unleash-proxy-client-swift

The unleash-proxy-client-swift makes it easy for native applications and other swift platforms to connect to the unleash proxy. The proxy will evaluate a feature toggle for a given context and return a list of feature flags relevant for the provided context.

The unleash-proxy-client-swift will then cache these toggles in a map in memory and refresh the configuration at a configurable interval, making queries against the toggle configuration extremely fast.

Requirements

• MacOS: 12.15
• iOS: 12

Installation

Follow the following steps in order to install the unleash-proxy-client-swift:

1. In your Xcode project go to File -> Swift Packages -> Add Package Dependency
2. Supply the link to this repository
3. Set the appropriate package constraints (typically up to next major version)
4. Let Xcode find and install the necessary packages

Once you're done, you should see SwiftEventBus and UnleashProxyClientSwift listed as dependencies in the file explorer of your project.

Usage

In order to get started you need to import and instantiate the unleash client:

iOS >= 13

import SwiftUI
import UnleashProxyClientSwift

// Setup Unleash in the context where it makes most sense

var unleash = UnleashProxyClientSwift.UnleashClient(
    unleashUrl: "https://<unleash-instance>/api/frontend",
    clientKey: "<client-side-api-token>", 
    refreshInterval: 15, 
    appName: "test", 
    context: ["userId": "c3b155b0-5ebe-4a20-8386-e0cab160051e"]
)

unleash.start()

iOS >= 12

import SwiftUI
import UnleashProxyClientSwift

// Setup Unleash in the context where it makes most sense

var unleash = UnleashProxyClientSwift.UnleashClientBase(
    unleashUrl: "https://<unleash-instance>/api/frontend", 
    clientKey: "<client-side-api-token>", 
    refreshInterval: 15, 
    appName: "test", 
    context: ["userId": "c3b155b0-5ebe-4a20-8386-e0cab160051e"]
)

unleash.start()

In the example above we import the UnleashProxyClientSwift and instantiate the client. You need to provide the following parameters:

• unleashUrl: the full url to either the Unleash front-end API OR an Unleash proxy [String]
• clientKey: either an client-side API token if you use the front-end API (how) or a proxy client key if you use the proxy [String]
• refreshInterval: the polling interval in seconds [Int]. Set to 0to only poll once and disable a periodic polling
• appName: the application name identifier [String]
• context: the context parameters except from appName and environment which should be specified explicitly in the init [[String: String]]

Running unleash.start() will make the first request against the proxy and retrieve the feature toggle configuration, and set up the polling interval in the background.

NOTE: While waiting to boot up the configuration may not be available, which means that asking for a feature toggle may result in a false if the configuration has not loaded. In the event that you need to be certain that the configuration is loaded we emit an event you can subscribe to, once the configuration is loaded. See more in the Events section.

Once the configuration is loaded you can ask against the cache for a given feature toggle:

if unleash.isEnabled(name: "ios") {
    // do something
} else {
   // do something else
}

You can also set up variants and use them in a similar fashion:

var variant = unleash.getVariant(name: "ios")
if variant.enabled {
    // do something
} else {
   // do something else
}

Available options

The Unleash SDK takes the following options:

option	required	default	description
unleashUrl	yes	n/a	The Unleash Edge/Proxy URL to connect to. E.g.: https://examples.com/proxy
clientKey	yes	n/a	The Unleash Edge/Proxy Secret to be used
appName	no	unleash-swift-client	The name of the application using this SDK. Will be used as part of the metrics sent to Unleash Edge/Proxy. Will also be part of the Unleash Context.
environment	no	default	The name of the environment using this SDK. Will be used as part of the metrics sent to Unleash Edge/Proxy. Will also be part of the Unleash Context.
refreshInterval	no	15	How often, in seconds, the SDK should check for updated toggle configuration. If set to 0 will disable checking for updates
metricsInterval	no	30	How often, in seconds, the SDK should send usage metrics back to Unleash Edge/Proxy
disableMetrics	no	false	Set this option to true if you want to disable usage metrics
context	no	[:]	The initial context parameters except from appName and `environment which are specified as top level fields
customHeaders	no	[:]	Additional headers to use when making HTTP requests to the Unleash Edge/Proxy. In case of name collisions with the default headers, the customHeaders value will be used.
bootstrap	no	empty list of toggles	The Unleash Edge/Proxy SDK can be initialised with an initial set of toggles, read from either a list of Toggles, or a jsonFile matching the structure of the response from the frontend API. These will be available instantly before the initial fetch.

