Function connectPreferred

pgconn/pgconn.go:247–310

connectPreferred attempts to connect to the preferred host from connectOneConfigs. The connections are attempted in order. If a connection is successful it is returned. If no connection is successful then all errors are returned. If a connection attempt returns a [NotPreferredError], then that host

(ctx context.Context, config *Config, connectOneConfigs []*connectOneConfig)

// order. If a connection is successful it is returned. If no connection is successful then all errors are returned. If
// a connection attempt returns a [NotPreferredError], then that host will be used if no other hosts are successful.
func connectPreferred(ctx context.Context, config *Config, connectOneConfigs []*connectOneConfig) (*PgConn, []error) {
	octx := ctx
	var allErrors []error

	var fallbackConnectOneConfig *connectOneConfig
	for i, c := range connectOneConfigs {
		// ConnectTimeout restricts the whole connection process.
		if config.ConnectTimeout != 0 {
			// create new context first time or when previous host was different
			if i == 0 || (connectOneConfigs[i].address != connectOneConfigs[i-1].address) {
				var cancel context.CancelFunc
				ctx, cancel = context.WithTimeout(octx, config.ConnectTimeout)
				defer cancel()
			}
		} else {
			ctx = octx
		}

		pgConn, err := connectOne(ctx, config, c, false)
		if pgConn != nil {
			return pgConn, nil
		}

		allErrors = append(allErrors, err)

		var pgErr *PgError
		if errors.As(err, &pgErr) {
			// pgx will try next host even if libpq does not in certain cases (see #2246)
			// consider change for the next major version

			const ERRCODE_INVALID_PASSWORD = "28P01"
			const ERRCODE_INVALID_CATALOG_NAME = "3D000"   // db does not exist
			const ERRCODE_INSUFFICIENT_PRIVILEGE = "42501" // missing connect privilege

			// auth failed due to invalid password, db does not exist or user has no permission
			if pgErr.Code == ERRCODE_INVALID_PASSWORD ||
				pgErr.Code == ERRCODE_INVALID_CATALOG_NAME ||
				pgErr.Code == ERRCODE_INSUFFICIENT_PRIVILEGE {
				return nil, allErrors
			}
		}

		var npErr *NotPreferredError
		if errors.As(err, &npErr) {
			fallbackConnectOneConfig = c
		}
	}

	if fallbackConnectOneConfig != nil {
		fallbackCtx := octx
		if config.ConnectTimeout != 0 {
			var cancel context.CancelFunc
			fallbackCtx, cancel = context.WithTimeout(octx, config.ConnectTimeout)
			defer cancel()
		}
		pgConn, err := connectOne(fallbackCtx, config, fallbackConnectOneConfig, true)
		if err == nil {
			return pgConn, nil