problem with unpredictable values of variable

[Matthijs Sypkens Smit <matthijs@xxxxxxxxxxxxx>]

Hi all,

I'm very interested in using the state-threads library or actually the 
server-example that's implemented with this library, but I'm experiencing 
some troubles.

I have quite some experience in coding C, but little experience with either 
threads or tcp/ip programming in C.

The problem is this:
I've tried to modifiy the server example to be able to return inputted 
strings in uppercase. Herefor I changed handle_session(...) to look like this:
---
void handle_session(long srv_socket_index, st_netfd_t cli_nfd) {
  char buf[512];

  struct in_addr *from = st_netfd_getspecific(cli_nfd);

  if (st_read(cli_nfd, buf, sizeof(buf), SEC2USEC(REQUEST_TIMEOUT)) < 0) {
    err_sys_report(errfd, "WARN: can't read request from %s: st_read",
                   inet_ntoa(*from));
    return;
  }

  if (st_write(cli_nfd, to_uppercase(buf), strlen(buf), -1) == -1) {
    err_sys_report(errfd, "WARN: can't write response to %s: st_write",
                   inet_ntoa(*from));
    return;
  }

  RQST_COUNT(srv_socket_index)++;
}
---
and added the function:
---
char* to_uppercase(char *string) {
        int i;

        for (i = 0; string[i] != '\0'; i++)
                string[i] = toupper(string[i]);

        return string;
}
---

This seemed to work at first, but today I discovered that the array of 
characters `buf' sometimes later on contained text I had inputted earlier, 
but in uppercase. I suspect that I'm either making a dumb mistake or are 
totally missing some vital concept here.

Might using '\0' not be a smart way to determine the end of a string or am I 
making some off-by-one error which causes this?

To further demonstrate the problem, the following examples:
An example of a working session is:
---
[matthijs@helena /tmp]$ telnet helena 8000
Trying 192.168.79.13...
Connected to helena.
Escape character is '^]'.
test
TEST
Connection closed by foreign host.
---

Sometimes something like this happens:
---
[matthijs@helena /tmp]$ telnet helena 8000
Trying 192.168.79.13...
Connected to helena.
Escape character is '^]'.
test
TEST
T IS EEN MEGA-LANGE-TEST. EENS ZIEN WAT HIER GAAT GEBEUREN
Connection closed by foreign host.
---
Here `T IS EEN MEGA-LANGE-TEST. EENS ZIEN WAT HIER GAAT GEBEUREN' is 
something I typed in earlier in lowercase.

I don't understand why this would happen and I'm not even sure that this has 
to do with (the threading of) the state-threads library. I sure hope someone 
can shed some light at this problem.

TIA,


-- 
Matthijs