[lwip-devel] [task #7017] Implement DNS client

[Frédéric Bernon]

Follow-up Comment #29, task #7017 (project lwip):

>Unfortunately per-thread info isn't really sensible here - it is not just
the struct hostent that needs to be per-thread, but the contents of all the
pointers it points to. 

Yes, my own DNS client (socket based) need 5 fields per thread (hostent,
h_name, h_aliases, h_addr_list + addr) to do a clean job.

>This constraint (not being thread-safe) of gethostbyname is widely known and
any existing code should already be aware of it. People writing new code for
lwIP should read some documentation so they know it isn't thread-safe :-). 

Yes, this "socket" function design is not very good (like some old
functions). One of good point is we can add this feature to netconn wihtout
such problem (always under LWIP_DNS=1, of course). I think that such problem
(thread-safe) should be a port problem (like sys_timeouts). I understand that
some ports can be happy with just a simple static "set" of variables, but I
think we can provide a cleaner solution using macros for both cases. I will
thought about that and I'll propose something...

>Some implementations provide an alternative gethostbyname_r function, e.g.
from glibc

Yes, I have the same kind of interfaces on some stack

>I'm undecided on that personally, but I think this should not hold up 1.3. 

No, you're right, it shouldn't. But I will continue to work on that
(sequential api, and "todo list"): if it's good before 1.3.0, I will check in,
else, of course, it will wait the next release...


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