base64.c

/*********************************************************************
* Filename:   base64.c
* Author:     Brad Conte (brad AT bradconte.com)
* Copyright:
* Disclaimer: This code is presented "as is" without any guarantees.
* Details:    Implementation of the Base64 encoding algorithm.
*********************************************************************/

/*************************** HEADER FILES ***************************/
#include <stdlib.h>

#include "base64.h"

/****************************** MACROS ******************************/
#define NEWLINE_INVL 76

/**************************** VARIABLES *****************************/
// Note: To change the charset to a URL encoding, replace the '+' and '/' with '*' and '-'
static const BYTE charset[]={"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"};

/*********************** FUNCTION DEFINITIONS ***********************/
BYTE revchar(char ch)
{
   if (ch >= 'A' && ch <= 'Z')
       ch -= 'A';
   else if (ch >= 'a' && ch <='z')
       ch = ch - 'a' + 26;
   else if (ch >= '0' && ch <='9')
       ch = ch - '0' + 52;
   else if (ch == '+')
       ch = 62;
   else if (ch == '/')
       ch = 63;

   return(ch);
}

size_t base64_encode(const BYTE in[], BYTE out[], size_t len, int newline_flag)
{
   size_t idx, idx2, blks, blk_ceiling, left_over, newline_count = 0;

   blks = (len / 3);
   left_over = len % 3;

   if (out == NULL) {
       idx2 = blks * 4 ;
       if (left_over)
           idx2 += 4;
       if (newline_flag)
           idx2 += len / 57;   // (NEWLINE_INVL / 4) * 3 = 57. One newline per 57 input bytes.
   }
   else {
       // Since 3 input bytes = 4 output bytes, determine out how many even sets of
       // 3 bytes the input has.
       blk_ceiling = blks * 3;
       for (idx = 0, idx2 = 0; idx < blk_ceiling; idx += 3, idx2 += 4) {
           out[idx2]     = charset[in[idx] >> 2];
           out[idx2 + 1] = charset[((in[idx] & 0x03) << 4) | (in[idx + 1] >> 4)];
           out[idx2 + 2] = charset[((in[idx + 1] & 0x0f) << 2) | (in[idx + 2] >> 6)];
           out[idx2 + 3] = charset[in[idx + 2] & 0x3F];
           // The offical standard requires a newline every 76 characters.
           // (Eg, first newline is character 77 of the output.)
           if (((idx2 - newline_count + 4) % NEWLINE_INVL == 0) && newline_flag) {
               out[idx2 + 4] = '\n';
               idx2++;
               newline_count++;
           }
       }

       if (left_over == 1) {
           out[idx2]     = charset[in[idx] >> 2];
           out[idx2 + 1] = charset[(in[idx] & 0x03) << 4];
           out[idx2 + 2] = '=';
           out[idx2 + 3] = '=';
           idx2 += 4;
       }
       else if (left_over == 2) {
           out[idx2]     = charset[in[idx] >> 2];
           out[idx2 + 1] = charset[((in[idx] & 0x03) << 4) | (in[idx + 1] >> 4)];
           out[idx2 + 2] = charset[(in[idx + 1] & 0x0F) << 2];
           out[idx2 + 3] = '=';
           idx2 += 4;
       }
   }

   return(idx2);
}

size_t base64_decode(const BYTE in[], BYTE out[], size_t len)
{
   size_t idx, idx2, blks, blk_ceiling, left_over;

   if (in[len - 1] == '=')
       len--;
   if (in[len - 1] == '=')
       len--;

   blks = len / 4;
   left_over = len % 4;

   if (out == NULL) {
       if (len >= 77 && in[NEWLINE_INVL] == '\n')   // Verify that newlines where used.
           len -= len / (NEWLINE_INVL + 1);
       blks = len / 4;
       left_over = len % 4;

       idx = blks * 3;
       if (left_over == 2)
           idx ++;
       else if (left_over == 3)
           idx += 2;
   }
   else {
       blk_ceiling = blks * 4;
       for (idx = 0, idx2 = 0; idx2 < blk_ceiling; idx += 3, idx2 += 4) {
           if (in[idx2] == '\n')
               idx2++;
           out[idx]     = (revchar(in[idx2]) << 2) | ((revchar(in[idx2 + 1]) & 0x30) >> 4);
           out[idx + 1] = (revchar(in[idx2 + 1]) << 4) | (revchar(in[idx2 + 2]) >> 2);
           out[idx + 2] = (revchar(in[idx2 + 2]) << 6) | revchar(in[idx2 + 3]);
       }

       if (left_over == 2) {
           out[idx]     = (revchar(in[idx2]) << 2) | ((revchar(in[idx2 + 1]) & 0x30) >> 4);
           idx++;
       }
       else if (left_over == 3) {
           out[idx]     = (revchar(in[idx2]) << 2) | ((revchar(in[idx2 + 1]) & 0x30) >> 4);
           out[idx + 1] = (revchar(in[idx2 + 1]) << 4) | (revchar(in[idx2 + 2]) >> 2);
           idx += 2;
       }
   }

   return(idx);
}