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This adds the option to have lws do its own dns resolution on
the event loop, without blocking.  Existing implementations get
the name resolution done by the libc, which is blocking.  In
the case you are opening client connections but need to carefully
manage latency, another connection opening and doing the name
resolution becomes a big problem.

Currently it supports

 - ipv4 / A records
 - ipv6 / AAAA records
 - ipv4-over-ipv6 ::ffff:1.2.3.4 A record promotion for ipv6
 - only one server supported over UDP :53
 - nameserver discovery on linux, windows, freertos

It also has some nice advantages

 - lws-style paranoid response parsing
 - random unique tid generation to increase difficulty of poisoning
 - it's really integrated with the lws event loop, it does not spawn
   threads or use the libc resolver, and of course no blocking at all
 - platform-specific server address capturing (from /etc/resolv.conf
   on linux, windows apis on windows)
 - it has LRU caching
 - piggybacking (multiple requests before the first completes go on
   a list on the first request, not spawn multiple requests)
 - observes TTL in cache
 - TTL and timeout use lws_sul timers on the event loop
 - ipv6 pieces only built if cmake LWS_IPV6 enabled
2 contributors

Users who have contributed to this file

@lws-team @jvijtiuk
56 lines (43 sloc) 2.52 KB
Libwebsockets and included programs are provided under the terms of the
MIT license shown below, with the exception that some sources are under
a similar permissive license like BSD, or are explicitly CC0 / public
domain to remove any obstacles from basing differently-licensed code on
them.
Original liberal license retained:
- lib/misc/sha-1.c - 3-clause BSD license retained, link to original
- win32port/zlib - ZLIB license (see zlib.h)
- lib/tls/mbedtls/wrapper - Apache 2.0 (only built if linked against mbedtls)
- lib/misc/base64-decode.c - already MIT
Relicensed to MIT:
- lib/misc/daemonize.c - relicensed from Public Domain to MIT,
link to original Public Domain version
- lib/plat/windows/windows-resolv.c - relicensed from "Beerware v42" to MIT
Public Domain (CC-zero) to simplify reuse:
- test-apps/*.c
- test-apps/*.h
- minimal-examples/*
- lwsws/*
Although libwebsockets is available under a permissive license, it does not
change the reality of dealing with large lumps of external code... if your
copy diverges it is guaranteed to contain security problems after a while
and can be very painful to pick backports (especially since historically,
we are very hot on cleaning and refactoring the codebase). The least
painful and lowest risk way remains sending your changes and fixes upstream
to us so you can easily use later releases and fixes.
MIT License applied to libwebsockets:
https://opensource.org/licenses/MIT
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The above copyright notice and this permission notice shall be included in
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