api: support iproto feature discovery

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

After this patch, the request will be sent on `dial`, before
authentication is performed. Connector stores server info in connection
internals. After that, user may call API handles to check if it is
possible to use a feature.

Feature check iterates over lists to check if feature is
enabled. It seems that iterating over a small list is way faster than
building a map, see [2]. Benchmark tests show that this check is rather
fast (0.5 ns for both client and server check on HP ProBook 440 G5) so
it is not necessary to cache it in any way.

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 [3] for more info.

1. tarantool/tarantool#6253
2. https://stackoverflow.com/a/52710077/11646599
3. tarantool/tarantool-python#262

Closes #120

Author: DifferentialOrange

Diff for: CHANGELOG.md

@@ -10,6 +10,8 @@ Versioning](http://semver.org/spec/v2.0.0.html) except to the first release.
 
 ### Added
 
+- Support IProto feature discovery (#120).
+
 ### Changed
 
 ### Fixed

Diff for: connection.go

@@ -146,6 +146,9 @@ type Connection struct {
 	lenbuf  [PacketLengthBytes]byte
 
 	lastStreamId uint64
+
+	serverProtocolVersion ProtocolVersion
+	serverFeatures        []Feature
 }
 
 var _ = Connector(&Connection{}) // Check compatibility with connector interface.
@@ -502,6 +505,13 @@ func (conn *Connection) dial() (err error) {
 	conn.Greeting.Version = bytes.NewBuffer(greeting[:64]).String()
 	conn.Greeting.auth = bytes.NewBuffer(greeting[64:108]).String()
 
+	// IPROTO_ID requests can be processed without authentication.
+	// https://www.tarantool.io/en/doc/latest/dev_guide/internals/iproto/requests/#iproto-id
+	if err = conn.loadProtocolInfo(w, r); err != nil {
+		connection.Close()
+		return err
+	}
+
 	// Auth
 	if opts.User != "" {
 		scr, err := scramble(conn.Greeting.auth, opts.Pass)
@@ -603,33 +613,43 @@ func (conn *Connection) writeAuthRequest(w *bufio.Writer, scramble []byte) (err
 	return conn.writeRequest(w, req, "auth")
 }
 
-func (conn *Connection) readResponse(r io.Reader) (resp Response, err error) {
+func (conn *Connection) writeProtocolInfoRequest(w *bufio.Writer, version ProtocolVersion,
+	features []Feature) (err error) {
+	req := newProtocolInfoRequest(version, features)
+	return conn.writeRequest(w, req, "iproto id")
+}
+
+func (conn *Connection) readResponse(r io.Reader, reqName string) (resp Response, err error) {
 	respBytes, err := conn.read(r)
 	if err != nil {
-		return resp, errors.New("auth: read error " + err.Error())
+		return resp, errors.New(reqName + ": read error " + err.Error())
 	}
 	resp = Response{buf: smallBuf{b: respBytes}}
 	err = resp.decodeHeader(conn.dec)
 	if err != nil {
-		return resp, errors.New("auth: decode response header error " + err.Error())
+		return resp, errors.New(reqName + ": decode response header error " + err.Error())
 	}
 	err = resp.decodeBody()
 	if err != nil {
 		switch err.(type) {
 		case Error:
 			return resp, err
 		default:
-			return resp, errors.New("auth: decode response body error " + err.Error())
+			return resp, errors.New(reqName + ": decode response body error " + err.Error())
 		}
 	}
 	return resp, nil
 }
 
 func (conn *Connection) readAuthResponse(r io.Reader) (err error) {
-	_, err = conn.readResponse(r)
+	_, err = conn.readResponse(r, "auth")
 	return err
 }
 
