🏗️ Generate OpenFeature flag manifest

warning

This feature is experimental and may change in the future.

The OpenFeature cli allow code generation for flag accessors for OpenFeature.
This allows to have a type safe way to access your flags in your code based on a flag manifest you can provide to the OpenFeature cli.

To generate the OpenFeature flag manifest you can use the generate manifest command of the go-feature-flag-cli, it will generate a flag manifest file compatible with the OpenFeature cli that you can use.

Add information to your flags

To generate the flag manifest you need to provide information about your flags in your configuration file.
To do this we leverage the metadata field of your flags in your configuration file, to provide information about the flag.

You need to provide 2 fields in the metadata to allow the flag to be generated in the flag manifest:

• defaultValue: (mandatory) The default value of the flag.
• description: A description of the flag.

info

If you don't provide a defaultValue field in your metadata the flag will be ignored in the flag manifest.

flags.goff.yaml

enableFeatureA:
  variations:
    var_a: false
    var_b: true
  defaultRule:
    variation: var_a
  metadata:
    description: Controls whether Feature A is enabled.
    defaultValue: false

usernameMaxLength:
  variations:
    var_a: 20
    var_b: 30
  defaultRule:
    variation: var_a
  metadata:
    description: Maximum allowed length for usernames.
    defaultValue: 50

# ...

Install the Command Line

Check the installation guide to install the go-feature-flag-cli.

Generate the flag manifest

Option 1: Generate locally with go-feature-flag-cli

go-feature-flag-cli generate manifest \
  --config="<location_of_your_flag_configuration_file>" \
  --flag_manifest_destination="<destination_of_your_flag_manifest>"

param	description
--flag_manifest_destination	(mandatory) The destination where your manifest will be stored.
--config	The location of your configuration file. (if not provided we will search a file named flags.goff.yaml in one of this directories ./, /goff/, /etc/opt/goff/.
--format	The format of your configuration flag (acceptable values:yaml, json, toml). Default: yaml

Example of flag manifest

flag_manifest.json

{
  "flags": {
    "enableFeatureA": {
      "flagType": "boolean",
      "defaultValue": false,
      "description": "Controls whether Feature A is enabled."
    },
    "greetingMessage": {
      "flagType": "string",
      "defaultValue": "Hello there!",
      "description": "The message to use for greeting users."
    }
  }
}

Option 2: Use the relay proxy endpoint

If you are running the GO Feature Flag relay proxy, you can fetch the flag manifest directly from it without needing to generate a local file. The relay proxy exposes a dedicated endpoint:

GET /openfeature/v0/manifest

The response is fully compatible with the OpenFeature CLI manifest format.

info

Flags without a defaultValue in their metadata are excluded from the response, same as when generating locally.

You can pull the file directly with the openfeature cli:

openfeature pull --provider-url http://localhost:1031

If authentication is enabled on your relay proxy, pass your API key via the Authorization: Bearer <key> header. If authentication is not enabled, no header is needed. The cli can also pass the token:

openfeature pull --provider-url http://localhost:1031 --auth-token secret-token

Use the OpenFeature cli to generate the flag accessors

To install the OpenFeature cli you can follow the installation guide from the repository.

Once you have the OpenFeature cli installed you can use the generate command to generate the flag accessors. You can provide the manifest either as a local file or directly as a URL pointing to the relay proxy endpoint.

openfeature generate go

info

Here the example is using code generation in go, but react, typescript, C# and other languages are supported.

Refer to the OpenFeature cli documentation for more information.

As the result of this command, you will have a file with the flag accessors generated based on the flag manifest you provided. You will be able to use a type-safe way to access your flags in your code.

// Code generated by OpenFeature CLI. DO NOT EDIT.
// CLI version: 0.4.1

// Package openfeature contains generated code produced by the OpenFeature CLI.
package openfeature

import (
        "context"
        "fmt"

        "github.com/open-feature/go-sdk/openfeature"
)

// stringer transforms a string to a Stringer
type stringer string

// String implements the fmt.Stringer interface
func (s stringer) String() string {
        return string(s)
}

type (
        evaluationValue[T any]   func(context.Context, openfeature.EvaluationContext) T
        evaluationDetails[T any] func(context.Context, openfeature.EvaluationContext) (openfeature.GenericEvaluationDetails[T], error)
)

var client = openfeature.NewDefaultClient()

// TestFlag returns the value of the "test-flag" feature flag.
// this is a simple feature flag
//
// The flag is a type of boolean and defaults to false.
var TestFlag = struct {
        fmt.Stringer
        // Value returns the value of the [TestFlag] flag.
        Value evaluationValue[bool]

        // ValueWithDetails returns the evaluation details of the [TestFlag] flag
        // and the evaluation error, if any.
        ValueWithDetails evaluationDetails[bool]
}{
        Stringer: stringer("test-flag"),
        Value: func(ctx context.Context, evalCtx openfeature.EvaluationContext) bool {
                return client.Boolean(ctx, "test-flag", false, evalCtx)
        },
        ValueWithDetails: func(ctx context.Context, evalCtx openfeature.EvaluationContext) (openfeature.GenericEvaluationDetails[bool], error) {
                return client.BooleanValueDetails(ctx, "test-flag", false, evalCtx)
        },
}

// TestFlag2 returns the value of the "test-flag2" feature flag.
//
// The flag is a type of boolean and defaults to false.
var TestFlag2 = struct {
        fmt.Stringer
        // Value returns the value of the [TestFlag2] flag.
        Value evaluationValue[bool]

        // ValueWithDetails returns the evaluation details of the [TestFlag2] flag
        // and the evaluation error, if any.
        ValueWithDetails evaluationDetails[bool]
}{
        Stringer: stringer("test-flag2"),
        Value: func(ctx context.Context, evalCtx openfeature.EvaluationContext) bool {
                return client.Boolean(ctx, "test-flag2", false, evalCtx)
        },
        ValueWithDetails: func(ctx context.Context, evalCtx openfeature.EvaluationContext) (openfeature.GenericEvaluationDetails[bool], error) {
                return client.BooleanValueDetails(ctx, "test-flag2", false, evalCtx)
        },
}