Always defer *sql.Rows.Close and consult with Err (#844)

* Always defer *sql.Rows.Close and consult with Err

database/sql.Rows.Next() makes sure to call Close only after exhausting
result rows which would NOT happen when returning early from a bad Scan.
Close being idempotent makes it a great candidate to get always deferred
regardless of what happens later on the result set.

This change also makes sure call Err() after exhausting Next() and
propagate non-nil results from it as the documentation advises.

Closes #764

Signed-off-by: Kiril Vladimiroff <kiril@vladimiroff.org>

* Override named result parameters in last returns

Signed-off-by: Kiril Vladimiroff <kiril@vladimiroff.org>

* Do the same over new changes that got merged

Signed-off-by: Kiril Vladimiroff <kiril@vladimiroff.org>

Co-authored-by: Neil Alexander <neilalexander@users.noreply.github.com>

clientapi/auth/storage/accounts/account_data_table.go

@@ -90,6 +90,7 @@ func (s *accountDataStatements) selectAccountData(
 	if err != nil {
 		return
 	}
+	defer rows.Close() // nolint: errcheck
 
 	global = []gomatrixserverlib.ClientEvent{}
 	rooms = make(map[string][]gomatrixserverlib.ClientEvent)
@@ -114,8 +115,7 @@ func (s *accountDataStatements) selectAccountData(
 			global = append(global, ac)
 		}
 	}
-
-	return
+	return global, rooms, rows.Err()
 }
 
 func (s *accountDataStatements) selectAccountDataByType(

clientapi/auth/storage/accounts/membership_table.go

@@ -122,11 +122,10 @@ func (s *membershipStatements) selectMembershipsByLocalpart(
 	for rows.Next() {
 		var m authtypes.Membership
 		m.Localpart = localpart
-		if err := rows.Scan(&m.RoomID, &m.EventID); err != nil {
-			return nil, err
+		if err = rows.Scan(&m.RoomID, &m.EventID); err != nil {
+			return
 		}
 		memberships = append(memberships, m)
 	}
-
-	return
+	return memberships, rows.Err()
 }

clientapi/auth/storage/accounts/threepid_table.go

@@ -97,6 +97,7 @@ func (s *threepidStatements) selectThreePIDsForLocalpart(
 	if err != nil {
 		return
 	}
+	defer rows.Close() // nolint: errcheck
 
 	threepids = []authtypes.ThreePID{}
 	for rows.Next() {
@@ -110,8 +111,7 @@ func (s *threepidStatements) selectThreePIDsForLocalpart(
 			Medium:  medium,
 		})
 	}
-
-	return
+	return threepids, rows.Err()
 }
 
 func (s *threepidStatements) insertThreePID(

clientapi/auth/storage/devices/devices_table.go

@@ -226,6 +226,7 @@ func (s *devicesStatements) selectDevicesByLocalpart(
 	if err != nil {
 		return devices, err
 	}
+	defer rows.Close() // nolint: errcheck
 
 	for rows.Next() {
 		var dev authtypes.Device
@@ -237,5 +238,5 @@ func (s *devicesStatements) selectDevicesByLocalpart(
 		devices = append(devices, dev)
 	}
 
-	return devices, nil
+	return devices, rows.Err()
 }