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Re: Bug report for release 2.4 on linux

From: Uwe F Mayer <mayer@tux.org>
Date: Tue, 29 Feb 2000 18:11:42 -0500 (EST)
To: jose.kahan@w3.org
cc: www-amaya@w3.org
Message-ID: <Pine.LNX.4.10.10002291808300.24697-100000@gwyn.tux.org>
More about symbolic hostname resolution with Amaya. First of all, the
error message I am getting when using a symbolic URL is this one:

	The requested URL could not be retrieved
	While trying to retrieve the URL:http://www.yahoo.com/
	The following error was encountered:
	Connection Failed
	The system returned:
	(51) www.yahoo.com
	This means that:
	The remote site or server may be down or non-existent.
	Please try again soon

I was asked what system I am running, so here is some info on that:
Toshiba 4015CDT Laptop, 96MB RAM, Pentium II 266 MHz, running Linux.
This is a libc5 based system, however, the libc6 libraries are
installed also. This was originally a Slackware-based installation,
but is by now heavily modified. "uname -a" gives:
Linux tosca 2.2.12 #1 Tue Nov 16 10:56:02 MET 1999 i686 unknown

It was suggested that there is a problem with the gethostbyname
routine on my machine. I therefore wrote a little C program that just
places this system call, and it seems to have some problem depending
on what C library one uses. It seems that there is a problem with
glibc2 to be precise. Here is a sample run while on-line (I use
dial-up networking), using a libc-5.4.46 based binary, and it works
just fine:

	tosca:~/tmp$ ./gethostbyname-libc5 finanzen.de.yahoo.com
	gethostbyname returned h_errno = 0, which should mean:
	no problem
	
	official name of host:  de.finance.yahoo.com
	alias list [0]:         finanzen.de.yahoo.com
	host address type:      2
	length of address:      4
	address list [0]:       194.237.109.9
	address list [1]:       194.237.109.10
	address list [2]:       194.237.109.15
	
I also have access to a glibc2 (libc-2.0.7) based system. I compiled
the gethostname test program there, got it back to my machine, and ran
it, dynamically linked against glibc2, of course, but a newer
version, libc-2.1.2. This is what I got:

	tosca:~$ tmp/gethostbyname-glibc2 finanzen.de.yahoo.com
	gethostbyname returned h_errno = 2, which should mean:
	Non-Authoritive Host not found, or SERVERFAIL
	Segmentation fault

Thus it occurred to me, that maybe my C library is bad (I did compile
it myself ;-)). Hence I installed the libc-2.0.7 libraries from the
other machine, and ran the same binary as before, but now dynamically
linked against libc-2.0.7:

	tosca:~/tmp$ ./gethostbyname-glibc2 finanzen.de.yahoo.com
	gethostbyname returned h_errno = 1, which should mean:
	Authoritative Answer Host not found
	
	official name of host:  de.finance.yahoo.com
	alias list [0]:         finanzen.de.yahoo.com
	host address type:      2
	length of address:      4
	address list [0]:       194.237.109.10
	address list [1]:       194.237.109.15
	address list [2]:       194.237.109.9
	
Clearly something is wrong here, because the glibc2 version of
gethostname reports an error through its error variable h_errno, while
there really was no error. The source code to gethostbyname is
appended at the end of this email.

Curiously enough however, using libc-2.0.7 did in fact fix my DNS
problems with Amaya!

Just to make sure I also down-loaded the source of Amaya and compiled
it, and that libc-5.4.46 based binary worked fine (well, there were
obvious LessTif based problems, but that's a different story).

It would be interesting to know if Amaya really does have a problem
with libc-2.1.2, or if it was just my copy of the C library that is
bad. Anyways, it seems clear now that Amaya's code is not at
fault, at least as long as one uses the right library versions.

The only problem is now that RealPlayerG2 needs libc-2.1 to run. Oh
well, I'll write a wrapper script to load the correct version and edit
the binary to get the correct dynamic loader.

Cheers,

Uwe
<mayer@tux.org>
---------------------------------------------------------------------
/* 
   Sat Feb 12 11:05:27 MET 2000
   Uwe F. Mayer <mayer@tux.org>

   This program reads out the results of a gethostname() call.
   It takes a single argument which is a DNS IP address.
   
   */

#include <stdlib.h>
#include <stdio.h>
#include <netdb.h>
extern int h_errno;

int main(int argc, char * argv[]){
  int i,j;
  struct hostent *hostname;
  hostname=(struct hostent *)malloc(sizeof(struct hostent));
  hostname=gethostbyname(argv[1]);
  printf("gethostbyname returned h_errno = %d, which should mean:\n",
    h_errno);
  switch (h_errno){
  case NETDB_INTERNAL:
    printf("internal error in gethostbyname()\n");break;
  case NETDB_SUCCESS:
    printf("no problem\n");break;
  case HOST_NOT_FOUND:
    printf("Authoritative Answer Host not found\n");break;
  case TRY_AGAIN:
    printf("Non-Authoritive Host not found, or SERVERFAIL\n");break;
  case NO_RECOVERY:
    printf("Non recoverable errors, FORMERR, REFUSED, NOTIMP\n");break;
  case NO_DATA:
    printf("Valid name, no data record of requested type\n");break;
  default:
    printf("invalid return code in h_errno after gethostbyname() call\n");
  }
  /*
     We will try to print the results anyways, regardless of the error
     code. Of course, that might lead to "Segmentation fault" errors.
  */
  printf("\nofficial name of host:  %s\n",hostname->h_name);
  i=0;
  while (((*hostname).h_aliases)[i] != NULL){
    printf("alias list [%d]:         %s\n",i,hostname->h_aliases[i]);
    i++;
  }
  printf("host address type:      %d\n",hostname->h_addrtype);
  printf("length of address:      %d\n",hostname->h_length);
  i=0;
  while (((*hostname).h_addr_list)[i] != NULL){
    printf("address list [%d]:       ",i);
    for(j=0;j<hostname->h_length;j++){
	printf("%d",(int)(unsigned char)(hostname->h_addr_list[i][j]));
	if (j!=hostname->h_length-1){
	  printf(".");
	}
    }
    printf("\n");
    i++;
  }
  printf("\n");
  return(0);
}
Received on Wednesday, 1 March 2000 02:55:54 UTC

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