api: support iproto 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
stores server info in connection internals. After that, user may call
`IsProtocolVersionSupported` and `IsProtocolFeatureSupported` handles to
check if it is possible to use a feature.

`IsProtocolFeatureSupported` 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 [3]. Benchmark tests show that this check is rather
fast (0.5 ns 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 [2] for more info.

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

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 +146,8 @@ type Connection struct {
 	lenbuf  [PacketLengthBytes]byte
 
 	lastStreamId uint64
+
+	serverProtocolInfo protocolInfo
 }
 
 var _ = Connector(&Connection{}) // Check compatibility with connector interface.
@@ -391,6 +393,13 @@ func Connect(addr string, opts Opts) (conn *Connection, err error) {
 		}
 	}
 
+	if err = conn.loadProtocolInfo(); err != nil {
+		conn.mutex.Lock()
+		defer conn.mutex.Unlock()
+		conn.closeConnection(err, true)
+		return nil, err
+	}
+
 	return conn, err
 }
 
@@ -687,6 +696,10 @@ func (conn *Connection) reconnect(neterr error, c net.Conn) {
 			conn.closeConnection(neterr, false)
 			if err := conn.createConnection(true); err != nil {
 				conn.closeConnection(err, true)
+			} else {
+				if err = conn.loadProtocolInfo(); err != nil {
+					conn.closeConnection(err, true)
+				}
 			}
 		}
 	} else {
@@ -1163,3 +1176,54 @@ 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() error {
+	var ok bool
+
+	resp, err := conn.exchangeProtocolInfo(
+		ClientProtocolVersion,
+		ClientProtocolFeatures)
+
+	if err != nil {
+		if resp.Code == ErrUnknownRequestType {
+			// IPROTO_ID requests are not supported by server.
+			conn.serverProtocolInfo = protocolInfo{
+				version:  ProtocolVersionUnsupported,
+				features: []ProtocolFeature{},
+			}
+			return nil
+		}
+
+		return err
+	}
+
+	if len(resp.Data) == 0 {
+		return fmt.Errorf("Unexpected response on protocol info exchange: no data")
+	}
+
+	conn.serverProtocolInfo, ok = resp.Data[0].(protocolInfo)
+	if !ok {
+		return fmt.Errorf("Unexpected response on protocol info exchange: wrong data")
+	}
+
+	return nil
+}
+
+// IsProtocolVersionSupported checks if expected protocol version
+// is supported by both server and client.
+// Since 1.10.0
+func (conn *Connection) IsProtocolVersionSupported(version ProtocolVersion) bool {
+	return (version <= ClientProtocolVersion) &&
+		(version <= conn.serverProtocolInfo.version)
+}
+
+// IsProtocolFeatureSupported checks if expected protocol feature
+// is supported by both server and client.
+// Since 1.10.0
+func (conn *Connection) IsProtocolFeatureSupported(feature ProtocolFeature) bool {
+	return isFeatureSupported(feature, ClientProtocolFeatures) &&
+		isFeatureSupported(feature, conn.serverProtocolInfo.features)
+}

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: example_test.go

@@ -334,8 +334,18 @@ func ExampleCommitRequest() {
 	conn := example_connect()
 	defer conn.Close()
 
+	if conn.IsProtocolFeatureSupported(ProtocolFeatureStreams) != true {
+		fmt.Printf("Streams are not supported")
+		return
+	}
+
 	stream, _ := conn.NewStream()
 
+	if conn.IsProtocolFeatureSupported(ProtocolFeatureTransactions) != true {
+		fmt.Printf("Transactions are not supported")
+		return
+	}
+
 	// Begin transaction
 	req = tarantool.NewBeginRequest()
 	resp, err = stream.Do(req).Get()
@@ -410,8 +420,18 @@ func ExampleRollbackRequest() {
 	conn := example_connect()
 	defer conn.Close()
 
+	if conn.IsProtocolFeatureSupported(ProtocolFeatureStreams) != true {
+		fmt.Printf("Streams are not supported")
+		return
+	}
+
 	stream, _ := conn.NewStream()
 
+	if conn.IsProtocolFeatureSupported(ProtocolFeatureTransactions) != true {
+		fmt.Printf("Transactions are not supported")
+		return
+	}
+
 	// Begin transaction
 	req = tarantool.NewBeginRequest()
 	resp, err = stream.Do(req).Get()
@@ -486,8 +506,18 @@ func ExampleBeginRequest_TxnIsolation() {
 	conn := example_connect()
 	defer conn.Close()
 
+	if conn.IsProtocolFeatureSupported(ProtocolFeatureStreams) != true {
+		fmt.Printf("Streams are not supported")
+		return
+	}
+
 	stream, _ := conn.NewStream()
 
+	if conn.IsProtocolFeatureSupported(ProtocolFeatureTransactions) != true {
+		fmt.Printf("Transactions are not supported")
+		return
+	}
+
 	// Begin transaction
 	req = tarantool.NewBeginRequest().
 		TxnIsolation(tarantool.ReadConfirmedLevel).

