protocol: add capabilities to version payload

closes #871

pkg/network/capability/capability.go

@@ -0,0 +1,111 @@
+package capability
+
+import (
+	"errors"
+
+	"github.com/nspcc-dev/neo-go/pkg/io"
+)
+
+// MaxCapabilities is the maximum number of capabilities per payload
+const MaxCapabilities = 32
+
+// Capabilities is a list of Capability
+type Capabilities []Capability
+
+// DecodeBinary implements Serializable interface.
+func (cs *Capabilities) DecodeBinary(br *io.BinReader) {
+	br.ReadArray(cs, MaxCapabilities)
+	br.Err = cs.checkUniqueCapabilities()
+}
+
+// EncodeBinary implements Serializable interface.
+func (cs *Capabilities) EncodeBinary(br *io.BinWriter) {
+	br.WriteArray(*cs)
+}
+
+// checkUniqueCapabilities checks whether payload capabilities have unique type.
+func (cs Capabilities) checkUniqueCapabilities() error {
+	err := errors.New("capabilities with the same type are not allowed")
+	var isFullNode, isTCP, isWS bool
+	for _, cap := range cs {
+		switch cap.Type {
+		case FullNode:
+			if isFullNode {
+				return err
+			}
+			isFullNode = true
+		case TCPServer:
+			if isTCP {
+				return err
+			}
+			isTCP = true
+		case WSServer:
+			if isWS {
+				return err
+			}
+			isWS = true
+		}
+	}
+	return nil
+}
+
+// Capability describes network service available for node
+type Capability struct {
+	Type Type
+	Data io.Serializable
+}
+
+// DecodeBinary implements Serializable interface.
+func (c *Capability) DecodeBinary(br *io.BinReader) {
+	c.Type = Type(br.ReadB())
+	switch c.Type {
+	case FullNode:
+		c.Data = &Node{}
+	case TCPServer, WSServer:
+		c.Data = &Server{}
+	default:
+		br.Err = errors.New("unknown node capability type")
+	}
+	c.Data.DecodeBinary(br)
+}
+
+// EncodeBinary implements Serializable interface.
+func (c *Capability) EncodeBinary(bw *io.BinWriter) {
+	if c.Data == nil {
+		bw.Err = errors.New("capability has no data")
+		return
+	}
+	bw.WriteB(byte(c.Type))
+	c.Data.EncodeBinary(bw)
+}
+
+// Node represents full node capability with start height
+type Node struct {
+	StartHeight uint32
+}
+
+// DecodeBinary implements Serializable interface.
+func (n *Node) DecodeBinary(br *io.BinReader) {
+	n.StartHeight = br.ReadU32LE()
+}
+
+// EncodeBinary implements Serializable interface.
+func (n *Node) EncodeBinary(bw *io.BinWriter) {
+	bw.WriteU32LE(n.StartHeight)
+}
+
+// Server represents TCP or WS server capability with port
+type Server struct {
+	// Port is the port this server is listening on
+	Port uint16
+}
+
+// DecodeBinary implements Serializable interface.
+func (s *Server) DecodeBinary(br *io.BinReader) {
+	s.Port = br.ReadU16LE()
+}
+
+// EncodeBinary implements Serializable interface.
+func (s *Server) EncodeBinary(bw *io.BinWriter) {
+	bw.WriteU16LE(s.Port)
+}