fix: (feature) Integration with Datadog RUM

exporter/datadogexporter/exporter.go

@@ -0,0 +1,200 @@
+package datadogexporter
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"sync"
+	"time"
+
+	"github.com/thomaspoignant/go-feature-flag/exporter"
+	"github.com/thomaspoignant/go-feature-flag/internal"
+	"github.com/thomaspoignant/go-feature-flag/utils/fflog"
+)
+
+const (
+	// DatadogDefaultSite is the default Datadog site (US1).
+	DatadogDefaultSite = "datadoghq.com"
+	// DatadogDefaultSource is the default source tag for logs.
+	DatadogDefaultSource = "go-feature-flag"
+	// DatadogDefaultService is the default service tag for logs.
+	DatadogDefaultService = "go-feature-flag"
+)
+
+// Exporter sends feature flag evaluation events to Datadog using the HTTP Log intake API.
+// Events are sent as structured logs that can be queried in Datadog Log Explorer
+// and correlated with RUM sessions using user identifiers.
+type Exporter struct {
+	// APIKey is the Datadog API key used for authentication.
+	// This is required and can be obtained from your Datadog account.
+	APIKey string
+
+	// Site is the Datadog site to send data to (e.g., "datadoghq.com", "datadoghq.eu", "us5.datadoghq.com").
+	// Defaults to "datadoghq.com" (US1) if not specified.
+	Site string
+
+	// Source is the source tag for logs. Defaults to "go-feature-flag".
+	Source string
+
+	// Service is the service name for logs. Defaults to "go-feature-flag".
+	Service string
+
+	// Tags is a list of tags to attach to every log entry (e.g., ["env:production", "team:backend"]).
+	Tags []string
+
+	httpClient internal.HTTPClient
+	init       sync.Once
+}
+
+// datadogLogEntry represents a single log entry to send to Datadog.
+type datadogLogEntry struct {
+	// DDSource is the source of the log (integration name).
+	DDSource string `json:"ddsource"`
+	// DDTags is a comma-separated list of tags.
+	DDTags string `json:"ddtags,omitempty"`
+	// Hostname is the name of the originating host.
+	Hostname string `json:"hostname,omitempty"`
+	// Service is the name of the application or service generating the logs.
+	Service string `json:"service,omitempty"`
+	// Message is the log message.
+	Message string `json:"message"`
+	// Timestamp is when the event occurred (ISO8601 format).
+	Timestamp string `json:"timestamp,omitempty"`
+	// FeatureFlag contains the feature flag evaluation details.
+	FeatureFlag datadogFeatureFlag `json:"feature_flag"`
+	// User contains the user context.
+	User datadogUser `json:"usr,omitempty"`
+}
+
+// datadogFeatureFlag represents feature flag data in Datadog's expected format.
+type datadogFeatureFlag struct {
+	// Key is the feature flag key.
+	Key string `json:"key"`
+	// Value is the evaluated value of the feature flag.
+	Value any `json:"value"`
+	// Variation is the variation name that was evaluated.
+	Variation string `json:"variation"`
+	// Version is the version of the flag configuration.
+	Version string `json:"version,omitempty"`
+	// Default indicates if the default value was returned.
+	Default bool `json:"default"`
+}
+
+// datadogUser represents user context for correlation with RUM.
+type datadogUser struct {
+	// ID is the user identifier.
+	ID string `json:"id,omitempty"`
+}
+
+// Export sends feature flag evaluation events to Datadog.
+func (e *Exporter) Export(
+	ctx context.Context,
+	_ *fflog.FFLogger,
+	events []exporter.ExportableEvent,
+) error {
+	e.init.Do(func() {
+		if e.httpClient == nil {
+			e.httpClient = internal.DefaultHTTPClient()
+		}
+		if e.Site == "" {
+			e.Site = DatadogDefaultSite
+		}
+		if e.Source == "" {
+			e.Source = DatadogDefaultSource
+		}
+		if e.Service == "" {
+			e.Service = DatadogDefaultService
+		}
+	})
+
+	if e.APIKey == "" {
+		return fmt.Errorf("datadog exporter: API key is required")
+	}
+
+	hostname, _ := os.Hostname()
+
+	logEntries := make([]datadogLogEntry, 0, len(events))
+	for _, event := range events {
+		featureEvent, ok := event.(exporter.FeatureEvent)
+		if !ok {
+			continue
+		}
+		msg := fmt.Sprintf(
+			"Feature flag '%s' evaluated to '%v' for user '%s'",
+			featureEvent.Key, featureEvent.Value, featureEvent.UserKey)
+		entry := datadogLogEntry{
+			DDSource:  e.Source,
+			DDTags:    e.buildTags(),
+			Hostname:  hostname,
+			Service:   e.Service,
+			Message:   msg,
+			Timestamp: time.Unix(featureEvent.CreationDate, 0).Format(time.RFC3339),
+			FeatureFlag: datadogFeatureFlag{
+				Key:       featureEvent.Key,
+				Value:     featureEvent.Value,
+				Variation: featureEvent.Variation,
+				Version:   featureEvent.Version,
+				Default:   featureEvent.Default,
+			},
+			User: datadogUser{
+				ID: featureEvent.UserKey,
+			},
+		}
+		logEntries = append(logEntries, entry)
+	}
+
+	if len(logEntries) == 0 {
+		return nil
+	}
+
+	payload, err := json.Marshal(logEntries)
+	if err != nil {
+		return fmt.Errorf("datadog exporter: failed to marshal events: %w", err)
+	}
+
+	endpoint := fmt.Sprintf("https://http-intake.logs.%s/api/v2/logs", e.Site)
+	request, err := http.NewRequestWithContext(ctx, http.MethodPost, endpoint, io.NopCloser(bytes.NewReader(payload)))
+	if err != nil {
+		return fmt.Errorf("datadog exporter: failed to create request: %w", err)
+	}
+
+	request.Header.Set("Content-Type", "application/json")
+	request.Header.Set("DD-API-KEY", e.APIKey)
+
+	response, err := e.httpClient.Do(request)
+	if err != nil {
+		return fmt.Errorf("datadog exporter: failed to send request: %w", err)
+	}
+	defer func() { _ = response.Body.Close() }()
+
+	if response.StatusCode >= 400 {
+		body, _ := io.ReadAll(response.Body)
+		return fmt.Errorf("datadog exporter: received HTTP %d: %s", response.StatusCode, string(body))
+	}
+
+	return nil
+}
+
+// buildTags creates a comma-separated string of tags.
+func (e *Exporter) buildTags() string {
+	if len(e.Tags) == 0 {
+		return ""
+	}
+	result := ""
+	for i, tag := range e.Tags {
+		if i > 0 {
+			result += ","
+		}
+		result += tag
+	}
+	return result
+}
+
+// IsBulk returns true because this exporter sends events in bulk.
+func (e *Exporter) IsBulk() bool {
+	return true
+}