How to construct Data/NSData from UnsafeMutablePointer<T> - ios

Question

Background: I am using OpenSSL library to create PKCS12 file in Swift. I have the certificate and private key stored in Keychain.
Problem: I am able to create a PKCS12 file and store it in the app bundle successfully. When I want to use the PKCS12 file (e.g. Receive a auth challenge from a HTTPS server), I can load the file by using SecPKCS12Import() function provided by Apple. Now, instead of generating a physical file, I want to generate the PKCS12 object in flight whenever I need it. It will be stored in memory. Since I am new to Swift, I am seeking help for converting from UnsafeMutablePointer to Data.
You will understand more when you read my following code:
Previously, I have my createP12 function implemented as:
createP12(pemCert: String, pemPK: String) {
// .......
// Code to load certificate and private key Object..
guard let p12 = PKCS12_create(passPhrase, name, privateKey, certificate, nil, NID_pbe_WithSHA1And3_Key_TripleDES_CBC, NID_pbe_WithSHA1And3_Key_TripleDES_CBC, 0, 0, 0) else {
ERR_print_errors_fp(stderr)
return
}
// Save p12 to file
let fileManager = FileManager.default
let tempDirectory = NSTemporaryDirectory() as NSString
let path = tempDirectory.appendingPathComponent("ssl.p12")
fileManager.createFile(atPath: path, contents: nil, attributes: nil)
guard let fileHandle = FileHandle(forWritingAtPath: path) else {
LogUtils.logError("Cannot open file handle: \(path)")
return
}
let p12File = fdopen(fileHandle.fileDescriptor, "w")
i2d_PKCS12_fp(p12File, p12)
fclose(p12File)
fileHandle.closeFile()
}
Then when I want to read the p12 file, I can call
let p12Data = NSData(contentsOfFile: Bundle.main.path(forResource: mainBundleResource, ofType:resourceType)!)! as Data
var items: CFArray?
let certOptions: NSDictionary = [kSecImportExportPassphrase as NSString: passwordStr as NSString]
self.securityError = SecPKCS12Import(p12Data as NSData, certOptions, &items)
// Code to read attributes
From createP12() function, I firstly got a p12 object in type of UnsafeMutablePointer<PKCS12> then store it in the file. Instead, now I want to pass p12 directly to the pkcs12 reader function. To do so, I have to firstly convert p12 object into a Data/NSData object since that's what required by SecPKCS12Import() function.
So, long story short, how can I construct a Data/NSData object from the p12 object which is in type of UnsafaMutablePointer<PKCS12> thus I can pass it into SecPKCS12Import()?

Answer 1

This should work (it compiles but I could not test it). The idea is to write the PKCS12 object to a memory buffer and then create Data
from the buffer:
func p12ToData(p12: UnsafeMutablePointer<PKCS12>) -> Data {
// Write PKCS12 to memory buffer:
let mbio = BIO_new(BIO_s_mem())
i2d_PKCS12_bio(mbio, p12)
// Get pointer to memory buffer and number of bytes. The
// # define BIO_get_mem_data(b,pp) BIO_ctrl(b,BIO_CTRL_INFO,0,(char *)pp)
// macro is not imported to Swift.
var ptr = UnsafeRawPointer(bitPattern: 1)!
let cnt = BIO_ctrl(mbio, BIO_CTRL_INFO, 1, &ptr)
// Create data from pointer and count:
let data = Data(bytes: ptr, count: cnt)
// Release memory buffer:
BIO_free(mbio)
return data
}