Go · ConfigCat Docs

Getting Started:

1. Get the SDK with `go`

go get gopkg.in/configcat/go-sdk.v2

2. Import the ConfigCat package

import gopkg.in/configcat/go-sdk.v2

3. Create the ConfigCat client with your API Key

client := configcat.NewClient("<PLACE-YOUR-API-KEY-HERE>")

4. Get your setting value

isMyAwesomeFeatureEnabled, ok := client.GetValueForUser("key-of-my-awesome-feature", false, user).(bool)
if ok && isMyAwesomeFeatureEnabled {
    doTheNewThing()
} else {
    doTheOldThing()
}

Or use the async APIs:

client.GetValueAsyncForUser("key-of-my-awesome-feature", false, func(result interface{}) {
    isMyAwesomeFeatureEnabled, ok := result.(bool)
    if ok && isMyAwesomeFeatureEnabled {
        doTheNewThing()
    } else {
        doTheOldThing()
    }
})

5. Stop ConfigCat client

You can safely shut down the client instance and release all associated resources on application exit.

client.Close()

Creating the ConfigCat Client

ConfigCat Client is responsible for:

managing the communication between your application and ConfigCat servers.
caching your setting values and feature flags.
serving values quickly in a failsafe way.

configcat.NewClient(<apiKey>) returns a client with default options.

Arguments	Description
`apiKey`	API Key to access your feature flags and configurations. Get it from ConfigCat Dashboard.

Custom configuration options

configcat.NewCustomClient(<apiKey>, config) returns a client with custom configuration.

Arguments	Description
`apiKey`	API Key to access your feature flags and configurations. Get it from ConfigCat Dashboard.
`config`	An object which contains the custom configuration.

You can get and customize the default configuration options:

config := configcat.DefaultClientConfig()

Properties	Type	Description
`BaseUrl`	string	Obsolete Sets the CDN base url (forward proxy, dedicated subscription) from where the sdk will download the configurations.
`Cache`	ConfigCache	Sets a custom cache implementation for the client. See below.
`MaxWaitTimeForSyncCalls`	time.Duration	Sets a timeout value for the synchronous methods of the library (`GetValue()`, `GetValueForUser()`, `Refresh()`) which means when a sync call takes longer than the timeout, it'll return with the default value.
`HttpTimeout`	time.Duration	Sets maximum wait time for a HTTP response.
`Transport`	http.RoundTripper	Sets the transport options for the underlying HTTP calls.
`Logger`	configcat.Logger	Sets the `Logger` implementation used by the SDK for logging.
`PolicyFactory`	func(ConfigProvider, *ConfigStore) RefreshPolicy	Sets a custom refresh policy implementation for the client. See below.

Then you can pass it to the NewCustomClient() method:

client := configcat.NewCustomClient("<PLACE-YOUR-API-KEY-HERE>", config)

We strongly recommend you to use the ConfigCatClient as a Singleton object in your application

Anatomy of `GetValue()`

Parameters	Description
`key`	Setting-specific key. Set on ConfigCat Dashboard for each setting.
`defaultValue`	This value will be returned in case of an error.

value := client.GetValue(
    "keyOfMySetting", // Setting Key
    false // Default value
)

Anatomy of `GetValueForUser()`

Parameters	Description
`key`	Setting-specific key. Set on ConfigCat Dashboard for each setting.
`defaultValue`	This value will be returned in case of an error.
`user`	User Object. Essential when using Targeting. Read more about Targeting.

value := client.GetValueForUser(
    "keyOfMySetting", // Setting Key
    false // Default value
    configcat.NewUser("435170f4-8a8b-4b67-a723-505ac7cdea92") // User Object
)

User Object

The User Object is essential if you'd like to use ConfigCat's Targeting feature.

