mDNS Failure Outside loop()

[lbussy]

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. (N/A)
• I have filled out all fields below.

Platform

• Hardware: ESP-12S
• Core Version: SDK:2.2.1(cfd48f3)/Core:2.5.2=20502000/lwIP:STABLE-2_1_2_RELEASE/glue:1.1-7-g82abda3/BearSSL:a143020
• Development Env: Platformio
• Operating System: Windows

Settings in IDE

• Module: Wemos D1 mini r2
• Flash Mode: qio
• Flash Size: 4Mb
• lwip Variant: v2 Lower Memory
• Reset Method: ck
• Flash Frequency: 40Mhz
• CPU Frequency: 80Mhz
• Upload Using: SERIAL
• Upload Speed: 460800

Problem Description

mDNS resolution fails with -5 when called with Ticker, however works (the first time) when called in the loop().

MCVE Sketch

#include <WiFiClient.h>
#include <ESP8266WiFi.h>
#include <Ticker.h>
#include <Arduino.h>

void setup();
void loop();

void setup()
{
    Serial.begin(74880);
    Serial.setDebugOutput(true);
    Serial.flush();
    WiFi.begin(F("Xxxxxx"), F("xxxxxxxx"));
    Serial.println();
    Serial.print(F("Waiting for connection."));
    while (WiFi.status() != WL_CONNECTED)     {
        Serial.print(F("."));
        delay(500);
    }
    Serial.println();
    Serial.println(F("Connected."));
    Serial.print(F("DNS #1: "));
    Serial.print(WiFi.dnsIP().toString().c_str());
    Serial.print(F(", DNS #2: "));
    Serial.println(WiFi.dnsIP(1).toString().c_str());
}

void loop() {
    IPAddress resolvedIP;
    const char* host = "raspberrypi.local";
    if (!WiFi.hostByName(host, resolvedIP)) {
        Serial.print(F("Host lookup failed for "));
        Serial.println(host);
    }
    Serial.print(F("Host: "));
    Serial.print(host);
    Serial.print(", IP: ");
    Serial.println(resolvedIP.toString().c_str());

    Ticker lookup;
    lookup.attach(10, [lookup]() {
        IPAddress resolvedIP;
        const char* host = "raspberrypi.local";
        if (!WiFi.hostByName(host, resolvedIP)) {
            Serial.print(F("Host lookup failed for "));
            Serial.println(host);
        }
        Serial.print(F("Host: "));
        Serial.print(host);
        Serial.print(", IP: ");
        Serial.println(resolvedIP.toString().c_str());
    });

    while (true) { yield(); }
}

Debug Messages

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

load 0x4010f000, len 1384, room 16
tail 8
chksum 0x2d
csum 0x2d
v8b899c12
~ld

SDK:2.2.1(cfd48f3)/Core:2.5.2=20502000/lwIP:STABLE-2_1_2_RELEASE/glue:1.1-7-g82abda3/BearSSL:a143020
scandone

Waiting for connection....wifi evt: 2
...scandone
state: 0 -> 2 (b0)
.state: 2 -> 3 (0)
state: 3 -> 5 (10)
add 0
aid 3
cnt

connected with Xxxxxx, channel 8
dhcp client start...
wifi evt: 0
ip:192.xxx.xxx.155,mask:255.255.255.0,gw:192.xxx.xxx.1
wifi evt: 3

Connected.
DNS #1: 1.1.1.1, DNS #2: 1.0.0.1
[hostByName] request IP for: raspberrypi.local
[hostByName] Host: raspberrypi.local IP: 192.xxx.xxx.131
Host: raspberrypi.local, IP: 192.xxx.xxx.131
pm open,type:2 0
[hostByName] request IP for: raspberrypi.local
[hostByName] Host: raspberrypi.local lookup error: -5!
Host lookup failed for raspberrypi.local
Host: raspberrypi.local, IP: (IP unset)

[devyte]

This has nothing to do with mDNS. This is normal DNS.
To be specific, WiFi.hostByName() does DNS resolution only, but your hostname is .local which is mDNS.
For mDNS use the MDNS class.
Closing due to user error.