make GetHosts() query system.local

- remove Conn.localHostInfo() and add Session.hostInfoFromIter()
- add ringDescriber.getLocalHostInfo()
- remove local host from ringDescriber.getClusterPeerInfo() returned slice
- make ringDescriber.GetHosts() call ringDescriber.getLocalHostInfo() in addition to ringDescriber.getClusterPeerInfo()

conn.go

@@ -1651,6 +1651,10 @@ func (c *Conn) querySystemPeers(ctx context.Context, version cassVersion) *Iter
 	}
 }
 
+func (c *Conn) querySystemLocal(ctx context.Context) *Iter {
+	return c.query(ctx, "SELECT * FROM system.local WHERE key='local'")
+}
+
 func (c *Conn) awaitSchemaAgreement(ctx context.Context) (err error) {
 	const localSchemas = "SELECT schema_version FROM system.local WHERE key='local'"
 
@@ -1721,23 +1725,6 @@ func (c *Conn) awaitSchemaAgreement(ctx context.Context) (err error) {
 	return fmt.Errorf("gocql: cluster schema versions not consistent: %+v", schemas)
 }
 
-func (c *Conn) localHostInfo(ctx context.Context) (*HostInfo, error) {
-	row, err := c.query(ctx, "SELECT * FROM system.local WHERE key='local'").rowMap()
-	if err != nil {
-		return nil, err
-	}
-
-	port := c.conn.RemoteAddr().(*net.TCPAddr).Port
-
-	// TODO(zariel): avoid doing this here
-	host, err := c.session.hostInfoFromMap(row, &HostInfo{connectAddress: c.host.connectAddress, port: port})
-	if err != nil {
-		return nil, err
-	}
-
-	return c.session.ring.addOrUpdate(host), nil
-}
-
 var (
 	ErrQueryArgLength    = errors.New("gocql: query argument length mismatch")
 	ErrTimeoutNoResponse = errors.New("gocql: no response received from cassandra within timeout period")

control.go

@@ -269,11 +269,14 @@ type connHost struct {
 
 func (c *controlConn) setupConn(conn *Conn) error {
 	// we need up-to-date host info for the filterHost call below
-	host, err := conn.localHostInfo(context.TODO())
+	iter := conn.querySystemLocal(context.TODO())
+	host, err := c.session.hostInfoFromIter(iter, conn.host.connectAddress, conn.conn.RemoteAddr().(*net.TCPAddr).Port)
 	if err != nil {
 		return err
 	}
 
+	host = c.session.ring.addOrUpdate(host)
+
 	if c.session.cfg.filterHost(host) {
 		return fmt.Errorf("host was filtered: %v", host.ConnectAddress())
 	}

host_source.go

@@ -559,12 +559,54 @@ func (s *Session) hostInfoFromMap(row map[string]interface{}, host *HostInfo) (*
 	return host, nil
 }
 
+func (s *Session) hostInfoFromIter(iter *Iter, connectAddress net.IP, defaultPort int) (*HostInfo, error) {
+	rows, err := iter.SliceMap()
+	if err != nil {
+		// TODO(zariel): make typed error
+		return nil, err
+	}
+
+	if len(rows) == 0 {
+		return nil, errors.New("query returned 0 rows")
+	}
+
+	host, err := s.hostInfoFromMap(rows[0], &HostInfo{connectAddress: connectAddress, port: defaultPort})
+	if err != nil {
+		return nil, err
+	}
+	return host, nil
+}
+
+// Ask the control node for the local host info
+func (r *ringDescriber) getLocalHostInfo() (*HostInfo, error) {
+	if r.session.control == nil {
+		return nil, errNoControl
+	}
+
+	iter := r.session.control.withConnHost(func(ch *connHost) *Iter {
+		return ch.conn.querySystemLocal(context.TODO())
+	})
+
+	if iter == nil {
+		return nil, errNoControl
+	}
+
+	host, err := r.session.hostInfoFromIter(iter, nil, r.session.cfg.Port)
+	if err != nil {
+		return nil, fmt.Errorf("could not retrieve local host info: %w", err)
+	}
+	return host, nil
+}
+
 // Ask the control node for host info on all it's known peers
-func (r *ringDescriber) getClusterPeerInfo() ([]*HostInfo, error) {
-	var hosts []*HostInfo
+func (r *ringDescriber) getClusterPeerInfo(localHost *HostInfo) ([]*HostInfo, error) {
+	if r.session.control == nil {
+		return nil, errNoControl
+	}
+
+	var peers []*HostInfo
 	iter := r.session.control.withConnHost(func(ch *connHost) *Iter {
-		hosts = append(hosts, ch.host)
-		return ch.conn.querySystemPeers(context.TODO(), ch.host.version)
+		return ch.conn.querySystemPeers(context.TODO(), localHost.version)
 	})
 
 	if iter == nil {
@@ -589,10 +631,10 @@ func (r *ringDescriber) getClusterPeerInfo() ([]*HostInfo, error) {
 			continue
 		}
 
-		hosts = append(hosts, host)
+		peers = append(peers, host)
 	}
 
-	return hosts, nil
+	return peers, nil
 }
 
 // Return true if the host is a valid peer
@@ -609,11 +651,17 @@ func (r *ringDescriber) GetHosts() ([]*HostInfo, string, error) {
 	r.mu.Lock()
 	defer r.mu.Unlock()
 
-	hosts, err := r.getClusterPeerInfo()
+	localHost, err := r.getLocalHostInfo()
+	if err != nil {
+		return r.prevHosts, r.prevPartitioner, err
+	}
+
+	peerHosts, err := r.getClusterPeerInfo(localHost)
 	if err != nil {
 		return r.prevHosts, r.prevPartitioner, err
 	}
 
+	hosts := append([]*HostInfo{localHost}, peerHosts...)
 	var partitioner string
 	if len(hosts) > 0 {
 		partitioner = hosts[0].Partitioner()