Hostname creation cleanup, and a minimal variant or PR#5397 to fix bad DNS name

wled00/fcn_declare.h

@@ -409,7 +409,8 @@ size_t printSetFormValue(Print& settingsScript, const char* key, int val);
 size_t printSetFormValue(Print& settingsScript, const char* key, const char* val);
 size_t printSetFormIndex(Print& settingsScript, const char* key, int index);
 size_t printSetClassElementHTML(Print& settingsScript, const char* key, const int index, const char* val);
-void prepareHostname(char* hostname);
+void getWLEDhostname(char* hostname, size_t maxLen, bool preferMDNS=false); // maxLen = hostname buffer size including \0; if preferMDNSname=true, use mdns name (sanitized)
+void prepareHostname(char* hostname, size_t maxLen);                        // legacy function - not recommended for new code
 [[gnu::pure]] bool isAsterisksOnly(const char* str, byte maxLen);
 bool requestJSONBufferLock(uint8_t moduleID=JSON_LOCK_UNKNOWN);
 void releaseJSONBufferLock();

wled00/network.cpp

@@ -413,9 +413,8 @@ void WiFiEvent(WiFiEvent_t event)
       if (!apActive) {
         WiFi.disconnect(true); // disable WiFi entirely
       }
-      // convert the "serverDescription" into a valid DNS hostname (alphanumeric)
-      char hostname[64];
-      prepareHostname(hostname);
+      char hostname[64] = {'\0'}; // any "hostname" within a Fully Qualified Domain Name (FQDN) must not exceed 63 characters
+      getWLEDhostname(hostname, sizeof(hostname), true); // create DNS name based on mDNS name if set, or fall back to standard WLED server name
       ETH.setHostname(hostname);
       showWelcomePage = false;
       break;

wled00/util.cpp

@@ -127,28 +127,65 @@ size_t printSetClassElementHTML(Print& settingsScript, const char* key, const in
 }
 
 
-
-void prepareHostname(char* hostname)
-{
-  sprintf_P(hostname, PSTR("wled-%*s"), 6, escapedMac.c_str() + 6);
-  const char *pC = serverDescription;
-  unsigned pos = 5;          // keep "wled-"
-  while (*pC && pos < 24) { // while !null and not over length
-    if (isalnum(*pC)) {     // if the current char is alpha-numeric append it to the hostname
-      hostname[pos] = *pC;
-      pos++;
-    } else if (*pC == ' ' || *pC == '_' || *pC == '-' || *pC == '+' || *pC == '!' || *pC == '?' || *pC == '*') {
-      hostname[pos] = '-';
-      pos++;
+// in-place hostname sanitizer, extracted from prepareHostname()
+static void sanitizeHostname(char* hostname, size_t maxLen) {
+  if (hostname == nullptr || maxLen < 1 || strlen(hostname) < 1) return;
+
+  char *pC = hostname;
+  unsigned pos = 0;
+  while (*pC && pos < maxLen) {
+    char c = *pC;
+    if (isalnum((unsigned char)c)) {
+      hostname[pos++] = c;
+    } else if (c == ' ' || c == '_' || c == '-' || c == '+' || c == '!' || c == '?' || c == '*') { // convert certain characters to hyphens
+      if (pos > 0 && hostname[pos -1] != '-') hostname[pos++] = '-'; // keep single non-leading hyphens only
     }
-    // else do nothing - no leading hyphens and do not include hyphens for all other characters.
+    // else: drop any character not valid in a DNS hostname label
     pC++;
   }
-  //last character must not be hyphen
-  if (pos > 5) {
-    while (pos > 4 && hostname[pos -1] == '-') pos--;
-    hostname[pos] = '\0'; // terminate string (leave at least "wled")
+  // Hostname must not end with a hyphen.
+  while (pos > 0 && hostname[pos -1] == '-') pos--;
+  hostname[min(pos, maxLen-1)] = '\0'; // terminate string
+}
+
+/*
+ * Stores sanitized hostname into buffer provided by caller
+ *   maxLen = hostname buffer size including \0
+ *   preferMDNSname -> use mDNS name if set, otherwise fall back to WLED "server description" name (legacy behaviour)
+ */
+void getWLEDhostname(char* hostname, size_t maxLen, bool preferMDNS) {
+  if (maxLen <= 6) { strlcpy(hostname, "wled", maxLen); return; } // buffer too small (should not happen)
+  if (preferMDNS && (strlen(cmDNS) > 0) && (strcmp_P(cmDNS, PSTR(DEFAULT_MDNS_NAME)) != 0)) {     // avoid "x" = not set (use wled-MAC)
+    strlcpy(hostname, cmDNS, maxLen);
+    sanitizeHostname(hostname, maxLen);  // sanitize cmDNS name
+    if (strlen(hostname) < 1) {          // if result is empty -> fall back to wled-MAC
+      snprintf_P(hostname, maxLen, PSTR("wled-%*s"), 6, escapedMac.c_str() + 6);
+      hostname[maxLen -1] = '\0';        // ensure string termination
+    }
+  } else {
+    prepareHostname(hostname, maxLen); // use legacy hostname based on "server description" - already sanitized
   }
+  DEBUG_PRINTF_P(PSTR("getWLEDHostname: '%s'\n"), hostname);
+}
+
+/* Legacy hostname construction:
+ *   Start with "wled-" + serverDescription as suffix.
+ *   Sanitize only the suffix (always keep wled- prefix intact).
+ *   If the sanitized suffix ends up empty, fall back to wled-<mac>.
+ */
+void prepareHostname(char* hostname, size_t maxLen)
+{
+  if (maxLen <= 6) { strlcpy(hostname, "wled", maxLen); return; } // buffer too small (should not happen)
+  if (strncasecmp_P(serverDescription, PSTR("wled"), 4) == 0)     // avoid wled-WLED-... as a hostname
+    strlcpy(hostname, serverDescription, maxLen);
+  else
+    snprintf_P(hostname, maxLen, PSTR("wled-%s"), serverDescription);
+  hostname[maxLen -1] = '\0';                             // ensure string termination
+
+  size_t sanOffset = hostname[4] != '-' ? 4 : 5;            // ensure that "WLED foo" and "WLED!foo" get sanitized
+  sanitizeHostname(hostname+sanOffset, maxLen-sanOffset);   // sanitize name, keep "wled-" intact
+  if (strlen(hostname) <= sanOffset)
+    snprintf_P(hostname, maxLen, PSTR("wled-%*s"), 6, escapedMac.c_str() + 6); // fallback to wled-MAC if sanitization cleaned everything
 }
 
