func NewMongoCommunityConn()

in common/community_client.go [81:166]
61 lines of code
13 McCabe index (conditional complexity)

func NewMongoCommunityConn(url string, connectMode string, timeout bool, readConcern,
	writeConcern string, sslRootFile string) (*MongoCommunityConn, error) {

	clientOps := options.Client().ApplyURI(url)

	// tls tlsInsecure + tlsCaFile
	if sslRootFile != "" {
		tlsConfig := new(tls.Config)

		err := addCACertFromFile(tlsConfig, sslRootFile)
		if err != nil {
			return nil, fmt.Errorf("load rootCaFile[%v] failed: %v", sslRootFile, err)
		}

		// not check hostname
		tlsConfig.InsecureSkipVerify = true

		clientOps.SetTLSConfig(tlsConfig)
	}

	// read concern
	switch readConcern {
	case ReadWriteConcernDefault:
	default:
		clientOps.SetReadConcern(readconcern.New(readconcern.Level(readConcern)))
	}

	// write concern
	switch writeConcern {
	case ReadWriteConcernMajority:
		clientOps.SetWriteConcern(writeconcern.New(writeconcern.WMajority()))
	}

	// read pref
	readPreference := readpref.Primary()
	switch connectMode {
	case VarMongoConnectModePrimary:
		readPreference = readpref.Primary()
	case VarMongoConnectModeSecondaryPreferred:
		readPreference = readpref.SecondaryPreferred()
	case VarMongoConnectModeStandalone:
		// TODO, no standalone, choose nearest
		fallthrough
	case VarMongoConnectModeNearset:
		readPreference = readpref.Nearest()
	default:
		readPreference = readpref.Primary()
	}
	clientOps.SetReadPreference(readPreference)

	// set timeout
	if !timeout {
		clientOps.SetConnectTimeout(0)
	} else {
		clientOps.SetConnectTimeout(20 * time.Minute)
	}

	//clientOps.SetMaxConnIdleTime(1 * time.Hour)

	// create default context
	ctx := context.Background()

	// connect
	client, err := mongo.NewClient(clientOps)
	if err != nil {
		return nil, fmt.Errorf("new client failed: %v", err)
	}
	if err := client.Connect(ctx); err != nil {
		return nil, fmt.Errorf("connect to %s failed: %v", BlockMongoUrlPassword(url, "***"), err)
	}

	// ping
	if err = client.Ping(ctx, clientOps.ReadPreference); err != nil {
		return nil, fmt.Errorf("ping to %v failed: %v\n"+
			"If Mongo Server is standalone(single node) Or conn address is different with mongo server address"+
			" try atandalone mode by mongodb://ip:port/admin?connect=direct",
			BlockMongoUrlPassword(url, "***"), err)
	}

	LOG.Info("New session to %s successfully", BlockMongoUrlPassword(url, "***"))
	return &MongoCommunityConn{
		Client: client,
		URL:    url,
		ctx:    ctx,
	}, nil
}