NSData_HexAdditions

@interface NSData (NSData_HexAdditions)
- (NSData *)dataFromHexString;
@end

#define IS_HEX(c) ((c >= '0' && c <= '9') || (c >= 'a' && c <= 'f') || (c >='A' && c <= 'F'))

@implementation NSData (NSData_HexAdditions)

/*
 * Takes an NSData encoding an ASCII string representing hexadecimal data,
 * and reads it into an NSData of the represented bytes.
 * Ignores non-hex characters, might drop the last nibble.
 * E.g., "ABC\r\nDE" -> 0xABCD
 */
- (NSData *)dataFromHexString;
{
	const unsigned char *bytes = [self bytes];
	
	// Read all hexadecimal characters into array
	unsigned char *hexChars = calloc(sizeof(char), [self length]);
	const unsigned char *s;
	int charCount = 0;
	for (s = bytes; s < bytes + [self length]; s++) {
		if (IS_HEX(*s)) {
			hexChars[charCount++] = *s;
		}
	}
			
	// Convert pairs of hexadecimal characters to bytes
	unsigned char *dataBuffer = calloc(sizeof(char), charCount / 2);
	char c[3] = "XX";
	int byteCount = 0;
	for (s = hexChars; s < hexChars + charCount - 1; s += 2) {
		c[0] = s[0];
		c[1] = s[1];
		dataBuffer[byteCount++] = (char)(strtol(c, NULL, 16));
	}
	
	NSData *data = [NSData dataWithBytes:dataBuffer length:byteCount];
	free(dataBuffer);
	free(hexChars);
	
	return data;
}

@end