Hey, I am trying to use Swift `thows` with kotlin...

# ios

[Patryk Drozd]

Hey,
I am trying to use Swift thows with kotlin.

Swift

@objcMembers public class AESCryptoBridge: NSObject {
    public func test() throws {
        throw CryptoError.invalidData
    }
}

On Kotlin I have access to NSError but I have no idea how to use is. Is there any resource that will explain me how to work with?

AESCryptoBridge().testAndReturnError("I have no idea how to use NSError Pointer here")

I found this code but alloc is deprecated if I am correct

val errorPointer: CPointer<ObjCObjectVar<NSError?>> = alloc<ObjCObjectVar<NSError?>>().ptr

Update: I found the solution 🙂

val error = memScoped {
    allocPointerTo<ObjCObjectVar<NSError?>>()
}
AESCryptoBridge().testAndReturnError(error.value)

[Landry Norris]

Note that the code in the update has a memory error, since the pointer is freed after the memScoped exits. You should set the 'error' variable inside the memScoped, and keep all code that uses it inside. If you don't, the allocator can choose to allocate something else over where 'error' was originally allocated, since it's freed.

[Patryk Drozd]

ohh good to know!

so I should do something like this

memScoped {
    val error = allocPointerTo<ObjCObjectVar<NSError?>>()

    SwiftCryptoBridge().initializeMACKeyWithKeyAlias(keyAlias.alias, error.value)

    if (error.value != null) {
        throw IllegalStateException("initializeMACKey Failed for $keyAlias with error: $error")
    } else {
        print("initializeMACKey Successful for: $keyAlias")
    }
}

[Landry Norris]

Yes. Now the error is allocated for the full time you're using it.

[Patryk Drozd]

Hey, I am writing tests for my logic and I found behaviour I didn't expect.

This is my Swift function

public func verifyChain(derCertificates: [Data]) throws {
    print("<-- Before Swift Throws")
    throw CertificateManagerError.invalidCertificateData
    print("<-- After Swift Throws")
}

And here Kotlin

actual override fun verifyChain(certs: List<Certificate>): Result<Unit> = memScoped {
            if (certs.isEmpty()) {
                return Result.failure(IllegalStateException("Certificate list is empty!"))
            }

            val dataCertificates = certs.map { (it.asPlatformCert() as ByteArray).toNSData() }

            val error = allocPointerTo<ObjCObjectVar<NSError?>>()
            Log.d("tag", "Enter Swift")
                certificateManager.verifyChainWithDerCertificates(
                    dataCertificates,
                    error.value,
                )
            Log.d("tag", "Leaved Swift")

            if (error.value != null) {
                return Result.failure(IllegalStateException("Verify Chain Failed with error: $error."))
            }

            Log.d("tag", "Error value before return ${error.value}")

        return Result.success(Unit)
    }

Somehow everything passed with this in my logs
Debug: (🛠️) AGENT-tag: Enter Swift
Debug: (🛠️) AGENT-tag: Leaved Swift
Debug: (🛠️) AGENT-tag: Error value before return null
<-- Before Swift Throws
BUILD SUCCESSFUL in 10s

Kotlin Code didn't waited for Swift to finish. so I didn't received NSError pointer when I needed.

Do you have maybe idea how to fix it?