Thread: server-client injecting random char's?

i created a simple server-client application in which simple I/O is sent and received. but apparently, when the client sends a packet and the server receives it, the buffer to which the data is received is injected with random characters, usually caused because of there not being a string termination (\0), but there is.

here's the client:

Code:

#include <stdlib.h>
#include <stdio.h>
#include <windows.h>
#include "Headers\\sock.h"

int main()
{
    sock s;
    char data[512];

    startup();

    opensock(&s);
    printf("Connection[%d]\n",sockconnect(&s, "127.0.0.1", 43594));

    while(1) {
        scanf("%s", data);
        data[strlen(data)] = '\0';
        if (send((SOCKET) s, data, strlen(data), 0) == -1)
           break;
        else
            printf("SENT %s\n", data);

        int i;
        for (i = 0; i < strlen(data); i++)
            data[i] = 0;
    }

    return 0;
}

here is the server:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <windows.h>
#include "Headers\\sock.h"

typedef struct {
    sockinf *sin;
    int threadnum;
} sockinf_;

void handle(void *s)
{
    sockinf_ *sn = (sockinf_ *)s;
    char buff[512];

    printf("Client[%d]: Connected from %s\n", sn->threadnum, getip(sn->sin->addr));

    while(1) {
        if (read(&(sn->sin->s), buff, 512) > 0) {
            printf("Length %d\n", strlen(buff));
            buff[strlen(buff)] = '\0';
            printf("Client[%d]: %s\n", sn->threadnum, buff); 
            int i;
            for (i = 0; i < strlen(buff); i++)
                buff[i] = 0;
        }
        Sleep(1000);
    }
}

int main()
{
    sock s;

    printf("%d\n",startup());

    printf("%d\n", opensock(&s));
    printf("%d\n",sockbind(&s, 43594));
    if (start(&s, 100) != -1)
        printf("Started server..\n");

    int i;
    
    for (i = 1;; i++) {
        sockinf_ ss;
        sockinf ii = acceptsock(&s);
        ss.sin = &ii;
        ss.threadnum = i;
        _beginthread(handle, 0, (void *)&ss);
    }       
}

by the way, it has nothing to do with the 'sock' header i provide since it directly uses the winsock functions and returns the same return code.

Originally Posted by Salem

> data[strlen(data)] = '\0';
This does nothing - think about it.

it wouldn't work because strlen() looks for \0, but i do not know of any other way of doing this.

Originally Posted by Salem

> if (send((SOCKET) s, data, strlen(data), 0) == -1)
There are many other results as well.
In particular, send() may only be partially successful.

i am very aware of that. but right now i am only checking to see if it returns -1, because when it does, it usually means the socket is disconnected.

Originally Posted by Salem

> _beginthread(handle, 0, (void *)&ss);
Passing a pointer to a local is really bad news. Existing threads end up with trashed data the next time around the loop you go.

would something like: '_beginthread(handle, 0, ((void *))(sockinf_ *)&ss);' be better?

Originally Posted by Salem

> if (read(&(sn->sin->s), buff, 512) > 0)
Do something like

Code:

n = read(&(sn->sin->s), buff, sizeof(buff)-1)
if ( n > 0 ) {
    buff[n] = '\0';
} else if ( n == 0 ) {
  // closed
} else {
  // error
}

You can't use strlen() as you've no idea if a \0 has been sent, and read() won't add one for you just in case.

here's my read function:

Code:

int read(sock *s, char *buff, int max)
{
    int i = recv((SOCKET) *s, buff, max, 0);
    if (i > 0)
        buff[i] = '\0';

    return i;
}

but it's still not terminating the string...