Delivery-Date: Tue Sep  9 20:07:42 2008
Message-Id: <200809100307.m8A374cF005625@bourbon.usc.edu>
To: cs551@merlot.usc.edu
Subject: Re: Regarding data being sent
Date: Tue, 09 Sep 2008 20:07:04 -0700
From: Bill Cheng <william@bourbon.usc.edu>

Someone wrote:

  > I had performed that same test with no luck. I am using cygwin, could that
  > be the problem?
  > 
  > struct hostent *p_hostent = NULL;
  > p_hostent = gethostbyname("www.cs.usc.xxxx");
  > assert(p_hostent == NULL); 

Interesting!  On my cygwin at home, "www.cs.usc.xxxx" also
resolves to "24.28.193.9"!  I then ran the following on cygwin:

    nslookup www.cs.usc.xxxx

I got:

    *** Can't find server name for address 192.168.1.1: Non-existent domain
    *** Default servers are not available
    Non-authoritative answer:
    Server:  UnKnown
    Address:  192.168.1.1

    Name:    www.cs.usc.xxxx.rr.com
    Address:  24.28.193.9

Since it matches what nslookup is returning, the good news is
that the code seems to be doing the right thing!  My service
provider is rr.com.  May be their resolver is being aggressive.

This is probably not a cygwin thing but a rr.com thing!
--
Bill Cheng // bill.cheng@usc.edu <URL:http://merlot.usc.edu/william/usc/>


-----Original Message-----
From: Bill Cheng [mailto:william@bourbon.usc.edu] 
Sent: Tuesday, September 09, 2008 8:08 AM
To: cs551@merlot.usc.edu
Subject: Re: Regarding data being sent

Someone wrote:

  > I thought I was doing that. I was using your example from Lecture 2 and it
  > seems that commenting out this line "memset(&my_addr, 0, sizeof(struct
  > sockaddr_in));" made things behave properly. I am still confused though,
  > because I was checking h_errno returned by gethostbyname() and it was always
  > 0. Is there significance to this addr: 24.28.193.9 as it was the default
  > when hostnames were not resolved correctly

I just wrote a tiny program to call gethostbyname("www.cs.usc.xxxx") and it
returns NULL.  Please do the same!  May be this function is not working
right for you because you have bugs in other parts of your program!
--
Bill Cheng // bill.cheng@usc.edu <URL:http://merlot.usc.edu/william/usc/>


  -----Original Message-----
  From: Bill Cheng [mailto:william@bourbon.usc.edu]
  Sent: Monday, September 08, 2008 8:52 PM
  To: cs551@merlot.usc.edu
  Subject: Re: Regarding data being sent
  
  Someone wrote:
  
    > Well I thought that when I call inet_aton() with www.cs.usc.xxxx 0
should be
    > returned (as opposed to 24.28.193.9 and a non zero return val) so that
I
    > could identify it and send the failure response message. Sounds like I
might
    > be missing something simple.
    >
    >  The inet_aton() routine interprets the specified character string as
an
    >    Internet address, placing the address into the structure provided.
It
    >    returns 1 if the string was successfully interpreted, or 0 if the
string
    >    is invalid.  The inet_addr() and inet_network() functions return
numbers
    >    suitable for use as Internet addresses and Internet network
numbers,
    >    respectively.
  
  Ah!  I see what you are asking now.  inet_aton() expects the input to be
  dotted numbers!  It's a simple format conversion routine.  So, you should
  not use it to resolve hostnames to IP addresses.  You should check the
  input.
  If the input is in the dotted number format, then you should call
  inet_aton().  If it looks like a hostname, you should call
gethostbyname().
  --
  Bill Cheng // bill.cheng@usc.edu <URL:http://merlot.usc.edu/william/usc/>
  
  
  -----Original Message-----
  From: Bill Cheng [mailto:william@bourbon.usc.edu]
  Sent: Monday, September 08, 2008 8:23 PM
  To: cs551@merlot.usc.edu
  Subject: Re: Regarding data being sent
  
  Someone wrote:
  
    > When I pass in strings like cs.usc.xxxx to inet_aton() I get
24.28.193.9
  and
    > a non-zero return value, but when I pass in nonsense like werwerw the
    > function returns 0 as the man pages say it will. Valid address work
just
    > fine. Any idea what might be causing that?
  
  Hmm...  I'm not sure what you are asking.  Sounds like it's doing what you
  want.  Could you give a more concrete example of when it does something
you
  don't want?
  --
  Bill Cheng // bill.cheng@usc.edu <URL:http://merlot.usc.edu/william/usc/>
  
  
  -----Original Message-----
  From: Bill Cheng [mailto:william@bourbon.usc.edu]
  Sent: Monday, September 08, 2008 6:57 PM
  To: cs551@merlot.usc.edu
  Subject: Re: Regarding data being sent
  
  Someone wrote:
  
    > Is it acceptable if I print the IP of nunki at the server instead of
the
    > localhost (127.0.0.1)
  
  The adr command is to get the IP address given a hostname.
  So, you should return the IP address if there is one.
  --
  Bill Cheng // bill.cheng@usc.edu <URL:http://merlot.usc.edu/william/usc/>