 

wled00/wled.cpp

@@ -507,8 +507,12 @@ void WLED::setup()
   #ifndef ESP8266
   WiFi.setScanMethod(WIFI_ALL_CHANNEL_SCAN);
   WiFi.persistent(true); // storing credentials in NVM fixes boot-up pause as connection is much faster, is disabled after first connection
+  // ESP32 DNS name must be set before the first connection to the DHCP server; otherwise, the default ESP name (such as "esp32s3-267D0C") will be used.
+  char hostname[64] = {'\0'};
+  getWLEDhostname(hostname, sizeof(hostname), true);   // create DNS name based on mDNS name if set, or fall back to standard WLED server name
+  WiFi.setHostname(hostname);
   #else
-  WiFi.persistent(false); // on ES8266 using NVM for wifi config has no benefit of faster connection
+  WiFi.persistent(false); // on ESP8266 using NVM for wifi config has no benefit of faster connection
   #endif
   WiFi.onEvent(WiFiEvent);
   WiFi.mode(WIFI_STA); // enable scanning
@@ -691,6 +695,18 @@ void WLED::initConnection()
   WiFi.setPhyMode(force802_3g ? WIFI_PHY_MODE_11G : WIFI_PHY_MODE_11N);
 #endif
 
+  char hostname[64] = {'\0'};
+  getWLEDhostname(hostname, sizeof(hostname), true); // create DNS name based on mDNS name if set, or fall back to standard WLED server name
+
+#ifdef ARDUINO_ARCH_ESP32
+  // Reset mode to NULL to force a full STA mode transition, so that WiFi.mode(WIFI_STA) below actually applies the hostname (and TX power, etc.).
+  // This is required on reconnects when mode is already WIFI_STA.
+  WiFi.mode(WIFI_MODE_NULL);
+  apActive = false;           // the AP is physically torn down by WIFI_MODE_NULL
+  delay(5);                   // give the WiFi stack time to complete the mode transition
+  WiFi.setHostname(hostname);
+#endif
+
   if (multiWiFi[selectedWiFi].staticIP != 0U && multiWiFi[selectedWiFi].staticGW != 0U) {
     WiFi.config(multiWiFi[selectedWiFi].staticIP, multiWiFi[selectedWiFi].staticGW, multiWiFi[selectedWiFi].staticSN, dnsAddress);
   } else {
@@ -718,10 +734,6 @@ void WLED::initConnection()
 
     DEBUG_PRINTF_P(PSTR("Connecting to %s...\n"), multiWiFi[selectedWiFi].clientSSID);
 
-    // convert the "serverDescription" into a valid DNS hostname (alphanumeric)
-    char hostname[25];
-    prepareHostname(hostname);
-
 #ifdef WLED_ENABLE_WPA_ENTERPRISE
     if (multiWiFi[selectedWiFi].encryptionType == WIFI_ENCRYPTION_TYPE_PSK) {
       DEBUG_PRINTLN(F("Using PSK"));
@@ -774,8 +786,7 @@ void WLED::initConnection()
 #ifdef ARDUINO_ARCH_ESP32
     WiFi.setTxPower(wifi_power_t(txPower));
     WiFi.setSleep(!noWifiSleep);
-    WiFi.setHostname(hostname);
-#else
+#else // ESP8266 accepts a hostname set after WiFi interface initialization
     wifi_set_sleep_type((noWifiSleep) ? NONE_SLEEP_T : MODEM_SLEEP_T);
     WiFi.hostname(hostname);
 #endif