Bootstrapping

You can provide the initial toggle state to the Unleash client SDK. This is useful when you have a known initial state for your feature toggles. This toggle state can be bootstrapped to the client via a list of toggles, or from a file matching a response from the frontend API. For example:

Bootstrap from hard-coded list

// Note variant and payload can be optional.
let bootstrapList = Bootstrap
    .toggles(
        [
            Toggle(name: "Foo", enabled: true),
            Toggle(
                name: "Bar", 
                enabled: false, 
                variant: Variant(
                    name: "bar",
                    enabled: true,
                    featureEnabled: true,
                    payload: Payload(type: "string", value: "baz")
                )
            )
        ]
    )

Bootstrap from file matching frontend API response

{
  "toggles": [
      {
        "name": "no-variant",
        "enabled": true
      },
      {
        "name": "disabled-with-variant-disabled-no-payload",
        "enabled": false,
        "variant": {
            "name": "foo",
            "enabled": false,
            "feature_enabled": false
        }
      },
      {
        "name": "enabled-with-variant-enabled-and-payload",
        "enabled": true,
        "variant": {
            "name": "bar",
            "enabled": true,
            "feature_enabled": true,
            "payload": {
                "type": "string",
                "value": "baz"
            }
        }
      }
  ]
}

guard let filePath = Bundle.main.path(forResource: "FeatureResponseFile", ofType: "json") else {
    // Handle missing file
}

let boostrapFile = Bootsrap.jsonFile(path: filePath)

Using the bootstrap list of toggles

Whether from a hard-coded list, or a json file, the boostrap toggles can be injected into the Unleash Edge/proxy client either at initialisation time, or when calling start. For example:

import SwiftUI
import UnleashProxyClientSwift

// Setup Unleash in the context where it makes most sense

let unleash = UnleashClient(
    unleashUrl: "https://<unleash-instance>/api/frontend", 
    clientKey: "<client-side-api-token>",
    bootstrap: .toggles([Toggle(name: "Foo", enabled: true)])
)

// Toggles can be accessed now ahead of starting client
let isFooEnabled = unleash.isEnabled(name: "Foo") // true

// Or provide when starting in case of slow/faulty connection
unleash.start(bootstrap: .jsonFile("path/to/json/file"))

// Or using async-await concurrency (>= iOS13)
await unleash.start(bootstrap: .jsonFile("path/to/json/file"))

Important notices

• If you initialise the Unleash Edge/proxy client with a Poller, you should inject the bootstrap directly into the poller. Any bootstrapped toggles inject into the Unleash client will be ignored when a poller is also injected.
• Any bootstrapped toggles will be removed after the first initial fetch
• If bootstrap toggles are provided when calling start, the first fetch will be at the next refresh interval specified (default 15 seconds)
• Calling updateContext(...) before the first fetch will remove bootstrapped toggles.

Update context

In order to update the context you can use the following method:

var context: [String: String] = [:]
context["userId"] = "c3b155b0-5ebe-4a20-8386-e0cab160051e"
unleash.updateContext(context: context)

This will stop and start the polling interval in order to renew polling with new context values.

You can use any of the predefined fields. If you need to support custom properties pass them as the second argument:

var context: [String: String] = [:]
context["userId"] = "c3b155b0-5ebe-4a20-8386-e0cab160051e"
var properties: [String: String] = [:]
properties["customKey"] = "customValue";
unleash.updateContext(context: context, properties: properties)

Events

The proxy client emits events that you can subscribe to. The following events are available:

• "ready"
• "update"
• "sent" (metrics sent)
• "error" (metrics sending error)

Usage them in the following manner:

func handleReady() {
    // do this when unleash is ready
}

unleash.subscribe(name: "ready", callback: handleReady)

func handleUpdate() {
    // do this when unleash is updated
}

unleash.subscribe(name: "update", callback: handleUpdate)

Alternatively these are discoverable and usable as a typed enum UnleashEvent like so:

unleash.subscribe(.ready, callback: handleUpdate)

The ready event is fired once the client has received it's first set of feature toggles and cached it in memory. Every subsequent event will be an update event that is triggered if there is a change in the feature toggle configuration.

Releasing

Note: To release the package you'll need to have CocoaPods installed.

First, you'll need to add a tag. Releasing the tag is enough for the Swift package manager, but it's polite to also ensure CocoaPods users can also consume the code.

git tag -a 0.0.4 -m "v0.0.4"

Please make sure that that tag is pushed to remote.

The next few commands assume that you have CocoaPods installed and available on your shell.

First, validate your session with cocoapods with the following command:

pod trunk register <email> "Your name"

The email that owns this package is the general unleash team email. Cocoapods will send a link to this email, click it to validate your shell session.

Bump the version number of the package, you can find this in UnleashProxyClientSwift.podspec, we use SemVer for this project. Once that's committed and merged to main:

Linting the podspec is always a good idea:

pod spec lint UnleashProxyClientSwift.podspec

Once that succeeds, you can do the actual release:

pod trunk push UnleashProxyClientSwift.podspec --allow-warnings

Testing

In order to test this package you can run the swift test command. To test thread safety, run swift test with:

swift test --sanitize=thread

This will give you warnings in the console when you have any data races.