feat(flags): fall back to /decide endpoint for GetFeatureFlag and…

… `GetAllFlags` so that users can use this library without needing a personal API Key (#46)

* initial commit

* info about the personal api key

* adding docs

* logs and comments

* adding changelog

CHANGELOG.md

@@ -1,4 +1,10 @@
-# 2.0.0 - 2022-08-15
+# Changelog
+
+## 2.0.1 - 2024-08-07
+
+1. The client will fall back to the `/decide` endpoint when evaluating feature flags if the user does not wish to provide a PersonalApiKey.  This fixes an issue where users were unable to use this SDK without providing a PersonalApiKey.  This fallback will make feature flag usage less performant, but will save users money by not making them pay for public API access.
+
+## 2.0.0 - 2022-08-15
 
 Breaking changes:
 

README.md

@@ -21,7 +21,15 @@ import (
 )
 
 func main() {
-    client := posthog.New(os.Getenv("POSTHOG_API_KEY"))
+    client := posthog.New(os.Getenv("POSTHOG_API_KEY")) // This value must be set to the project API key in PostHog
+    // alternatively, you can do 
+    // client, _ := posthog.NewWithConfig(
+    //     os.Getenv("POSTHOG_API_KEY"),
+    //     posthog.Config{
+    //         PersonalApiKey: "your personal API key", // Set this to your personal API token you want feature flag evaluation to be more performant.  This will incur more costs, though
+    //         Endpoint:       "https://us.i.posthog.com",
+    //     },
+    // )
     defer client.Close()
 
