MapboxVoiceController requires access token in Info.plist

[1ec5]

This SDK is designed so that the application can specify a Mapbox access token programmatically at runtime as an alternative to specifying it in the Info.plist file. However, by default, if the application specifies the access token by setting MGLAccountManager.accessToken and passing an access token into Directions(accessToken:), instructions are spoken by VoiceOver instead of by Amazon Polly via the Mapbox Voice API.

Diagnosis

By default, NavigationViewController(for:styles:navigationService:voiceController:) creates a MapboxVoiceController with no arguments:

mapbox-navigation-ios/MapboxNavigation/NavigationViewController.swift

Line 369 in 9c49ade

self.voiceController = voiceController ?? MapboxVoiceController()

By default, MapboxVoiceController(speechClient:dataCache:audioPlayerType:) creates a SpeechSynthesizer with no access token:

mapbox-navigation-ios/MapboxNavigation/MapboxVoiceController.swift

Line 38 in 9c49ade

@objc public init(speechClient: SpeechSynthesizer = SpeechSynthesizer(accessToken: nil), dataCache: BimodalDataCache = DataCache(), audioPlayerType: AVAudioPlayer.Type? = nil) {

By default, SpeechSynthesizer reads the access token out of the Info.plist file:

https://github.com/mapbox/mapbox-speech-swift/blob/b6b7a8f430efdd9a2945fb2a91347dfc501e7428/MapboxSpeech/MapboxSpeech.swift#L9

With a Debug build of MapboxSpeech, this assertion would fail:

https://github.com/mapbox/mapbox-speech-swift/blob/b6b7a8f430efdd9a2945fb2a91347dfc501e7428/MapboxSpeech/MapboxSpeech.swift#L89-L90

But in a Release build, the library would request audio without an access token, and the Voice API would return an error, causing MapboxVoiceController to fall back to VoiceOver via RouteVoiceController.

Workaround

let voiceController = MapboxVoiceController(speechClient: SpeechSynthesizer(accessToken: "pk.feedCafeDeadBeefBadeBede"))
let navigationViewController = NavigationViewController(for: route, navigationService: navigationService, voiceController: voiceController)

Proposed fix

A fix would look similar to the workaround: by default, NavigationViewController would create a MapboxVoiceController that uses the same access token and API endpoint as the NavigationService:

MapboxVoiceController(speechClient: SpeechSynthesizer(accessToken: navigationService.directions.accessToken))

For this to work, RouteOptions.accessToken needs to be made public: mapbox/mapbox-directions-swift#308.

Note that MapboxNavigationService(route:directions:locationSource:eventsManagerType:simulating:routerType:) also defaults to Directions.shared, which reads the access token from the Info.plist file:

mapbox-navigation-ios/MapboxCoreNavigation/NavigationService.swift

Line 246 in 9c49ade

self.directions = directions ?? Directions.shared

So even with this fix, the application would still be required to pass a NavigationService into NavigationViewController(for:styles:navigationService:voiceController:) instead of relying on the default NavigationService. Specifying an access token at runtime requires a lot of fiddling, which is why the Info.plist key is supported as a global configuration option.

/cc @mapbox/navigation-ios