snapshot engine in go

flipt-engine-go/.gitignore

@@ -0,0 +1 @@
+.idea

flipt-engine-go/engine.go

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+package flipt_engine_go
+
+import (
+	"context"
+	"errors"
+	"time"
+
+	"go.uber.org/zap"
+)
+
+type Config struct {
+	Enabled    bool
+	Host       string
+	Version    string
+	Timeout    time.Duration
+	Interval   time.Duration
+	Namespaces []string
+}
+
+type Engine struct {
+	cfg      *Config
+	http     *HTTPParser
+	snapshot *Snapshot
+	logger   *zap.Logger
+}
+
+func NewEngine(
+	cfg *Config,
+	http *HTTPParser,
+	snapshot *Snapshot,
+	logger *zap.Logger,
+
+) *Engine {
+	return &Engine{
+		cfg:      cfg,
+		http:     http,
+		snapshot: snapshot,
+		logger:   logger,
+	}
+}
+
+func (r *Engine) Run(ctx context.Context) {
+	defer func() {
+		if p := recover(); p != nil {
+			r.logger.Error("panic occurred in flipt client-side engine", zap.Any("panic", p))
+		}
+	}()
+
+	// initial snapshot
+	err := r.replaceSnapshot(ctx)
+	if err != nil {
+		if errors.Is(err, context.Canceled) {
+			return
+		}
+		r.logger.Error("replace snapshot", zap.Error(err))
+	}
+
+	ticker := time.NewTicker(r.cfg.Interval)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-ticker.C:
+			err := r.replaceSnapshot(ctx)
+			if err != nil {
+				if errors.Is(err, context.Canceled) {
+					return
+				}
+				r.logger.Error("replace snapshot", zap.Error(err))
+			}
+		}
+	}
+}
+
+func (r *Engine) replaceSnapshot(ctx context.Context) error {
+	r.snapshot.cleanStore() // clear from memory before making a backup
+
+	for _, namespace := range r.cfg.Namespaces {
+		response, err := r.http.Do(ctx, namespace)
+		if err != nil {
+			return err
+		}
+
+		doc, err := r.http.Parse(response)
+		if err != nil {
+			return err
+		}
+
+		evalNamespace := r.snapshot.makeSnapshot(doc)
+		r.snapshot.replaceStore(evalNamespace)
+	}
+
+	return nil
+}

flipt-engine-go/errors.go

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+package flipt_engine_go
+
+import (
+	"errors"
+)
+
+var (
+	ErrNotFound = errors.New("not found")
+	ErrInvalid  = errors.New("invalid")
+)