     // Capture an event
@@ -54,10 +62,37 @@ func main() {
       Properties: posthog.NewProperties().
         Set("$current_url", "https://example.com"),
     })
+
+    // Check if a feature flag is enabled
+    isMyFlagEnabled, err := client.IsFeatureEnabled(
+            FeatureFlagPayload{
+                Key:        "flag-key",
+                DistinctId: "distinct_id_of_your_user",
+            })
+
+    if isMyFlagEnabled == true {
+        // Do something differently for this user
+    }
 }
 
 ```
 
+## Testing Locally
+
+You can run your Go app against a local build of `posthog-go` by making the following change to your `go.mod` file for whichever your app, e.g.
+
+```Go
+module example/posthog-go-app
+
+go 1.22.5
+
+require github.com/posthog/posthog-go v0.0.0-20240327112532-87b23fe11103
+
+require github.com/google/uuid v1.3.0 // indirect
+
+replace github.com/posthog/posthog-go => /path-to-your-local/posthog-go
+```
+
 ## Questions?
 
 ### [Join our Slack community.](https://join.slack.com/t/posthogusers/shared_invite/enQtOTY0MzU5NjAwMDY3LTc2MWQ0OTZlNjhkODk3ZDI3NDVjMDE1YjgxY2I4ZjI4MzJhZmVmNjJkN2NmMGJmMzc2N2U3Yjc3ZjI5NGFlZDQ)

config.go

@@ -18,8 +18,11 @@ type Config struct {
 	// `DefaultEndpoint` by default.
 	Endpoint string
 
-	// You must specify a Personal API Key to use feature flags
-	// More information on how to get one: https://posthog.com/docs/api/overview
+	// Specifying a Personal API key will make feature flag evaluation more performant,
+	// but it's not required for feature flags.  If you don't have a personal API key,
+	// you can leave this field empty, and all of the relevant feature flag evaluation
+	// methods will still work.
+	// Information on how to get a personal API key: https://posthog.com/docs/api/overview
 	PersonalApiKey string
 
 	// The flushing interval of the client. Messages will be sent when they've

feature_flags_test.go

@@ -325,7 +325,7 @@ func TestFlagGroup(t *testing.T) {
 				t.Errorf("Expected personProperties to be map[region:Canada], got %s", reqBody.PersonProperties)
 			}
 
-			groupPropertiesEquality := reflect.DeepEqual(reqBody.GroupProperties, map[string]Properties{"company": Properties{"name": "Project Name 1"}})
+			groupPropertiesEquality := reflect.DeepEqual(reqBody.GroupProperties, map[string]Properties{"company": {"name": "Project Name 1"}})
 			if !groupPropertiesEquality {
 				t.Errorf("Expected groupProperties to be map[company:map[name:Project Name 1]], got %s", reqBody.GroupProperties)
 			}

featureflags.go

@@ -311,7 +311,7 @@ func (poller *FeatureFlagsPoller) computeFlagLocally(
 		groupName, exists := poller.groups[fmt.Sprintf("%d", *flag.Filters.AggregationGroupTypeIndex)]
 
 		if !exists {
-			errMessage := "Flag has unknown group type index"
+			errMessage := "flag has unknown group type index"
 			return nil, errors.New(errMessage)
 		}
 
@@ -467,7 +467,7 @@ func matchCohort(property FlagProperty, properties Properties, cohorts map[strin
 	cohortId := fmt.Sprint(property.Value)
 	propertyGroup, ok := cohorts[cohortId]
 	if !ok {
-		return false, fmt.Errorf("Can't match cohort: cohort %s not found", cohortId)
+		return false, fmt.Errorf("can't match cohort: cohort %s not found", cohortId)
 	}
 
 	return matchPropertyGroup(propertyGroup, properties, cohorts)
@@ -578,7 +578,7 @@ func matchProperty(property FlagProperty, properties Properties) (bool, error) {
 		return false, &InconclusiveMatchError{"Can't match properties with operator is_not_set"}
 	}
 
-	override_value, _ := properties[key]
+	override_value := properties[key]
 
 	if operator == "exact" {
 		switch t := value.(type) {
@@ -637,7 +637,7 @@ func matchProperty(property FlagProperty, properties Properties) (bool, error) {
 			valueString = strconv.Itoa(valueInt)
 			r, err = regexp.Compile(valueString)
 		} else {
-			errMessage := "Regex expression not allowed"
+			errMessage := "regex expression not allowed"
 			return false, errors.New(errMessage)
 		}
 
@@ -653,7 +653,7 @@ func matchProperty(property FlagProperty, properties Properties) (bool, error) {
 			valueString = strconv.Itoa(valueInt)
 			match = r.MatchString(valueString)
 		} else {
-			errMessage := "Value type not supported"
+			errMessage := "value type not supported"
 			return false, errors.New(errMessage)
 		}
 
