From dcc7464f46d14ecc9e09a16b5e64029d618a08b8 Mon Sep 17 00:00:00 2001
From: Kleissner <peter@kleissner.investments>
Date: Mon, 1 Mar 2021 01:05:37 +0100
Subject: [PATCH] New function IsNetworkErrorFatal to invalidate connections on
 fatal network errors. Use connection.Expires field to trigger removal of
 inactive connections after a while.

---
 Commands.go          | 11 +++++++----
 Connection.go        | 10 ++++++++--
 Network Detection.go | 20 +++++++++++++++++++-
 3 files changed, 34 insertions(+), 7 deletions(-)

diff --git a/Commands.go b/Commands.go
index 1589696..69d2977 100644
--- a/Commands.go
+++ b/Commands.go
@@ -98,7 +98,6 @@ func autoPingAll() {
 	for {
 		time.Sleep(time.Second)
 		thresholdInvalidate := time.Now().Add(-connectionInvalidate * time.Second)
-		thresholdRemove := time.Now().Add(-(connectionRemove + connectionInvalidate) * time.Second)
 		thresholdPingOut := time.Now().Add(-pingTime * time.Second)
 
 		for _, peer := range PeerlistGet() {
@@ -107,19 +106,23 @@ func autoPingAll() {
 				// Check if no incoming packet for the last X seconds. Regularly sent pings should result in incoming packets.
 				if connection.LastPacketIn.Before(thresholdInvalidate) {
 					peer.invalidateActiveConnection(connection)
+					continue
 				}
 
 				// Send ping if none was sent recently and no incoming packet was received recently.
 				if connection.LastPacketIn.Before(thresholdPingOut) && connection.LastPingOut.Before(thresholdPingOut) {
-					peer.sendConnection(&PacketRaw{Command: CommandPing}, connection)
+					if err := peer.sendConnection(&PacketRaw{Command: CommandPing}, connection); IsNetworkErrorFatal(err) {
+						peer.invalidateActiveConnection(connection)
+					}
 					connection.LastPingOut = time.Now()
+					continue
 				}
 			}
 
 			// handle inactive connections
 			for _, connection := range peer.GetConnections(false) {
-				// Remove connections that have been inactive for a long time; only if there is at least an active connection, or at least two other inactive ones.
-				if connection.LastPacketIn.Before(thresholdRemove) && (len(peer.connectionActive) >= 1 || len(peer.connectionInactive) > 2) {
+				// If the inactive connection is expired, remove it; although only if there is at least one active connection, or two other inactive ones.
+				if (len(peer.connectionActive) >= 1 || len(peer.connectionInactive) > 2) && connection.Expires.Before(time.Now()) {
 					peer.removeInactiveConnection(connection)
 					continue
 				}
diff --git a/Connection.go b/Connection.go
index b25541f..c626e44 100644
--- a/Connection.go
+++ b/Connection.go
@@ -23,6 +23,7 @@ type Connection struct {
 	LastPacketIn  time.Time    // Last time an incoming packet was received.
 	LastPacketOut time.Time    // Last time an outgoing packet was attempted to send.
 	LastPingOut   time.Time    // Last ping out.
+	Expires       time.Time    // Inactive connections only: Expiry date. If it does not become active by that date, it will be considered expired and removed.
 }
 
 // Equal checks if the connection was established other the same network adapter using the same IP address. Port is intentionally not checked.
@@ -94,6 +95,9 @@ func (peer *PeerInfo) invalidateActiveConnection(input *Connection) {
 	peer.Lock()
 	defer peer.Unlock()
 
+	// Change the status to inactive and start the expiration. If the connection does not become valid by that date, it will be removed.
+	input.Expires = time.Now().Add(connectionRemove * time.Second)
+
 	// remove from connectionLatest if selected so it won't be used by standard send function
 	if peer.connectionLatest == input {
 		peer.connectionLatest = nil
@@ -111,7 +115,7 @@ func (peer *PeerInfo) invalidateActiveConnection(input *Connection) {
 			}
 			peer.connectionActive = activeNew
 
-			return
+			break
 		}
 	}
 }
@@ -166,7 +170,9 @@ func (peer *PeerInfo) send(packet *PacketRaw) (err error) {
 
 		// Invalid connection, immediately invalidate. Fallback to broadcast to all other active ones.
 		// Windows: A common error when the network adapter is disabled is "wsasendto: The requested address is not valid in its context".
-		peer.invalidateActiveConnection(c)
+		if IsNetworkErrorFatal(err) {
+			peer.invalidateActiveConnection(c)
+		}
 	}
 
 	// If no latest connection available, broadcast on all available connections.
diff --git a/Network Detection.go b/Network Detection.go
index 0ad6ec9..6f308c1 100644
--- a/Network Detection.go	
+++ b/Network Detection.go	
@@ -6,7 +6,10 @@ Author:     Peter Kleissner
 
 package core
 
-import "net"
+import (
+	"net"
+	"strings"
+)
 
 // FindInterfaceByIP finds an interface based on the IP. The IP must be available at the interface.
 func FindInterfaceByIP(ip net.IP) (iface *net.Interface, ipnet *net.IPNet) {
@@ -69,3 +72,18 @@ func IsIPv4(IP net.IP) bool {
 func IsIPv6(IP net.IP) bool {
 	return IP.To4() == nil && IP.To16() != nil
 }
+
+// IsNetworkErrorFatal checks if a network error indicates a broken connection.
+// Not every network error indicates a broken connection. This function prevents from over-dropping connections.
+func IsNetworkErrorFatal(err error) bool {
+	if err == nil {
+		return false
+	}
+
+	// Windows: A common error when the network adapter is disabled is "wsasendto: The requested address is not valid in its context".
+	if strings.Contains(err.Error(), "requested address is not valid in its context") {
+		return true
+	}
+
+	return false
+}