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vendor/go.mongodb.org/mongo-driver/x/mongo/driverlegacy/read.go

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+// 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 driverlegacy
+
+import (
+	"context"
+
+	"go.mongodb.org/mongo-driver/bson"
+	"go.mongodb.org/mongo-driver/mongo/readpref"
+	"go.mongodb.org/mongo-driver/x/mongo/driver/description"
+	"go.mongodb.org/mongo-driver/x/mongo/driver/session"
+	"go.mongodb.org/mongo-driver/x/mongo/driver/topology"
+	"go.mongodb.org/mongo-driver/x/mongo/driver/uuid"
+	"go.mongodb.org/mongo-driver/x/network/command"
+)
+
+// 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) {
+
+	if cmd.Session != nil && cmd.Session.PinnedServer != nil {
+		selector = cmd.Session.PinnedServer
+	}
+	ss, err := topo.SelectServerLegacy(ctx, selector)
+	if err != nil {
+		return nil, err
+	}
+
+	conn, err := ss.ConnectionLegacy(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
+}