ffclient

README

v0.x.x to v1.x.x migration

Version v1.0.0 has introduced a new flag format that push the limits of GO Feature Flag even further. BUT the flag format from all the versions v0.x.x are still compatible and supported by the v1.0.0. We recommend you to migrate your configuration file following the migration guide.

🎛️ GO Feature Flag

What is GO Feature Flag?

GO Feature Flag is a simple, complete and lightweight feature flag solution 100% open source.

The solution has been built to start experiencing the usage of feature flags in your code without having to contract with any vendor.

GO Feature Flag has started to be a solution only for the GO language, but with the new standardization of feature flags by Openfeature project, now the solution is available for multiple languages (JAVA, typescript, javascript, ...) with a simple API server (called the relay proxy) to host.

ℹ️ Info
If you are not familiar with feature flags, also called feature toggles, you can read this article from Martin Fowler where he explains why this is a great pattern.
I've also written an article which explains why feature flags can fasten your iteration cycle.

What can I do with GO Feature Flag?

• Storing your configuration flags file on various locations (HTTP, S3, Kubernetes, see full list.
• Configuring your flags in various format (JSON, TOML and YAML).
• Adding complex rules to target your users.
• Use a complex rollout strategy for your flags :
  • Run A/B testing experimentation.
  • Progressively rollout a feature.
  • Schedule your flag updates.
• Exporting your flags usage data (S3, Google cloud storage, file, ...).
• Getting notified when a flag has been changed (webhook and slack).
• Use GO Feature Flag in several languages with Open Feature SDKs.

https://user-images.githubusercontent.com/17908063/168597893-e957e648-b795-4b5f-94d5-265d272a2137.mp4

The code of this demo is available in thomaspoignant/go-feature-flag-demo repository.

Getting started

Before starting to use GO Feature Flag you should decide if you want to use the GO Module directly or if you want to install the relay proxy.

The GO module is perfect and simple to use if your need is to use GO Feature Flag only in GO, if your project has more languages I recommend you to use the Open Feature SDKs.

Using the GO Module

Installation

go get github.com/thomaspoignant/go-feature-flag

Create a feature flag configuration

Create a new YAML file containing your first flag configuration.

# 20% of the users will use the variation "my-new-feature"
test-flag:
  variations:
    my-new-feature: true
    my-old-feature: false
  defaultRule:
    percentage:
      my-new-feature: 20
      my-old-feature: 80

This flag split the usage of this flag, 20% will use the variation my-new-feature and 80% the variation my-old-feature.

SDK Initialisation

First, you need to initialize the ffclient with the location of your backend file.

err := ffclient.Init(ffclient.Config{
    PollingInterval: 3 * time.Second,
    Retriever:      &fileretriever.Retriever{
        Path: "flag-config.yaml",
    },
})
defer ffclient.Close()

This example will load a file from your local computer and will refresh the flags every 3 seconds (if you omit the PollingInterval, the default value is 60 seconds).

ℹ info
This is a basic configuration to test locally, in production it is better to use a remote place to store your feature flag configuration file.
Look at the list of available options in the Store your feature flag file page.

Evaluate your flags

Now you can evaluate your flags anywhere in your code.

user := ffuser.NewUser("user-unique-key")
hasFlag, _ := ffclient.BoolVariation("test-flag", user, false)
if hasFlag {
    // flag "test-flag" is true for the user
} else {
    // flag "test-flag" is false for the user
}

The full documentation is available on https://docs.gofeatureflag.org
You can find more examples in the examples/ directory.

Using Open Feature SDKs

Create a feature flag configuration

Create a new YAML file containing your first flag configuration.

# 20% of the users will use the variation "my-new-feature"
test-flag:
  variations:
    my-new-feature: true
    my-old-feature: false
  defaultRule:
    percentage:
      my-new-feature: 20
      my-old-feature: 80

This flag split the usage of this flag, 20% will use the variation my-new-feature and 80% the variation my-old-feature.

Create a relay proxy configuration file

Create a new YAML file containing the configuration of your relay proxy.

listen: 1031
pollingInterval: 1000
startWithRetrieverError: false
retriever:
  kind: file
  path: /goff/flag-config.yaml
exporter:
  kind: log

Install the relay proxy

And we will run the relay proxy locally to make the API available.
The default port will be 1031.

