From cbe187d008c91f4be3167ca3c32c2febc82d5344 Mon Sep 17 00:00:00 2001
From: MichalK <kuritka@gmail.com>
Date: Fri, 2 Jul 2021 10:05:26 +0200
Subject: [PATCH] [Fix] Use default gateway, when bridge network doesn't have
 it (#666, @kuritka)

Signed-off-by: kuritka <kuritka@gmail.com>
---
 pkg/runtimes/docker/network.go | 35 +++++++++++++++++++++-------------
 1 file changed, 22 insertions(+), 13 deletions(-)

diff --git a/pkg/runtimes/docker/network.go b/pkg/runtimes/docker/network.go
index 7d0fc6a3..80f62f4c 100644
--- a/pkg/runtimes/docker/network.go
+++ b/pkg/runtimes/docker/network.go
@@ -80,23 +80,11 @@ func (d Docker) GetNetwork(ctx context.Context, searchNet *k3d.ClusterNetwork) (
 
 	// for networks that have an IPAM config, we inspect that as well (e.g. "host" network doesn't have it)
 	if len(networkList[0].IPAM.Config) > 0 {
-		prefix, err := netaddr.ParseIPPrefix(networkList[0].IPAM.Config[0].Subnet)
+		network.IPAM, err = d.parseIPAM(networkList[0].IPAM.Config[0])
 		if err != nil {
 			return nil, err
 		}
 
-		gateway, err := netaddr.ParseIP(networkList[0].IPAM.Config[0].Gateway)
-		if err != nil {
-			return nil, err
-		}
-
-		network.IPAM = k3d.IPAM{
-			IPPrefix: prefix,
-			IPsUsed: []netaddr.IP{
-				gateway,
-			},
-		}
-
 		for _, container := range networkList[0].Containers {
 			if container.IPv4Address != "" {
 				ip, err := netaddr.ParseIP(container.IPv4Address)
@@ -348,3 +336,24 @@ func (d Docker) getFreeSubnetPrefix(ctx context.Context) (netaddr.IPPrefix, erro
 	return fakenet.IPAM.IPPrefix, nil
 
 }
+
+// parseIPAM Returns an IPAM structure with the subnet and gateway filled in. If some of the values
+// cannot be parsed, an error is returned. If gateway is empty, the function calculates the default gateway.
+func (d Docker) parseIPAM(config network.IPAMConfig) (ipam k3d.IPAM, err error){
+	var gateway netaddr.IP
+	ipam = k3d.IPAM{ IPsUsed: []netaddr.IP{}}
+
+	ipam.IPPrefix, err = netaddr.ParseIPPrefix(config.Subnet)
+	if err != nil {
+		return
+	}
+
+	if config.Gateway == "" {
+		gateway = ipam.IPPrefix.IP.Next()
+	} else  {
+		gateway, err = netaddr.ParseIP(config.Gateway)
+	}
+	ipam.IPsUsed = append(ipam.IPsUsed, gateway)
+
+	return
+}