network: add getaddr message handling

Respond with known good addresses.

pkg/network/payload/address.go

@@ -62,6 +62,14 @@ type AddressList struct {
 	Addrs []*AddressAndTime
 }
 
+// NewAddressList creates a list for n AddressAndTime elements.
+func NewAddressList(n int) *AddressList {
+	alist := AddressList{
+		Addrs: make([]*AddressAndTime, n),
+	}
+	return &alist
+}
+
 // DecodeBinary implements the Payload interface.
 func (p *AddressList) DecodeBinary(r io.Reader) error {
 	br := util.BinReader{R: r}

pkg/network/payload/address_test.go

@@ -35,7 +35,7 @@ func TestEncodeDecodeAddress(t *testing.T) {
 
 func TestEncodeDecodeAddressList(t *testing.T) {
 	var lenList uint8 = 4
-	addrList := &AddressList{make([]*AddressAndTime, lenList)}
+	addrList := NewAddressList(int(lenList))
 	for i := 0; i < int(lenList); i++ {
 		e, _ := net.ResolveTCPAddr("tcp", fmt.Sprintf("127.0.0.1:200%d", i))
 		addrList.Addrs[i] = NewAddressAndTime(e, time.Now())

pkg/network/server.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"fmt"
 	"math/rand"
+	"net"
 	"sync"
 	"time"
 
@@ -19,6 +20,7 @@ const (
 	minPeers       = 5
 	maxPeers       = 20
 	maxBlockBatch  = 200
+	maxAddrsToSend = 200
 	minPoolCount   = 30
 )
 
@@ -294,6 +296,22 @@ func (s *Server) handleAddrCmd(p Peer, addrs *payload.AddressList) error {
 	return nil
 }
 
+// handleGetAddrCmd sends to the peer some good addresses that we know of.
+func (s *Server) handleGetAddrCmd(p Peer) error {
+	addrs := s.discovery.GoodPeers()
+	if len(addrs) > maxAddrsToSend {
+		addrs = addrs[:maxAddrsToSend]
+	}
+	alist := payload.NewAddressList(len(addrs))
+	ts := time.Now()
+	for i, addr := range addrs {
+		// we know it's a good address, so it can't fail
+		netaddr, _ := net.ResolveTCPAddr("tcp", addr)
+		alist.Addrs[i] = payload.NewAddressAndTime(netaddr, ts)
+	}
+	return p.WriteMsg(NewMessage(s.Net, CMDAddr, alist))
+}
+
 // requestHeaders will send a getheaders message to the peer.
 // The peer will respond with headers op to a count of 2000.
 func (s *Server) requestHeaders(p Peer) error {
@@ -338,6 +356,9 @@ func (s *Server) handleMessage(peer Peer, msg *Message) error {
 		case CMDAddr:
 			addrs := msg.Payload.(*payload.AddressList)
 			return s.handleAddrCmd(peer, addrs)
+		case CMDGetAddr:
+			// it has no payload
+			return s.handleGetAddrCmd(peer)
 		case CMDHeaders:
 			headers := msg.Payload.(*payload.Headers)
 			go s.handleHeadersCmd(peer, headers)