log: simplify fix for datarace when rotating files

log/handler.go

@@ -158,17 +158,10 @@ func RotatingFileHandler(path string, limit uint, formatter Format) (Handler, er
 	if counter == nil {
 		counter = new(countingWriter)
 	}
-	h := FuncHandler(func(r *Record) error {
-		_, err := counter.Write(formatter.Format(r))
-		return err
-	})
+	h := StreamHandler(counter, formatter)
 
 	return FuncHandler(func(r *Record) error {
-		// lazy evaluate, this needs no lock.
-		lazyEvaluateRecord(r)
-
 		counter.Lock()
-		defer counter.Unlock()
 		if counter.count > limit {
 			counter.Close()
 			counter.w = nil
@@ -180,11 +173,13 @@ func RotatingFileHandler(path string, limit uint, formatter Format) (Handler, er
 				0600,
 			)
 			if err != nil {
+				counter.Unlock()
 				return err
 			}
 			counter.w = f
 			counter.count = 0
 		}
+		counter.Unlock()
 		return h.Log(r)
 	}), nil
 }
@@ -392,33 +387,31 @@ func BufferedHandler(bufSize int, h Handler) Handler {
 // it if you write your own Handler.
 func LazyHandler(h Handler) Handler {
 	return FuncHandler(func(r *Record) error {
-		lazyEvaluateRecord(r)
-		return h.Log(r)
-	})
-}
-
-func lazyEvaluateRecord(r *Record) {
-	// go through the values (odd indices) and reassign
-	// the values of any lazy fn to the result of its execution
-	hadErr := false
-	for i := 1; i < len(r.Ctx); i += 2 {
-		if lz, ok := r.Ctx[i].(Lazy); ok {
-			v, err := evaluateLazy(lz)
-			if err != nil {
-				hadErr = true
-				r.Ctx[i] = err
-			} else {
-				if cs, ok := v.(stack.CallStack); ok {
-					v = cs.TrimBelow(r.Call).TrimRuntime()
+		// go through the values (odd indices) and reassign
+		// the values of any lazy fn to the result of its execution
+		hadErr := false
+		for i := 1; i < len(r.Ctx); i += 2 {
+			lz, ok := r.Ctx[i].(Lazy)
+			if ok {
+				v, err := evaluateLazy(lz)
+				if err != nil {
+					hadErr = true
+					r.Ctx[i] = err
+				} else {
+					if cs, ok := v.(stack.CallStack); ok {
+						v = cs.TrimBelow(r.Call).TrimRuntime()
+					}
+					r.Ctx[i] = v
 				}
-				r.Ctx[i] = v
 			}
 		}
-	}
 
-	if hadErr {
-		r.Ctx = append(r.Ctx, errorKey, "bad lazy")
-	}
+		if hadErr {
+			r.Ctx = append(r.Ctx, errorKey, "bad lazy")
+		}
+
+		return h.Log(r)
+	})
 }
 
 func evaluateLazy(lz Lazy) (interface{}, error) {