Strange socket problems on NetBSD.

[Nate Hill]

As an exercise, I'm writing an ident server on my NetBSD box. I've searched
everywhere and can't find anything about these problems. The four relevant
lines are:

//syslog(LOG_DEBUG, (char *)strlen(input));
i = recv(infd, input, strlen(input), 0);
syslog(LOG_DEBUG, input);
send(infd, input, strlen(input), 0);

Now, the reason that the first line is commented is that, if uncommented it
somehow bypasses the next three... read() doesn't block and send() doesn't
do anything:

Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
Connection closed by foreign host.

Now, if I comment that I get normal behavior except the input isn't
stored/sent correctly:

Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
foobar
foobConnection closed by foreign host.

It only returns the first four characters all times. I also had similar
behavior at one point: It return the first three then a question mark -
foo?. When I use sizeof(input) I get loads of random characters.

--
Nate Hill <vugdeox@freeshell.org>

[William Ahern]

Nate Hill <vugdeox@freeshell.org> wrote:

> As an exercise, I'm writing an ident server on my NetBSD box. I've searched
> everywhere and can't find anything about these problems. The four relevant
> lines are:
>
> //syslog(LOG_DEBUG, (char *)strlen(input));

you can't cast the return value of strlen() to a character pointer. that's
non-sensical.

> i = recv(infd, input, strlen(input), 0);

it's possible that you mean to say sizeof(input) instead of strlen(input).
but then make sure input is defined as char input[SOME_SIZE], and not char
*input. of course, you better make sure the ident protocol guarantees you
are sent a fixed sized datum.

> syslog(LOG_DEBUG, input);
> send(infd, input, strlen(input), 0);

strings in C are char arrays (or pointers from char arrays). in order
to use strlen() you need the string to be terminated by NUL character: '\0'.
odds are the data you are being sent isn't terminated by a NUL character, but
more likely a newline '\n'.

i think you need to revisit some very basic C lessons.

read the comp.lang.c FAQ.

- Bill

[William Ahern]

Nate Hill <vugdeox@freeshell.org> wrote:

> Thanks for the answers, I will try to look at it again.
>

>> i think you need to revisit some very basic C lessons.

>
> Revisit? I never learned any basic C.
>
> I think my first C book was "Mastering Algorithms with C".

in that case, buy the "C Programming Lanuage" (2nd Edition), authored by
Brian Kernighan and Dennis Ritchie (aka the K&R book). this is requisite,
even if you are an ace programmer in some other language. i'm usually the
last person to push for a dead-tree book, but this book is a must.
it's thin and packed w/ everything you'll need to know about ANSI C.
the best tutorial and the best reference, period.

then, once you start reading the book, run through the comp.lang.c FAQ:

[url]http://www.eskimo.com/~scs/C-faq/top.html[/url]

sometimes it helps to read the answer in order to learn the question.

stick w/ ANSI C and ANSI C library routines for awhile before you move
on to Unix interfaces. you can still do an ident server w/o direct
access to the sockets. inetd can fire up your program and connect
stdin/stdout to the socket. that way you can use fread()/fwrite() (ANSI
interface) rather than read()/write() or send()/recv() (Unix interface).

it doesn't hurt to lurk on comp.lang.c. some of those guys write the
language standards, literally.

$0.02

- Bill

[Nate Hill]

William Ahern wrote:

> Nate Hill <vugdeox@freeshell.org> wrote:

>> Thanks for the answers, I will try to look at it again.
>>

>>> i think you need to revisit some very basic C lessons.

>>
>> Revisit? I never learned any basic C.
>>
>> I think my first C book was "Mastering Algorithms with C".

>
> in that case, buy the "C Programming Lanuage" (2nd Edition), authored by
> Brian Kernighan and Dennis Ritchie (aka the K&R book). this is requisite,
> even if you are an ace programmer in some other language. i'm usually the
> last person to push for a dead-tree book, but this book is a must.
> it's thin and packed w/ everything you'll need to know about ANSI C.
> the best tutorial and the best reference, period.
>
> then, once you start reading the book, run through the comp.lang.c FAQ:
>
> [url]http://www.eskimo.com/~scs/C-faq/top.html[/url]
>
> sometimes it helps to read the answer in order to learn the question.
>
> stick w/ ANSI C and ANSI C library routines for awhile before you move
> on to Unix interfaces. you can still do an ident server w/o direct
> access to the sockets. inetd can fire up your program and connect
> stdin/stdout to the socket. that way you can use fread()/fwrite() (ANSI
> interface) rather than read()/write() or send()/recv() (Unix interface).
>
> it doesn't hurt to lurk on comp.lang.c. some of those guys write the
> language standards, literally.

I can't purchase anything. however I have seen this book and Stevens book at
the library. I will read them.

--
Nate Hill <vugdeox@freeshell.org>