ignore the invalid utf-8

NSData+UTF8.m

- (NSData *)cleanUTF8:(NSData *)data {
    // this function is from
    // https://stackoverflow.com/questions/3485190/nsstring-initwithdata-returns-null
    //
    //
    iconv_t cd = iconv_open("UTF-8", "UTF-8"); // convert to UTF-8 from UTF-8
    int one = 1;
    iconvctl(cd, ICONV_SET_DISCARD_ILSEQ, &one); // discard invalid characters
    size_t inbytesleft, outbytesleft;
    inbytesleft = outbytesleft = data.length;
    char *inbuf  = (char *)data.bytes;
    char *outbuf = malloc(sizeof(char) * data.length);
    char *outptr = outbuf;
    if (iconv(cd, &inbuf, &inbytesleft, &outptr, &outbytesleft)
        == (size_t)-1) {
        NSLog(@"this should not happen, seriously");
        return nil;
    }
    NSData *result = [NSData dataWithBytes:outbuf length:data.length - outbytesleft];
    iconv_close(cd);
    free(outbuf);
    return result;
}