Do not keep more than 3 DNS servers and init default DNS struct (#1671)

* do not store more than 3 dns servers

* initialize default value for dns config

* added rn

* huh I forgot to change it after testing

docs/rn/0.47.md

@@ -34,3 +34,9 @@ Containerlab now [generates an SSH config](../manual/inventory.md#ssh-config) fi
 * podman exec command fix #1653
 * APT/YUM repositories are now automatically added to all SR Linux nodes. They are used to install NDK apps and CLI plugins provided by Nokia #1657
 * SR Linux's mgmt0.0 interface is now auto-configured with the correct IP-MTU value #1658
+
+## Patches
+
+### 0.47.1
+
+* Do not extract more than 3 DNS servers from the host's resolv.conf #1671

types/topology.go

@@ -516,7 +516,15 @@ func (t *Topology) GetNodeDns(name string) *DNSConfig {
 			return kindDNS
 		}
 	}
-	return t.GetDefaults().GetDns()
+
+	defaultDNS := t.GetDefaults().GetDns()
+	if defaultDNS == nil {
+		// initialize defaultDNS to an empty DNSConfig struct
+		// so that we don't have to check for nil in the caller
+		defaultDNS = &DNSConfig{}
+	}
+
+	return defaultDNS
 }
 
 // GetCertificateConfig returns the certificate configuration for the given node.

utils/resolve.go

@@ -51,8 +51,16 @@ func ExtractDNSServersFromResolvConf(filesys fs.FS, filenames []string) ([]strin
 	}
 
 	DNSServers := make([]string, 0, len(DNSServersMap))
+	var count int
 	for k := range DNSServersMap {
+		if count == 3 {
+			// keep only the first three DNS servers
+			// since C DNS resolver can't handle more
+			break
+		}
 		DNSServers = append(DNSServers, k)
+		count++
 	}
+
 	return DNSServers, nil
 }

utils/resolve_test.go

@@ -46,6 +46,35 @@ search .
 			want:    nil,
 			wantErr: false,
 		},
+		{
+			name: "One file with more than 3 dns servers",
+			args: args{
+				filesys: fstest.MapFS{
+					"etc/resolv.conf": &fstest.MapFile{
+						Data: []byte(
+							`
+# This is /run/systemd/resolve/stub-resolv.conf managed by man:systemd-resolved(8).
+# Do not edit.
+#
+# This file might be symlinked as /etc/resolv.conf. If you're looking at
+# /etc/resolv.conf and seeing this text, you have followed the symlink.
+
+nameserver 1.1.1.1
+nameserver 1.1.1.2
+nameserver 1.1.1.3
+nameserver 1.1.1.4
+nameserver 1.1.1.5
+options edns0 trust-ad
+search .					
+`,
+						),
+					},
+				},
+				filenames: []string{"etc/resolv.conf"},
+			},
+			want:    []string{"1.1.1.1", "1.1.1.2", "1.1.1.3"},
+			wantErr: false,
+		},
 		{
 			name: "Two files local dns and two remote, two results",
 			args: args{
@@ -85,7 +114,7 @@ search .
 			wantErr: false,
 		},
 		{
-			name: "Duplicat 8.8.8.8",
+			name: "Duplicate 8.8.8.8",
 			args: args{
 				filesys: fstest.MapFS{
 					"etc/resolv.conf": &fstest.MapFile{
@@ -128,11 +157,13 @@ search .
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			got, err := ExtractDNSServersFromResolvConf(tt.args.filesys, tt.args.filenames)
+
 			if (err != nil) != tt.wantErr {
 				t.Errorf("ExtractDNSServerFromResolvConf() error = %v, wantErr %v", err, tt.wantErr)
 				return
 			}
-			if diff := cmp.Diff(tt.want, got, cmpopts.SortSlices(func(s1, s2 string) bool {
+
+			if diff := cmp.Diff(got, tt.want, cmpopts.SortSlices(func(s1, s2 string) bool {
 				switch strings.Compare(s1, s2) {
 				case -1:
 					return false