iproto: support feature discovery

Since version 2.10.0 Tarantool supports feature discovery [1]. Client
can send the schema version and supported features and receive
server-side schema version and supported features information to tune
its behavior.

After this patch, the request will be send on `Connect`. Connector will
use protocol version that is minimal of connector version (now it's 3)
and server version. Feature will be enabled if both client and server
supports it (for now client does not support any features from the
list). Unknown request type error response is expected for pre-2.10.0
versions. In this case, protocol version would be
ProtocolVersionUnsupported (-1) and no features would be enabled.

For now it doesn't seems like exposing protocol version and enabled
features is useful for a client so private variables are used to store
this info. Getters added in export_test for tests.

Traces of IPROTO_FEATURE_GRACEFUL_SHUTDOWN flag and protocol version 4
could be found in Tarantool source code but they were removed in the
following commits before the release and treated like they never
existed. We also ignore them here too. See [2] for more info.

1. tarantool/tarantool#6253
2. tarantool/tarantool-python#262

Closes #120

Author: DifferentialOrange

Diff for: connection.go

@@ -35,6 +35,9 @@ const (
 type ConnEventKind int
 type ConnLogKind int
 
+var clientProtocolVersion int64 = 3
+var clientFeatures []uint64 = []uint64{}
+
 const (
 	// Connected signals that connection is established or reestablished.
 	Connected ConnEventKind = iota + 1
@@ -146,6 +149,13 @@ type Connection struct {
 	lenbuf  [PacketLengthBytes]byte
 
 	lastStreamId uint64
+
+	// protocolVersion is IProto max protocol version supported both by
+	// client and server. Equal to ProtocolVersionUnsupported is server
+	// does not support IPROTO_ID.
+	protocolVersion int64
+	// features contains the list of features supported both by client and server.
+	features []uint64
 }
 
 var _ = Connector(&Connection{}) // Check compatibility with connector interface.
@@ -391,6 +401,10 @@ func Connect(addr string, opts Opts) (conn *Connection, err error) {
 		}
 	}
 
+	if err = conn.checkFeatures(); err != nil {
+		return nil, err
+	}
+
 	return conn, err
 }
 
@@ -1163,3 +1177,63 @@ func (conn *Connection) NewStream() (*Stream, error) {
 		Conn: conn,
 	}, nil
 }
+
+func (conn *Connection) checkFeatures() error {
+	resp, err := conn.exchangeProtocolVersion(clientProtocolVersion, clientFeatures)
+
+	if err != nil {
+		if resp.Code == ErUnknownRequestType {
+			// IPROTO_ID is not supported by server.
+			conn.protocolVersion = ProtocolVersionUnsupported
+			conn.features = []uint64{}
+			return nil
+		}
+
+		return err
+	}
+
+	if len(resp.Data) == 0 {
+		return fmt.Errorf("Unexpected response on protocol version exchange: no data")
+	}
+
+	server, ok := resp.Data[0].(*protocolVersionResponse)
+	if !ok {
+		return fmt.Errorf("Unexpected response on protocol version exchange: wrong data")
+	}
+
+	conn.protocolVersion = minInt64(server.protocolVersion, clientProtocolVersion)
+	conn.features = intersect(server.features, clientFeatures)
+
+	return nil
+}
+
+func intersect(arr1 []uint64, arr2 []uint64) []uint64 {
+	var res []uint64 = make([]uint64, minInt(len(arr1), len(arr2)))
+	var i int = 0
+
+	for _, el1 := range arr1 {
+		for _, el2 := range arr2 {
+			if el1 == el2 {
+				res[i] = (el1)
+			}
+		}
+	}
+
+	return res[0:i]
+}
+
+func minInt(v1 int, v2 int) int {
+	if v1 > v2 {
+		return v2
+	}
+
+	return v1
+}
+
+func minInt64(v1 int64, v2 int64) int64 {
+	if v1 > v2 {
+		return v2
+	}
+
+	return v1
+}