Diff for: protocol.go

@@ -0,0 +1,44 @@
+package tarantool
+
+type ProtocolVersion uint64
+type ProtocolFeature uint64
+
+type protocolInfo struct {
+	version  ProtocolVersion
+	features []ProtocolFeature
+}
+
+const ProtocolVersionUnsupported ProtocolVersion = 0
+
+const (
+	// Streams support.
+	ProtocolFeatureStreams ProtocolFeature = 0
+	// Interactive tranactions support.
+	ProtocolFeatureTransactions ProtocolFeature = 1
+	// Support of MP_ERROR object over MessagePack.
+	ProtocolFeatureErrorExtension ProtocolFeature = 2
+	// Support of watchers.
+	ProtocolFeatureWatchers ProtocolFeature = 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 ClientProtocolFeatures = []ProtocolFeature{
+	ProtocolFeatureStreams,
+	ProtocolFeatureTransactions,
+}
+
+func isFeatureSupported(feature ProtocolFeature, supportedFeatures []ProtocolFeature) 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 +1106,68 @@ 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(protocolVersion ProtocolVersion,
+	protocolFeatures []ProtocolFeature) *protocolInfoRequest {
+	req := new(protocolInfoRequest)
+	req.requestCode = IdRequestCode
+	req.version = protocolVersion
+	req.features = protocolFeatures
+	return req
+}
+
+// exchangeProtocolInfo sends info about client protocol
+// and receives info about server protocol in response.
+func (conn *Connection) exchangeProtocolInfo(version ProtocolVersion,
+	features []ProtocolFeature) (resp *Response, err error) {
+	req := newProtocolInfoRequest(version, features)
+	return conn.Do(req).Get()
+}
+
+// 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 +147,15 @@ 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: []ProtocolFeature{},
+		}
+
+		var protocolFeature ProtocolFeature
+		isProtocolInfoResponse := false
 
 		d := newDecoder(&resp.buf)
 
@@ -190,6 +197,24 @@ 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([]ProtocolFeature, larr)
+				for i := 0; i < larr; i++ {
+					if err = d.Decode(&protocolFeature); err != nil {
+						return err
+					}
+					serverProtocolInfo.features[i] = protocolFeature
+				}
 			default:
 				if err = d.Skip(); err != nil {
 					return err
@@ -204,6 +229,11 @@ 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}

Diff for: tarantool_test.go

@@ -2830,6 +2830,50 @@ func TestStream_DoWithClosedConn(t *testing.T) {
 	}
 }
 
+func TestConnectionProtocolInfo(t *testing.T) {
+	conn := test_helpers.ConnectWithValidation(t, server, opts)
+
+	isProtocolInfoUnsupported, err := test_helpers.IsTarantoolVersionLess(2, 10, 0)
+	if err != nil {
+		t.Fatalf("Unexpected error has been caught: %s", err.Error())
+	}
+	// 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.
+	// So each release Tarantool >= 2.10 have protocol version >= 3.
+	// (Tarantool 2.10.4 still has version 3.)
+	minProtocolVersion := ProtocolVersion(1)
+	tarantool210ProtocolVersion := ProtocolVersion(3)
+
+	if isProtocolInfoUnsupported {
+		require.Equal(t, conn.IsProtocolVersionSupported(minProtocolVersion), false)
+		require.Equal(t, conn.IsProtocolFeatureSupported(ProtocolFeatureStreams), false)
+		require.Equal(t, conn.IsProtocolFeatureSupported(ProtocolFeatureTransactions), false)
+		require.Equal(t, conn.IsProtocolFeatureSupported(ProtocolFeatureErrorExtension), false)
+		require.Equal(t, conn.IsProtocolFeatureSupported(ProtocolFeatureWatchers), false)
+	} else {
+		require.Equal(t, conn.IsProtocolVersionSupported(tarantool210ProtocolVersion), true)
+		require.Equal(t, conn.IsProtocolFeatureSupported(ProtocolFeatureStreams), true)
+		require.Equal(t, conn.IsProtocolFeatureSupported(ProtocolFeatureTransactions), true)
+		require.Equal(t, conn.IsProtocolFeatureSupported(ProtocolFeatureErrorExtension), false)
+		require.Equal(t, conn.IsProtocolFeatureSupported(ProtocolFeatureWatchers), false)
+	}
+}
+
+func BenchmarkConnectionProtocolFeature(b *testing.B) {
+	conn := test_helpers.ConnectWithValidation(b, server, opts)
+	defer conn.Close()
+
+	b.ResetTimer()
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			_ = conn.IsProtocolFeatureSupported(ProtocolFeatureStreams)
+		}
+	})
+}
+
 // 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