MDNS.setInstanceName("XXXXXXX") causing crashes

[debsahu]

Basic Infos

• This issue complies with the issue POLICY doc.
• I have read the documentation at readthedocs and the issue is not addressed there.
• I have tested that the issue is present in current master branch (aka latest git).
• I have searched the issue tracker for a similar issue.
• If there is a stack dump, I have decoded it.
• I have filled out all fields below.

Platform

• Hardware: [ESP-12]
• Core Version: [core v2.5.0-beta3]
• Development Env: [Arduino IDE|Platformio]
• Operating System: [Windows]

Settings in IDE

• Module: [Nodemcu]
• Flash Mode: [qio]
• Flash Size: [4MB/1MB]
• lwip Variant: [v2 Lower Memory|Higher Bandwidth]
• Reset Method: [nodemcu]
• Flash Frequency: [40Mhz]
• CPU Frequency: [80Mhz]
• Upload Using: [SERIAL]
• Upload Speed: [115200] (serial upload only)

Problem Description

MDNS.setInstanceName("XXXXXXXXXXXXXXX"); when paired with MDNS.update(); in loop() causes crashes.

MCVE Sketch

Below is the mDNS_Web_Server example with MDNS.setInstanceName("XXXXXXXXXXXXXXX"); line added before MDNS.begin();

/*
  ESP8266 mDNS responder sample

  This is an example of an HTTP server that is accessible
  via http://esp8266.local URL thanks to mDNS responder.

  Instructions:
  - Update WiFi SSID and password as necessary.
  - Flash the sketch to the ESP8266 board
  - Install host software:
    - For Linux, install Avahi (http://avahi.org/).
    - For Windows, install Bonjour (http://www.apple.com/support/bonjour/).
    - For Mac OSX and iOS support is built in through Bonjour already.
  - Point your browser to http://esp8266.local, you should see a response.

*/


#include <ESP8266WiFi.h>
#include <ESP8266mDNS.h>
#include <WiFiClient.h>

#ifndef STASSID
#define STASSID "iHacKedUrWiFi"
#define STAPSK  "aishu1357"
#endif

const char* ssid = STASSID;
const char* password = STAPSK;

// TCP server at port 80 will respond to HTTP requests
WiFiServer server(80);

void setup(void) {
  Serial.begin(115200);

  // Connect to WiFi network
  WiFi.mode(WIFI_STA);
  WiFi.begin(ssid, password);
  Serial.println("");

  // Wait for connection
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("");
  Serial.print("Connected to ");
  Serial.println(ssid);
  Serial.print("IP address: ");
  Serial.println(WiFi.localIP());

  // Set up mDNS responder:
  // - first argument is the domain name, in this example
  //   the fully-qualified domain name is "esp8266.local"
  // - second argument is the IP address to advertise
  //   we send our IP address on the WiFi network
  MDNS.setInstanceName("XXXXXXXXXXXXXXX");
  if (!MDNS.begin("esp8266")) {
    Serial.println("Error setting up MDNS responder!");
    while (1) {
      delay(1000);
    }
  }
  Serial.println("mDNS responder started");

  // Start TCP (HTTP) server
  server.begin();
  Serial.println("TCP server started");

  // Add service to MDNS-SD
  MDNS.addService("http", "tcp", 80);
}

void loop(void) {

  MDNS.update();

  // Check if a client has connected
  WiFiClient client = server.available();
  if (!client) {
    return;
  }
  Serial.println("");
  Serial.println("New client");

  // Wait for data from client to become available
  while (client.connected() && !client.available()) {
    delay(1);
  }

  // Read the first line of HTTP request
  String req = client.readStringUntil('\r');

  // First line of HTTP request looks like "GET /path HTTP/1.1"
  // Retrieve the "/path" part by finding the spaces
  int addr_start = req.indexOf(' ');
  int addr_end = req.indexOf(' ', addr_start + 1);
  if (addr_start == -1 || addr_end == -1) {
    Serial.print("Invalid request: ");
    Serial.println(req);
    return;
  }
  req = req.substring(addr_start + 1, addr_end);
  Serial.print("Request: ");
  Serial.println(req);
  client.flush();

