Getting a hex string out of NSData

NSData+HexString.m

@implementation NSData (HexString)

- (NSString *)hex_hexString {
    NSMutableString *out = [NSMutableString stringWithCapacity:self.length * 2];
    [self enumerateByteRangesUsingBlock:^(const void *bytes, NSRange byteRange, BOOL *stop) {
        for (NSUInteger i = 0; i < byteRange.length; i++) {
            [out appendFormat:@"%02x", ((unsigned char *)bytes)[i]];
        }
    }];
    return out;
}

@end

The use of enumerateByteRangesUsingBlock: keeps this moderately efficient for non-contiguous NSData, and shouldn't have an impact on contiguous NSData.