Simple user object creation:

user = configcat.NewUser("435170f4-8a8b-4b67-a723-505ac7cdea92")

user = configcat.NewUser("john@example.com")

Customized user object creation:

Arguments	Description
`identifier`	Unique identifier of a user in your application. Can be any value, even an email address.
`email`	Optional parameter for easier targeting rule definitions.
`country`	Optional parameter for easier targeting rule definitions.
`custom`	Optional dictionary for custom attributes of a user for advanced targeting rule definitions. e.g. User role, Subscription type.

custom := map[string]string{}
custom["SubscriptionType"] = "Pro"
custom["UserRole"] = "Admin"
user := configcat.NewUserWithAdditionalAttributes("435170f4-8a8b-4b67-a723-505ac7cdea92",
    "john@example.com", "United Kingdom", custom)

`GetAllKeys()`

You can get all the setting keys from your configuration by calling the GetAllKeys() method of the ConfigCatClient.

client := configcat.NewClient("#YOUR-API-KEY#")
keys, err := client.GetAllKeys()

Polling Modes

The ConfigCat SDK supports 3 different polling mechanisms to acquire the setting values from ConfigCat. After latest setting values are downloaded, they are stored in the internal cache then all requests are served from there. With the following polling modes, you can customize the SDK to best fit to your application's lifecycle.

Auto polling (default)

The ConfigCat SDK downloads the latest values and stores them automatically every 60 seconds.

Use the NewAutoPollingPolicy method to create the policy.

config := configcat.DefaultClientConfig()
config.PolicyFactory = func(configProvider configcat.ConfigProvider, store *configcat.ConfigStore) configcat.RefreshPolicy {
    return configcat.NewAutoPollingPolicy(configProvider, store, 
    // The auto poll interval
    time.Second * 120)
}
       
client := configcat.NewCustomClient("<PLACE-YOUR-API-KEY-HERE>", config)

You have the option to configure the polling interval and an configChanged callback that will be notified when a new configuration is fetched. The policy calls the given method only, when the new configuration is differs from the cached one.

config := configcat.DefaultClientConfig()
config.PolicyFactory = func(configProvider configcat.ConfigProvider, store *configcat.ConfigStore) configcat.RefreshPolicy {
    return configcat.NewAutoPollingPolicyWithChangeListener(configProvider, store,
        // The auto poll interval
        time.Second * 120,
        // The callback called when the configuration changes
        func(config string, parser *configcat.ConfigParser) {
            result, err := parser.Parse(config, "key-of-my-awesome-feature")
            if err != nil {
                isMyAwesomeFeatureEnabled, ok := result.(bool)
                if ok && isMyAwesomeFeatureEnabled {
                    //show your awesome feature to the world!
                }
            }
        })
}
       
client := configcat.NewCustomClient("<PLACE-YOUR-API-KEY-HERE>", config)

Lazy loading

When calling getValue() the ConfigCat SDK downloads the latest setting values if they are not present or expired in the cache. In this case the getValue() will return the setting value after the cache is updated.

Use the NewLazyLoadingPolicy method to create the policy.

config := configcat.DefaultClientConfig()
config.PolicyFactory = func(configProvider configcat.ConfigProvider, store *configcat.ConfigStore) configcat.RefreshPolicy {
    return configcat.NewExpiringCachePolicy(configProvider, store, 
    // The cache expiration interval
    time.Second * 120,
    // True for async, false for sync refresh
    true)
}
       
client := configcat.NewCustomClient("<PLACE-YOUR-API-KEY-HERE>", config)

Use the asyncRefresh option parameter of the NewLazyLoadingPolicy to define how do you want to handle the expiration of the cached configuration. If you choose asynchronous refresh then when a request is being made on the cache while it's expired, the previous value will be returned immediately until the fetching of the new configuration is completed.

If you set the .asyncRefresh() to false, the refresh operation will be awaited until the fetching of the new configuration is completed.

