From 42614f5e5bce108beecffc3816b88455dd3cec02 Mon Sep 17 00:00:00 2001
From: Nicolas Bouliane <nbouliane@digitalocean.com>
Date: Sun, 20 Mar 2022 13:26:10 -0400
Subject: [PATCH] arp: set and check arp state

---
 arp.go     | 12 +++++++-----
 network.go |  8 ++++----
 2 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/arp.go b/arp.go
index 2e0c4b6..dd97321 100644
--- a/arp.go
+++ b/arp.go
@@ -54,12 +54,12 @@ const (
 )
 
 // Add either adds a new entry or updates an ArpEntry in the ArpTable syncmap.
-func (t *ArpTable) Add(IP string, mac net.HardwareAddr, timeNow time.Time) error {
+func (t *ArpTable) Add(IP string, mac net.HardwareAddr, timeNow time.Time, status ArpStatus) error {
 	if IP == "" {
 		return errors.New("valid IP address must be provided")
 	}
 	ip := net.ParseIP(IP)
-	t.ArpMap.Store(IP, &ArpEntry{IP: ip, Mac: mac, Status: StatusReady, Timestamp: timeNow})
+	t.ArpMap.Store(IP, &ArpEntry{IP: ip, Mac: mac, Status: status, Timestamp: timeNow})
 	return nil
 }
 
@@ -78,8 +78,10 @@ func (t *ArpTable) Get(IP string) (*ArpEntry, bool, error) {
 		return nil, false, errors.New("invalid ARP entry type")
 	}
 
-	if arpEntry.Mac == nil {
-		return nil, false, errors.New("invalid ARP entry")
+	// Update the status from waiting to stale to express that the waiting time (2seconds) has expired
+	// This will allow us to send again an ARP request
+	if arpEntry.Status == StatusWaiting && arpEntry.Timestamp.Add(time.Second*2).Before(time.Now()) {
+		arpEntry.Status = StatusStale
 	}
 
 	return arpEntry, found, nil
@@ -138,7 +140,7 @@ func GenerateARPRequest(arpTable *ArpTable, srcMAC []byte, dstIP string, srcIP s
 
 	// FIXME this function should be .Upsert() (Add or Update the entry)
 	if arpTable != nil {
-		err := arpTable.Add(dstIP, net.HardwareAddr{}, time.Now())
+		err := arpTable.Add(dstIP, net.HardwareAddr{}, time.Now(), StatusWaiting)
 		if err != nil {
 			return nil, fmt.Errorf("unable to add waiting ARP entry: %v", err)
 		}
diff --git a/network.go b/network.go
index c3ad6f8..06ceb98 100644
--- a/network.go
+++ b/network.go
@@ -148,7 +148,7 @@ func ReadUTUN() {
 			Lerror.Printf("unable to retrieve ARP entry for %v: %v", dstIP.String(), err)
 		}
 
-		if found {
+		if found && entry.Status == StatusReady {
 			// We found the destination MAC in the ARP table, continue to craft
 			// the ethernet header of the IP packet.
 
@@ -163,7 +163,7 @@ func ReadUTUN() {
 			}
 			Ldebug.Printf("wrote %d bytes to vswitch\n", b)
 
-		} else {
+		} else if !found || found && entry.Status == StatusStale {
 
 			// TODO: Queue ethernet frame while ARP is being resolving the dst MAC address
 
@@ -394,7 +394,7 @@ func connSwitch(ctx context.Context, cancel context.CancelFunc, config *tls.Conf
 				if oper == OperationReply {
 					Ldebug.Printf("Received ARP response\n")
 					// We received an ARP response
-					err := arpTable.Add(spa.String(), sha, time.Now())
+					err := arpTable.Add(spa.String(), sha, time.Now(), StatusReady)
 					if err != nil {
 						Lerror.Printf("unable to update ARP entry: %v", err)
 					}
@@ -405,7 +405,7 @@ func connSwitch(ctx context.Context, cancel context.CancelFunc, config *tls.Conf
 					// ETH src MAC match the arp SHA AND arp SPA match TPA
 					if bytes.Equal(frameBuf[10:16], frameBuf[26:32]) && bytes.Equal(frameBuf[32:36], frameBuf[42:46]) {
 						Ldebug.Printf("we received an GARP")
-						arpTable.Add(spa.String(), sha, time.Now())
+						arpTable.Add(spa.String(), sha, time.Now(), StatusReady)
 					} else {
 						// We received an ARP request, send a response
 						sendBuf := GenerateARPReply(gMAC[0:6], sha, tpa, spa)