+func (conn *Connection) readProtocolInfoResponse(r io.Reader) (resp Response, err error) {
+	return conn.readResponse(r, "iproto id")
+}
+
 func (conn *Connection) createConnection(reconnect bool) (err error) {
 	var reconnects uint
 	for conn.c == nil && conn.state == connDisconnected {
@@ -1173,3 +1193,71 @@ func (conn *Connection) NewStream() (*Stream, error) {
 		Conn: conn,
 	}, nil
 }
+
+// loadProtocolInfo sends info about client protocol,
+// receives info about server protocol in response
+// and store in in connection serverProtocolInfo.
+func (conn *Connection) loadProtocolInfo(w *bufio.Writer, r *bufio.Reader) error {
+	var resp Response
+	var err error
+
+	err = conn.writeProtocolInfoRequest(w, ClientProtocolVersion, ClientFeatures)
+	if err != nil {
+		return err
+	}
+
+	resp, err = conn.readProtocolInfoResponse(r)
+	if err != nil {
+		tarantoolError, ok := err.(Error)
+		if ok && tarantoolError.Code == ErrUnknownRequestType {
+			// IPROTO_ID requests are not supported by server.
+			conn.serverProtocolVersion = ProtocolVersionUnsupported
+			conn.serverFeatures = []Feature{}
+
+			return nil
+		}
+
+		return err
+	}
+
+	if len(resp.Data) == 0 {
+		return fmt.Errorf("Unexpected response on protocol info exchange: no data")
+	}
+
+	serverProtocolInfo, ok := resp.Data[0].(protocolInfo)
+	if !ok {
+		return fmt.Errorf("Unexpected response on protocol info exchange: wrong data")
+	}
+	conn.serverProtocolVersion = serverProtocolInfo.version
+	conn.serverFeatures = serverProtocolInfo.features
+
+	return nil
+}
+
+// ServerProtocolVersion returns protocol version supported by
+// connected Tarantool server.
+// Since 1.10.0
+func (conn *Connection) ServerProtocolVersion() ProtocolVersion {
+	return conn.serverProtocolVersion
+}
+
+// ClientProtocolVersion returns protocol version supported by
+// Go connection client.
+// Since 1.10.0
+func (conn *Connection) ClientProtocolVersion() ProtocolVersion {
+	return ClientProtocolVersion
+}
+
+// DoesServerSupportFeature checks if expected feature
+// is supported by connected Tarantool server.
+// Since 1.10.0
+func (conn *Connection) DoesServerSupportFeature(feature Feature) bool {
+	return isFeatureSupported(feature, conn.serverFeatures)
+}
+
+// DoesClientSupportFeature checks if expected feature
+// is supported by Go connection client.
+// Since 1.10.0
+func (conn *Connection) DoesClientSupportFeature(feature Feature) bool {
+	return isFeatureSupported(feature, ClientFeatures)
+}

Diff for: connection_pool/connection_pool.go

@@ -1028,3 +1028,47 @@ func newErrorFuture(err error) *tarantool.Future {
 	fut.SetError(err)
 	return fut
 }
+
+// ServerProtocolVersion returns protocol version supported by
+// Tarantool server for a connection selected by userMode from connPool.
+// Since 1.10.0
+func (connPool *ConnectionPool) ServerProtocolVersion(userMode Mode) (tarantool.ProtocolVersion, error) {
+	conn, err := connPool.getNextConnection(userMode)
+	if err != nil {
+		return tarantool.ProtocolVersionUnsupported, err
+	}
+	return conn.ServerProtocolVersion(), nil
+}
+
+// ClientProtocolVersion returns protocol version supported by
+// Go connection client for a connection selected by userMode from connPool.
+// Since 1.10.0
+func (connPool *ConnectionPool) ClientProtocolVersion(userMode Mode) (tarantool.ProtocolVersion, error) {
+	conn, err := connPool.getNextConnection(userMode)
+	if err != nil {
+		return tarantool.ProtocolVersionUnsupported, err
+	}
+	return conn.ClientProtocolVersion(), nil
+}
+
+// DoesServerSupportFeature checks if expected feature is supported
+// by Tarantool server for a connection selected by userMode from connPool.
+// Since 1.10.0
+func (connPool *ConnectionPool) DoesServerSupportFeature(feature tarantool.Feature, userMode Mode) (bool, error) {
+	conn, err := connPool.getNextConnection(userMode)
+	if err != nil {
+		return false, err
+	}
+	return conn.DoesServerSupportFeature(feature), nil
+}
+
+// DoesClientSupportFeature checks if expected feature is supported
+// by Go connection client for a connection selected by userMode from connPool.
+// Since 1.10.0
+func (connPool *ConnectionPool) DoesClientSupportFeature(feature tarantool.Feature, userMode Mode) (bool, error) {
+	conn, err := connPool.getNextConnection(userMode)
+	if err != nil {
+		return false, err
+	}
+	return conn.DoesClientSupportFeature(feature), nil
+}

