Base64 encoding C library for Unix.

The following is a pair of encode and decode functions.

#define OK                  (0)
#define FAIL                (-1)
#define BUFOVER             (-2)
#define CHAR64(c)           (((c) < 0 || (c) > 127) ? -1 : index_64[(c)])
static char     basis_64[] =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????";
static char     index_64[128] = {
   -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
   -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
   -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,
   52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,
   -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
   15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,
   -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
   41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1
};






int             encode64(const char *_in, unsigned inlen,
                       char *_out, unsigned outmax, unsigned *outlen)
{

   const unsigned char *in = (const unsigned char *) _in;
   unsigned char  *out = (unsigned char *) _out;
   unsigned char   oval;
   char           *blah;
   unsigned        olen;

   olen = (inlen + 2) / 3 * 4;
   if (outlen)
       *outlen = olen;
   if (outmax < olen)
       return BUFOVER;

   blah = (char *) out;
   while (inlen >= 3)
   {
/* user provided max buffer size; make sure we don't go over it */
       *out++ = basis_64[in[0] >> 2];
       *out++ = basis_64[((in[0] << 4) & 0x30) | (in[1] >> 4)];
       *out++ = basis_64[((in[1] << 2) & 0x3c) | (in[2] >> 6)];
       *out++ = basis_64[in[2] & 0x3f];
       in += 3;
       inlen -= 3;
   }
   if (inlen > 0)
   {
/* user provided max buffer size; make sure we don't go over it */
       *out++ = basis_64[in[0] >> 2];
       oval = (in[0] << 4) & 0x30;
       if (inlen > 1)
           oval |= in[1] >> 4;
       *out++ = basis_64[oval];
       *out++ = (inlen < 2) ? '=' : basis_64[(in[1] << 2) & 0x3c];
       *out++ = '=';
   }

   if (olen < outmax)
       *out = '\0';

   return OK;

}




int             decode64(const char *in, unsigned inlen, char *out, unsigned *outlen)
{

   unsigned        len = 0,
                   lup;
   int             c1,
                   c2,
                   c3,
                   c4;

   if (in[0] == '+' && in[1] == ' ')
       in += 2;

   if (*in == '\0')
       return FAIL;

   for (lup = 0; lup < inlen / 4; lup++)
   {
       c1 = in[0];
       if (CHAR64(c1) == -1)
           return FAIL;
       c2 = in[1];
       if (CHAR64(c2) == -1)
           return FAIL;
       c3 = in[2];
       if (c3 != '=' && CHAR64(c3) == -1)
           return FAIL;
       c4 = in[3];
       if (c4 != '=' && CHAR64(c4) == -1)
           return FAIL;
       in += 4;
       *out++ = (CHAR64(c1) << 2) | (CHAR64(c2) >> 4);
       ++len;
       if (c3 != '=')
       {
           *out++ = ((CHAR64(c2) << 4) & 0xf0) | (CHAR64(c3) >> 2);
           ++len;
           if (c4 != '=')
           {
               *out++ = ((CHAR64(c3) << 6) & 0xc0) | CHAR64(c4);
               ++len;
           }
       }
   }

   *out = 0;
   *outlen = len;

   return OK;

}

Axter : Thanks for your help.  Can you briefly tell me the meaning of each argument?


Thanks!
Benson

encode64(const char *_in, unsigned inlen,
                      char *_out, unsigned outmax, unsigned *outlen)

Example code:

char MyMsg[] = "Hello World";

char DestinationBuf[1024];

int TotalEncodeLen;
encode64(MyMsg, sizeof(MyMsg), DestinationBuf, &TotalEncodeLen);

The above copde will encode MyMsg string.

To decode it use decode64.

int TotalDecodeLen;
decode64(SourceBuf, sizeof(SourceBuf), DestBuf, &TotalDecodeLen);

Axter : Thanks for your help.  Can you briefly tell me the meaning of each argument?


Thanks!
Benson

Axter : There are 5 arguments of encode64.  Your example is a bit different.

>>There are 5 arguments of encode64.  Your example is a
>>bit different.

I overlooked that.

encode64(
const char *_in, //Pointer to original string
unsigned inlen,  //Length of original string
char *_out, //Pointer to destination buffer
unsigned outmax, //Length of destination buffer
unsigned *outlen //Address of a variable that will be modified to take the new length of the buffer after encode is complete
);

char MyMsg[] = "Hello World";

char DestinationBuf[1024];

int TotalEncodeLen;
encode64(MyMsg, sizeof(MyMsg), DestinationBuf, sizeof(DestinationBuf), &TotalEncodeLen);

benson,
Did I answer your question?

Axter :  Yes!  Thank you very much :)