base64.c

Go to the documentation of this file.

#include "base64.h"
#include "str.h"
#include "stralloc.h"
 
#define B64PAD '='
 
static const char *b64alpha =
  "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
 
/* returns 0 ok, 1 illegal, -1 problem */
 
int b64decode(const unsigned char *in,int len,stralloc *out)
/* stralloc *out =>  not null terminated */
{
  int p = 0;
  int n;
  unsigned int x;
  int i, j;
  char *s;
  unsigned char b[3];
 
  if (len == 0) {
    if (!stralloc_copys(out,"")) return -1;
    return 0;
  }
 
  while (in[len - 1] == B64PAD) {
    p++;
    len--;
  }
 
  n = (len + p) / 4;
  i = (n * 3) - p;
  if (!stralloc_ready(out,i)) return -1;
  out->len = i;
  s = out->s;
 
  for (i = 0; i < n - 1; i++) {
    x = 0;
    for (j = 0; j < 4; j++) {
      if (in[j] >= 'A' && in[j] <= 'Z')
        x = (x << 6) + (unsigned int) (in[j] - 'A' + 0);
      else if (in[j] >= 'a' && in[j] <= 'z')
        x = (x << 6) + (unsigned int) (in[j] - 'a' + 26);
      else if (in[j] >= '0' && in[j] <= '9')
        x = (x << 6) + (unsigned int) (in[j] - '0' + 52);
      else if (in[j] == '+')
        x = (x << 6) + 62;
      else if (in[j] == '/')
        x = (x << 6) + 63;
      else if (in[j] == '-') // base64url
        x = (x << 6) + 62;
      else if (in[j] == '_') // base64url
        x = (x << 6) + 63;
      else if (in[j] == '=')
        x = (x << 6);
      else return 1;
    }
 
    s[2] = (unsigned char) (x & 255); x >>= 8;
    s[1] = (unsigned char) (x & 255); x >>= 8;
    s[0] = (unsigned char) (x & 255); x >>= 8;
    s += 3; in += 4;
  }
 
  x = 0;
  for (j = 0; j < 4; j++) {
    if (in[j] >= 'A' && in[j] <= 'Z')
      x = (x << 6) + (unsigned int) (in[j] - 'A' + 0);
    else if (in[j] >= 'a' && in[j] <= 'z')
      x = (x << 6) + (unsigned int) (in[j] - 'a' + 26);
    else if (in[j] >= '0' && in[j] <= '9')
      x = (x << 6) + (unsigned int) (in[j] - '0' + 52);
    else if (in[j] == '+')
      x = (x << 6) + 62;
    else if (in[j] == '/')
      x = (x << 6) + 63;
    else if (in[j] == '-') // base64url
      x = (x << 6) + 62;
    else if (in[j] == '_') // base64url
      x = (x << 6) + 63;
    else if (in[j] == '=')
      x = (x << 6);
    else return 1;
  }
 
  b[2] = (unsigned char) (x & 255); x >>= 8;
  b[1] = (unsigned char) (x & 255); x >>= 8;
  b[0] = (unsigned char) (x & 255); x >>= 8;
 
  for (i = 0; i < 3 - p; i++)
    s[i] = b[i];
 
  return 0;
}
 
int b64encode(stralloc *in,stralloc *out)
{
  unsigned char a, b, c;
  int i;
  char *s;
 
  if (in->len == 0)
  {
    if (!stralloc_copys(out,"")) return -1;
    return 0;
  }
 
  i = in->len / 3 * 4 + 4;   
  if (!stralloc_ready(out,i)) return -1;
  s = out->s;
 
  for (i = 0; i < in->len; i += 3) {
    a = in->s[i];
    b = i + 1 < in->len ? in->s[i + 1] : 0;
    c = i + 2 < in->len ? in->s[i + 2] : 0;
 
    *s++ = b64alpha[a >> 2];
    *s++ = b64alpha[((a & 3 ) << 4) | (b >> 4)];
 
    if (i + 1 >= in->len) *s++ = B64PAD;
    else *s++ = b64alpha[((b & 0x0f) << 2) | (c >> 6)];
 
    if (i + 2 >= in->len) *s++ = B64PAD;
    else *s++ = b64alpha[c & 0x3f];
  }
  out->len = s - out->s;
  return 0;
}