# Launch the container
docker run \
  -p 1031:1031 \
  -v $(pwd)/flag-config.yaml:/goff/flag-config.yaml \
  -v $(pwd)/goff-proxy.yaml:/goff/goff-proxy.yaml \
  thomaspoignant/go-feature-flag-relay-proxy:latest

If you don't want to use docker to install the relay proxy you can follow the documentation.

Use Open Feature SDK

In this example, we are using the javascript SDK, but it is still relevant for all the languages.

Install dependencies

npm i @openfeature/js-sdk @openfeature/go-feature-flag-provider

Init your Open Feature client

In your app initialization you have to create a client using the Open Feature SDK and initialize it.

const {OpenFeature} = require("@openfeature/js-sdk");
const {GoFeatureFlagProvider} = require("@openfeature/go-feature-flag-provider");


// init Open Feature SDK with GO Feature Flag provider
const goFeatureFlagProvider = new GoFeatureFlagProvider({
  endpoint: 'http://localhost:1031/' // DNS of your instance of relay proxy
});
OpenFeature.setProvider(goFeatureFlagProvider);
const featureFlagClient = OpenFeature.getClient('my-app')

Evaluate your flag

Now you can evaluate your flags anywhere in your code using this client.

// Context of your flag evaluation.
// With GO Feature Flag you MUST have a targetingKey that is a unique identifier of the user.
const userContext = {
  targetingKey: '1d1b9238-2591-4a47-94cf-d2bc080892f1', // user unique identifier (mandatory)
  firstname: 'john',
  lastname: 'doe',
  email: 'john.doe@gofeatureflag.org',
  admin: true, // this field is used in the targeting rule of the flag "flag-only-for-admin"
  // ...
};

const adminFlag = await featureFlagClient.getBooleanValue('flag-only-for-admin', false, userContext);
if (adminFlag) {
   // flag "flag-only-for-admin" is true for the user
  console.log("new feature");
} else {
  // flag "flag-only-for-admin" is false for the user
}

Can I use GO Feature Flag with any language?

Originally GO Feature Flag was built to be a GOlang only library, but it limits the ecosystem too much.
To be compatible with more languages we have implemented the GO Feature Flag Relay Proxy. It is a service you can host that provides an API to evaluate your flags, you can call it using HTTP to get your variation.

Since we believe in standardization we are also implementing OpenFeature providers to interact with this API in the language of your choice.
(OpenFeature is still at an early stage, so not all languages are supported and expect some changes in the future)

For now, we have providers for python, java, typescript, javascript, GO and .NET.

Where do I store my flags file?

The module supports different ways of retrieving the flag file.
Available retrievers are:

• GitHub
• HTTP endpoint
• AWS S3
• Local file
• Google Cloud Storage
• Kubernetes ConfigMaps

See the full list and more information.

Flags file format

GO Feature Flag core feature is to centralize all your feature flags in a single file and to avoid hosting and maintaining a backend server to manage them.

Your file should be a YAML, JSON or TOML file with a list of flags (examples: YAML, JSON, TOML).

The easiest way to create your configuration file is to use GO Feature Flag Editor available at https://editor.gofeatureflag.org.
If you prefer to do it manually please follow the instruction bellow.

A flag configuration looks like this:

YAML

# This is your configuration for your first flag
first-flag:
  variations: # All possible return value for your feature flag
    A: false
    B: true
  targeting: # If you want to target a subset of your users in particular
    - query: key eq "random-key"
      percentage:
        A: 0
        B: 100
  defaultRule: # When no targeting match we use the defaultRule
    variation: A

# A second example of a flag configuration
second-flag:
  variations:
    A: "valueA"
    B: "valueB"
    defaultValue: "a default value"
  targeting:
    - name: legacyRuleV0
      query: key eq "not-a-key"
      percentage:
        A: 10
        B: 90
  defaultRule:
    name: legacyDefaultRule
    variation: defaultValue
  version: "12"
  experimentation: 
    start: 2021-03-20T00:00:00.1-05:00
    end: 2021-03-21T00:00:00.1-05:00

JSON

{
  "first-flag": {
    "variations": {
      "A": false,
      "B": true
    },
    "targeting": [
      {
        "query": "key eq \"random-key\"",
        "percentage": {
          "A": 0,
          "B": 100
        }
      }
    ],
    "defaultRule": {
      "variation": "A"
    }
  },
  
