This is the Go Server-Side SDK for the 100% open-source feature flags management platform FeatBit.

The FeatBit Server-Side SDK for Go is designed primarily for use in multi-user systems such as web servers and applications.

We use websocket to make the local data synchronized with the FeatBit server, and then store them in memory by default. Whenever there is any change to a feature flag or its related data, this change will be pushed to the SDK and the average synchronization time is less than 100 ms. Be aware the websocket connection may be interrupted due to internet outage, but it will be resumed automatically once the problem is gone.

If you want to use your own data source, see Offline Mode.

Go Server Side SDK is based on go 1.13, so you need to install go 1.13 or above.

go get github.com/featbit/featbit-go-sdk

Before using the SDK, you need to obtain the environment secret and SDK URLs.

Follow the documentation below to retrieve these values

• How to get the environment secret
• How to get the SDK URLs

Note that the envSecret, streamUrl and eventUrl are required to initialize the SDK.

The following code demonstrates basic usage of the SDK.

package main

import (
	"fmt"
	"github.com/featbit/featbit-go-sdk"
	"github.com/featbit/featbit-go-sdk/interfaces"
)

func main() {
	envSecret := "<replace-with-your-env-secret>"
	streamingUrl := "ws://localhost:5100"
	eventUrl := "http://localhost:5100"

	client, err := featbit.NewFBClient(envSecret, streamingUrl, eventUrl)

	defer func() {
		if client != nil {
			// ensure that the SDK shuts down cleanly and has a chance to deliver events to FeatBit before the program exits
			_ = client.Close()
		}
	}()

	if err == nil && client.IsInitialized() {
		user, _ := interfaces.NewUserBuilder("<replace-with-your-user-key>").UserName("<replace-with-your-user-name>").Build()
		_, ed, _ := client.BoolVariation("<replace-with-your-feature-flag-key>", user, false)
		fmt.Printf("flag %s, returns %s for user %s, reason: %s \n", ed.KeyName, ed.Variation, user.GetKey(), ed.Reason)
	} else {
		fmt.Println("SDK initialization failed")
    }
}

• Go Demo

Applications SHOULD instantiate a single FBClient instance for the lifetime of the application. In the case where an application needs to evaluate feature flags from different environments, you may create multiple clients, but they should still be retained for the lifetime of the application rather than created per request or per thread.

The bootstrapping is in fact the call of constructor of featbit.FBClient, in which the SDK will be initialized, using streaming from your feature management platform.

The constructor will return when it successfully connects, or when the timeout set by featbit.FBConfig.StartWait(default: 15 seconds) expires, whichever comes first. If it has not succeeded in connecting when the timeout elapses, you will receive the client in an uninitialized state where feature flags will return default values; it will still continue trying to connect in the background unless there has been an net.DNSError or you close the client. You can detect whether initialization has succeeded by calling featbit.FBClient.IsInitialized().

If featbit.FBClient.IsInitialized() returns True, it means the featbit.FBClient has succeeded at some point in connecting to feature flag center, otherwise client has not yet connected to feature flag center, or has permanently failed. In this state, feature flag evaluations will always return default values.

config := featbit.FBConfig{StartWait: 10 * time.Second}
// DO NOT forget to close the client when you don't need it anymore
client, err := featbit.MakeCustomFBClient(envSecret, streamingUrl, eventUrl, config)
if err == nil && client.IsInitialized() {
    // the client is ready
}

If you prefer to have the constructor return immediately, and then wait for initialization to finish at some other point, you can use featbit.FBClient.GetDataUpdateStatusProvider(), which will return an implementation of interfaces.DataUpdateStatusProvider. This interface has a WaitForOKState method that will block until the client has successfully connected, or until the timeout expires.

config := featbit.FBConfig{StartWait: 0}
// DO NOT forget to close the client when you don't need it anymore
client, err := featbit.MakeCustomFBClient(envSecret, streamingUrl, eventUrl, config)
if err != nil {
    return
}
ok := client.GetDataSourceStatusProvider().WaitForOKState(10 * time.Second)
if ok {
    // the client is ready
}

To check if the client is ready is optional. Even if the client is not ready, you can still evaluate feature flags, but the default value will be returned if SDK is not yet initialized.

In most cases, you don't need to care about featbit.FBConfig and the internal components, just initialize SDK like:

client, err := featbit.NewFBClient(envSecret, streamingUrl, eventUrl)

envSecret sdkKey(envSecret) is id of your project in FeatBit feature flag center

streamingURL: URL of your feature management platform to synchronize feature flags, user segments, etc.

eventURL: URL of your feature management platform to send analytics events

StartWait: how long the constructor will block awaiting a successful data sync. Setting this to a zero or negative duration will not block and cause the constructor to return immediately.

Offline: Set whether SDK is offline. when set to true no connection to your feature management platform anymore

featbit.FBConfig provides advanced configuration options for setting the SDK component, or you want to customize the behavior of build-in components.

