fix(mdns): defer setup-state mutation until validated; drop dead setters

Two cursorbot findings on 57968fd:

1. handleSetup assigned config.LocalAuthMode before validating the
   password (length, bcrypt). On validation failure it returned
   without SaveConfig, but the in-memory LocalAuthMode was already
   dirty — so a subsequent restartMdns (e.g. from
   networkStateChanged) would publish `setup=true` over Bonjour
   even though the device hadn't actually been set up, and the
   "Device is already set up" guard at the top of handleSetup
   would refuse the user's retry. Move the assignment after all
   validation succeeds, and roll back the in-memory state if
   SaveConfig itself fails.

2. SetService / SetLocalNames / SetListenOptions (and their inner
   set* helpers) are unused — only SetOptions is called from
   restartMdns. Since they could even mislead future maintainers
   into bypassing the atomic SetOptions path, drop them along with
   the now-unused `reflect` import.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: mcuelenaere

internal/mdns/mdns.go

@@ -20,7 +20,6 @@ package mdns
 import (
 	"fmt"
 	"net"
-	"reflect"
 	"strings"
 
 	"github.com/jetkvm/kvm/internal/logging"
@@ -327,60 +326,6 @@ func (m *MDNS) Stop() error {
 	return err
 }
 
-func (m *MDNS) setLocalNames(localNames []string) {
-	m.lock.Lock()
-	defer m.lock.Unlock()
-
-	if reflect.DeepEqual(m.localNames, localNames) {
-		return
-	}
-
-	m.localNames = localNames
-}
-
-func (m *MDNS) setListenOptions(listenOptions *MDNSListenOptions) {
-	m.lock.Lock()
-	defer m.lock.Unlock()
-
-	if m.listenOptions != nil &&
-		listenOptions != nil &&
-		m.listenOptions.IPv4 == listenOptions.IPv4 &&
-		m.listenOptions.IPv6 == listenOptions.IPv6 {
-		return
-	}
-
-	m.listenOptions = listenOptions
-}
-
-func (m *MDNS) setService(service *MDNSService) {
-	m.lock.Lock()
-	defer m.lock.Unlock()
-
-	if reflect.DeepEqual(m.service, service) {
-		return
-	}
-
-	m.service = service
-}
-
-// SetLocalNames sets the local names and restarts the mDNS server
-func (m *MDNS) SetLocalNames(localNames []string) error {
-	m.setLocalNames(localNames)
-	return m.Restart()
-}
-
-// SetListenOptions sets the listen options and restarts the mDNS server
-func (m *MDNS) SetListenOptions(listenOptions *MDNSListenOptions) error {
-	m.setListenOptions(listenOptions)
-	return m.Restart()
-}
-
-// SetService sets the advertised DNS-SD service and restarts the mDNS server
-func (m *MDNS) SetService(service *MDNSService) error {
-	m.setService(service)
-	return m.Restart()
-}
-
 // SetOptions sets the local names, listen options, and service, then
 // restarts the mDNS server. All three fields are updated under a
 // single lock acquisition so a concurrent restart can't observe a

web.go

@@ -870,8 +870,13 @@ func handleSetup(c *gin.Context) {
 		return
 	}
 
-	config.LocalAuthMode = req.LocalAuthMode
-
+	// Validate the full request and compute the new state BEFORE
+	// touching config. If any check fails we return early and leave
+	// the device in its pre-setup state — otherwise an aborted setup
+	// would leave LocalAuthMode set in memory and trip the
+	// "already set up" guard on retry (and leak `setup=true` over
+	// mDNS on the next restartMdns).
+	var newHashedPassword, newAuthToken string
 	if req.LocalAuthMode == "password" {
 		if req.Password == "" {
 			passwordRateLimiter.RecordFailure(ip)
@@ -890,30 +895,38 @@ func handleSetup(c *gin.Context) {
 			return
 		}
 
-		// Hash the password
 		hashedPassword, err := bcrypt.GenerateFromPassword([]byte(req.Password), bcrypt.DefaultCost)
 		if err != nil {
 			c.JSON(http.StatusInternalServerError, gin.H{"error": "Failed to hash password"})
 			return
 		}
 
-		config.HashedPassword = string(hashedPassword)
-		config.LocalAuthToken = uuid.New().String()
-
-		// Set the cookie
-		c.SetCookie("authToken", config.LocalAuthToken, authTokenMaxAge, "/", "", false, true)
-	} else {
-		// For noPassword mode, ensure the password field is empty
-		config.HashedPassword = ""
-		config.LocalAuthToken = ""
+		newHashedPassword = string(hashedPassword)
+		newAuthToken = uuid.New().String()
 	}
 
-	err := SaveConfig()
-	if err != nil {
+	// All validation passed — commit. If SaveConfig fails, roll the
+	// in-memory state back so a retry can succeed.
+	prevAuthMode := config.LocalAuthMode
+	prevHashedPassword := config.HashedPassword
+	prevAuthToken := config.LocalAuthToken
+
+	config.LocalAuthMode = req.LocalAuthMode
+	config.HashedPassword = newHashedPassword
+	config.LocalAuthToken = newAuthToken
+
+	if err := SaveConfig(); err != nil {
+		config.LocalAuthMode = prevAuthMode
+		config.HashedPassword = prevHashedPassword
+		config.LocalAuthToken = prevAuthToken
 		c.JSON(http.StatusInternalServerError, gin.H{"error": "Failed to save config"})
 		return
 	}
 
+	if req.LocalAuthMode == "password" {
+		c.SetCookie("authToken", config.LocalAuthToken, authTokenMaxAge, "/", "", false, true)
+	}
+
 	// Refresh the mDNS advertisement so the `setup=` TXT record
 	// flips from false to true now that the device is provisioned.
 	restartMdns()