Go Server SDK

statsig-io/go-sdk

Getting Started

The following will outline how to get up and running with Statsig for Go.

Create an Account

To work with the SDK, you will need a Statsig account. If you don't yet have an account, you can sign up for a free one here. You could skip this for now, but you will need an SDK key and some gates/experiments to use with the SDK in just a minute.

Installation

via the go get CLI:

go get github.com/statsig-io/go-sdk

Or, add a dependency on the most recent version of the SDK in go.mod:

require (
  github.com/statsig-io/go-sdk v1.26.0
)

See the Releases tab in GitHub for the latest versions.

Initialize the SDK

After installation, you will need to initialize the SDK using a Server Secret Key from the statsig console.

info

Do NOT embed your Server Secret Key in client-side applications, or expose it in any external-facing documents. However, if you do accidentally expose it, you can create a new one in the Statsig console.

There is also an optional parameter named options that allows you to pass in a StatsigOptions to customize the SDK.

import (
  statsig "github.com/statsig-io/go-sdk"
)

statsig.Initialize("server-secret-key")

// Or, if you want to initialize with certain options
statsig.InitializeWithOptions("server-secret-key", &Options{Environment: Environment{Tier: "staging"}})

initialize will perform a network request. After initialize completes, virtually all SDK operations will be synchronous (See Evaluating Feature Gates in the Statsig SDK). The SDK will fetch updates from Statsig in the background, independently of your API calls.

Working with the SDK

Checking a Gate

Now that your SDK is initialized, let's fetch a Feature Gate. Feature Gates can be used to create logic branches in code that can be rolled out to different users from the Statsig Console. Gates are always CLOSED or OFF (think return false;) by default.

From this point on, all APIs will require you to specify the user (see Statsig user) associated with the request. For example, check a gate for a certain user like this:

user := statsig.User{UserID: "some_user_id"}
feature := statsig.CheckGate(user, "use_new_feature")
if feature {
  // Gate is on, enable new feature
} else {
  // Gate is off
}

Reading a Dynamic Config

Feature Gates can be very useful for simple on/off switches, with optional but advanced user targeting. However, if you want to be able send a different set of values (strings, numbers, and etc.) to your clients based on specific user attributes, e.g. country, Dynamic Configs can help you with that. The API is very similar to Feature Gates, but you get an entire json object you can configure on the server and you can fetch typed parameters from it. For example:

config := statsig.GetConfig(user, "awesome_product_details")

// The 2nd parameter is the default value to be used in case the given parameter name does not exist on
// the Dynamic Config object. This can happen when there is a typo, or when the user is offline and the
// value has not been cached on the client.
itemName := config.GetString("product_name", "Awesome Product v1");
double price = config.GetNumber("price", 10.0);
bool shouldDiscount = config.GetBool("discount", false);

// Or just get the whole json object backing this config if you prefer
json := config.Value

Getting an Layer/Experiment

Then we have Layers/Experiments, which you can use to run A/B/n experiments. We offer two APIs, but we recommend the use of layers to enable quicker iterations with parameter reuse.

// Values via getLayer

layer := Statsig.GetLayer(user, "user_promo_experiments");
promoTitle := layer.GetString("title", "Welcome to Statsig!");
discount := layer.GetDouble("discount", 0.1);

// or, via getExperiment

titleExperiment := Statsig.GetExperiment(user, "new_user_promo_title");
priceExperiment := Statsig.GetExperiment(user, "new_user_promo_price");

promoTitle := titleExperiment.GetString("title", "Welcome to Statsig!");
discount := priceExperiment.GetNumber("discount", 0.1);

...

price := msrp * (1 - discount);

// getting the layer name that an experiment belongs to

userPromoLayer := Statsig.GetExperimentLayer("new_user_promo_title");

Asynchronous APIs

We mentioned earlier that after calling initialize most SDK APIs would run synchronously, so why are getConfig and checkGate asynchronous?

The main reason is that older versions of the SDK might not know how to interpret new types of gate conditions. In such cases the SDK will make an asynchronous call to our servers to fetch the result of a check. This can be resolved by upgrading the SDK, and we will warn you if this happens.

For more details, read our blog post about SDK evaluations. If you have any questions, please ask them in our Feedback Repository.

