Don't overwrite global err before return (#1293)

Signed-off-by: Olivier Charvin <git@olivier.pfad.fr>

appservice/storage/postgres/appservice_events_table.go

@@ -111,19 +111,19 @@ func (s *eventsStatements) selectEventsByApplicationServiceID(
 	eventsRemaining bool,
 	err error,
 ) {
-	// Retrieve events from the database. Unsuccessfully sent events first
-	eventRows, err := s.selectEventsByApplicationServiceIDStmt.QueryContext(ctx, applicationServiceID)
-	if err != nil {
-		return
-	}
 	defer func() {
-		err = eventRows.Close()
 		if err != nil {
 			log.WithFields(log.Fields{
 				"appservice": applicationServiceID,
 			}).WithError(err).Fatalf("appservice unable to select new events to send")
 		}
 	}()
+	// Retrieve events from the database. Unsuccessfully sent events first
+	eventRows, err := s.selectEventsByApplicationServiceIDStmt.QueryContext(ctx, applicationServiceID)
+	if err != nil {
+		return
+	}
+	defer checkNamedErr(eventRows.Close, &err)
 	events, maxID, txnID, eventsRemaining, err = retrieveEvents(eventRows, limit)
 	if err != nil {
 		return
@@ -132,6 +132,13 @@ func (s *eventsStatements) selectEventsByApplicationServiceID(
 	return
 }
 
+// checkNamedErr calls fn and overwrite err if it was nil and fn returned non-nil
+func checkNamedErr(fn func() error, err *error) {
+	if e := fn(); e != nil && *err == nil {
+		*err = e
+	}
+}
+
 func retrieveEvents(eventRows *sql.Rows, limit int) (events []gomatrixserverlib.HeaderedEvent, maxID, txnID int, eventsRemaining bool, err error) {
 	// Get current time for use in calculating event age
 	nowMilli := time.Now().UnixNano() / int64(time.Millisecond)

appservice/storage/sqlite3/appservice_events_table.go

@@ -116,19 +116,19 @@ func (s *eventsStatements) selectEventsByApplicationServiceID(
 	eventsRemaining bool,
 	err error,
 ) {
-	// Retrieve events from the database. Unsuccessfully sent events first
-	eventRows, err := s.selectEventsByApplicationServiceIDStmt.QueryContext(ctx, applicationServiceID)
-	if err != nil {
-		return
-	}
 	defer func() {
-		err = eventRows.Close()
 		if err != nil {
 			log.WithFields(log.Fields{
 				"appservice": applicationServiceID,
 			}).WithError(err).Fatalf("appservice unable to select new events to send")
 		}
 	}()
+	// Retrieve events from the database. Unsuccessfully sent events first
+	eventRows, err := s.selectEventsByApplicationServiceIDStmt.QueryContext(ctx, applicationServiceID)
+	if err != nil {
+		return
+	}
+	defer checkNamedErr(eventRows.Close, &err)
 	events, maxID, txnID, eventsRemaining, err = retrieveEvents(eventRows, limit)
 	if err != nil {
 		return
@@ -137,6 +137,13 @@ func (s *eventsStatements) selectEventsByApplicationServiceID(
 	return
 }
 
+// checkNamedErr calls fn and overwrite err if it was nil and fn returned non-nil
+func checkNamedErr(fn func() error, err *error) {
+	if e := fn(); e != nil && *err == nil {
+		*err = e
+	}
+}
+
 func retrieveEvents(eventRows *sql.Rows, limit int) (events []gomatrixserverlib.HeaderedEvent, maxID, txnID int, eventsRemaining bool, err error) {
 	// Get current time for use in calculating event age
 	nowMilli := time.Now().UnixNano() / int64(time.Millisecond)

appservice/workers/transaction_scheduler.go

@@ -101,6 +101,9 @@ func worker(db storage.Database, ws types.ApplicationServiceWorkerState) {
 		// Backoff if the application service does not respond
 		err = send(client, ws.AppService, txnID, transactionJSON)
 		if err != nil {
+			log.WithFields(log.Fields{
+				"appservice": ws.AppService.ID,
+			}).WithError(err).Error("unable to send event")
 			// Backoff
 			backoff(&ws, err)
 			continue
@@ -207,7 +210,7 @@ func send(
 	appservice config.ApplicationService,
 	txnID int,
 	transaction []byte,
-) error {
+) (err error) {
 	// PUT a transaction to our AS
 	// https://matrix.org/docs/spec/application_service/r0.1.2#put-matrix-app-v1-transactions-txnid
 	address := fmt.Sprintf("%s/transactions/%d?access_token=%s", appservice.URL, txnID, url.QueryEscape(appservice.HSToken))
@@ -220,14 +223,7 @@ func send(
 	if err != nil {
 		return err
 	}
-	defer func() {
-		err := resp.Body.Close()
-		if err != nil {
-			log.WithFields(log.Fields{
-				"appservice": appservice.ID,
-			}).WithError(err).Error("unable to close response body from application service")
-		}
-	}()
+	defer checkNamedErr(resp.Body.Close, &err)
 
 	// Check the AS received the events correctly
 	if resp.StatusCode != http.StatusOK {
@@ -237,3 +233,10 @@ func send(
 
 	return nil
 }
+
+// checkNamedErr calls fn and overwrite err if it was nil and fn returned non-nil
+func checkNamedErr(fn func() error, err *error) {
+	if e := fn(); e != nil && *err == nil {
+		*err = e
+	}
+}

internal/sqlutil/partition_offset_table.go

@@ -18,8 +18,6 @@ import (
 	"context"
 	"database/sql"
 	"strings"
-
-	"github.com/matrix-org/util"
 )
 