  String s;
  if (req == "/") {
    IPAddress ip = WiFi.localIP();
    String ipStr = String(ip[0]) + '.' + String(ip[1]) + '.' + String(ip[2]) + '.' + String(ip[3]);
    s = "HTTP/1.1 200 OK\r\nContent-Type: text/html\r\n\r\n<!DOCTYPE HTML>\r\n<html>Hello from ESP8266 at ";
    s += ipStr;
    s += "</html>\r\n\r\n";
    Serial.println("Sending 200");
  } else {
    s = "HTTP/1.1 404 Not Found\r\n\r\n";
    Serial.println("Sending 404");
  }
  client.print(s);

  Serial.println("Done with client");
}

Debug Messages

Connected to YYYYYYYYYY
IP address: 192.168.YYY.YYY
mDNS responder started
TCP server started

Exception (28):
epc1=0x402090d2 epc2=0x00000000 epc3=0x00000000 excvaddr=0x00000000 depc=0x00000000

>>>stack>>>

ctx: cont
sp: 3ffffcb0 end: 3fffffc0 offset: 01a0
3ffffe50:  4020a860 f100a8c0 3ffee860 00000030  
3ffffe60:  4020a860 00000000 2d0e5604 40206d3c  
3ffffe70:  00000001 3ffee78c 3ffffeb0 00000001  
3ffffe80:  402091d2 3ffffeb0 3ffee78c 402091e6  
3ffffe90:  00000002 00000001 3fff01ac 40206e88  
3ffffea0:  3fffdad0 3ffee78c 3fff01ac 40204e14  
3ffffeb0:  00030000 3fff01ac 00000001 00000000  
3ffffec0:  40230000 00000000 000003e8 3ffee860  
3ffffed0:  3fffdad0 3ffee78c 3ffee78c 4020527a  
3ffffee0:  4020a860 00000000 3ffee750 402034fc  
3ffffef0:  3fffdad0 3ffee78c 3ffee82c 402060fb  
3fffff00:  3fffdad0 00000000 3ffee82c 402045fe  
3fffff10:  00000010 00000000 3ffee82c 402026af  
3fffff20:  4020a748 00000000 00001388 40100500  
3fffff30:  00000000 00000000 3fffff7c 40100948  
3fffff40:  3ffe86a3 3ffee78c 3fffff70 402098f0  
3fffff50:  3ffe86a3 3ffee78c 3ffee7f4 4020990c  
3fffff60:  3ffe86a3 3ffee78c 3ffee7f4 40202612  
3fffff70:  00000000 00000000 00000000 00000000  
3fffff80:  00000000 00000000 feefeffe feefeffe  
3fffff90:  00000000 00000000 00000001 40209ecd  
3fffffa0:  3fffdad0 00000000 3ffee82c 40209f58  
3fffffb0:  feefeffe feefeffe 3ffe8514 401009a5  
<<<stack<<<

 ets Jan  8 2013,rst cause:2, boot mode:(3,6)

load 0x4010f000, len 1384, room 16 
tail 8
chksum 0x2d
csum 0x2d
v21db8fc9
~ld

Stack Trace:

Exception 28: LoadProhibited: A load referenced a page mapped with an attribute that does not permit loads
PC: 0x402090d2: esp8266::MDNSImplementation::MDNSResponder::_sendMDNSMessage_Multicast(esp8266::MDNSImplementation::MDNSResponder::stcMDNSSendParameter&, int) at C:\Users\IIIIIIIIIIII\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.5.0-beta3\libraries\ESP8266mDNS\src\LEAmDNS_Transfer.cpp line 121
EXCVADDR: 0x00000000