Logging an Event

Now that you have a Feature Gate or an Experiment set up, you may want to track some custom events and see how your new features or different experiment groups affect these events. This is super easy with Statsig - simply call the Log Event API and specify the user and event name to log; you additionally provide some value and/or an object of metadata to be logged together with the event:

statsig.LogEvent(Event{
        User: user,
        EventName: "add_to_cart",
                Value: "SKU_12345",
        Metadata: map[string]string{"price": "9.99","item_name": "diet_coke_48_pack"},
    })

Retrieving Feature Gate Metadata

In certain scenarios, you may need more information about a gate evaluation than just a boolean value. For additional metadata about the evaluation, use the Get Feature Gate API, which returns a FeatureGate object

user := statsig.User{UserID: "some_user_id"}
feature := statsig.GetGate(user, "use_new_feature")
if feature.Value {
  // Gate is on, enable new feature
  fmt.Print(feature.EvaluationDetails.Reason)
}

Statsig User

When calling APIs that require a user, you should pass as much information as possible in order to take advantage of advanced gate and config conditions (like country or OS/browser level checks), and correctly measure impact of your experiments on your metrics/events. The userID field is required because it's needed to provide a consistent experience for a given user (click here to understand further why it's important to always provide a userID).

Besides userID, we also have email, ip, userAgent, country, locale and appVersion as top-level fields on StatsigUser. In addition, you can pass any key-value pairs in an object/dictionary to the custom field and be able to create targeting based on them.

Note that while typing is lenient on the StatsigUser object to allow you to pass in nubmers, strings, arrays, objects, and potentially even enums or classes, the evaluation operators will only be able to operate on primitive types - mostly strings and numbers. While we attempt to smartly cast custom field types to match the operator, we cannot guarantee evaluation results for other types. For example, setting an array as a custom field will only ever be compared as a string - there is no operator to match a value in that array.

Private Attributes

Have sensitive user PII data that should not be logged? No problem, we have a solution for it! On the StatsigUser object we also have a field called privateAttributes, which is a simple object/dictionary that you can use to set private user attributes. Any attribute set in privateAttributes will only be used for evaluation/targeting, and removed from any logs before they are sent to Statsig server.

For example, if you have feature gates that should only pass for users with emails ending in "@statsig.com", but do not want to log your users' email addresses to Statsig, you can simply add the key-value pair { email: "my_user@statsig.com" } to privateAttributes on the user and that's it!

Statsig Options

You can specify optional parameters with options when initializing using InitializeWithOptions()

type Options struct {
    API                string      `json:"api"`
    Environment        Environment `json:"environment"`
    LocalMode          bool        `json:"localMode"`
    ConfigSyncInterval time.Duration
    IDListSyncInterval time.Duration
  BootstrapValues      string
    RulesUpdatedCallback func(rules string, time int64)
}

• Environment: default nil
  • An object you can use to set environment variables that apply to all of your users in the same session and will be used for targeting purposes.
  • The most common usage is to set the environment tier (string), and have feature gates pass/fail for specific environments. The accepted values are "production", "staging" and "development".
• LocalMode: default false
  • Pass true to this option to turn on Local Mode for the SDK, which will stop the SDK from issuing any network requests and make it only operate with only local overrides (If supported) and cache.
    Note: Since no network requests will be made, a dummy SDK key starting with "secret-" can be used. (eg "secret-key")
• ConfigSyncInterval: default 10 seconds
  • The interval to poll for gate/experiment/config changes.
• IDListSyncInterval: default 1 minute
  • The interval to poll for ID list changes.
• BootstrapValues: default nil
  • A string that represents all rules for all feature gates, dynamic configs and experiments. It can be provided to bootstrap the Statsig server SDK at initialization in case your server runs into network issue or Statsig server is down temporarily.
• RulesUpdatedCallback: default nil
  • The callback that gets invoked whenever the rulesets are updated. It's called with a JSON string that represents the rulesets, and a timestamp for when the rules were updated.
• UserPersistentStorage: IUserPersistentStorage default nil
  • A persistent storage adapter for running sticky experiments.

Shutting Statsig Down

Because we batch and periodically flush events, some events may not have been sent when your app/server shuts down.

To make sure all logged events are properly flushed, you should tell Statsig to shutdown when your app/server is closing:

statsig.Shutdown()

Local Overrides v1.3.0+

If you want to locally override gates/configs/experiments/layers, there are a set of override APIs as follows. Coupling this with StatsigOptions.localMode can be useful when writing unit tests.

func OverrideGate(gate string, val bool)

func OverrideConfig(config string, val map[string]interface{})

note

1. These only apply locally - they do not update definitions in the Statsig console or elsewhere.
2. The local override API is not designed to be a full mock. They are only a convenient way to override the value of the gate/config/etc.

Data Store

If you would like to implement your own caching logic, or have finer control over the network requests sent to Statsig, you can implement your own DataStore. You can provide a DataStore via StatsigOptions.DataStore.

If you would like to know more about how Data Stores work, you can read more about the concept here.