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
 

Diff for: protocol.go

@@ -0,0 +1,44 @@
+package tarantool
+
+type ProtocolVersion uint64
+type Feature uint64
+
+type protocolInfo struct {
+	version  ProtocolVersion
+	features []Feature
+}
+
+const ProtocolVersionUnsupported ProtocolVersion = 0
+
+const (
+	// Streams support.
+	FeatureStreams Feature = 0
+	// Interactive transactions support.
+	FeatureTransactions Feature = 1
+	// Support of MP_ERROR object over MessagePack.
+	FeatureErrorExtension Feature = 2
+	// Support of watchers.
+	FeatureWatchers Feature = 3
+)
+
+// Protocol version supported by connector. Version 3
+// was introduced in Tarantool 2.10.0 and used in latest 2.10.4.
+const ClientProtocolVersion ProtocolVersion = 3
+
+// Protocol features supported by connector.
+var ClientFeatures = []Feature{
+	FeatureStreams,
+	FeatureTransactions,
+}
+
+func isFeatureSupported(feature Feature, supportedFeatures []Feature) bool {
+	// It seems that iterating over a small list is way faster
+	// than building a map: https://stackoverflow.com/a/52710077/11646599
+	for _, supportedFeature := range supportedFeatures {
+		if feature == supportedFeature {
+			return true
+		}
+	}
+
+	return false
+}

Diff for: request.go

@@ -1106,3 +1106,60 @@ func (req *ExecuteRequest) Context(ctx context.Context) *ExecuteRequest {
 	req.ctx = ctx
 	return req
 }
+
+// protocolInfoRequest informs the server about supported protocol
+// version and features.
+type protocolInfoRequest struct {
+	baseRequest
+	protocolInfo
+}
+
+// newProtocolInfoRequest returns a new protocolInfoRequest.
+func newProtocolInfoRequest(version ProtocolVersion,
+	features []Feature) *protocolInfoRequest {
+	req := new(protocolInfoRequest)
+	req.requestCode = IdRequestCode
+	req.version = version
+	req.features = features
+	return req
+}
+
+// Body fills an encoder with the protocol version request body.
+func (req *protocolInfoRequest) Body(res SchemaResolver, enc *encoder) error {
+	return req.fillProtocolInfoRequest(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 *protocolInfoRequest) Context(ctx context.Context) *protocolInfoRequest {
+	req.ctx = ctx
+	return req
+}
+
+func (req *protocolInfoRequest) fillProtocolInfoRequest(enc *encoder) error {
+	enc.EncodeMapLen(2)
+
+	encodeUint(enc, KeyVersion)
+	if err := enc.Encode(req.version); err != nil {
+		return err
+	}
+
+	encodeUint(enc, KeyFeatures)
+
+	t := len(req.features)
+	if err := enc.EncodeArrayLen(t); err != nil {
+		return err
+	}
+
+	for _, feature := range req.features {
+		if err := enc.Encode(feature); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}

Diff for: response.go

@@ -147,8 +147,14 @@ func (resp *Response) decodeBody() (err error) {
 		offset := resp.buf.Offset()
 		defer resp.buf.Seek(offset)
 
-		var l int
+		var l, larr int
 		var stmtID, bindCount uint64
+		var serverProtocolInfo protocolInfo = protocolInfo{
+			version:  ProtocolVersionUnsupported,
+			features: []Feature{},
+		}
+		var feature Feature
+		isProtocolInfoResponse := false
 
 		d := newDecoder(&resp.buf)
 
@@ -190,6 +196,24 @@ func (resp *Response) decodeBody() (err error) {
 				if bindCount, err = d.DecodeUint64(); err != nil {
 					return err
 				}
+			case KeyVersion:
+				isProtocolInfoResponse = true
+				if err = d.Decode(&serverProtocolInfo.version); err != nil {
+					return err
+				}
+			case KeyFeatures:
+				isProtocolInfoResponse = true
+				if larr, err = d.DecodeArrayLen(); err != nil {
+					return err
+				}
+
+				serverProtocolInfo.features = make([]Feature, larr)
+				for i := 0; i < larr; i++ {
+					if err = d.Decode(&feature); err != nil {
+						return err
+					}
+					serverProtocolInfo.features[i] = feature
+				}
 			default:
 				if err = d.Skip(); err != nil {
 					return err
@@ -204,6 +228,11 @@ func (resp *Response) decodeBody() (err error) {
 			}
 			resp.Data = []interface{}{stmt}
 		}
+
+		if isProtocolInfoResponse {
+			resp.Data = []interface{}{serverProtocolInfo}
+		}
+
 		if resp.Code != OkCode && resp.Code != PushCode {
 			resp.Code &^= ErrorCodeBit
 			err = Error{resp.Code, resp.Error}