Re: DNS caching(?) page-hangup issues and Opera 10.X

Kenneth Crudup <[email protected]> writes:

> I'm using the latest X64 build (which I guess is now 10.60), but for a
> long time now Opera always hangs up resolving hostnames every time I
> switch networks on my laptop.
>
> It's apparently trying to cache the previous DNS server; eventually it
> must be uncaching what it knows, as after a while I don't get hung up
> on "looking up hostname _____" (and since the page-loading timeout is
> less than the DNS resolution timeout, many times pages just stop loading
> over DNS issues).

It hangs on DNS lookups?  That's odd.  I doubt very much that we are
caching DNS server addresses, as we should not do DNS lookups ourselves.
We should be using the C library's DNS lookup functions
(e.g. gethostbyname, getaddrinfo).

Assuming that this is true, and that your observations are correct, the
obvious conclusion would be that the C library is where the problem is.
If that is true, it should be possible to test with a simple test
program.

> Is there any setting I can use to either flush DNS or stop it from
> caching DNS? I'd much rather prefer to use my local caching server on
> 127.1 anyway.

And you are sure it isn't this caching server that caches which DNS
server it is using?


Here's a test program, which looks up each name in turn.  Run it (on a
set of names which are not cached on your system...), wait for the first
lookup to be done (to be sure the C library has properly initialized the
DNS subsystem) and then switch network and see if the same problem
occurs.

(You may want to change the "sleep" parameter if 10 seconds between each
lookup isn't to your liking.  Also, this is using the classic but now
obsolete "gethostbyname".  I don't know exactly what opera is doing
these days.  But probably it ends up doing the same thing internally
anyway.)

eirik


#include <netdb.h>
#include <stdio.h>
#include <unistd.h>

int main(int argc, char ** argv)
{
	if (argc < 2)
	{
		fprintf(stderr, "usage: lookuphostloop <hostname> <hostname>...\n");
		return 1;
	};


	for (int hostnum = 1; hostnum < argc; hostnum ++)
	{
		if (hostnum > 1)
			sleep(10);
		char * hostname = argv[hostnum];
		printf("Looking up %s ... ", hostname);
		struct hostent * he = gethostbyname(hostname);
		if (he == 0)
		{
			printf("error\n");
		}
		else if (he->h_addr_list[0] == 0)
		{
			printf("none\n");
		}
		else
		{
			for (int i = 0; i < he->h_length; i++)
			{
				if (i != 0)
					printf(".");
				printf("%d", ((unsigned char *)(he->h_addr_list[0]))[i]);
			};
			printf("\n");
		};

	};
	return 0;
};
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