.NET SDK Reference

This topic explains how to use the Harness Feature Flags (FF) SDK in your .NET application.

In Version 1.1.4 of the .NET SDK, the package name for installing the SDK changed from ff-netF48-server-sdk to ff-dotnet-server-sdk. To use this version, make sure you remove the old package name and use the new one. You can do this by using the following commands: Remove the old package dotnet remove package ff-netF48-server-sdk Add the new packagedotnet add package ff-dotnet-server-sdk

This topic describes how to use the Harness Feature Flags .NET SDK for your .Net application.

For getting started quickly, you can use our sample code from the .NET SDK README. You can also clone and run a sample application from the .NET SDK GitHub Repository.

Before you begin

Make sure you read and understand:

• Feature Flags Overview

• Getting Started with Feature Flags

• Client-Side and Server-Side SDKs

• Communication Strategy Between SDKs and Harness Feature Flags

Version

Latest SDK version can be found on GitHub Release Page

If you are using an older version of the .NET Framework, it may not default the security protocol to TLS 1.2. For compatibility with this SDK, set the protocol to TLS 1.2 by using the following:

System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;

Requirements

To use this SDK, make sure you:

• Install .NET Framework 4.8 or newer, or .Net 5.0.104 or newer.

The library is packaged as multi-target and supports the netstandard 2.0 set of API's as well as net461 for older frameworks.*

• Download the SDK from our GitHub repository

• Create a .NET application, or clone our sample application.

• Create a Feature Flag on the Harness Platform. If you are following along with the SDK README sample code, make sure your flag is called harnessappdemodarkmode.

• Create a server SDK key and make a copy of it

Install the SDK

Install the SDK by using the dotnet add package command, for example:

dotnet add package ff-dotnet-server-sdk --version 1.4.0

In Version 1.1.4 of the .NET SDK, the package name for installing the SDK changed from ff-netF48-server-sdk to ff-dotnet-server-sdk. To use this version, make sure you remove the old package name and use the new one. You can do this by using the following commands: Remove the old package dotnet remove package ff-netF48-server-sdk Add the new packagedotnet add package ff-dotnet-server-sdk

To initialize the .NET SDK, you need to:

1. Add your Server SDK key to connect to your Harness Environment.

2. Add a Target that you want to Evaluate against a Feature Flag.

3. (Optional) Configure the SDK.

4. Complete the initialization with the SDK using the Server SDK Key, Target, and Configuration parameters you set.

Add the Server SDK Key

To connect to the correct Environment that you set up on the Harness Platform, you need to add the Server SDK Key from that Environment. Input the Client SDK Key into the sdkKey parameter, for example:

public static String apiKey = "YOUR_API_KEY";

Add a Target

What is a Target?

Targets are used to control which users see which Variation of a Feature Flag, for example, if you want to do internal testing, you can enable the Flag for some users and not others. When creating a Target, you give it a name and a unique identifier. Often Targets are users but you can create a Target from anything that can be uniquely identified, such as an app or a machine.

For more information about Targets, go to Targeting Users With Flags.

To add a Target, build it and pass in arguments for the following:

Parameter	Description	Required?	Example
Identifier	Unique ID for the Target.Read Regex requirements for Target names and identifiers below for accepted characters.	Required	.Identifier("HT_1")
Name	Name for this Target. This does not have to be unique. Note: If you don’t provide a value, the name will be the same as the identifier.Read Regex requirements for Target names and identifiers below for accepted characters.	OptionalNote: If you don't want to send a name, don't send the parameter. Sending an empty argument will cause an error.	.Name("Harness_Target_1")
Attributes	Additional data you can store for a Target, such as email addresses or location.	Optional	.Attributes(new Dictionary<string, string>(){{"email", "[e-mail]"}})

Regex requirements for Target names and identifiers

Identifier

Regex: ^[A-Za-z0-9.@_-]*$ Must consist of only alphabetical characters, numbers, and the following symbols: . (period) @ (at sign) -(dash) _ (underscore)

The characters can be lowercase or uppercase but cannot include accented letters, for example Cafe_789.

Name Regex: ^[\\p{L}\\d .@_-]*$

Must consist of only alphabetical characters, numbers, and the following symbols: . (period) @ (at sign) -(dash) _ (underscore) (space)

The characters can be lowercase or uppercase and can include accented letters, for example Café_123.

For example:

Target target = Target.builder()
    .Name(".NET SDK Target 1")
    .Identifier("DotNetTarget1")
    .Attributes(new Dictionary<string, string>(){{"email", "[e-mail]"}})
    .build();

Configure the SDK

When initializing the SDK, you also have the option of providing alternative configuration by using Config.Builder().

