Fix panic when no keys present for srl node (#1604)

* fix keys catenation for 0.0 builds when no keys present

* added rn

docs/rn/0.45.md

@@ -24,3 +24,9 @@ Now @steiler enhanced this functionality by making sure that if a user provides
 * #1571 - ansible proxy variable is added to containerlab produced ansible inventory
 * #1592 - ca cert and node certs now have a default country code set to US
 * #1583 - default link MTU is now fixed to be 9500 again
+
+## Patches
+
+### 0.45.1
+
+* fix panic when no keys are present for srlinux node

nodes/srl/srl.go

@@ -565,7 +565,7 @@ func (n *srl) addDefaultConfig(ctx context.Context) error {
 
 	// in srlinux >= v23.10+ linuxadmin and admin user ssh keys can only be configured via the cli
 	// so we add the keys to the template data for rendering.
-	if semver.Compare(n.swVersion.String(), "v23.10") >= 0 || n.swVersion.major == "0" {
+	if len(n.sshPubKeys) > 0 && (semver.Compare(n.swVersion.String(), "v23.10") >= 0 || n.swVersion.major == "0") {
 		tplData.SSHPubKeys = catenateKeys(n.sshPubKeys)
 	}
 

nodes/srl/sshkey.go

@@ -2,7 +2,6 @@ package srl
 
 import (
 	"bytes"
-	"fmt"
 	"strings"
 
 	"golang.org/x/crypto/ssh"
@@ -14,19 +13,30 @@ import (
 // for users.
 func catenateKeys(in []ssh.PublicKey) string {
 	var keys strings.Builder
+	// pre-allocate the string builder capacity
+	keys.Grow(len(in) * 100)
 	// iterate through keys
-	for _, k := range in {
+	for i, k := range in {
 		// extract the keys in AuthorizedKeys format (e.g. "ssh-rsa <KEY>")
 		ks := bytes.TrimSpace(ssh.MarshalAuthorizedKey(k))
-		// add a seperator, leading quote, the key string and trailing quote
-		fmt.Fprintf(&keys, " \"%s\"", ks)
+		// add a separator, leading quote, the key string and trailing quote
+		if i > 0 {
+			keys.WriteByte(' ')
+		}
+		keys.WriteByte('"')
+		keys.Write(ks)
+		keys.WriteByte('"')
 	}
-	// return all but the first leading seperator of the string builders content as string
-	return keys.String()[1:]
+	// return the string builders content as string
+	return keys.String()
 }
 
 // filterSSHPubKeys removes non-rsa keys from n.sshPubKeys until srl adds support for them.
 func (n *srl) filterSSHPubKeys() {
+	if len(n.sshPubKeys) == 0 {
+		return
+	}
+
 	var filteredKeys []ssh.PublicKey
 
 	for _, k := range n.sshPubKeys {