  "second-flag": {
    "variations": {
      "A": "valueA",
      "B": "valueB",
      "defaultValue": "a default value"
    },
    "targeting": [
      {
        "name": "legacyRuleV0",
        "query": "key eq \"not-a-key\"",
        "percentage": {
          "A": 10,
          "B": 90
        }
      }
    ],
    "defaultRule": {
      "name": "legacyDefaultRule",
      "variation": "defaultValue"
    },
    "version": "12",
    "experimentation": {
      "start": "2021-03-20T05:00:00.100Z",
      "end": "2021-03-21T05:00:00.100Z"
    }
  }
}

TOML

[first-flag.variations]
A = false
B = true

[[first-flag.targeting]]
query = 'key eq "random-key"'

  [first-flag.targeting.percentage]
  A = 0
  B = 100

[first-flag.defaultRule]
variation = "A"

[second-flag]
version = "12"

  [second-flag.variations]
  A = "valueA"
  B = "valueB"
  defaultValue = "a default value"

  [[second-flag.targeting]]
  name = "legacyRuleV0"
  query = 'key eq "not-a-key"'

    [second-flag.targeting.percentage]
    A = 10
    B = 90

  [second-flag.defaultRule]
  name = "legacyDefaultRule"
  variation = "defaultValue"

  [second-flag.experimentation]
  start = 2021-03-20T05:00:00.100Z
  end = 2021-03-21T05:00:00.100Z

All the fields to create a flag are described in the documentation.

Rule format

The query format is based on the nikunjy/rules library.

All the operations can be written in capitalized or lowercase (ex: eq or EQ can be used).
Logical Operations supported are AND OR.

Compare Expression and their definitions (a|b means you can use either one of the two a or b):

eq|==: equals to 
ne|!=: not equals to
lt|<: less than 
gt|>: greater than
le|<=: less than equal to
ge|>=: greater than equal to 
co: contains 
sw: starts with 
ew: ends with
in: in a list
pr: present
not: not of a logical expression

Examples

• Select a specific user: key eq "example@example.com"
• Select all identified users: anonymous ne true
• Select a user with a custom property: userId eq "12345"

Users

Feature flag targeting and rollouts are all determined by the user you pass to your evaluation calls.

The only required field for a user is his unique key, it is used by the internals of GO Feature Flag to do a hash to define if the flag can apply to this user or not. You can use a primary key, an e-mail address, or a hash, as long as the same user always has the same key.
We recommend using a hash if possible.
All the other attributes are optional.

Since it is useful to make complex queries on your flag, you can add as many information fields you want to your user. It will be used when testing the targeting rules.

You can also distinguish logged-in users from anonymous users in the SDK (check documentation about anonymous users).

Variations

The Variation methods determine whether a flag is enabled or not for a specific user.

GO Feature Flag can manage more than boolean, the value of your flag can be any of these types:

• bool
• int
• float
• string
• json array
• json object

Example

result, _ := ffclient.BoolVariation("your.feature.key", user, false)

// result is now true or false depending on the setting of
// this boolean feature flag

Variation methods take the feature flag key, a user, and a default value.

The default value is returned when an error is encountered (ffclient not initialized, variation with wrong type, flag does not exist ...).

In the example, if the flag your.feature.key does not exist, the result will be false.
Not that you will always have a usable value in the result.

Get all flags for a specific user

If you want to send the information about a specific user to a front-end, you will want a snapshot of all the flags for this user at a specific time.

The method ffclient.AllFlagsState returns a snapshot of flag values and metadata.
The function is evaluating all available flags for the user and returns a flagstate.AllFlagsState object containing the information you need.

The MarshalJSON() function will return a JSON Object, that can be directly used by your front-end application.
More details in the documentation.

Rollout

A critical part of every new feature release is orchestrating the actual launch schedule between the Product, Engineering, and Marketing teams.

Delivering powerful user experiences typically requires software teams to manage complex releases and make manual updates at inconvenient times.

But it does not have to, having a complex rollout strategy allows you to have a lifecycle for your flags.

Complex rollout strategy available

• Canary releases - impact randomly a subset of your users.
• Progressive rollout - increase the percentage of your flag over time.
• Scheduled rollout - update your flag over time.
• Experimentation rollout - serve your feature only for a determined time (perfect for A/B testing).

Notifiers

If you want to be informed when a flag has changed, you can configure a notifier.

A notifier will send one notification to the targeted system to inform them that a new flag configuration has been loaded.

ℹ️ GO Feature Flag can handle more than one notifier at a time.