 // A PartitionOffset is the offset into a partition of the input log.
@@ -99,26 +97,28 @@ func (s *PartitionOffsetStatements) SetPartitionOffset(
 // selectPartitionOffsets returns all the partition offsets for the given topic.
 func (s *PartitionOffsetStatements) selectPartitionOffsets(
 	ctx context.Context, topic string,
-) ([]PartitionOffset, error) {
+) (results []PartitionOffset, err error) {
 	rows, err := s.selectPartitionOffsetsStmt.QueryContext(ctx, topic)
 	if err != nil {
 		return nil, err
 	}
-	defer func() {
-		err2 := rows.Close()
-		if err2 != nil {
-			util.GetLogger(ctx).WithError(err2).Error("selectPartitionOffsets: rows.close() failed")
-		}
-	}()
-	var results []PartitionOffset
+	defer checkNamedErr(rows.Close, &err)
 	for rows.Next() {
 		var offset PartitionOffset
-		if err := rows.Scan(&offset.Partition, &offset.Offset); err != nil {
+		if err = rows.Scan(&offset.Partition, &offset.Offset); err != nil {
 			return nil, err
 		}
 		results = append(results, offset)
 	}
-	return results, rows.Err()
+	err = rows.Err()
+	return results, err
+}
+
+// checkNamedErr calls fn and overwrite err if it was nil and fn returned non-nil
+func checkNamedErr(fn func() error, err *error) {
+	if e := fn(); e != nil && *err == nil {
+		*err = e
+	}
 }
 
 // UpsertPartitionOffset updates or inserts the partition offset for the given topic.

internal/sqlutil/sql.go

@@ -38,9 +38,18 @@ type Transaction interface {
 // was applied correctly. For example, 'database is locked' errors in sqlite will happen here.
 func EndTransaction(txn Transaction, succeeded *bool) error {
 	if *succeeded {
-		return txn.Commit() // nolint: errcheck
+		return txn.Commit()
 	} else {
-		return txn.Rollback() // nolint: errcheck
+		return txn.Rollback()
+	}
+}
+
+// EndTransactionWithCheck ends a transaction and overwrites the error pointer if its value was nil.
+// If the transaction succeeded then it is committed, otherwise it is rolledback.
+// Designed to be used with defer (see EndTransaction otherwise).
+func EndTransactionWithCheck(txn Transaction, succeeded *bool, err *error) {
+	if e := EndTransaction(txn, succeeded); e != nil && *err == nil {
+		*err = e
 	}
 }
 
@@ -53,12 +62,7 @@ func WithTransaction(db *sql.DB, fn func(txn *sql.Tx) error) (err error) {
 		return fmt.Errorf("sqlutil.WithTransaction.Begin: %w", err)
 	}
 	succeeded := false
-	defer func() {
-		err2 := EndTransaction(txn, &succeeded)
-		if err == nil && err2 != nil { // failed to commit/rollback
-			err = err2
-		}
-	}()
+	defer EndTransactionWithCheck(txn, &succeeded, &err)
 
 	err = fn(txn)
 	if err != nil {

roomserver/internal/input_latest_events.go

@@ -60,12 +60,7 @@ func (r *RoomserverInternalAPI) updateLatestEvents(
 		return fmt.Errorf("r.DB.GetLatestEventsForUpdate: %w", err)
 	}
 	succeeded := false
-	defer func() {
-		txerr := sqlutil.EndTransaction(updater, &succeeded)
-		if err == nil && txerr != nil {
-			err = txerr
-		}
-	}()
+	defer sqlutil.EndTransactionWithCheck(updater, &succeeded, &err)
 
 	u := latestEventsUpdater{
 		ctx:           ctx,

syncapi/consumers/keychange.go

@@ -95,9 +95,8 @@ func (s *OutputKeyChangeEventConsumer) updateOffset(msg *sarama.ConsumerMessage)
 }
 
 func (s *OutputKeyChangeEventConsumer) onMessage(msg *sarama.ConsumerMessage) error {
-	defer func() {
-		s.updateOffset(msg)
-	}()
+	defer s.updateOffset(msg)
+
 	var output api.DeviceMessage
 	if err := json.Unmarshal(msg.Value, &output); err != nil {
 		// If the message was invalid, log it and move on to the next message in the stream

syncapi/storage/shared/syncserver.go

@@ -455,13 +455,8 @@ func (d *Database) addPDUDeltaToResponse(
 	if err != nil {
 		return nil, err
 	}
-	var succeeded bool
-	defer func() {
-		txerr := sqlutil.EndTransaction(txn, &succeeded)
-		if err == nil && txerr != nil {
-			err = txerr
-		}
-	}()
+	succeeded := false
+	defer sqlutil.EndTransactionWithCheck(txn, &succeeded, &err)
 
 	stateFilter := gomatrixserverlib.DefaultStateFilter() // TODO: use filter provided in request
 
@@ -641,13 +636,8 @@ func (d *Database) getResponseWithPDUsForCompleteSync(
 	if err != nil {
 		return
 	}
-	var succeeded bool
-	defer func() {
-		txerr := sqlutil.EndTransaction(txn, &succeeded)
-		if err == nil && txerr != nil {
-			err = txerr
-		}
-	}()
+	succeeded := false
+	defer sqlutil.EndTransactionWithCheck(txn, &succeeded, &err)
 
 	// Get the current sync position which we will base the sync response on.
 	toPos, err = d.syncPositionTx(ctx, txn)