Make Close() method on Iterators return an error

graph/bolt/all_iterator.go

@@ -174,10 +174,11 @@ func (it *AllIterator) Contains(v graph.Value) bool {
 	return true
 }
 
-func (it *AllIterator) Close() {
+func (it *AllIterator) Close() error {
 	it.result = nil
 	it.buffer = nil
 	it.done = true
+	return nil
 }
 
 func (it *AllIterator) Size() (int64, bool) {

graph/bolt/iterator.go

@@ -106,10 +106,11 @@ func (it *Iterator) Clone() graph.Iterator {
 	return out
 }
 
-func (it *Iterator) Close() {
+func (it *Iterator) Close() error {
 	it.result = nil
 	it.buffer = nil
 	it.done = true
+	return nil
 }
 
 func (it *Iterator) isLiveValue(val []byte) bool {

graph/gaedatastore/iterator.go

@@ -130,12 +130,13 @@ func (it *Iterator) Reset() {
 	it.result = nil
 }
 
-func (it *Iterator) Close() {
+func (it *Iterator) Close() error {
 	it.buffer = nil
 	it.offset = 0
 	it.done = true
 	it.last = ""
 	it.result = nil
+	return nil
 }
 
 func (it *Iterator) Tagger() *graph.Tagger {

graph/iterator.go

@@ -136,7 +136,7 @@ type Iterator interface {
 	Describe() Description
 
 	// Close the iterator and do internal cleanup.
-	Close()
+	Close() error
 
 	// UID returns the unique identifier of the iterator.
 	UID() uint64

graph/iterator/all_iterator.go

@@ -55,7 +55,9 @@ func (it *Int64) Reset() {
 	it.at = it.min
 }
 
-func (it *Int64) Close() {}
+func (it *Int64) Close() error {
+	return nil
+}
 
 func (it *Int64) Clone() graph.Iterator {
 	out := NewInt64(it.min, it.max)

graph/iterator/and_iterator.go

@@ -263,12 +263,22 @@ func (it *And) cleanUp() {}
 // Close this iterator, and, by extension, close the subiterators.
 // Close should be idempotent, and it follows that if it's subiterators
 // follow this contract, the And follows the contract.
-func (it *And) Close() {
+//
+// Note: as this potentially involves closing multiple subiterators, only
+// the first error encountered while closing will be reported (if any).
+func (it *And) Close() error {
 	it.cleanUp()
-	it.primaryIt.Close()
+
+	var ret error
+
+	ret = it.primaryIt.Close()
 	for _, sub := range it.internalIterators {
-		sub.Close()
+		if err := sub.Close(); err != nil && ret != nil {
+			ret = err
+		}
 	}
+
+	return ret
 }
 
 // Register this as an "and" iterator.

graph/iterator/fixed_iterator.go

@@ -63,7 +63,9 @@ func (it *Fixed) Reset() {
 	it.lastIndex = 0
 }
 
-func (it *Fixed) Close() {}
+func (it *Fixed) Close() error {
+	return nil
+}
 
 func (it *Fixed) Tagger() *graph.Tagger {
 	return &it.tags

graph/iterator/hasa_iterator.go

@@ -247,11 +247,17 @@ func (it *HasA) Stats() graph.IteratorStats {
 }
 
 // Close the subiterator, the result iterator (if any) and the HasA.
-func (it *HasA) Close() {
+func (it *HasA) Close() error {
+	var ret error
+
 	if it.resultIt != nil {
-		it.resultIt.Close()
+		ret = it.resultIt.Close()
 	}
-	it.primaryIt.Close()
+	if err := it.primaryIt.Close(); err != nil && ret != nil {
+		ret = err
+	}
+
+	return ret
 }
 
 // Register this iterator as a HasA.

graph/iterator/iterator.go

@@ -114,7 +114,9 @@ func (it *Null) Size() (int64, bool) {
 
 func (it *Null) Reset() {}
 
-func (it *Null) Close() {}
+func (it *Null) Close() error {
+	return nil
+}
 
 // A null iterator costs nothing. Use it!
 func (it *Null) Stats() graph.IteratorStats {

graph/iterator/linksto_iterator.go

@@ -181,9 +181,17 @@ func (it *LinksTo) Result() graph.Value {
 }
 
 // Close our subiterators.
-func (it *LinksTo) Close() {
-	it.nextIt.Close()
-	it.primaryIt.Close()
+func (it *LinksTo) Close() error {
+	var ret error
+
+	if err := it.nextIt.Close(); err != nil && ret != nil {
+		ret = err
+	}
+	if err := it.primaryIt.Close(); err != nil && ret != nil {
+		ret = err
+	}
+
+	return ret
 }
 