Available notifiers are:

• Slack
• Webhook

Export data

GO Feature Flag allows you to export data about the usage of your flags.
It collects all the variations events and can save these events in several locations:

• Local file - create local files with the variation usages.
• Log - use your logger to write the variation usages.
• AWS S3 - export your variation usages to S3.
• Google Cloud Storage - export your variation usages to Google Cloud Storage.
• Webhook - export your variation usages by calling a webhook.

Currently, we are supporting only feature events.
It represents individual flag evaluations and is considered "full fidelity" events.

An example feature event below:

{
    "kind": "feature",
    "contextKind": "anonymousUser",
    "userKey": "ABCD",
    "creationDate": 1618228297,
    "key": "test-flag",
    "variation": "Default",
    "value": false,
    "default": false
}

The format of the data is described in the documentation. Events are collected and sent in bulk to avoid spamming your exporter.

How can I contribute?

This project is open for contribution, see the contributor's guide for some helpful tips.

Contributors

Thanks so much to our contributors.

Documentation

Overview

Package ffclient aids adding instrumentation to have feature flags in your app without any backend server.

Summary

This package and its subpackages contain bits of code to have an easy feature flag solution with no complex installation to do on your infrastructure and without using 3rd party vendor for this.

The ffclient package provides the entry point - initialization and the basic method to get your flags value.

Before using the module you need to initialized it this way:

func main() {
  err := ffclient.Init(ffclient.Config{
           PollingInterval: 3 * time.Second,
           HTTPRetriever: &httpretriever.Retriever{
             URL:    "http://example.com/flag-config.yaml",
           },
         })
  defer ffclient.Close()
  ...

This example will load a file from an HTTP endpoint and will refresh the flags every 3 seconds.

Now you can evalute your flags anywhere in your code.

func main() {
  ...
  user := ffuser.NewUser("user-unique-key")
  hasFlag, _ := ffclient.BoolVariation("test-flag", user, false)
  if hasFlag {
    //flag "test-flag" is true for the user
  } else {
    // flag "test-flag" is false for the user
  }
  ...

nolint: dupl

Index

• func AllFlagsState(user ffuser.User) flagstate.AllFlags
• func BoolVariation(flagKey string, user ffuser.User, defaultValue bool) (bool, error)
• func Close()
• func Float64Variation(flagKey string, user ffuser.User, defaultValue float64) (float64, error)
• func GetCacheRefreshDate() time.Time
• func GetFlagsFromCache() (map[string]flag.Flag, error)
• func Init(config Config) error
• func IntVariation(flagKey string, user ffuser.User, defaultValue int) (int, error)
• func JSONArrayVariation(flagKey string, user ffuser.User, defaultValue []interface{}) ([]interface{}, error)
• func JSONVariation(flagKey string, user ffuser.User, defaultValue map[string]interface{}) (map[string]interface{}, error)
• func StringVariation(flagKey string, user ffuser.User, defaultValue string) (string, error)
• type Config
  • func (c *Config) GetRetriever() (retriever.Retriever, error)
• type DataExporter
• type GoFeatureFlag
  • func New(config Config) (*GoFeatureFlag, error)
  • func (g *GoFeatureFlag) AllFlagsState(user ffuser.User) flagstate.AllFlags
  • func (g *GoFeatureFlag) BoolVariation(flagKey string, user ffuser.User, defaultValue bool) (bool, error)
  • func (g *GoFeatureFlag) Close()
  • func (g *GoFeatureFlag) Float64Variation(flagKey string, user ffuser.User, defaultValue float64) (float64, error)
  • func (g *GoFeatureFlag) GetCacheRefreshDate() time.Time
  • func (g *GoFeatureFlag) GetFlagsFromCache() (map[string]flag.Flag, error)
  • func (g *GoFeatureFlag) IntVariation(flagKey string, user ffuser.User, defaultValue int) (int, error)
  • func (g *GoFeatureFlag) JSONArrayVariation(flagKey string, user ffuser.User, defaultValue []interface{}) ([]interface{}, error)
  • func (g *GoFeatureFlag) JSONVariation(flagKey string, user ffuser.User, defaultValue map[string]interface{}) (map[string]interface{}, error)
  • func (g *GoFeatureFlag) RawVariation(flagKey string, user ffuser.User, sdkDefaultValue interface{}) (model.RawVarResult, error)
  • func (g *GoFeatureFlag) StringVariation(flagKey string, user ffuser.User, defaultValue string) (string, error)