You can configure the following base features of the SDK:

Name	Example	Description	Default Value
configUrl	ConfigUrl("https://config.ff.harness.io/api/1.0")	The URL used to fetch Feature Flag Evaluations. When using the Relay Proxy, change this to: http://localhost:7000	https://config.ff.harness.io/api/1.0
eventUrl	EventUrl("https://events.ff.harness.io/api/1.0")	The URL for posting metrics data to the Feature Flag service. When using the Relay Proxy, change this to: http://localhost:7000	https://events.ff.harness.io/api/1.0
pollingInterval	SetPollingInterval(60000)	The interval in milliseconds that we poll for changes when you are using stream mode.	60000 (milliseconds)
streamEnabled	SetStreamEnabled(true)	Set to true to enable streaming mode.Set to false to disable streaming mode.	true
analyticsEnabled	SetAnalyticsEnabled(true)	Set to true to enable analytics.Set to false to disable analytics.Note: When enabled, analytics data is posted every 60 seconds.	true

For example:

CfClient.Instance.Initialize(apiKey, Config.Builder()  
    .ConfigUrl("https://config.ff.harness.io/api/1.0")  
    .EventUrl("https://events.ff.harness.io/api/1.0")  
    .SetPollingInterval(60)  
    .SetStreamEnabled(true)  
    .SetAnalyticsEnabled(true)  
    .Build());

Complete the initialization

To complete the initialization, create an instance of the cfClient and pass in the apiKey and Config.Builder, for example:

CfClient.Instance.Initialize(apiKey, Config.Builder().Build());

Sample of initializing the SDK

        public static String apiKey = Environment.GetEnvironmentVariable("FF_API_KEY");
        public static String flagName = Environment.GetEnvironmentVariable("FF_FLAG_NAME") is string v && v.Length > 0 ? v : "harnessappdemodarkmode";  
  
        static void Main(string[] args)
        {  
  
            // Create a feature flag client  
            CfClient.Instance.Initialize(apiKey, Config.Builder().Build());
            CfClient.Instance.WaitForInitialization();
  
            // Create a target (different targets can get different results based on rules)  
            Target target = Target.builder()  
                            .Name("DotNetSDK")   
                            .Identifier("dotnetsdk")  
                            .Attributes(new Dictionary<string, string>(){{"location", "emea"}})  
                            .build();

Evaluate a Flag

Evaluating a Flag is when the SDK processes all Flag rules and returns the correct Variation of that Flag for the Target you provide.

If a matching Flag can’t be found, or the SDK can’t remotely fetch Flags, the default value is returned.

There are different methods for the different Variation types and for each method you need to pass in:

• Identifier of the Flag you want to evaluate

• The Target object you want to evaluate against

• The default Variation

For example:

Evaluate a boolean Variation

public bool boolVariation(string key, dto.Target target, bool defaultValue)

Evaluate a number Variation

public double numberVariation(string key, dto.Target target, double defaultValue)

Evaluate a string Variation

public string stringVariation(string key, dto.Target target, string defaultValue)

Evaluate a JSON Variation

public JObject jsonVariation(string key, dto.Target target, JObject defaultValue)

Listen for events

This method provides a way to listen to the different events that might be triggered by the SDK, indicating a specific change in the SDK.

client.InitializationCompleted += (sender, e) =>  
{  
    // fired when authentication is completed and recent configuration is fetched from server  
    Console.WriteLine("Notification Initialization Completed");  
};  
client.EvaluationChanged += (sender, identifier) =>  
{  
    // Fired when flag value changes.  
    Console.WriteLine($"Flag changed for {identifier}");  
};

Test your app is connected to Harness

When you receive a response showing the current status of your Feature Flag, go to the Harness Platform and toggle the Flag on and off. Then, check your app to verify if the Flag Variation displayed is updated with the Variation you toggled.

NOTE

The SDK must run for at least 60 seconds before it sends metrics. Please ensure metrics have not been disabled in the SDK.

Close the SDK client

In most applications, you won't need to close the SDK client.

However, you should close the SDK client if:

• Your application is about to terminate. Closing the client ensures that all associated resources are released.

• You have determined that you do not need to evaluate flags again in your application lifecycle.

IMPORTANT

The SDK does not evaluate flags after the client is closed.

