_t needlen = 3 * ((inlen >> 2) + 1);
582
583 *out = imalloc (needlen);
584 if (!*out)
585 return true;
586
587 if (!base64_decode_ctx (ctx, in, inlen, *out, &needlen))
588 {
589 free (*out);
590 *out = NULL;
591 return false;
592 }
593
594 if (outlen)
595 *outlen = needlen;
596
597 return true;
598 }