Diff for: const.go

@@ -18,6 +18,7 @@ const (
 	RollbackRequestCode  = 16
 	PingRequestCode      = 64
 	SubscribeRequestCode = 66
+	IdRequestCode        = 73
 
 	KeyCode         = 0x00
 	KeySync         = 0x01
@@ -41,6 +42,8 @@ const (
 	KeySQLBind      = 0x41
 	KeySQLInfo      = 0x42
 	KeyStmtID       = 0x43
+	KeyVersion      = 0x54
+	KeyFeatures     = 0x55
 	KeyTimeout      = 0x56
 	KeyTxnIsolation = 0x59
 
@@ -69,10 +72,18 @@ const (
 	RLimitDrop = 1
 	RLimitWait = 2
 
-	OkCode            = uint32(0)
-	PushCode          = uint32(0x80)
-	ErrorCodeBit      = 0x8000
-	PacketLengthBytes = 5
-	ErSpaceExistsCode = 0xa
-	IteratorCode      = 0x14
+	FeatureStreams        = uint64(0)
+	FeatureTransactions   = uint64(1)
+	FeatureErrorExtension = uint64(2)
+	FeatureWatchers       = uint64(3)
+
+	OkCode               = uint32(0)
+	PushCode             = uint32(0x80)
+	ErrorCodeBit         = 0x8000
+	PacketLengthBytes    = 5
+	ErSpaceExistsCode    = 0xa
+	ErUnknownRequestType = 0x30
+	IteratorCode         = 0x14
+
+	ProtocolVersionUnsupported = int64(-1)
 )

Diff for: export_test.go

@@ -114,3 +114,11 @@ func RefImplRollbackBody(enc *encoder) error {
 func NewEncoder(w io.Writer) *encoder {
 	return newEncoder(w)
 }
+
+func GetProtocolVersion(conn *Connection) int64 {
+	return conn.protocolVersion
+}
+
+func GetFeatures(conn *Connection) []uint64 {
+	return conn.features
+}

Diff for: request.go

@@ -1106,3 +1106,69 @@ func (req *ExecuteRequest) Context(ctx context.Context) *ExecuteRequest {
 	req.ctx = ctx
 	return req
 }
+
+// protocolVersionRequest informs the server about supported protocol
+// version and features.
+type protocolVersionRequest struct {
+	baseRequest
+	// TODO: or uint32? spaceId is uint32. On the other hand,
+	// spaceId is casted to uint64 underneath and protocolVersionRequest
+	// is not a request user would send explicitly.
+	// Need to ask Oleg about it.
+	protocolVersion int64
+	features        []uint64
+}
+
+// newProtocolVersionRequest returns a new protocolVersionRequest.
+func newProtocolVersionRequest(protocolVersion int64,
+	features []uint64) *protocolVersionRequest {
+	req := new(protocolVersionRequest)
+	req.requestCode = IdRequestCode
+	req.protocolVersion = protocolVersion
+	req.features = features
+	return req
+}
+
+// exchangeProtocolVersion sends info about client protocol
+// and receives info about server protocol in response.
+func (conn *Connection) exchangeProtocolVersion(protocolVersion int64,
+	features []uint64) (resp *Response, err error) {
+	req := newProtocolVersionRequest(protocolVersion, features)
+	return conn.Do(req).Get()
+}
+
+// Body fills an encoder with the protocol version request body.
+func (req *protocolVersionRequest) Body(res SchemaResolver, enc *encoder) error {
+	return req.fillProtocolVersionRequest(enc)
+}
+
+// Context sets a passed context to the request.
+//
+// Pay attention that when using context with request objects,
+// the timeout option for Connection does not affect the lifetime
+// of the request. For those purposes use context.WithTimeout() as
+// the root context.
+func (req *protocolVersionRequest) Context(ctx context.Context) *protocolVersionRequest {
+	req.ctx = ctx
+	return req
+}
+
+func (req *protocolVersionRequest) fillProtocolVersionRequest(enc *encoder) error {
+	enc.EncodeMapLen(2)
+
+	encodeUint(enc, KeyVersion)
+	encodeInt(enc, req.protocolVersion)
+
+	encodeUint(enc, KeyFeatures)
+
+	t := len(req.features)
+	if err := enc.EncodeArrayLen(t); err != nil {
+		return err
+	}
+
+	for _, v := range req.features {
+		encodeUint(enc, v)
+	}
+
+	return nil
+}

