Use encrypted dns proxy code in mullvad ios ios 818

[pinkisemils]

With these changes, we are practically finishing off the encrypted DNS proxy work. These changes make use of the FFI exposed in mullvad-ios::encrypted_dns_proxy to implement the transport provider for our MullvadRest module in Swift. Most of the great work here has been done by @buggmagnet.

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This change is 

[linear]

IOS-818 Use encrypted DNS proxy code in `mullvad-ios`

[rablador]

Reviewed 3 of 6 files at r1, all commit messages.
Reviewable status: 0 of 6 files reviewed, 2 unresolved discussions (waiting on @buggmagnet and @pinkisemils)

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ios/MullvadREST/Transport/TransportProvider.swift line 20 at r1 (raw file):

    private var currentTransportType: TransportStrategy.Transport
    private let parallelRequestsMutex = NSLock()
    private let encryptedDNSTransport: EncryptedDNSTransport!

Remove exclamation mark. A let constant that is assigned in an init function will always be non-optional.

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ios/MullvadREST/Transport/EncryptedDNS/EncryptedDNSTransport.swift line 21 at r1 (raw file):

    private let encryptedDnsProxy: EncryptedDNSProxy
    private let dispatchQueue = DispatchQueue(label: "net.mullvad.EncryptedDNSTransport")
    private var dnsProxyTask: URLSessionTask!

Should be optional since it's nilled in stop().

[rablador]

Reviewed 3 of 6 files at r1.
Reviewable status: 0 of 6 files reviewed, 3 unresolved discussions (waiting on @buggmagnet, @pinkisemils, and @rablador)

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ios/MullvadREST/Transport/EncryptedDNS/EncryptedDNSTransport.swift line 67 at r1 (raw file):

                    }
                    // Do not call the completion handler if the request was cancelled in flight
                    if let cancelledError = maybeError as? URLError, cancelledError.code == .cancelled {

Nit: Prefer a guard here, since we're returning early.

[buggmagnet]

Reviewable status: 0 of 6 files reviewed, 3 unresolved discussions (waiting on @rablador)

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ios/MullvadREST/Transport/TransportProvider.swift line 20 at r1 (raw file):

Previously, rablador (Jon Petersson) wrote…

Remove exclamation mark. A let constant that is assigned in an init function will always be non-optional.

Done

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ios/MullvadREST/Transport/EncryptedDNS/EncryptedDNSTransport.swift line 21 at r1 (raw file):

Previously, rablador (Jon Petersson) wrote…

Should be optional since it's nilled in stop().

Done

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ios/MullvadREST/Transport/EncryptedDNS/EncryptedDNSTransport.swift line 67 at r1 (raw file):

Previously, rablador (Jon Petersson) wrote…

Nit: Prefer a guard here, since we're returning early.

We discussed this offline and came to the conclusion that the current construction is fine as is.

[mojganii]

Reviewable status: 0 of 6 files reviewed, 4 unresolved discussions (waiting on @buggmagnet, @pinkisemils, and @rablador)

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ios/MullvadREST/Transport/TransportProvider.swift line 58 at r2 (raw file):

        if strategy == transportStrategy {
            if strategy.connectionTransport() == .encryptedDNS {

nit : we are doing to stop proxy in different ways, somewhere in deinit and some like here we calling that directly. maybe we need to unify them in one place.

[pinkisemils]

WAT https://github.com/mullvad/mullvadvpn-app/actions/runs/11051418946/job/30701257215?pr=6874#step:11:1995

[rablador]

Reviewed 2 of 2 files at r2, all commit messages.
Reviewable status: 0 of 6 files reviewed, 1 unresolved discussion (waiting on @buggmagnet, @pinkisemils, and @rablador)