--- /dev/null
+// Copyright (c) 2012, Suryandaru Triandana <syndtr@gmail.com>
+// All rights reserved.
+//
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Package iterator provides interface and implementation to traverse over
+// contents of a database.
+package iterator
+
+import (
+ "errors"
+
+ "github.com/syndtr/goleveldb/leveldb/util"
+)
+
+var (
+ ErrIterReleased = errors.New("leveldb/iterator: iterator released")
+)
+
+// IteratorSeeker is the interface that wraps the 'seeks method'.
+type IteratorSeeker interface {
+ // First moves the iterator to the first key/value pair. If the iterator
+ // only contains one key/value pair then First and Last would moves
+ // to the same key/value pair.
+ // It returns whether such pair exist.
+ First() bool
+
+ // Last moves the iterator to the last key/value pair. If the iterator
+ // only contains one key/value pair then First and Last would moves
+ // to the same key/value pair.
+ // It returns whether such pair exist.
+ Last() bool
+
+ // Seek moves the iterator to the first key/value pair whose key is greater
+ // than or equal to the given key.
+ // It returns whether such pair exist.
+ //
+ // It is safe to modify the contents of the argument after Seek returns.
+ Seek(key []byte) bool
+
+ // Next moves the iterator to the next key/value pair.
+ // It returns whether the iterator is exhausted.
+ Next() bool
+
+ // Prev moves the iterator to the previous key/value pair.
+ // It returns whether the iterator is exhausted.
+ Prev() bool
+}
+
+// CommonIterator is the interface that wraps common iterator methods.
+type CommonIterator interface {
+ IteratorSeeker
+
+ // util.Releaser is the interface that wraps basic Release method.
+ // When called Release will releases any resources associated with the
+ // iterator.
+ util.Releaser
+
+ // util.ReleaseSetter is the interface that wraps the basic SetReleaser
+ // method.
+ util.ReleaseSetter
+
+ // TODO: Remove this when ready.
+ Valid() bool
+
+ // Error returns any accumulated error. Exhausting all the key/value pairs
+ // is not considered to be an error.
+ Error() error
+}
+
+// Iterator iterates over a DB's key/value pairs in key order.
+//
+// When encounter an error any 'seeks method' will return false and will
+// yield no key/value pairs. The error can be queried by calling the Error
+// method. Calling Release is still necessary.
+//
+// An iterator must be released after use, but it is not necessary to read
+// an iterator until exhaustion.
+// Also, an iterator is not necessarily safe for concurrent use, but it is
+// safe to use multiple iterators concurrently, with each in a dedicated
+// goroutine.
+type Iterator interface {
+ CommonIterator
+
+ // Key returns the key of the current key/value pair, or nil if done.
+ // The caller should not modify the contents of the returned slice, and
+ // its contents may change on the next call to any 'seeks method'.
+ Key() []byte
+
+ // Value returns the key of the current key/value pair, or nil if done.
+ // The caller should not modify the contents of the returned slice, and
+ // its contents may change on the next call to any 'seeks method'.
+ Value() []byte
+}
+
+// ErrorCallbackSetter is the interface that wraps basic SetErrorCallback
+// method.
+//
+// ErrorCallbackSetter implemented by indexed and merged iterator.
+type ErrorCallbackSetter interface {
+ // SetErrorCallback allows set an error callback of the corresponding
+ // iterator. Use nil to clear the callback.
+ SetErrorCallback(f func(err error))
+}
+
+type emptyIterator struct {
+ util.BasicReleaser
+ err error
+}
+
+func (i *emptyIterator) rErr() {
+ if i.err == nil && i.Released() {
+ i.err = ErrIterReleased
+ }
+}
+
+func (*emptyIterator) Valid() bool { return false }
+func (i *emptyIterator) First() bool { i.rErr(); return false }
+func (i *emptyIterator) Last() bool { i.rErr(); return false }
+func (i *emptyIterator) Seek(key []byte) bool { i.rErr(); return false }
+func (i *emptyIterator) Next() bool { i.rErr(); return false }
+func (i *emptyIterator) Prev() bool { i.rErr(); return false }
+func (*emptyIterator) Key() []byte { return nil }
+func (*emptyIterator) Value() []byte { return nil }
+func (i *emptyIterator) Error() error { return i.err }
+
+// NewEmptyIterator creates an empty iterator. The err parameter can be
+// nil, but if not nil the given err will be returned by Error method.
+func NewEmptyIterator(err error) Iterator {
+ return &emptyIterator{err: err}
+}
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