| // Copyright (C) MongoDB, Inc. 2017-present. |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); you may |
| // not use this file except in compliance with the License. You may obtain |
| // a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 |
| |
| package driver |
| |
| import ( |
| "context" |
| |
| "github.com/mongodb/mongo-go-driver/bson" |
| "github.com/mongodb/mongo-go-driver/mongo/readpref" |
| "github.com/mongodb/mongo-go-driver/x/mongo/driver/session" |
| "github.com/mongodb/mongo-go-driver/x/mongo/driver/topology" |
| "github.com/mongodb/mongo-go-driver/x/mongo/driver/uuid" |
| "github.com/mongodb/mongo-go-driver/x/network/command" |
| "github.com/mongodb/mongo-go-driver/x/network/description" |
| ) |
| |
| // Read handles the full cycle dispatch and execution of a read command against the provided |
| // topology. |
| func Read( |
| ctx context.Context, |
| cmd command.Read, |
| topo *topology.Topology, |
| selector description.ServerSelector, |
| clientID uuid.UUID, |
| pool *session.Pool, |
| ) (bson.Raw, error) { |
| |
| ss, err := topo.SelectServer(ctx, selector) |
| if err != nil { |
| return nil, err |
| } |
| |
| conn, err := ss.Connection(ctx) |
| if err != nil { |
| return nil, err |
| } |
| defer conn.Close() |
| |
| if cmd.Session != nil && cmd.Session.TransactionRunning() { |
| // When command.read is directly used, this implies an operation level |
| // read preference, so we do not override it with the transaction read pref. |
| err = checkTransactionReadPref(cmd.ReadPref) |
| |
| if err != nil { |
| return nil, err |
| } |
| } |
| |
| // If no explicit session and deployment supports sessions, start implicit session. |
| if cmd.Session == nil && topo.SupportsSessions() { |
| cmd.Session, err = session.NewClientSession(pool, clientID, session.Implicit) |
| if err != nil { |
| return nil, err |
| } |
| defer cmd.Session.EndSession() |
| } |
| |
| return cmd.RoundTrip(ctx, ss.Description(), conn) |
| } |
| |
| func getReadPrefBasedOnTransaction(current *readpref.ReadPref, sess *session.Client) (*readpref.ReadPref, error) { |
| if sess != nil && sess.TransactionRunning() { |
| // Transaction's read preference always takes priority |
| current = sess.CurrentRp |
| err := checkTransactionReadPref(current) |
| if err != nil { |
| return nil, err |
| } |
| } |
| return current, nil |
| } |
| |
| func checkTransactionReadPref(pref *readpref.ReadPref) error { |
| if pref != nil && (pref.Mode() == readpref.SecondaryMode || |
| pref.Mode() == readpref.SecondaryPreferredMode || |
| pref.Mode() == readpref.NearestMode || |
| pref.Mode() == readpref.PrimaryPreferredMode) { |
| return command.ErrNonPrimaryRP |
| } |
| return nil |
| } |