Functions

func AllFlagsState

func AllFlagsState(user ffuser.User) flagstate.AllFlags

AllFlagsState return the values of all the flags for a specific user. If valid field is false it means that we had an error when checking the flags.

func BoolVariation

func BoolVariation(flagKey string, user ffuser.User, defaultValue bool) (bool, error)

BoolVariation return the value of the flag in boolean. An error is return if you don't have init the library before calling the function. If the key does not exist we return the default value.

func Close

func Close()

Close the component by stopping the background refresh and clean the cache.

func Float64Variation

func Float64Variation(flagKey string, user ffuser.User, defaultValue float64) (float64, error)

Float64Variation return the value of the flag in float64. An error is return if you don't have init the library before calling the function. If the key does not exist we return the default value.

func GetCacheRefreshDate

func GetCacheRefreshDate() time.Time

GetCacheRefreshDate gives the date of the latest refresh of the cache

func GetFlagsFromCache

func GetFlagsFromCache() (map[string]flag.Flag, error)

GetFlagsFromCache returns all the flags present in the cache with their current state when calling this method. If cache hasn't been initialized, an error reporting this is returned.

func Init

func Init(config Config) error

Init the feature flag component with the configuration of ffclient.Config

func main() {
  err := ffclient.Init(ffclient.Config{
           PollingInterval: 3 * time.Second,
           Retriever: &httpretriever.Retriever{
             URL:    "http://example.com/flag-config.yaml",
           },
         })
  defer ffclient.Close()

func IntVariation

func IntVariation(flagKey string, user ffuser.User, defaultValue int) (int, error)

IntVariation return the value of the flag in int. An error is return if you don't have init the library before calling the function. If the key does not exist we return the default value.

func JSONArrayVariation

func JSONArrayVariation(flagKey string, user ffuser.User, defaultValue []interface{}) ([]interface{}, error)

JSONArrayVariation return the value of the flag in []interface{}. An error is return if you don't have init the library before calling the function. If the key does not exist we return the default value.

func JSONVariation

func JSONVariation(
	flagKey string, user ffuser.User, defaultValue map[string]interface{},
) (map[string]interface{}, error)

JSONVariation return the value of the flag in map[string]interface{}. An error is return if you don't have init the library before calling the function. If the key does not exist we return the default value.

func StringVariation

func StringVariation(flagKey string, user ffuser.User, defaultValue string) (string, error)

StringVariation return the value of the flag in string. An error is return if you don't have init the library before calling the function. If the key does not exist we return the default value.

Types

type Config

type Config struct {
	// PollingInterval (optional) Poll every X time
	// The minimum possible is 1 second
	// Default: 60 seconds
	PollingInterval time.Duration

	// Logger (optional) logger use by the library
	// Default: No log
	Logger *log.Logger

	// Context (optional) used to call other services (HTTP, S3 ...)
	// Default: context.Background()
	Context context.Context

	// Environment (optional), can be checked in feature flag rules
	// Default: ""
	Environment string

	// Retriever is the component in charge to retrieve your flag file
	Retriever retriever.Retriever

	// Notifiers (optional) is the list of notifiers called when a flag change
	Notifiers []notifier.Notifier

	// FileFormat (optional) is the format of the file to retrieve (available YAML, TOML and JSON)
	// Default: YAML
	FileFormat string

	// DataExporter (optional) is the configuration where we store how we should output the flags variations results
	DataExporter DataExporter

	// StartWithRetrieverError (optional) If true, the SDK will start even if we did not get any flags from the retriever.
	// It will serve only default values until the retriever returns the flags.
	// The init method will not return any error if the flag file is unreachable.
	// Default: false
	StartWithRetrieverError bool

	// Offline (optional) If true, the SDK will not try to retrieve the flag file and will not export any data.
	// No notification will be send neither.
	// Default: false
	Offline bool
}

Config is the configuration of go-feature-flag. You should also have a retriever to specify where to read the flags file.

func (*Config) GetRetriever

func (c *Config) GetRetriever() (retriever.Retriever, error)

GetRetriever returns a retriever.FlagRetriever configure with the retriever available in the config.

type DataExporter

type DataExporter struct {
	// FlushInterval is the interval we are waiting to export the data.
	// example: if you set your FlushInterval to 1 minutes, we will send
	// the data every minute unless we reach the max event in cache before.
	FlushInterval time.Duration

