evaluation

README

LaunchDarkly Go SDK Evaluation Engine

Overview

This repository contains the internal feature flag evaluation logic and data model used by the LaunchDarkly Go SDK. It is packaged separately because it is also used by internal LaunchDarkly components. Applications using the LaunchDarkly Go SDK should not need to reference this package directly.

Note that the base import path is gopkg.in/launchdarkly/go-server-sdk-evaluation.v1, not github.com/launchdarkly/go-server-sdk-evaluation. This ensures that the package can be referenced not only as a Go module, but also by projects that use older tools like dep and govendor, because the 5.x release of the Go SDK supports either module or non-module usage. Future releases of this package, and of the Go SDK, may drop support for non-module usage.

Supported Go versions

This version of the project has been tested with Go 1.14 and higher.

Learn more

Check out our documentation for in-depth instructions on configuring and using LaunchDarkly. You can also head straight to the complete reference guide for the Go SDK, or the generated API documentation for this project.

Contributing

We encourage pull requests and other contributions from the community. Check out our contributing guidelines for instructions on how to contribute to this SDK.

About LaunchDarkly

• LaunchDarkly is a continuous delivery platform that provides feature flags as a service and allows developers to iterate quickly and safely. We allow you to easily flag your features and manage them from the LaunchDarkly dashboard. With LaunchDarkly, you can:
  • Roll out a new feature to a subset of your users (like a group of users who opt-in to a beta tester group), gathering feedback and bug reports from real-world use cases.
  • Gradually roll out a feature to an increasing percentage of users, and track the effect that the feature has on key metrics (for instance, how likely is a user to complete a purchase if they have feature A versus feature B?).
  • Turn off a feature that you realize is causing performance problems in production, without needing to re-deploy, or even restart the application with a changed configuration file.
  • Grant access to certain features based on user attributes, like payment plan (eg: users on the ‘gold’ plan get access to more features than users in the ‘silver’ plan). Disable parts of your application to facilitate maintenance, without taking everything offline.
• LaunchDarkly provides feature flag SDKs for a wide variety of languages and technologies. Check out our documentation for a complete list.
• Explore LaunchDarkly
  • launchdarkly.com for more information
  • docs.launchdarkly.com for our documentation and SDK reference guides
  • apidocs.launchdarkly.com for our API documentation
  • blog.launchdarkly.com for the latest product updates
  • Feature Flagging Guide for best practices and strategies

Documentation

Overview

Package evaluation contains the LaunchDarkly Go SDK feature flag evaluation engine.

Normal use of the Go SDK does not require referencing this package directly. It is used internally by the SDK, but is published and versioned separately so it can be used in other LaunchDarkly components without making the SDK versioning dependent on these internal APIs.

Index

• type DataProvider
• type Evaluator
  • func NewEvaluator(dataProvider DataProvider) Evaluator
• type PrerequisiteFlagEvent
• type PrerequisiteFlagEventRecorder

Types

type DataProvider

type DataProvider interface {
	// GetFeatureFlag attempts to retrieve a feature flag from the data store by key.
	//
	// The evaluator calls this method if a flag contains a prerequisite condition referencing
	// another flag.
	//
	// The method returns nil if the flag was not found. The DataProvider should treat any deleted
	// flag as "not found" even if the data store contains a deleted flag placeholder for it.
	GetFeatureFlag(key string) *ldmodel.FeatureFlag
	// GetSegment attempts to retrieve a user segment from the data store by key.
	//
	// The evaluator calls this method if a clause in a flag rule uses the OperatorSegmentMatch
	// test.
	//
	// The method returns nil if the segment was not found. The DataProvider should treat any deleted
	// segment as "not found" even if the data store contains a deleted segment placeholder for it.
	GetSegment(key string) *ldmodel.Segment
}

DataProvider is an abstraction for querying feature flags and user segments from a data store. The caller provides an implementation of this interface to NewEvaluator.

Flags and segments are returned by reference for efficiency only (on the assumption that the caller already has these objects in memory); the evaluator will never modify their properties.

type Evaluator

type Evaluator interface {
	// Evaluate evaluates a feature flag for the specified user.
	//
	// The flag is passed by reference only for efficiency; the evaluator will never modify any flag
	// properties. Passing a nil flag will result in a panic.
	//
	// The evaluator does not know anything about analytics events; generating any appropriate analytics
	// events is the responsibility of the caller, who can also provide a callback in prerequisiteFlagEventRecorder
	// to be notified if any additional evaluations were done due to prerequisites. The prerequisiteFlagEventRecorder
	// parameter can be nil if you do not need to track prerequisite evaluations.
	Evaluate(
		flag *ldmodel.FeatureFlag,
		user lduser.User,
		prerequisiteFlagEventRecorder PrerequisiteFlagEventRecorder,
	) ldreason.EvaluationDetail
}

Evaluator is the engine for evaluating feature flags.

func NewEvaluator

func NewEvaluator(dataProvider DataProvider) Evaluator

NewEvaluator creates an Evaluator, specifying a DataProvider that it will use if it needs to query additional feature flags or user segments during an evaluation.

type PrerequisiteFlagEvent

type PrerequisiteFlagEvent struct {
	// TargetFlagKey is the key of the feature flag that had a prerequisite.
	TargetFlagKey string
	// User is the user that the flag was evaluated for. We pass this back to the caller, even though the caller
	// already passed it to us in the Evaluate parameters, so that the caller can provide a stateless function for
	// PrerequisiteFlagEventRecorder rather than a closure (since closures are less efficient).
	User lduser.User
	// PrerequisiteFlag is the full configuration of the prerequisite flag. We need to pass the full flag here rather
	// than just the key because the flag's properties (such as TrackEvents) can affect how events are generated.
	// This is passed by reference for efficiency only, and will never be nil; the PrerequisiteFlagEventRecorder
	// must not modify the flag's properties.
	PrerequisiteFlag *ldmodel.FeatureFlag
	// PrerequisiteResult is the result of evaluating the prerequisite flag.
	PrerequisiteResult ldreason.EvaluationDetail
}

PrerequisiteFlagEvent is the parameter data passed to PrerequisiteFlagEventRecorder.

type PrerequisiteFlagEventRecorder

type PrerequisiteFlagEventRecorder func(PrerequisiteFlagEvent)

PrerequisiteFlagEventRecorder is a function that Evaluator.Evaluate() will call to record the result of a prerequisite flag evaluation.