NSData+MBBase64.m

static const char encodingTable[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

@implementation NSData (MBBase64)

+ (id)dataByDecodingBase64String:(NSString *)string;
{
	if (string == nil)
		[NSException raise:NSInvalidArgumentException format:nil];
	if ([string length] == 0)
		return [NSData data];
	
	static char *decodingTable = NULL;
	if (decodingTable == NULL)
	{
		decodingTable = malloc(256);
		if (decodingTable == NULL)
			return nil;
		memset(decodingTable, CHAR_MAX, 256);
		int i;
		for (i = 0; i < 64; i++)
			decodingTable[(short)encodingTable[i]] = i;
	}
	
	const char *characters = [string cStringUsingEncoding:NSASCIIStringEncoding];
	if (characters == NULL)     //  Not an ASCII string!
		return nil;
	char *bytes = malloc((([string length] + 3) / 4) * 3);
	if (bytes == NULL)
		return nil;
	int length = 0;
	
	int i = 0;
	while (YES)
	{
		char buffer[4];
		short bufferLength;
		for (bufferLength = 0; bufferLength < 4; i++)
		{
			if (characters[i] == '\0')
				break;
			if (isspace(characters[i]) || characters[i] == '=')
				continue;
			buffer[bufferLength] = decodingTable[(short)characters[i]];
			if (buffer[bufferLength++] == CHAR_MAX)      //  Illegal character!
			{
				free(bytes);
				return nil;
			}
		}
		
		if (bufferLength == 0)
			break;
		if (bufferLength == 1)      //  At least two characters are needed to produce one byte!
		{
			free(bytes);
			return nil;
		}
		
		//  Decode the characters in the buffer to bytes.
		bytes[length++] = (buffer[0] << 2) | (buffer[1] >> 4);
		if (bufferLength > 2)
			bytes[length++] = (buffer[1] << 4) | (buffer[2] >> 2);
		if (bufferLength > 3)
			bytes[length++] = (buffer[2] << 6) | buffer[3];
	}
	
	realloc(bytes, length);
	return [NSData dataWithBytesNoCopy:bytes length:length];
}

- (NSString *)stringEncodedBase64 ;
{
	if ([self length] == 0)
		return @"";
	
    char *characters = malloc((([self length] + 2) / 3) * 4);
	if (characters == NULL)
		return nil;
	int length = 0;
	
	int i = 0;
	while (i < [self length])
	{
		char buffer[3] = {0,0,0};
		short bufferLength = 0;
		while (bufferLength < 3 && i < [self length])
			buffer[bufferLength++] = ((char *)[self bytes])[i++];
		
		//  Encode the bytes in the buffer to four characters, including padding "=" characters if necessary.
		characters[length++] = encodingTable[(buffer[0] & 0xFC) >> 2];
		characters[length++] = encodingTable[((buffer[0] & 0x03) << 4) | ((buffer[1] & 0xF0) >> 4)];
		if (bufferLength > 1)
			characters[length++] = encodingTable[((buffer[1] & 0x0F) << 2) | ((buffer[2] & 0xC0) >> 6)];
		else characters[length++] = '=';
		if (bufferLength > 2)
			characters[length++] = encodingTable[buffer[2] & 0x3F];
		else characters[length++] = '=';	
	}
	
	return [[[NSString alloc] initWithBytesNoCopy:characters length:length encoding:NSASCIIStringEncoding freeWhenDone:YES] autorelease];
}

@end