	// MaxEventInMemory is the maximum number of event you keep in the cache
	// before sending the data to the Exporter.
	// We will send the data when the MaxEventInMemory is reach or if we have
	// waited the FlushInterval.
	MaxEventInMemory int64

	// Exporter is the configuration of your exporter.
	// You can see all available exporter in the exporter package.
	Exporter dataexporter.Exporter
}

DataExporter is the configuration of your export target.

type GoFeatureFlag

type GoFeatureFlag struct {
	// contains filtered or unexported fields
}

GoFeatureFlag is the main object of the library it contains the cache, the config and the update.

func New

func New(config Config) (*GoFeatureFlag, error)

New creates a new go-feature-flag instance that retrieve the config from a YAML file and return everything you need to manage your flags.

func (*GoFeatureFlag) AllFlagsState

func (g *GoFeatureFlag) AllFlagsState(user ffuser.User) flagstate.AllFlags

AllFlagsState return a flagstate.AllFlags that contains all the flags for a specific user.

func (*GoFeatureFlag) BoolVariation

func (g *GoFeatureFlag) BoolVariation(flagKey string, user ffuser.User, defaultValue bool) (bool, error)

BoolVariation return the value of the flag in boolean. An error is return if you don't have init the library before calling the function. If the key does not exist we return the default value. Note: Use this function only if you are using multiple go-feature-flag instances.

func (*GoFeatureFlag) Close

func (g *GoFeatureFlag) Close()

Close wait until thread are done

func (*GoFeatureFlag) Float64Variation

func (g *GoFeatureFlag) Float64Variation(flagKey string, user ffuser.User, defaultValue float64) (float64, error)

Float64Variation return the value of the flag in float64. An error is return if you don't have init the library before calling the function. If the key does not exist we return the default value. Note: Use this function only if you are using multiple go-feature-flag instances.

func (*GoFeatureFlag) GetCacheRefreshDate

func (g *GoFeatureFlag) GetCacheRefreshDate() time.Time

GetCacheRefreshDate gives the date of the latest refresh of the cache

func (*GoFeatureFlag) GetFlagsFromCache

func (g *GoFeatureFlag) GetFlagsFromCache() (map[string]flag.Flag, error)

GetFlagsFromCache returns all the flags present in the cache with their current state when calling this method. If cache hasn't been initialized, an error reporting this is returned.

func (*GoFeatureFlag) IntVariation

func (g *GoFeatureFlag) IntVariation(flagKey string, user ffuser.User, defaultValue int) (int, error)

IntVariation return the value of the flag in int. An error is return if you don't have init the library before calling the function. If the key does not exist we return the default value. Note: Use this function only if you are using multiple go-feature-flag instances.

func (*GoFeatureFlag) JSONArrayVariation

func (g *GoFeatureFlag) JSONArrayVariation(
	flagKey string, user ffuser.User, defaultValue []interface{},
) ([]interface{}, error)

JSONArrayVariation return the value of the flag in []interface{}. An error is return if you don't have init the library before calling the function. If the key does not exist we return the default value. Note: Use this function only if you are using multiple go-feature-flag instances.

func (*GoFeatureFlag) JSONVariation

func (g *GoFeatureFlag) JSONVariation(
	flagKey string, user ffuser.User, defaultValue map[string]interface{},
) (map[string]interface{}, error)

JSONVariation return the value of the flag in map[string]interface{}. An error is return if you don't have init the library before calling the function. If the key does not exist we return the default value. Note: Use this function only if you are using multiple go-feature-flag instances.

func (*GoFeatureFlag) RawVariation

func (g *GoFeatureFlag) RawVariation(flagKey string, user ffuser.User, sdkDefaultValue interface{},
) (model.RawVarResult, error)

RawVariation return the raw value of the flag (without any types). This raw result is mostly used by software built on top of go-feature-flag such as go-feature-flag relay proxy. If you are using directly the library you should avoid calling this function. Note: Use this function only if you are using multiple go-feature-flag instances.

func (*GoFeatureFlag) StringVariation

func (g *GoFeatureFlag) StringVariation(flagKey string, user ffuser.User, defaultValue string) (string, error)

StringVariation return the value of the flag in string. An error is return if you don't have init the library before calling the function. If the key does not exist we return the default value. Note: Use this function only if you are using multiple go-feature-flag instances.