network: implement getdata message handling in server

To properly implement relaying we need to answer these requests from other
nodes.

pkg/network/server.go

@@ -286,6 +286,39 @@ func (s *Server) handleInvCmd(p Peer, inv *payload.Inventory) error {
 	return p.WriteMsg(NewMessage(s.Net, CMDGetData, payload))
 }
 
+// handleInvCmd processes the received inventory.
+func (s *Server) handleGetDataCmd(p Peer, inv *payload.Inventory) error {
+	if !inv.Type.Valid() || len(inv.Hashes) == 0 {
+		return errInvalidInvType
+	}
+	switch inv.Type {
+	case payload.TXType:
+		for _, hash := range inv.Hashes {
+			tx, _, err := s.chain.GetTransaction(hash)
+			if err == nil {
+				err = p.WriteMsg(NewMessage(s.Net, CMDTX, tx))
+				if err != nil {
+					return err
+				}
+
+			}
+		}
+	case payload.BlockType:
+		for _, hash := range inv.Hashes {
+			b, err := s.chain.GetBlock(hash)
+			if err == nil {
+				err = p.WriteMsg(NewMessage(s.Net, CMDBlock, b))
+				if err != nil {
+					return err
+				}
+			}
+		}
+	case payload.ConsensusType:
+		// TODO (#431)
+	}
+	return nil
+}
+
 // handleAddrCmd will process received addresses.
 func (s *Server) handleAddrCmd(p Peer, addrs *payload.AddressList) error {
 	for _, a := range addrs.Addrs {
@@ -357,6 +390,9 @@ func (s *Server) handleMessage(peer Peer, msg *Message) error {
 		case CMDGetAddr:
 			// it has no payload
 			return s.handleGetAddrCmd(peer)
+		case CMDGetData:
+			inv := msg.Payload.(*payload.Inventory)
+			return s.handleGetDataCmd(peer, inv)
 		case CMDHeaders:
 			headers := msg.Payload.(*payload.Headers)
 			go s.handleHeadersCmd(peer, headers)