Get a hex string from NSData

NSData+Hex.h

#import <Foundation/Foundation.h>

@interface NSData (Hex)

- (NSString*)hexString;
- (NSString*)hexStringWithCaps:(BOOL)caps;
+ (NSData*)dataWithHexString:(NSString*)hexString;

@end

NSData+Hex.m

#import "NSData+Hex.h"

@implementation NSData (Hex)

- (NSString*)hexString
{
    return [self hexStringWithCaps:NO];
}

- (NSString*)hexStringWithCaps:(BOOL)caps
{
    const char *hex = caps ? "01234567890ABCDEF" : "0123456789abcdef";
    char *hexString = malloc(self.length*2);
    const uint8_t *bytes = self.bytes;
    for (size_t i = 0; i < self.length; i++)
    {
        hexString[2*i] = hex[(bytes[i] & 0xF0) >> 4];
        hexString[2*i+1] = hex[bytes[i] & 0x0F];
    }
    return [[NSString alloc] initWithBytesNoCopy:hexString length:self.length*2 encoding:NSASCIIStringEncoding freeWhenDone:YES];
}

+ (NSData*)dataWithHexString:(NSString*)hexString
{
    if (hexString == nil)
        return nil;
    hexString = [hexString stringByReplacingOccurrencesOfString:@"[^0-9a-f]" withString:@"" options:NSRegularExpressionSearch|NSCaseInsensitiveSearch range:NSMakeRange(0, hexString.length)];
    if (hexString.length % 2 != 0)
        return nil;
    uint8_t * const buf = malloc(hexString.length/2);
    uint8_t *wbuf = buf;
    const char *str = hexString.UTF8String;
    char hexchar[3] = "00";
    while (*str)
    {
        hexchar[0] = *str++;
        hexchar[1] = *str++;
        *wbuf = (uint8_t)strtol(hexchar, NULL, 16);
        wbuf++;
    }
    return [NSData dataWithBytesNoCopy:buf length:hexString.length/2 freeWhenDone:YES];
}

@end