Add parsing TABLETS_ROUTING_V1 extension

In order for Scylla to send the tablet info, the driver must tell
the database during connection handshake that it is able to
interpret it. It was implemented similarly to the
already-present LWT optimisation extension negotiation.

frame.go

@@ -427,6 +427,16 @@ func newFramerWithExts(compressor Compressor, version byte, cqlProtoExts []cqlPr
 		f.rateLimitingErrorCode = castedExt.rateLimitErrorCode
 	}
 
+	if tabletsExt := findCQLProtoExtByName(cqlProtoExts, tabletsRoutingV1); tabletsExt != nil {
+		_, ok := tabletsExt.(*tabletsRoutingV1Ext)
+		if !ok {
+			Logger.Println(
+				fmt.Errorf("Failed to cast CQL protocol extension identified by name %s to type %T",
+					tabletsRoutingV1, tabletsRoutingV1Ext{}))
+			return f
+		}
+	}
+
 	return f
 }
 

scylla.go

@@ -51,8 +51,38 @@ func findCQLProtoExtByName(exts []cqlProtocolExtension, name string) cqlProtocol
 const (
 	lwtAddMetadataMarkKey = "SCYLLA_LWT_ADD_METADATA_MARK"
 	rateLimitError        = "SCYLLA_RATE_LIMIT_ERROR"
+	tabletsRoutingV1      = "TABLETS_ROUTING_V1"
 )
 
+// "tabletsRoutingV1" CQL Protocol Extension.
+// This extension, if enabled (properly negotiated), allows Scylla server
+// to send a tablet information in `custom_payload`.
+//
+// Implements cqlProtocolExtension interface.
+type tabletsRoutingV1Ext struct {
+}
+
+var _ cqlProtocolExtension = &tabletsRoutingV1Ext{}
+
+// Factory function to deserialize and create an `tabletsRoutingV1Ext` instance
+// from SUPPORTED message payload.
+func newTabletsRoutingV1Ext(supported map[string][]string) *tabletsRoutingV1Ext {
+	if _, found := supported[tabletsRoutingV1]; found {
+		return &tabletsRoutingV1Ext{}
+	}
+	return nil
+}
+
+func (ext *tabletsRoutingV1Ext) serialize() map[string]string {
+	return map[string]string{
+		tabletsRoutingV1: "",
+	}
+}
+
+func (ext *tabletsRoutingV1Ext) name() string {
+	return tabletsRoutingV1
+}
+
 // "Rate limit" CQL Protocol Extension.
 // This extension, if enabled (properly negotiated), allows Scylla server
 // to send a special kind of error.
@@ -243,6 +273,11 @@ func parseCQLProtocolExtensions(supported map[string][]string) []cqlProtocolExte
 		exts = append(exts, rateLimitExt)
 	}
 
+	tabletsExt := newTabletsRoutingV1Ext(supported)
+	if tabletsExt != nil {
+		exts = append(exts, tabletsExt)
+	}
+
 	return exts
 }