Diff for: response.go

@@ -29,6 +29,11 @@ type SQLInfo struct {
 	InfoAutoincrementIds []uint64
 }
 
+type protocolVersionResponse struct {
+	protocolVersion int64
+	features        []uint64
+}
+
 func (meta *ColumnMetaData) DecodeMsgpack(d *decoder) error {
 	var err error
 	var l int
@@ -147,8 +152,11 @@ func (resp *Response) decodeBody() (err error) {
 		offset := resp.buf.Offset()
 		defer resp.buf.Seek(offset)
 
-		var l int
-		var stmtID, bindCount uint64
+		var l, larr int
+		var stmtID, bindCount, feature uint64
+		var protocolVersion int64
+		var features []uint64
+		isProtocolVersionResponse := false
 
 		d := newDecoder(&resp.buf)
 
@@ -190,6 +198,23 @@ func (resp *Response) decodeBody() (err error) {
 				if bindCount, err = d.DecodeUint64(); err != nil {
 					return err
 				}
+			case KeyVersion:
+				isProtocolVersionResponse = true
+				if protocolVersion, err = d.DecodeInt64(); err != nil {
+					return err
+				}
+			case KeyFeatures:
+				isProtocolVersionResponse = true
+				if larr, err = d.DecodeArrayLen(); err != nil {
+					return err
+				}
+				features = make([]uint64, larr)
+				for i := 0; i < larr; i++ {
+					if feature, err = d.DecodeUint64(); err != nil {
+						return err
+					}
+					features[i] = feature
+				}
 			default:
 				if err = d.Skip(); err != nil {
 					return err
@@ -204,6 +229,15 @@ func (resp *Response) decodeBody() (err error) {
 			}
 			resp.Data = []interface{}{stmt}
 		}
+
+		if isProtocolVersionResponse {
+			data := &protocolVersionResponse{
+				protocolVersion: protocolVersion,
+				features:        features,
+			}
+			resp.Data = []interface{}{data}
+		}
+
 		if resp.Code != OkCode && resp.Code != PushCode {
 			resp.Code &^= ErrorCodeBit
 			err = Error{resp.Code, resp.Error}

Diff for: tarantool_test.go

@@ -2830,6 +2830,32 @@ func TestStream_DoWithClosedConn(t *testing.T) {
 	}
 }
 
+func TestConnectionProtocolVersion(t *testing.T) {
+	conn := test_helpers.ConnectWithValidation(t, server, opts)
+
+	isProtocolVersionUnsupported, err := test_helpers.IsTarantoolVersionLess(2, 10, 0)
+	if err != nil {
+		t.Fatalf("Unexpected error has been caught: %s", err.Error())
+	}
+
+	protocolVersion := GetProtocolVersion(conn)
+	features := GetFeatures(conn)
+
+	if isProtocolVersionUnsupported {
+		require.Equal(t, protocolVersion, ProtocolVersionUnsupported)
+		require.ElementsMatch(t, features, []uint64{})
+	} else {
+		// First Tarantool protocol version (1) was introduced between
+		// 2.10.0-beta1 and 2.10.0-beta2. Versions 2 and 3 were also
+		// introduced between 2.10.0-beta1 and 2.10.0-beta2. Version 4
+		// was introduced between 2.10.0-beta2 and 2.10.0-rc1 and reverted
+		// back to version 3 in the same version interval.
+		// Tarantool 2.10.3 still has version 3.
+		require.GreaterOrEqual(t, protocolVersion, int64(3))
+		require.ElementsMatch(t, features, []uint64{})
+	}
+}
+
 // runTestMain is a body of TestMain function
 // (see https://pkg.go.dev/testing#hdr-Main).
 // Using defer + os.Exit is not works so TestMain body