Attempting to write a gets like function for tcp

[David Schwartz]

"James Blackwell" <jblack@comet.linuxguru.net> wrote in message
news:slrnbgnak2.sc5.jblack@comet.linuxguru.net...

> Is there something I'm doing obviously wrong here?

I'll stick to the most obvious stuff:

> struct connection {
> int conn_no;
> int bufflen;
> char *buffer;
> char *dataend;
> };
>
> #define BUFFLEN 16384
> char *tc_getline(struct connection *s) {
> char *retval;
> char *enter;
> int i;
> int bufferleft;
> int len;
>
>
> while ( s->buffer == s->dataend || !(enter=strchr(s->buffer,'\n') {
>
> len = s->dataend - s->buffer;
> bufferleft = s->bufflen - len;
>
> i = recv(
> s->conn_no,
> s->dataend,
> bufferleft,
> 0);
>
> s->dataend[i] = '\0';

Ack! What if 'i' is '-1' or zero?

> (s->dataend) += i;
> }
> len = enter - s->buffer+1;

If s->buffer==s->dataend, 'enter' may not contain anything meaningful!

> retval = strndup(s->buffer, len);
>
> len = s->dataend-enter;
> memmove(s->buffer, enter, s->dataend-enter);

Umm, 'enter' points to the '\n', so your buffer now starts with a '\n'!
That's certainly not what you want.

> s->dataend -= len;
>
> return retval;
> }

That's the most serious stuff I could find.

DS

[Derk Gwen]

James Blackwell <jblack@comet.linuxguru.net> wrote:
#
# Hello and greetings all!
#
# I have been trying to get this code snippet to work for hours and I'm
# just plain stuck. This function is supposed to basically act like a
# gets for tcp, returning a line of data each time its called (and
# buffering remaining data until asked for) but fails miserably.
#
# The algorithm that I came up with was along these lines:
#
# while ( tcp buffer is empty | no \n in buffer) {
# grab data from the socket
# add new data to the buffer
# }

In my naivetÂŽ, I would be tempted to do that as
FILE *socket = fdopen(socketnumber,"r+");
...
fgets(line,sizeof(line),socket);
...

--
Derk Gwen [url]http://derkgwen.250free.com/html/index.html[/url]
We found a loophole; they can't keep us out anymore.

[James Blackwell]

In article <vgns664f0nhi48@corp.supernews.com>, Derk Gwen wrote:

> James Blackwell <jblack@comet.linuxguru.net> wrote:
> #
> # Hello and greetings all!
> #
> # I have been trying to get this code snippet to work for hours and I'm
> # just plain stuck. This function is supposed to basically act like a
> # gets for tcp, returning a line of data each time its called (and
> # buffering remaining data until asked for) but fails miserably.
> #
> # The algorithm that I came up with was along these lines:
> #
> # while ( tcp buffer is empty | no \n in buffer) {
> # grab data from the socket
> # add new data to the buffer
> # }
>
> In my naivetÂŽ, I would be tempted to do that as
> FILE *socket = fdopen(socketnumber,"r+");
> ...
> fgets(line,sizeof(line),socket);
> ...

Grin. I'm the naive one, not you. Shortly before you probably wrote
this a swell aussie gentleman by the name of Chris McDonald pointed
out fdopen to me. fdopen/fgets was exactly what I was looking for.

fdopen was exactly the trick for me. Now I can stop trying to implement
a tcp version of fgets as one already exists!

One thing that surprises me, though. I don't think many of the socket
examples in the wild never actually get around to mentioning that fdopen
exists.

I do appreciate the advice though. As Chris said to me in private email,
"Network coding is now so simple it's almost boring."


Again, thank you
James Blackwell