On 16.02.2019 20:58, Roman Lwip wrote:
Hi,
I am using lwip as part of the espressif/arduino-esp32 library and
there is something I don't understand.
My question is about DNS implementation of lwip:
https://github.com/espressif/arduino-esp32/blob/master/tools/sdk/include/lwip/lwip/dns.h
If I understand correctly there is a lookup table, which contains the
host names, which have been queried before and their ip adress. Can I
add a host to that lookup table during runtime?
Yes, see |DNS_LOCAL_HOSTLIST, ||DNS_LOCAL_HOSTLIST_ISDYNAMIC and
||dns_local_addhost().|
||
|
|
So what I want is this: The ESP32 wakes up and only does the DNS query
(dns_gethostbyname), if the IP address of an MQTT server has changed,
because an IP change of that server is not likely to happen often. So
I would save the IP address over deep sleep and use it again, when the
ESP wakes up. Do I need a dynamic host list for that (the
DNS_LOCAL_HOSTLIST macro is undefined now)? Or can I edit the lookup
table directly?
No, you can't edit the lookup table directly. However, I don't get how
you detect the IP address has changed without using dns, as that's what
dns is for...?
Regards,
Simon
_______________________________________________
lwip-users mailing list
lwip-users@nongnu.org
https://lists.nongnu.org/mailman/listinfo/lwip-users