Decoding stack results
0x40206d3c: esp8266::MDNSImplementation::MDNSResponder::stcMDNS_RRDomain::addLabel(char const*, bool) at C:\Users\IIIIIIIIIIII\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.5.0-beta3\libraries\ESP8266mDNS\src\LEAmDNS_Structs.cpp line 676
0x402091d2: esp8266::MDNSImplementation::MDNSResponder::_sendMDNSMessage(esp8266::MDNSImplementation::MDNSResponder::stcMDNSSendParameter&) at C:\Users\IIIIIIIIIIII\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.5.0-beta3\libraries\ESP8266mDNS\src\LEAmDNS_Transfer.cpp line 94
0x402091e6: esp8266::MDNSImplementation::MDNSResponder::_sendMDNSMessage(esp8266::MDNSImplementation::MDNSResponder::stcMDNSSendParameter&) at C:\Users\IIIIIIIIIIII\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.5.0-beta3\libraries\ESP8266mDNS\src\LEAmDNS_Transfer.cpp line 95
0x40206e88: esp8266::MDNSImplementation::MDNSResponder::stcMDNS_RRQuestion::stcMDNS_RRQuestion() at C:\Users\IIIIIIIIIIII\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.5.0-beta3\libraries\ESP8266mDNS\src\LEAmDNS_Structs.cpp line 869
0x40204e14: esp8266::MDNSImplementation::MDNSResponder::_sendHostProbe() at C:\Users\IIIIIIIIIIII\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.5.0-beta3\libraries\ESP8266mDNS\src\LEAmDNS_Control.cpp line 1235
0x4020527a: esp8266::MDNSImplementation::MDNSResponder::_updateProbeStatus() at C:\Users\IIIIIIIIIIII\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.5.0-beta3\libraries\ESP8266mDNS\src\LEAmDNS_Control.cpp line 1053
0x402034fc: ESP8266WiFiSTAClass::isConnected() at C:\Users\IIIIIIIIIIII\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.5.0-beta3\libraries\ESP8266WiFi\src\ESP8266WiFiSTA.cpp line 339
0x402060fb: esp8266::MDNSImplementation::MDNSResponder::_process(bool) at C:\Users\IIIIIIIIIIII\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.5.0-beta3\libraries\ESP8266mDNS\src\LEAmDNS_Control.cpp line 82
0x402045fe: esp8266::MDNSImplementation::MDNSResponder::update() at C:\Users\IIIIIIIIIIII\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.5.0-beta3\libraries\ESP8266mDNS\src\LEAmDNS.cpp line 1095
0x402026af: loop() at C:\Users\IIIIIIIIIIII\AppData\Local\Temp\1\arduino_modified_sketch_795762/mDNS_Web_Server.ino line 80
0x40100500: _umm_free at C:\Users\IIIIIIIIIIII\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.5.0-beta3\cores\esp8266\umm_malloc\umm_malloc.c line 1300
0x40100948: free at C:\Users\IIIIIIIIIIII\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.5.0-beta3\cores\esp8266\umm_malloc\umm_malloc.c line 1760
0x402098f0: String::invalidate() at C:\Users\IIIIIIIIIIII\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.5.0-beta3\cores\esp8266\WString.cpp line 141
0x4020990c: String::~String() at C:\Users\IIIIIIIIIIII\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.5.0-beta3\cores\esp8266\WString.cpp line 125
0x40202612: setup() at C:\Users\IIIIIIIIIIII\AppData\Local\Temp\1\arduino_modified_sketch_795762/mDNS_Web_Server.ino line 72
0x40209ecd: esp_schedule() at C:\Users\IIIIIIIIIIII\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.5.0-beta3\cores\esp8266\core_esp8266_main.cpp line 95
0x40209f58: loop_wrapper() at C:\Users\IIIIIIIIIIII\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.5.0-beta3\cores\esp8266\core_esp8266_main.cpp line 125

[LaborEtArs]

In fact this is a bug in the mDNSResponder. The call to ‘setInstanceName’ before ‘begin()’ causes a skipping of the initialization code in ‘begin()’.
As a quick workaround you can place ‘setInstanceName’ after ‘begin’.

[devyte]

Closing via #5689 .