@@ -707,12 +707,12 @@ func matchProperty(property FlagProperty, properties Properties) (bool, error) {
 func validateOrderable(firstValue interface{}, secondValue interface{}) (float64, float64, error) {
 	convertedFirstValue, err := interfaceToFloat(firstValue)
 	if err != nil {
-		errMessage := "Value 1 is not orderable"
+		errMessage := "value 1 is not orderable"
 		return 0, 0, errors.New(errMessage)
 	}
 	convertedSecondValue, err := interfaceToFloat(secondValue)
 	if err != nil {
-		errMessage := "Value 2 is not orderable"
+		errMessage := "value 2 is not orderable"
 		return 0, 0, errors.New(errMessage)
 	}
 
@@ -809,7 +809,7 @@ func (poller *FeatureFlagsPoller) GetFeatureFlags() ([]FeatureFlag, error) {
 	_, closed := <-poller.loaded
 	if closed && poller.featureFlags == nil {
 		// There was an error with initial flag fetching
-		return nil, fmt.Errorf("Flags were not successfully fetched yet")
+		return nil, fmt.Errorf("flags were not successfully fetched yet")
 	}
 
 	return poller.featureFlags, nil

posthog.go

@@ -8,6 +8,7 @@ import (
 	"io"
 	"io/ioutil"
 	"net/http"
+	"net/url"
 	"sync"
 	"time"
 )
@@ -44,14 +45,19 @@ type Client interface {
 	// if the given flag is on or off for the user
 	GetFeatureFlag(FeatureFlagPayload) (interface{}, error)
 	//
+	// Get all flags - returns all flags for a user
+	GetAllFlags(FeatureFlagPayloadNoKey) (map[string]interface{}, error)
+	//
 	// Method forces a reload of feature flags
+	// NB: This is only available when using a PersonalApiKey
 	ReloadFeatureFlags() error
 	//
 	// Get feature flags - for testing only
+	// NB: This is only available when using a PersonalApiKey
 	GetFeatureFlags() ([]FeatureFlag, error)
 	//
-	// Get all flags - returns all flags for a user
-	GetAllFlags(FeatureFlagPayloadNoKey) (map[string]interface{}, error)
+	// Get the last captured event
+	GetLastCapturedEvent() *Capture
 }
 
 type client struct {
@@ -79,6 +85,11 @@ type client struct {
 	featureFlagsPoller *FeatureFlagsPoller
 
 	distinctIdsFeatureFlagsReported *SizeLimitedMap
+
+	// Last captured event
+	lastCapturedEvent *Capture
+	// Mutex to protect last captured event
+	lastEventMutex sync.RWMutex
 }
 
 // Instantiate a new client that uses the write key passed as first argument to
@@ -216,6 +227,7 @@ func (c *client) Enqueue(msg Message) (err error) {
 			}
 			m.Properties["$active_feature_flags"] = featureKeys
 		}
+		c.setLastCapturedEvent(m)
 		msg = m
 
 	default:
@@ -238,17 +250,28 @@ func (c *client) Enqueue(msg Message) (err error) {
 	return
 }
 
+func (c *client) setLastCapturedEvent(event Capture) {
+	c.lastEventMutex.Lock()
+	defer c.lastEventMutex.Unlock()
+	c.lastCapturedEvent = &event
+}
+
+func (c *client) GetLastCapturedEvent() *Capture {
+	c.lastEventMutex.RLock()
+	defer c.lastEventMutex.RUnlock()
+	if c.lastCapturedEvent == nil {
+		return nil
+	}
+	// Return a copy to avoid data races
+	eventCopy := *c.lastCapturedEvent
+	return &eventCopy
+}
+
 func (c *client) IsFeatureEnabled(flagConfig FeatureFlagPayload) (interface{}, error) {
 	if err := flagConfig.validate(); err != nil {
 		return false, err
 	}
 
-	if c.featureFlagsPoller == nil {
-		errorMessage := "specifying a PersonalApiKey is required for using feature flags"
-		c.Errorf(errorMessage)
-		return false, errors.New(errorMessage)
-	}
-
 	result, err := c.GetFeatureFlag(flagConfig)
 	if err != nil {
 		return nil, err
@@ -278,12 +301,19 @@ func (c *client) GetFeatureFlag(flagConfig FeatureFlagPayload) (interface{}, err
 		return false, err
 	}
 
-	if c.featureFlagsPoller == nil {
-		errorMessage := "specifying a PersonalApiKey is required for using feature flags"
-		c.Errorf(errorMessage)
-		return "false", errors.New(errorMessage)
+	var flagValue interface{}
+	var err error
+
+	if c.featureFlagsPoller != nil {
+		// get feature flag from the poller, which uses the personal api key
+		// this is only available when using a PersonalApiKey
+		flagValue, err = c.featureFlagsPoller.GetFeatureFlag(flagConfig)
+	} else {
+		// if there's no poller, get the feature flag from the decide endpoint
+		c.debugf("getting feature flag from decide endpoint")
+		flagValue, err = c.getFeatureFlagFromDecide(flagConfig.Key, flagConfig.DistinctId, flagConfig.Groups, flagConfig.PersonProperties, flagConfig.GroupProperties)
