Chat client in c - c

Question

Problem:
I need some help with an error in my code. The chat client works when I only have one client running but if i use more clients. Only the last client messages will show up on my server. my client.c seems to work since it is sending but for some reason recv() is not getting the previous client send().
How code works:
I set up my server and spawn a new thread whenever a new client connects. the thread will handle the messages i get form the client and print it on the server screen.
Code:
CLIENT.C
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <netdb.h>
#include <unistd.h>
#include <signal.h>
#include <assert.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
int main(int argc, char ** argv){
//get port
//int port = atoi(argv[1]);
int server_port = atoi(argv[1]);
char * name =argv[2];
int namelength = strlen(name);
//set up server adress and socket
int sock = socket(AF_INET,SOCK_STREAM,0);
struct sockaddr_in server;
memset(&server, 0, sizeof(server));
server.sin_family = AF_INET;
server.sin_addr.s_addr = inet_addr("127.0.0.1");
server.sin_port = htons(server_port);
//connect
if (connect(sock, (struct sockaddr *)&server, sizeof(server)) < 0) {
perror("connect failed");
exit(1);
}
//set up client name
char * buff = malloc(5000*sizeof(char));
//get the chatting
//char * other_message = malloc(5000*sizeof(char));
while(1){
printf("ENTER MESSAGE:\n");
char message[5000];
strcpy(message, name);
strcat(message,": ");
printf("%s", message);
scanf("%[^\n]",buff);
getchar();
strcat(message,buff);
int sent = send(sock , message , strlen(message) , MSG_DONTWAIT );
if (sent == -1)
perror("Send error: ");
else
printf("Sent bytes: %d\n", sent);
}
return 0;
}
SERVER.C
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <pthread.h>
#include <netdb.h>
#include <unistd.h>
#include <signal.h>
#include <assert.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
pthread_t * threads = NULL;
int * client_fd = NULL;
int num_clients;
int thread_num;
void * client_handler(void * cl)
{
int * client = (int *)cl;
char * message = malloc(5000*sizeof(char));
printf("Connected: %d\n",*client);
int byte=1;
//recieve the message from clients
while(1)
{
byte=recv(*client, message , 5000 , 0);
if(byte< 0)
break;
//send message to all other clients
printf("%s\n",message);
printf("Recieved bytes:%d\n",byte);
memset(message, 0, 5000);
/*for(i=0;i<num_clients;i++)
if(client_fd[i]!=*client)
send(*client , message , strlen(message),0);*/
}
printf("finished: %d\n",*client);
return NULL;
}
int main(int argc, char ** argv)
{
//get the port
int port = atoi(argv[1]);
//set up socket
int socket_fd = socket(AF_INET,SOCK_STREAM,0);
struct sockaddr_in server,client;
memset(&server, 0, sizeof(server));
server.sin_family = AF_INET;
server.sin_addr.s_addr = INADDR_ANY;
server.sin_port = htons(port);
//bind
if(bind(socket_fd, (struct sockaddr*)&server,sizeof(server)) < 0 ){
perror("binding error\n");
exit(1);
}
//listen
if( listen(socket_fd, 10) <0){
perror("binding error\n");
exit(1);
}
//accept incoming connectionns
threads = malloc(10*sizeof(pthread_t));
client_fd = malloc(10*sizeof(int));
int i=0;
int c = sizeof(struct sockaddr_in);
while(1)
{
int c_fd = accept(socket_fd,(struct sockaddr *)&client, (socklen_t*)&c);
if(c_fd < 0)
printf("error");
client_fd[i]=c_fd;
pthread_create(&threads[i],NULL,client_handler,(void *)(&c_fd));
i++;
num_clients=i;
}
return 0;
}

Answer 1

Sending C-style strings with strlen(). Does not send the terminating null. Use strlen()+1
Ignoring the value returned by recv(). TCP is a streaming protocol that only transfers bytes/octets. It does not transfer anything more complex. recv() may return one byte of your chat line, all of your chat line, or anything in between. To transfer any message more complex than one byte, you need a protocol and you must handle it. Yours is 'chat lines are null-terminated strings', so you need to call recv() in a loop and, using the returned value, concatenate the bytes received until the null arrives.
Trying to printf non-strings with "%s". You must not attempt to print out the received data until you are sure that a null has been received.