ubase64.c

   1 #include <stdio.h>
   2 #include <string.h>
   3 #include <errno.h>
   4 #include <stdlib.h>
   5
   6
   7 /***************************************************************************
   8 decode a base64 string in-place - simple and slow algorithm
   9   ***************************************************************************/
  10 static int base64_decode(char *s)
  11 {
  12         char *b64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
  13         int bit_offset, byte_offset, idx, i, n;
  14         unsigned char *d = (unsigned char *)s;
  15         char *p;
  16
  17         n=i=0;
  18
  19         while (*s && ((*s == '\n') || (p=strchr(b64,*s)))) {
  20                 if (*s == '\n') {
  21                         s++;
  22                         continue;
  23                 }
  24                 idx = (int)(p - b64);
  25                 byte_offset = (i*6)/8;
  26                 bit_offset = (i*6)%8;
  27                 d[byte_offset] &= ~((1<<(8-bit_offset))-1);
  28                 if (bit_offset < 3) {
  29                         d[byte_offset] |= (idx << (2-bit_offset));
  30                         n = byte_offset+1;
  31                 } else {
  32                         d[byte_offset] |= (idx >> (bit_offset-2));
  33                         d[byte_offset+1] = 0;
  34                         d[byte_offset+1] |= (idx << (8-(bit_offset-2))) & 0xFF;
  35                         n = byte_offset+2;
  36                 }
  37                 s++; i++;
  38         }
  39         /* null terminate */
  40         d[n] = 0;
  41         return n;
  42 }
  43
  44
  45 static int load_stdin(char **s)
  46 {
  47         char buf[1024];
  48         int length = 0;
  49
  50         *s = NULL;
  51
  52         while (1) {
  53                 int n = read(0, buf, sizeof(buf));
  54                 if (n == -1 && errno == EINTR) continue;
  55                 if (n <= 0) break;
  56
  57                 (*s) = realloc((*s), length + n + 1);
  58                 if (!(*s)) return 0;
  59
  60                 memcpy((*s)+length, buf, n);
  61                 length += n;
  62         }
  63
  64         (*s)[length] = 0;
  65
  66         return length;
  67 }
  68
  69 int main(int argc, char *argv[])
  70 {
  71         char *s;
  72         int n;
  73
  74         n = load_stdin(&s);
  75
  76         n = base64_decode(s);
  77         write(1, s, n);
  78         return 0;
  79 }