NetworkFactory: sets the SDK networking configuration, DO NOT change it unless you should set some advanced configuration such as HTTP Proxy, TLS etc.

factories.NetworkBuilder is the default NetworkFactory

factory := factories.NewNetworkBuilder()
factory.ProxyUrl("http://username:[email protected]:65233")

config := featbit.DefaultFBConfig
config.NetworkFactory = factory
client, err := featbit.MakeCustomFBClient(envSecret, streamingUrl, eventUrl, *config)
// or
config := featbit.FBConfig{NetworkFactory: factory}
client, err := featbit.MakeCustomFBClient(envSecret, streamingUrl, eventUrl, config)

DataStorageFactory sets the implementation of interfaces.DataStorage to be used for holding feature flags and related data received from feature flag center SDK sets the implementation of the data storage, in using factories.InMemoryStorageBuilder by default to instantiate a memory data storage. Developers can customize the data storage to persist received data in redis, mongodb, etc.

DataSynchronizerFactory SDK sets the implementation of the interfaces.DataSynchronizer that receives feature flag data from feature flag center, in using factories.StreamingBuilder by default If Developers would like to know what the implementation is, they can read the GoDoc and source code.

InsightProcessorFactory SDK which sets the implementation of interfaces.InsightProcessor to be used for processing analytics events. using a factory object. The default is factories.InsightProcessorBuilder. If Developers would like to know what the implementation is, they can read the GoDoc and source code.

It's not recommended to change the default factories in the featbit.FBConfig

A collection of attributes that can affect flag evaluation, usually corresponding to a user of your application. This object contains built-in properties(key, userName). The key and userName are required. The key must uniquely identify each user; this could be a username or email address for authenticated users, or an ID for anonymous users. The userName is used to search your user quickly. You may also define custom properties with arbitrary names and values.

// FBUser creation
user, err := NewUserBuilder("key").UserName("name").Custom("property", "value").Build()

SDK calculates the value of a feature flag for a given user, and returns a flag value and interfaces.EvalDetail that describes the way that the value was determined.

SDK will initialize all the related data(feature flags, segments etc.) in the bootstrapping and receive the data updates in real time, as mentioned in Bootstrapping.

After initialization, the SDK has all the feature flags in the memory and all evaluation is done locally and synchronously, the average evaluation time is < 10 ms.

SDK supports String, Boolean, and Number and Json as the return type of flag values:

• Variation(for string)
• BoolVariation
• IntVariation
• DoubleVariation
• JsonVariation

// be sure that SDK is initialized before evaluation
// DO not forget to close client when you are done with it
if client.isInitialized() {
    // Flag value
    // returns a string variation
    variation, detail, _ := client.Variation("flag key", user, "Not Found")
}

featbit.FBClient.AllLatestFlagsVariations(user) returns all variations for a given user. You can retrieve the flag value or details for a specific flag key:

• GetStringVariation
• GetBoolVariation
• GetIntVariation
• GetDoubleVariation
• GetJsonVariation

// be sure that SDK is initialized before evaluation
// DO not forget to close client when you are done with it
if client.isInitialized() {
    // get all variations for a given user in your project 
    allState, _ := client.AllLatestFlagsVariations(user)
    variation, detail, _ := allState.GetStringVariation("flag key", "Not Found")
}

Note that if evaluation called before Go SDK client initialized, you set the wrong flag key/user for the evaluation or the related feature flag is not found, SDK will return the default value you set. interfaces.EvalDetail will explain the details of the latest evaluation including error raison.

In some situations, you might want to stop making remote calls to FeatBit. Here is how:

config := featbit.DefaultFBConfig
featbit.Offline = true
featbit.StartWait = 1 * time.Millisecond
client, err := featbit.MakeCustomFBClient(envSecret, streamingUrl, eventUrl, *config)
// or
config := FBConfig{Offline: true, StartWait: 1 * time.Millisecond}
client, err := featbit.MakeCustomFBClient(envSecret, streamingUrl, eventUrl, config)

When you put the SDK in offline mode, no insight message is sent to the server and all feature flag evaluations return fallback values because there are no feature flags or segments available. If you want to use your own data source, SDK allows users to populate feature flags and segments data from a JSON string. Here is an example: fbclient_test_data.json.

The format of the data in flags and segments is defined by FeatBit and is subject to change. Rather than trying to construct these objects yourself, it's simpler to request existing flags directly from the FeatBit server in JSON format and use this output as the starting point for your file. Here's how:

# replace http://localhost:5100 with your evaluation server url
curl -H "Authorization: <your-env-secret>" http://localhost:5100/api/public/sdk/server/latest-all > featbit-bootstrap.json

Then you can use this file to initialize the SDK in offline mode:

// first load data from file and then 
ok, _ := client.InitializeFromExternalJson(string(jsonBytes))

We support automatic experiments for page-views and clicks, you just need to set your experiment on FeatBit platform, then you should be able to see the result in near real time after the experiment is started.

In case you need more control over the experiment data sent to our server, we offer a method to send custom event.

// for the percentage experiment
client.TrackPercentageMetric(user, eventName)
// for the numeric experiment
client.TrackNumericMetric(user, eventName, numericValue)

Make sure featbit.FBClient.TrackPercentageMetric() or featbit.FBClient.TrackNumericMetric() is called after the related feature flag is called, otherwise the custom event may not be included into the experiment result.

• If you have a specific question about using this sdk, we encourage you to ask it in our slack.
• If you encounter a bug or would like to request a feature, submit an issue.

• Connect To Go Sdk