convert c char to swift - ios

Question

I am trying to conver the following code to swift:
static unsigned char rsa2048Asn1Header[] = {
0x30, 0x82, 0x01, 0x22, 0x30, 0x0d, 0x06, 0x09, 0x2a, 0x86, 0x48, 0x86,
0xf7, 0x0d, 0x01, 0x01, 0x01, 0x05, 0x00, 0x03, 0x82, 0x01, 0x0f, 0x00
};
static unsigned char rsa4096Asn1Header[] = {
0x30, 0x82, 0x02, 0x22, 0x30, 0x0d, 0x06, 0x09, 0x2a, 0x86, 0x48, 0x86,
0xf7, 0x0d, 0x01, 0x01, 0x01, 0x05, 0x00, 0x03, 0x82, 0x02, 0x0f, 0x00
};
static unsigned char ecDsaSecp256r1Asn1Header[] = {
0x30, 0x59, 0x30, 0x13, 0x06, 0x07, 0x2a, 0x86, 0x48, 0xce, 0x3d, 0x02,
0x01, 0x06, 0x08, 0x2a, 0x86, 0x48, 0xce, 0x3d, 0x03, 0x01, 0x07, 0x03,
0x42, 0x00
};
static unsigned char *asn1HeaderBytes[3] = { rsa2048Asn1Header, rsa4096Asn1Header, ecDsaSecp256r1Asn1Header };
static unsigned int asn1HeaderSizes[3] = { sizeof(rsa2048Asn1Header), sizeof(rsa4096Asn1Header), sizeof(ecDsaSecp256r1Asn1Header) };
My swift code looks like this:
let rsa2048Asn1Header:[CUnsignedChar] = [0x30, 0x82, 0x01, 0x22, 0x30, 0x0d, 0x06, 0x09, 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d,0x01, 0x01, 0x01, 0x05, 0x00, 0x03, 0x82, 0x01, 0x0f, 0x00]
let rsa4096Asn1Header:[CUnsignedChar] = [0x30, 0x82, 0x01, 0x22, 0x30, 0x0d, 0x06, 0x09, 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x01, 0x01, 0x01, 0x05, 0x00, 0x03, 0x82, 0x01, 0x0f, 0x00]
let ecDsaSecp256r1Asn1Header:[CUnsignedChar] = [0x30, 0x59, 0x30, 0x13, 0x06, 0x07, 0x2a, 0x86, 0x48, 0xce, 0x3d, 0x02, 0x01, 0x06, 0x08, 0x2a, 0x86, 0x48, 0xce, 0x3d, 0x03, 0x01, 0x07, 0x03, 0x42, 0x00]
let asn1HeaderBytes:[[CUnsignedChar]] = [rsa2048Asn1Header, rsa4096Asn1Header, ecDsaSecp256r1Asn1Header]
let asn1HeaderSizes:[UInt] = [sizeof(rsa2048Asn1Header.dynamicType).toUInt, sizeof(rsa4096Asn1Header.dynamicType).toUInt, sizeof(ecDsaSecp256r1Asn1Header.dynamicType).toUInt]
However i failing at his badly, per example using rsa2048Asn1Header and converting it to NSData:
let data:NSData = NSData(bytes: rsa2048Asn1Header, length:strideofValue(rsa2048Asn1Header))
swift prints with length 8:
<30820122 300d0609>
objc for the following code:
[NSData dataWithBytes:rsa2048Asn1Header length:sizeof(rsa2048Asn1Header)];
prints
<30820122 300d0609 2a864886 f70d0101 01050003 82010f00> size: 24
looking at apple documentation, strideOfvalue should return the right size for each one of those [CUnsignedChar] but that doesnt seem to be the case, my question is shouldnt a [CUnsignedChar] have same size as usigned char [] in objc, if not what could i use to change?
also [[CUnsignedChar]] makes no sense whatsoever in my head, how would the code below convert to swift, should i convert those arrays to an NSString and extract the CString when required, if so what encoding should I use?
static unsigned char *asn1HeaderBytes[3] = { rsa2048Asn1Header, rsa4096Asn1Header, ecDsaSecp256r1Asn1Header };

Answer 1

I don't think strideofValue is the function you are looking for. I haven't heard of it before, but the documentation states:
Returns the least possible interval between distinct instances of T in memory. The result is always positive.
If this is returning 8, that means that the minimum distance between [CUnsignedChar]s in memory is 8 bytes.
To use NSData(data:length:) properly, the second parameter needs to be the size of the array. You can use the count property for this:
let data: NSData = NSData(bytes: rsa2048Asn1Header, length:rsa2048Asn1Header.count)
[[CUnsignedChar]] is an array of arrays (two-dimensional array) of CUnsignedChar.
Your headers are raw bytes, so technically no encoding is 'correct' to convert to NSString. The cryptographic headers you have don't appear to be strings, and contain unprintable characters.

Answer 2

You should not use strideofValue function. 'strideofValue' it's not a replacement for 'sizeof'. Just go for ".count" property.