--- /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
+
+import (
+ "github.com/syndtr/goleveldb/leveldb/comparer"
+ "github.com/syndtr/goleveldb/leveldb/errors"
+ "github.com/syndtr/goleveldb/leveldb/util"
+)
+
+type dir int
+
+const (
+ dirReleased dir = iota - 1
+ dirSOI
+ dirEOI
+ dirBackward
+ dirForward
+)
+
+type mergedIterator struct {
+ cmp comparer.Comparer
+ iters []Iterator
+ strict bool
+
+ keys [][]byte
+ index int
+ dir dir
+ err error
+ errf func(err error)
+ releaser util.Releaser
+}
+
+func assertKey(key []byte) []byte {
+ if key == nil {
+ panic("leveldb/iterator: nil key")
+ }
+ return key
+}
+
+func (i *mergedIterator) iterErr(iter Iterator) bool {
+ if err := iter.Error(); err != nil {
+ if i.errf != nil {
+ i.errf(err)
+ }
+ if i.strict || !errors.IsCorrupted(err) {
+ i.err = err
+ return true
+ }
+ }
+ return false
+}
+
+func (i *mergedIterator) Valid() bool {
+ return i.err == nil && i.dir > dirEOI
+}
+
+func (i *mergedIterator) First() bool {
+ if i.err != nil {
+ return false
+ } else if i.dir == dirReleased {
+ i.err = ErrIterReleased
+ return false
+ }
+
+ for x, iter := range i.iters {
+ switch {
+ case iter.First():
+ i.keys[x] = assertKey(iter.Key())
+ case i.iterErr(iter):
+ return false
+ default:
+ i.keys[x] = nil
+ }
+ }
+ i.dir = dirSOI
+ return i.next()
+}
+
+func (i *mergedIterator) Last() bool {
+ if i.err != nil {
+ return false
+ } else if i.dir == dirReleased {
+ i.err = ErrIterReleased
+ return false
+ }
+
+ for x, iter := range i.iters {
+ switch {
+ case iter.Last():
+ i.keys[x] = assertKey(iter.Key())
+ case i.iterErr(iter):
+ return false
+ default:
+ i.keys[x] = nil
+ }
+ }
+ i.dir = dirEOI
+ return i.prev()
+}
+
+func (i *mergedIterator) Seek(key []byte) bool {
+ if i.err != nil {
+ return false
+ } else if i.dir == dirReleased {
+ i.err = ErrIterReleased
+ return false
+ }
+
+ for x, iter := range i.iters {
+ switch {
+ case iter.Seek(key):
+ i.keys[x] = assertKey(iter.Key())
+ case i.iterErr(iter):
+ return false
+ default:
+ i.keys[x] = nil
+ }
+ }
+ i.dir = dirSOI
+ return i.next()
+}
+
+func (i *mergedIterator) next() bool {
+ var key []byte
+ if i.dir == dirForward {
+ key = i.keys[i.index]
+ }
+ for x, tkey := range i.keys {
+ if tkey != nil && (key == nil || i.cmp.Compare(tkey, key) < 0) {
+ key = tkey
+ i.index = x
+ }
+ }
+ if key == nil {
+ i.dir = dirEOI
+ return false
+ }
+ i.dir = dirForward
+ return true
+}
+
+func (i *mergedIterator) Next() bool {
+ if i.dir == dirEOI || i.err != nil {
+ return false
+ } else if i.dir == dirReleased {
+ i.err = ErrIterReleased
+ return false
+ }
+
+ switch i.dir {
+ case dirSOI:
+ return i.First()
+ case dirBackward:
+ key := append([]byte{}, i.keys[i.index]...)
+ if !i.Seek(key) {
+ return false
+ }
+ return i.Next()
+ }
+
+ x := i.index
+ iter := i.iters[x]
+ switch {
+ case iter.Next():
+ i.keys[x] = assertKey(iter.Key())
+ case i.iterErr(iter):
+ return false
+ default:
+ i.keys[x] = nil
+ }
+ return i.next()
+}
+
+func (i *mergedIterator) prev() bool {
+ var key []byte
+ if i.dir == dirBackward {
+ key = i.keys[i.index]
+ }
+ for x, tkey := range i.keys {
+ if tkey != nil && (key == nil || i.cmp.Compare(tkey, key) > 0) {
+ key = tkey
+ i.index = x
+ }
+ }
+ if key == nil {
+ i.dir = dirSOI
+ return false
+ }
+ i.dir = dirBackward
+ return true
+}
+
+func (i *mergedIterator) Prev() bool {
+ if i.dir == dirSOI || i.err != nil {
+ return false
+ } else if i.dir == dirReleased {
+ i.err = ErrIterReleased
+ return false
+ }
+
+ switch i.dir {
+ case dirEOI:
+ return i.Last()
+ case dirForward:
+ key := append([]byte{}, i.keys[i.index]...)
+ for x, iter := range i.iters {
+ if x == i.index {
+ continue
+ }
+ seek := iter.Seek(key)
+ switch {
+ case seek && iter.Prev(), !seek && iter.Last():
+ i.keys[x] = assertKey(iter.Key())
+ case i.iterErr(iter):
+ return false
+ default:
+ i.keys[x] = nil
+ }
+ }
+ }
+
+ x := i.index
+ iter := i.iters[x]
+ switch {
+ case iter.Prev():
+ i.keys[x] = assertKey(iter.Key())
+ case i.iterErr(iter):
+ return false
+ default:
+ i.keys[x] = nil
+ }
+ return i.prev()
+}
+
+func (i *mergedIterator) Key() []byte {
+ if i.err != nil || i.dir <= dirEOI {
+ return nil
+ }
+ return i.keys[i.index]
+}
+
+func (i *mergedIterator) Value() []byte {
+ if i.err != nil || i.dir <= dirEOI {
+ return nil
+ }
+ return i.iters[i.index].Value()
+}
+
+func (i *mergedIterator) Release() {
+ if i.dir != dirReleased {
+ i.dir = dirReleased
+ for _, iter := range i.iters {
+ iter.Release()
+ }
+ i.iters = nil
+ i.keys = nil
+ if i.releaser != nil {
+ i.releaser.Release()
+ i.releaser = nil
+ }
+ }
+}
+
+func (i *mergedIterator) SetReleaser(releaser util.Releaser) {
+ if i.dir == dirReleased {
+ panic(util.ErrReleased)
+ }
+ if i.releaser != nil && releaser != nil {
+ panic(util.ErrHasReleaser)
+ }
+ i.releaser = releaser
+}
+
+func (i *mergedIterator) Error() error {
+ return i.err
+}
+
+func (i *mergedIterator) SetErrorCallback(f func(err error)) {
+ i.errf = f
+}
+
+// NewMergedIterator returns an iterator that merges its input. Walking the
+// resultant iterator will return all key/value pairs of all input iterators
+// in strictly increasing key order, as defined by cmp.
+// The input's key ranges may overlap, but there are assumed to be no duplicate
+// keys: if iters[i] contains a key k then iters[j] will not contain that key k.
+// None of the iters may be nil.
+//
+// If strict is true the any 'corruption errors' (i.e errors.IsCorrupted(err) == true)
+// won't be ignored and will halt 'merged iterator', otherwise the iterator will
+// continue to the next 'input iterator'.
+func NewMergedIterator(iters []Iterator, cmp comparer.Comparer, strict bool) Iterator {
+ return &mergedIterator{
+ iters: iters,
+ cmp: cmp,
+ strict: strict,
+ keys: make([][]byte, len(iters)),
+ }
+}
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