Data Store Interface

You can write you own custom Data Stores that implement the following interface:

type IDataAdapter interface {
    /**
     * Returns the data stored for a specific key
     */
    Get(key string) string
    /**
     * Updates data stored for each key
     */
    Set(key string, value string)
    /**
     * Startup tasks to run before any get/set calls can be made
     */
    Initialize()
    /**
     * Cleanup tasks to run when statsig is shutdown
     */
    Shutdown()
    /**
         * Determines whether the SDK should poll for updates from
       * the data adapter (instead of Statsig network) for the given key
    */
    ShouldBeUsedForQueryingUpdates(key string) bool
}

Example Implementation

type dataAdapterExample struct {
    store map[string]string
    mu    sync.RWMutex
}

func (d *dataAdapterExample) Get(key string) string {
    d.mu.RLock()
    defer d.mu.RUnlock()
    return d.store[key]
}

func (d *dataAdapterExample) Set(key string, value string) {
    d.mu.Lock()
    defer d.mu.Unlock()
    d.store[key] = value
}

func (d *dataAdapterExample) Initialize() {}

func (d *dataAdapterExample) Shutdown() {}

func (d *dataAdapterExample) ShouldBeUsedForQueryingUpdates(key string) bool {
    return false
}

User Persistent Storage

A custom storage adapter that allows the SDK the persist values for users in active experiments. In otherwords, allowing you to run experiments with sticky bucketing. You can provide a persistent storage adapter via StatsigOptions.UserPersistentStorage.

You can read more about the concept here.

Storage Interface

You can write you own custom storage that implements the following interface:

type IUserPersistentStorage interface {
    /**
     * Returns the data stored for a specific key
     */
    Load(key string) (string, bool)

    /**
     * Updates data stored for a specific key
     */
    Save(key string, data string)
}

Example Implementation

type userPersistentStorageExample struct {
    store      map[string]string
    loadCalled int
    saveCalled int
}

func (d *userPersistentStorageExample) Load(key string) (string, bool) {
    d.loadCalled++
    val, ok := d.store[key]
    return val, ok
}

func (d *userPersistentStorageExample) Save(key string, value string) {
    d.saveCalled++
    d.store[key] = value
}

FAQ

How do I run experiments for logged out users?

See the guide on device level experiments

How can I mock Statsig in tests

We recommend using the Local Override APIs in v1.3.0+, in combination with the LocalMode option in StatsigOptions to force gate/config values in test environments and remove network access to statsig servers.

For example:

c := NewClientWithOptions(secret, &Options{LocalMode: true})

user := User{
    UserID: "123",
}
gateDefault := c.CheckGate(user, "any_gate")
// "any_gate" is false by default

c.OverrideGate("any_gate", true)
// "any_gate" is now true

See also https://github.com/statsig-io/go-sdk/blob/main/overrides_test.go

Reference

StatsigUser

// User specific attributes for evaluating Feature Gates, Experiments, and DynamicConfigs
//
// NOTE: UserID or a customID is **required** - see https://docs.statsig.com/messages/serverRequiredUserID
// PrivateAttributes are only used for user targeting/grouping in feature gates, dynamic configs,
// experiments and etc; they are omitted in logs.
type User struct {
    UserID             string                 `json:"userID"`
    Email              string                 `json:"email"`
    IpAddress          string                 `json:"ip"` // Many jurisdictions categorize this as PII; verify whether you should log this. 
    UserAgent          string                 `json:"userAgent"`
    Country            string                 `json:"country"`
    Locale             string                 `json:"locale"`
    AppVersion         string                 `json:"appVersion"`
    Custom             map[string]interface{} `json:"custom"`
    PrivateAttributes  map[string]interface{} `json:"privateAttributes"`
    StatsigEnvironment map[string]string      `json:"statsigEnvironment"`
    CustomIDs          map[string]string      `json:"customIDs"`
}

StatsigOptions

// Advanced options for configuring the Statsig SDK
type Options struct {
    API                   string      `json:"api"`
    Environment           Environment `json:"environment"`
    LocalMode             bool        `json:"localMode"`
    ConfigSyncInterval    time.Duration
    IDListSyncInterval    time.Duration
    LoggingInterval       time.Duration
    LoggingMaxBufferSize  int
    BootstrapValues       string
    RulesUpdatedCallback  func(rules string, time int64)
    InitTimeout           time.Duration
    DataAdapter           IDataAdapter
    OutputLoggerOptions   OutputLoggerOptions
    StatsigLoggerOptions  StatsigLoggerOptions
    EvaluationCallbacks   EvaluationCallbacks
    DisableCDN            bool // Disables use of CDN for downloading config specs
    UserPersistentStorage IUserPersistentStorage
    IPCountryOptions      IPCountryOptions
    UAParserOptions       UAParserOptions
}