 // We won't ever have a new result, but our subiterators might.

graph/iterator/materialize_iterator.go

@@ -69,11 +69,11 @@ func (it *Materialize) Reset() {
 	it.index = -1
 }
 
-func (it *Materialize) Close() {
-	it.subIt.Close()
+func (it *Materialize) Close() error {
 	it.containsMap = nil
 	it.values = nil
 	it.hasRun = false
+	return it.subIt.Close()
 }
 
 func (it *Materialize) Tagger() *graph.Tagger {

graph/iterator/not_iterator.go

@@ -123,9 +123,19 @@ func (it *Not) NextPath() bool {
 	return false
 }
 
-func (it *Not) Close() {
-	it.primaryIt.Close()
-	it.allIt.Close()
+// Close closes the primary and all iterators.  If an error occurs, only the
+// first one will be returned.
+func (it *Not) Close() error {
+	var ret error
+
+	if err := it.primaryIt.Close(); err != nil && ret != nil {
+		ret = err
+	}
+	if err := it.allIt.Close(); err != nil && ret != nil {
+		ret = err
+	}
+
+	return ret
 }
 
 func (it *Not) Type() graph.Type { return graph.Not }

graph/iterator/optional_iterator.go

@@ -57,8 +57,8 @@ func (it *Optional) Reset() {
 	it.lastCheck = false
 }
 
-func (it *Optional) Close() {
-	it.subIt.Close()
+func (it *Optional) Close() error {
+	return it.subIt.Close()
 }
 
 func (it *Optional) Tagger() *graph.Tagger {

graph/iterator/or_iterator.go

@@ -241,12 +241,21 @@ func (it *Or) cleanUp() {}
 
 // Close this graph.iterator, and, by extension, close the subiterators.
 // Close should be idempotent, and it follows that if it's subiterators
-// follow this contract, the And follows the contract.
-func (it *Or) Close() {
+// follow this contract, the Or follows the contract.
+//
+// Note: as this potentially involves closing multiple subiterators, only
+// the first error encountered while closing will be reported (if any).
+func (it *Or) Close() error {
 	it.cleanUp()
+
+	var ret error
 	for _, sub := range it.internalIterators {
-		sub.Close()
+		if err := sub.Close(); err != nil && ret != nil {
+			ret = err
+		}
 	}
+
+	return ret
 }
 
 func (it *Or) Optimize() (graph.Iterator, bool) {

graph/iterator/value_comparison_iterator.go

@@ -92,8 +92,8 @@ func (it *Comparison) doComparison(val graph.Value) bool {
 	}
 }
 
-func (it *Comparison) Close() {
-	it.subIt.Close()
+func (it *Comparison) Close() error {
+	return it.subIt.Close()
 }
 
 func RunIntOp(a int64, op Operator, b int64) bool {

graph/leveldb/all_iterator.go

@@ -145,11 +145,12 @@ func (it *AllIterator) Contains(v graph.Value) bool {
 	return true
 }
 
-func (it *AllIterator) Close() {
+func (it *AllIterator) Close() error {
 	if it.open {
 		it.iter.Release()
 		it.open = false
 	}
+	return nil
 }
 
 func (it *AllIterator) Size() (int64, bool) {

graph/leveldb/iterator.go

@@ -109,11 +109,12 @@ func (it *Iterator) Clone() graph.Iterator {
 	return out
 }
 
-func (it *Iterator) Close() {
+func (it *Iterator) Close() error {
 	if it.open {
 		it.iter.Release()
 		it.open = false
 	}
+	return nil
 }
 
 func (it *Iterator) isLiveValue(val []byte) bool {

graph/memstore/iterator.go

@@ -105,7 +105,9 @@ func (it *Iterator) Clone() graph.Iterator {
 	return m
 }
 
-func (it *Iterator) Close() {}
+func (it *Iterator) Close() error {
+	return nil
+}
 
 func (it *Iterator) checkValid(index int64) bool {
 	return it.qs.log[index].DeletedBy == 0

graph/mongo/iterator.go

@@ -99,8 +99,8 @@ func (it *Iterator) Reset() {
 
 }
 
-func (it *Iterator) Close() {
-	it.iter.Close()
+func (it *Iterator) Close() error {
+	return it.iter.Close()
 }
 
 func (it *Iterator) Tagger() *graph.Tagger {