WiFi.config() can not set DNS.

[nnnntosh]

Hardware:

Board: ESP32 Dev Module
Core Installation/update date: 1/Aug/2017
IDE name: Arduino IDE
Flash Frequency: ?
Upload Speed: 115200

Description:

I am trying to set DNS with WiFi.config(), but DNS lookup ( gethostbyname()) fails.

WiFi.config(ip, gateway, subnet, dns1, dns2);

I tried debugging ESP-IDF. and I have found that DNS response was dropped.
This is the code below.

esp-idf/components/lwip/core/dns.c

        /* Check whether response comes from the same network address to which the
           question was sent. (RFC 5452) */
        if (!ip_addr_cmp(addr, &dns_servers[entry->server_idx])) {
          /* call callback to indicate error, clean up memory and return */
          goto responseerr;
        }

ip_addr_cmp() checks that addr->type matches, but they were not the same.

I checked how to set up DNS with WiFi.config(). Nothing is set to addr->type, it is undefined value.

arduino-esp32/libraries/WiFi/src/WiFiSTA.cpp

    if(dns1 != (uint32_t)0x00000000) {
        // Set DNS1-Server
        d.u_addr.ip4.addr = static_cast<uint32_t>(dns1);
        dns_setserver(0, &d);
    }

I also found that DNS works correctly when I modify the code as follows.

    if(dns1 != (uint32_t)0x00000000) {
        // Set DNS1-Server
        d.u_addr.ip4.addr = static_cast<uint32_t>(dns1);
        IP_SET_TYPE(&d, IPADDR_TYPE_V4);
        dns_setserver(0, &d);
    }

By the way, I think that ip_addr_set_ip4_u32() should be used,
It is not possible because the following build error appears due to gcc option [- Werror = address].

error: the address of 'd' will always evaluate as 'true' [-Werror=address]

[me-no-dev]

Nice catch!

[hutje]

WiFi.setDNS() isn't recognized as function... It is once called in the esp32 WIFI library as keyword but never used.