Results.Close should return error (#230)

Results.Close should always return error. Even if it is not currently used for anything, having the ability to return error allows for higher level functionality to handle error conditiond that may be important for future code. This was removed in v0.8.0, as it did not serve a functional purpose.

Author: gammazero

Diff for: keytransform/keytransform.go

@@ -94,8 +94,8 @@ func (d *Datastore) Query(ctx context.Context, q dsq.Query) (dsq.Results, error)
 			}
 			return r, true
 		},
-		Close: func() {
-			cqr.Close()
+		Close: func() error {
+			return cqr.Close()
 		},
 	})
 	return dsq.NaiveQueryApply(nq, qr), nil

Diff for: mount/mount.go

@@ -140,11 +140,12 @@ func (h *querySet) Pop() interface{} {
 	return last
 }
 
-func (h *querySet) close() {
+func (h *querySet) close() error {
 	for _, qr := range h.heads {
 		qr.results.Close()
 	}
 	h.heads = nil
+	return nil
 }
 
 func (h *querySet) addResults(mount ds.Key, results query.Results) {

Diff for: query/query.go

@@ -153,7 +153,7 @@ type Results interface {
 	Next() <-chan Result      // returns a channel to wait for the next result
 	NextSync() (Result, bool) // blocks and waits to return the next result, second parameter returns false when results are exhausted
 	Rest() ([]Entry, error)   // waits till processing finishes, returns all entries at once.
-	Close()                   // client may call Close to signal early exit
+	Close() error             // client may call Close to signal early exit
 	Done() <-chan struct{}    // signals that Results is closed
 }
 
@@ -187,9 +187,10 @@ func (r *results) Rest() ([]Entry, error) {
 	return es, nil
 }
 
-func (r *results) Close() {
+func (r *results) Close() error {
 	r.cancel()
 	<-r.closed
+	return nil
 }
 
 func (r *results) Query() Query {
@@ -273,17 +274,17 @@ func ResultsFromIterator(q Query, iter Iterator) Results {
 	}
 }
 
-func noopClose() {}
+func noopClose() error { return nil }
 
 type Iterator struct {
 	Next  func() (Result, bool)
-	Close func() // note: might be called more than once
+	Close func() error // note: might be called more than once
 }
 
 type resultsIter struct {
 	query   Query
 	next    func() (Result, bool)
-	close   func()
+	close   func() error
 	results *results
 }
 
@@ -318,14 +319,15 @@ func (r *resultsIter) Rest() ([]Entry, error) {
 	return es, nil
 }
 
-func (r *resultsIter) Close() {
+func (r *resultsIter) Close() error {
 	if r.results != nil {
 		// Close results collector. It will call r.close().
 		r.results.Close()
 	} else {
 		// Call r.close() since there is no collector to call it when closed.
 		r.close()
 	}
+	return nil
 }
 
 func (r *resultsIter) Query() Query {

Diff for: query/query_impl.go

@@ -18,8 +18,8 @@ func NaiveFilter(qr Results, filter Filter) Results {
 				}
 			}
 		},
-		Close: func() {
-			qr.Close()
+		Close: func() error {
+			return qr.Close()
 		},
 	})
 }
@@ -43,12 +43,12 @@ func NaiveLimit(qr Results, limit int) Results {
 			limit--
 			return qr.NextSync()
 		},
-		Close: func() {
+		Close: func() error {
 			if closed {
-				return
+				return nil
 			}
 			closed = true
-			qr.Close()
+			return qr.Close()
 		},
 	})
 }
@@ -65,8 +65,8 @@ func NaiveOffset(qr Results, offset int) Results {
 			}
 			return qr.NextSync()
 		},
-		Close: func() {
-			qr.Close()
+		Close: func() error {
+			return qr.Close()
 		},
 	})
 }

Diff for: query/query_test.go

@@ -200,7 +200,7 @@ func TestResultsFromIteratorNoClose(t *testing.T) {
 	testResultsFromIterator(t, getKeysViaChan, nil)
 }
 
-func testResultsFromIterator(t *testing.T, getKeys func(rs Results) []string, close func()) {
+func testResultsFromIterator(t *testing.T, getKeys func(rs Results) []string, close func() error) {
 	i := 0
 	results := ResultsFromIterator(Query{}, Iterator{
 		Next: func() (Result, bool) {
@@ -221,8 +221,9 @@ func testResultsFromIterator(t *testing.T, getKeys func(rs Results) []string, cl
 
 func testResultsFromIteratorWClose(t *testing.T, getKeys func(rs Results) []string) {
 	closeCalled := 0
-	testResultsFromIterator(t, getKeys, func() {
+	testResultsFromIterator(t, getKeys, func() error {
 		closeCalled++
+		return nil
 	})
 	if closeCalled != 1 {
 		t.Errorf("close called %d times, expect it to be called just once", closeCalled)