 	}
-	flagValue, err := c.featureFlagsPoller.GetFeatureFlag(flagConfig)
+
 	if *flagConfig.SendFeatureFlagEvents && !c.distinctIdsFeatureFlagsReported.contains(flagConfig.DistinctId, flagConfig.Key) {
 		c.Enqueue(Capture{
 			DistinctId: flagConfig.DistinctId,
@@ -296,6 +326,7 @@ func (c *client) GetFeatureFlag(flagConfig FeatureFlagPayload) (interface{}, err
 		})
 		c.distinctIdsFeatureFlagsReported.add(flagConfig.DistinctId, flagConfig.Key)
 	}
+
 	return flagValue, err
 }
 
@@ -314,12 +345,20 @@ func (c *client) GetAllFlags(flagConfig FeatureFlagPayloadNoKey) (map[string]int
 		return nil, err
 	}
 
-	if c.featureFlagsPoller == nil {
-		errorMessage := "specifying a PersonalApiKey is required for using feature flags"
-		c.Errorf(errorMessage)
-		return nil, errors.New(errorMessage)
+	var flagsValue map[string]interface{}
+	var err error
+
+	if c.featureFlagsPoller != nil {
+		// get feature flags from the poller, which uses the personal api key
+		// this is only available when using a PersonalApiKey
+		flagsValue, err = c.featureFlagsPoller.GetAllFlags(flagConfig)
+	} else {
+		// if there's no poller, get the feature flags from the decide endpoint
+		c.debugf("getting all feature flags from decide endpoint")
+		flagsValue, err = c.getAllFeatureFlagsFromDecide(flagConfig.DistinctId, flagConfig.Groups, flagConfig.PersonProperties, flagConfig.GroupProperties)
 	}
-	return c.featureFlagsPoller.GetAllFlags(flagConfig)
+
+	return flagsValue, err
 }
 
 // Close and flush metrics.
@@ -336,7 +375,7 @@ func (c *client) Close() (err error) {
 	return
 }
 
-// Asychronously send a batched requests.
+// Asynchronously send a batched requests.
 func (c *client) sendAsync(msgs []message, wg *sync.WaitGroup, ex *executor) {
 	wg.Add(1)
 
@@ -558,3 +597,77 @@ func (c *client) getFeatureVariants(distinctId string, groups Groups, personProp
 	}
 	return featureVariants, nil
 }
+
+func (c *client) makeDecideRequest(distinctId string, groups Groups, personProperties Properties, groupProperties map[string]Properties) (*DecideResponse, error) {
+	requestData := DecideRequestData{
+		ApiKey:           c.key,
+		DistinctId:       distinctId,
+		Groups:           groups,
+		PersonProperties: personProperties,
+		GroupProperties:  groupProperties,
+	}
+
+	requestDataBytes, err := json.Marshal(requestData)
+	if err != nil {
+		return nil, fmt.Errorf("unable to marshal decide endpoint request data: %v", err)
+	}
+
+	decideEndpoint := "decide/?v=2"
+	url, err := url.Parse(c.Endpoint + "/" + decideEndpoint)
+	if err != nil {
+		return nil, fmt.Errorf("creating url: %v", err)
+	}
+
+	req, err := http.NewRequest("POST", url.String(), bytes.NewReader(requestDataBytes))
+	if err != nil {
+		return nil, fmt.Errorf("creating request: %v", err)
+	}
+
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("User-Agent", "posthog-go (version: "+Version+")")
+
+	res, err := c.http.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("sending request: %v", err)
+	}
+	defer res.Body.Close()
+
+	if res.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("unexpected status code from /decide/: %d", res.StatusCode)
+	}
+
+	resBody, err := ioutil.ReadAll(res.Body)
+	if err != nil {
+		return nil, fmt.Errorf("error reading response from /decide/: %v", err)
+	}
+
+	var decideResponse DecideResponse
+	err = json.Unmarshal(resBody, &decideResponse)
+	if err != nil {
+		return nil, fmt.Errorf("error parsing response from /decide/: %v", err)
+	}
+
+	return &decideResponse, nil
+}
+
+func (c *client) getFeatureFlagFromDecide(key string, distinctId string, groups Groups, personProperties Properties, groupProperties map[string]Properties) (interface{}, error) {
+	decideResponse, err := c.makeDecideRequest(distinctId, groups, personProperties, groupProperties)
+	if err != nil {
+		return nil, err
+	}
+
+	if value, ok := decideResponse.FeatureFlags[key]; ok {
+		return value, nil
+	}
+
+	return false, nil
+}
+
+func (c *client) getAllFeatureFlagsFromDecide(distinctId string, groups Groups, personProperties Properties, groupProperties map[string]Properties) (map[string]interface{}, error) {
+	decideResponse, err := c.makeDecideRequest(distinctId, groups, personProperties, groupProperties)
+	if err != nil {
+		return nil, err
+	}
+
+	return decideResponse.FeatureFlags, nil
+}