replication: refactor driving logic (no more explicit state machine)

replication/logic/replication_logic_context.go

@@ -0,0 +1,28 @@
+package logic
+
+import (
+	"context"
+
+	"github.com/zrepl/zrepl/logger"
+)
+
+type contextKey int
+
+const (
+	contextKeyLog contextKey = iota
+)
+
+type Logger = logger.Logger
+
+func WithLogger(ctx context.Context, l Logger) context.Context {
+	ctx = context.WithValue(ctx, contextKeyLog, l)
+	return ctx
+}
+
+func getLogger(ctx context.Context) Logger {
+	l, ok := ctx.Value(contextKeyLog).(Logger)
+	if !ok {
+		l = logger.NewNullLogger()
+	}
+	return l
+}