type EvaluationCallbacks struct {
    GateEvaluationCallback       func(name string, result bool, exposure *ExposureEvent)
    ConfigEvaluationCallback     func(name string, result DynamicConfig, exposure *ExposureEvent)
    ExperimentEvaluationCallback func(name string, result DynamicConfig, exposure *ExposureEvent)
    LayerEvaluationCallback      func(name string, param string, result DynamicConfig, exposure *ExposureEvent)
    ExposureCallback             func(name string, exposure *ExposureEvent)
    IncludeDisabledExposures     bool
}

type OutputLoggerOptions struct {
    LogCallback            func(message string, err error)
    EnableDebug            bool
    DisableInitDiagnostics bool
    DisableSyncDiagnostics bool
}

type StatsigLoggerOptions struct {
    DisableInitDiagnostics bool
    DisableSyncDiagnostics bool
    DisableApiDiagnostics  bool
    DisableAllLogging      bool
}

type IPCountryOptions struct {
    Disabled     bool // Fully disable IP to country lookup
    LazyLoad     bool // Load in background
    EnsureLoaded bool // Wait until loaded when needed
}

type UAParserOptions struct {
    Disabled     bool // Fully disable UA parser
    LazyLoad     bool // Load in background
    EnsureLoaded bool // Wait until loaded when needed
}

// See https://docs.statsig.com/guides/usingEnvironments
type Environment struct {
    Tier   string            `json:"tier"`
    Params map[string]string `json:"params"`
}

// options for getClientInitializeResponse
type GCIROptions struct {
    IncludeLocalOverrides bool
    ClientKey             string
}

Event

type Event struct {
    EventName string            `json:"eventName"`
    User      User              `json:"user"`
    Value     string            `json:"value"`
    Metadata  map[string]string `json:"metadata"`
    Time      int64             `json:"time"`
}

FeatureGate

type FeatureGate struct {
    Name              string             `json:"name"`
    Value             bool               `json:"value"`
    RuleID            string             `json:"rule_id"`
    GroupName         string             `json:"group_name"`
    EvaluationDetails *EvaluationDetails `json:"evaluation_details"`
}

DynamicConfig

type DynamicConfig struct {
    Name              string                 `json:"name"`
    Value             map[string]interface{} `json:"value"`
    RuleID            string                 `json:"rule_id"`
    GroupName         string                 `json:"group_name"`
    EvaluationDetails *EvaluationDetails     `json:"evaluation_details"`
  AllocatedExperimentName string           `json:"allocated_experiment_name"`
  GetString(key string, fallback string) string
  GetNumber(key string, fallback float64) float64
  GetBool(key string, fallback bool) bool
  GetSlice(key string, fallback []interface{}) []interface{}
  GetMap(key string, fallback map[string]interface{}) map[string]interface{}
}

Layer

type Layer struct {
    Name              string                 `json:"name"`
    Value             map[string]interface{} `json:"value"`
    RuleID            string                 `json:"rule_id"`
    GroupName         string                 `json:"group_name"`
    EvaluationDetails *EvaluationDetails     `json:"evaluation_details"`
  AllocatedExperimentName string           `json:"allocated_experiment_name"`
  GetString(key string, fallback string) string
  GetNumber(key string, fallback float64) float64
  GetBool(key string, fallback bool) bool
  GetSlice(key string, fallback []interface{}) []interface{}
  GetMap(key string, fallback map[string]interface{}) map[string]interface{}
}

EvaluationDetails

const (
    reasonNetwork            evaluationReason = "Network"
    reasonBootstrap          evaluationReason = "Bootstrap"
    reasonLocalOverride      evaluationReason = "LocalOverride"
    reasonUnrecognized       evaluationReason = "Unrecognized"
    reasonUninitialized      evaluationReason = "Uninitialized"
    reasonDataAdapter        evaluationReason = "DataAdapter"
    reasonNetworkNotModified evaluationReason = "NetworkNotModified"
    reasonPersisted          evaluationReason = "Persisted"
)

type EvaluationDetails struct {
    Reason         evaluationReason
    ConfigSyncTime int64
    InitTime       int64
    ServerTime     int64
}

DataAdapter

/**
 * An adapter for implementing custom storage of config specs.
 * Can be used to bootstrap Statsig (priority over bootstrapValues if both provided)
 * Also useful for backing up cached data
 */
type IDataAdapter interface {
    /**
     * Returns the data stored for a specific key
     */
    get(key string) string

    /**
     * Updates data stored for each key
     */
    set(key string, value string)

    /**
     * Startup tasks to run before any get/set calls can be made
     */
    initialize()

    /**
     * Cleanup tasks to run when statsig is shutdown
     */
    shutdown()

    /**
    * Determines whether the SDK should poll for updates from
    * the data adapter for the given key
    * @param key - Key of stored item to poll from data adapter
    */
    supportsPollingUpdatesFor?(key string)
}