base64.c

/*******************************************************************

Base64 Encoding/Decoding Library

Author: freecode http://freecode-freecode.blogspot.com/
*******************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/**
* characters used for Base64 encoding
*/
const char *BASE64_CHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

/**
* encode three bytes using base64 ( RFC 3548 )
*
* @param triple three bytes that should be encoded
* @param result buffer of four characters where the result is stored
*/
void _base64_encode_triple( unsigned char triple[ 3 ] , char result[ 4 ] )
{
	int tripleValue, i;

	tripleValue = triple[ 0 ] ;
	tripleValue *= 256;
	tripleValue += triple[ 1 ];
	tripleValue *= 256;
	tripleValue += triple[ 2 ];

	for ( i=0; i<4; i++ )
	{
		result[ 3-i ] = BASE64_CHARS[ tripleValue%64 ];
		tripleValue /= 64;
	}
}

/**
* encode an array of bytes using Base64 ( RFC 3548 )
*
* @param source the source buffer
* @param sourcelen the length of the source buffer
* @param target the target buffer
* @param targetlen the length of the target buffer
* @return 1 on success, 0 otherwise
*/
int base64_encode( unsigned char *source, size_t sourcelen, char *target, size_t targetlen )
{
	/* check if the result will fit in the target buffer */
	if ( ( sourcelen+2 )/3*4 > targetlen-1 )
		return 0;

	/* encode all full triples */
	while ( sourcelen >= 3 )
	{
		_base64_encode_triple( source, target );
		sourcelen -= 3;
		source += 3;
		target += 4;
	}

	/* encode the last one or two characters */
	if ( sourcelen > 0 )
	{
		unsigned char temp[ 3 ] ;
		memset( temp, 0, sizeof( temp ) );
		memcpy( temp, source, sourcelen );
		_base64_encode_triple( temp, target );
		target[ 3 ] = '=';
		if ( sourcelen == 1 )
			target[ 2 ] = '=';

		target += 4;
	}

	/* terminate the string */
	target[ 0 ] = 0;

	return 1;
}

/**
* determine the value of a base64 encoding character
*
* @param base64char the character of which the value is searched
* @return the value in case of success ( 0-63 ), -1 on failure
*/
int _base64_char_value( char base64char )
{
	if ( base64char >= 'A' && base64char <= 'Z' )
		return base64char-'A';
	if ( base64char >= 'a' && base64char <= 'z' )
		return base64char-'a'+26;
	if ( base64char >= '0' && base64char <= '9' )
		return base64char-'0'+2*26;
	if ( base64char == '+' )
		return 2*26+10;
	if ( base64char == '/' )
		return 2*26+11;
	return -1;
}

/**
* decode a 4 char base64 encoded byte triple
*
* @param quadruple the 4 characters that should be decoded
* @param result the decoded data
* @return lenth of the result ( 1, 2 or 3 ), 0 on failure
*/
int _base64_decode_triple( char quadruple[ 4 ], unsigned char *result )
{
	int i, triple_value, bytes_to_decode = 3, only_equals_yet = 1;
	int char_value[ 4 ];

	for ( i=0; i<4; i++ )
		char_value[ i ] = _base64_char_value( quadruple[ i ] );

	/* check if the characters are valid */
	for ( i=3; i>=0; i-- )
	{
		if ( char_value[ i ] < 0 )
		{
			if ( only_equals_yet && quadruple[ i ] =='=' )
			{
				/* we will ignore this character anyway, make it something
				* that does not break our calculations */
				char_value[ i ]=0;
				bytes_to_decode--;
				continue;
			}
			return 0;
		}
		/* after we got a real character, no other '=' are allowed anymore */
		only_equals_yet = 0;
	}

	/* if we got "====" as input, bytes_to_decode is -1 */
	if ( bytes_to_decode < 0 )
		bytes_to_decode = 0;

	/* make one big value out of the partial values */
	triple_value = char_value[ 0 ];
	triple_value *= 64;
	triple_value += char_value[ 1 ] ;
	triple_value *= 64;
	triple_value += char_value[ 2 ];
	triple_value *= 64;
	triple_value += char_value[ 3 ];

	/* break the big value into bytes */
	for ( i=bytes_to_decode; i<3; i++ )
		triple_value /= 256;
	for ( i=bytes_to_decode-1; i>=0; i-- )
	{
		result[ i ] = triple_value%256;
		triple_value /= 256;
	}

	return bytes_to_decode;
}

/**
* decode base64 encoded data
*
* @param source the encoded data ( zero terminated )
* @param target pointer to the target buffer
* @param targetlen length of the target buffer
* @return length of converted data on success, -1 otherwise
*/
size_t base64_decode( char *source, unsigned char *target, size_t targetlen )
{
	char *src, *tmpptr;
	char quadruple[ 4 ], tmpresult[ 3 ];
	int i;
	int tmplen = 3;
	size_t converted = 0;

	/* concatinate '===' to the source to handle unpadded base64 data */
	src = ( char * )malloc( strlen( source )+5 );
	if ( src == NULL )
		return -1;
	strcpy( src, source );
	strcat( src, "====" );
	tmpptr = src;

	/* convert as long as we get a full result */
	while ( tmplen == 3 )
	{
		/* get 4 characters to convert */
		for ( i=0; i<4; i++ )
		{
			/* skip invalid characters - we won't reach the end */
			while ( *tmpptr != '=' && _base64_char_value( *tmpptr )<0 )
				tmpptr++;

			quadruple[ i ]= *( tmpptr++ );
		}

		/* convert the characters */
		tmplen = _base64_decode_triple( quadruple, ( unsigned char* )tmpresult );

		/* check if the fit in the result buffer */
		if ( targetlen < tmplen )
		{
			free( src );
			return -1;
		}

		/* put the partial result in the result buffer */
		memcpy( target, tmpresult, tmplen );
		target += tmplen;
		targetlen -= tmplen;
		converted += tmplen;
	}

	free( src );
	return converted;
}