Additional options

Develop on your local environment

By default, you are connected to the Harness environment but you can use a local connector to develop in your local environment, for example:

LocalConnector connector = new LocalConnector("local");  
client = new CfClient(connector);

Store flags offline

You can store your last Flag configuration for the SDK to use if your application is offline or you have an asynchronous startup. For example:

FileMapStore fileStore = new FileMapStore("Non-Freemium");  
LocalConnector connector = new LocalConnector("local");  
client = new CfClient(connector, Config.builder().store(fileStore).build()); 

If you don’t store your Flag configuration and your application is offline, the Flags will be evaluated based on the defaultValue.

Configure your logger

1.2.x - Microsoft.Extensions.Logging

With version 1.2.x and above you can use Microsoft.Extensions.Logging to provide an ILoggerFactory on the config builder. For example:

dotnet add package Serilog.Extensions.Logging dotnet add package Serilog.Sinks.Console

var loggerFactory = new SerilogLoggerFactory(
    new LoggerConfiguration()
        .MinimumLevel.Verbose()
        .WriteTo.Console()
        .CreateLogger());

var config = Config.Builder()
    ...
    .LoggerFactory(loggerFactory)
    .Build();

1.1.x - Serilog

On older SDK versions you need to use Serilog as your logger for that SDK. To do this, add the Serilog package, for example:

dotnet add package Serilog

You can then configure the logger to write to the console with debug, for example:

// Logger  
Log.Logger = new LoggerConfiguration()  
    .MinimumLevel.Debug()  
    .WriteTo.Console()  
    .CreateLogger();

Use the Relay Proxy

When using your Feature Flag SDKs with a Harness Relay Proxy you need to change the default ConfigURL and EventURL that we use. You can pass the URLs in when initializing the SDK, for example:

CfClient.Instance.Initialize(apikey, Config.Builder()  
            .ConfigUrl("http://localhost:7000")  
            .EventUrl("http://localhost:7000")  
            .Build());

Sample code for a .NET application

Here is a sample code for integrating with the .NET SDK:

using System;  
using System.Collections.Generic;  
using io.harness.cfsdk.client.dto;  
using io.harness.cfsdk.client.api;  
using System.Threading;  
  
namespace getting_started
{  
    class Program  
    {  
  
        public static String apiKey = Environment.GetEnvironmentVariable("FF_API_KEY");  
        public static String flagName = Environment.GetEnvironmentVariable("FF_FLAG_NAME") is string v && v.Length > 0 ? v : "harnessappdemodarkmode";  
  
        static void Main(string[] args)
        {  
  
            // Create a feature flag client  
            CfClient.Instance.Initialize(apiKey, Config.Builder().Build());
            CfClient.Instance.WaitForInitialization();
              
            // Create a target (different targets can get different results based on rules)  
  
            Target target = Target.builder()  
                            .Name("Harness_Target_1")   
                            .Identifier("HT_1")  
                            .Attributes(new Dictionary<string, string>(){{"email", "[e-mail]"}})  
                            .build();  
  
            // Loop forever reporting the state of the flag  
            while (true)  
            {  
                bool resultBool = CfClient.Instance.boolVariation(flagName, target, false);  
                Console.WriteLine("Flag variation " + resultBool);  
                Thread.Sleep(10 * 1000);  
            }  
        }  
    }  
}

Troubleshooting

The SDK logs the following codes for certain lifecycle events, for example authentication, which can aid troubleshooting.

Code	Description	Log Level
1000	Successfully initialized	Info
1001	Failed to initialize due to authentication error	Error
1002	Failed to initialize due to a missing or empty API key	Error
1003	WaitForInitialization configuration option was provided and the SDK is waiting for initialization to finish	Info
2000	Successfully authenticated	Info
2001	Authentication failed with a non-recoverable error	Error
2002	Authentication failed and is retrying	Warn
2003	Authentication failed and max retries have been exceeded	Error
3000	SDK closing	Info
3001	SDK closed successfully	Info
4000	Polling service started	Info
4001	Polling service stopped	Info
5000	Streaming connected	Info
5001	Streaming disconnected	Warn
5002	Streaming event received	Debug
5003	Streaming disconnected and is retrying to connect	Info
5004	Streaming service stopped	Info
5005	Stream is still retrying to connect after 4 attempts	Warn
6000	Evaluation was successful	Debug
6001	Evaluation failed and the default value was returned	Info
7000	Metrics service has started	Info
7001	Metrics service has stopped	Info
7002	Metrics posting failed	Warn
7003	Metrics posting success	Debug
7004	Metrics max target size exceeded	Warn
7007	Metrics max evaluation size reached	Warn