[#1085] writecache: allow to ignore errors during iteration

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

pkg/local_object_storage/writecache/iterate.go

@@ -12,10 +12,28 @@ import (
 // ErrNoDefaultBucket is returned by IterateDB when default bucket for objects is missing.
 var ErrNoDefaultBucket = errors.New("no default bucket")
 
+// IterationPrm contains iteration parameters.
+type IterationPrm struct {
+	handler      func([]byte) error
+	ignoreErrors bool
+}
+
+// WithHandler sets a callback to be executed on every object.
+func (p *IterationPrm) WithHandler(f func([]byte) error) *IterationPrm {
+	p.handler = f
+	return p
+}
+
+// WithIgnoreErrors sets a flag indicating that errors should be ignored.
+func (p *IterationPrm) WithIgnoreErrors(ignore bool) *IterationPrm {
+	p.ignoreErrors = ignore
+	return p
+}
+
 // Iterate iterates over all objects present in write cache.
 // This is very difficult to do correctly unless write-cache is put in read-only mode.
 // Thus we silently fail if shard is not in read-only mode to avoid reporting misleading results.
-func (c *cache) Iterate(f func([]byte) error) error {
+func (c *cache) Iterate(prm *IterationPrm) error {
 	c.modeMtx.RLock()
 	defer c.modeMtx.RUnlock()
 	if c.mode != ModeReadOnly {
@@ -28,7 +46,7 @@ func (c *cache) Iterate(f func([]byte) error) error {
 			if _, ok := c.flushed.Peek(string(k)); ok {
 				return nil
 			}
-			return f(data)
+			return prm.handler(data)
 		})
 	})
 	if err != nil {
@@ -39,8 +57,8 @@ func (c *cache) Iterate(f func([]byte) error) error {
 		if _, ok := c.flushed.Peek(addr.String()); ok {
 			return nil
 		}
-		return f(data)
-	}))
+		return prm.handler(data)
+	}).WithIgnoreErrors(prm.ignoreErrors))
 }
 
 // IterateDB iterates over all objects stored in bbolt.DB instance and passes them to f until error return.