Manual polling

With this policy every new configuration request on the ConfigCatClient will trigger a new fetch over HTTP.

config := configcat.DefaultClientConfig()
config.PolicyFactory = func(configProvider configcat.ConfigProvider, store *configcat.ConfigStore) configcat.RefreshPolicy {
    return configcat.NewManualPollingPolicy(configProvider, store)
}
       
client := configcat.NewCustomClient("<PLACE-YOUR-API-KEY-HERE>", config)

Custom Policy

You can also implement your custom refresh policy by satisfying the RefreshPolicy interface.

type CustomPolicy struct {
    configcat.ConfigRefresher
}

func NewCustomPolicy(fetcher configcat.ConfigProvider, store *configcat.ConfigStore) *NewCustomPolicy {
    return &NewCustomPolicy{ ConfigRefresher: ConfigRefresher{ Fetcher:fetcher, Store:store }}
}

func (policy *NewCustomPolicy) GetConfigurationAsync() *configcat.AsyncResult {
    // this method will be called when the configuration is requested from the ConfigCat client.
    // you can access the config fetcher through the policy.Fetcher and the internal store via policy.Store
}

The AsyncResult and the Async are internal types used to signal back to the caller about the completion of a given task like Futures.

Then you can simply inject your custom policy implementation into the ConfigCat client:

config := configcat.DefaultClientConfig()
config.PolicyFactory = func(configProvider configcat.ConfigProvider, store *configcat.ConfigStore) configcat.RefreshPolicy {
    return NewCustomPolicy(configProvider, store)
}

client := configcat.NewCustomClient("<PLACE-YOUR-API-KEY-HERE>", config)

Custom Cache

You have the option to inject your custom cache implementation into the client. All you have to do is to satisfy the ConfigCache interface:

type CustomCache struct {
}

func (cache *CustomCache) Get() (string, error) {
    // here you have to return with the cached value
}

func (cache *CustomCache) Set(value string) error {
    // here you have to store the new value in the cache
}

Then use your custom cache implementation:

config := configcat.DefaultClientConfig()
config.Cache = CustomCache{}

client := configcat.NewCustomClient("<PLACE-YOUR-API-KEY-HERE>", config)

Force refresh

Any time you want to refresh the cached configuration with the latest one, you can call the Refresh() or RefreshAsync() method of the library, which will initiate a new fetch and will update the local cache.

HTTP Proxy

You can use the Transport config option to set up http transport related (like proxy) settings for the http client used by the SDK:

config := configcat.DefaultClientConfig()
config.Transport = &http.Transport{
    Proxy: http.ProxyURL(url.Parse("<PROXY-URL>")),
}
client := configcat.NewCustomClient("<PLACE-YOUR-API-KEY-HERE>", config)

Logging

The default logger used by the SDK is logrus, but you have the option to override it with your logger via the Logger config option, it only has to satisfy the Logger interface:

import {
    "github.com/configcat/go-sdk"
    "github.com/sirupsen/logrus"
}
config := configcat.DefaultClientConfig()
config.Logger = logrus.New()

client := configcat.NewCustomClient("<PLACE-YOUR-API-KEY-HERE>", config)

Setting log levels

import {
    "github.com/configcat/go-sdk"
    "github.com/sirupsen/logrus"
}

logger := logrus.New()
logger.SetLevel(logrus.InfoLevel)
config := configcat.DefaultClientConfig()
config.Logger = logger

client := configcat.NewCustomClient("<PLACE-YOUR-API-KEY-HERE>", config)

Available log levels:

Level	Description
ErrorLevel	Only error level events are logged.
WarnLevel	Errors and Warnings are logged.
InfoLevel	Errors, Warnings and feature flag evaluation is logged.
DebugLevel	All of the above plus debug info is logged.

Info level logging helps to inspect the feature flag evaluation process:

ConfigCat - INFO - Evaluate 'isPOCFeatureEnabled'
INFO[0000] Evaluating rule: [Email:] [CONTAINS] [@something.com] => no match 
INFO[0000] Evaluating rule: [Email:] [CONTAINS] [@example.com] => no match 
INFO[0000] Returning false.

Sample Applications

Sample Console App

Look under the hood

ConfigCat Go SDK's repository on GitHub