Implementing threads with sockets in C - c

Question

so i'm trying to implement a basic client-server calculator with threads. I was able to implement the communication between cliente-server with sockets but i'm at a loss when i try to add threads to the code.
This is my first time using this forum so please sorry if i'm making a dumb question but i already searched for some answers and i can't find anything that helps :(
I can upload my whole code bit for now i think this will suffice:
Creating a thread in main:
while(cliente_socket_fd = accept(socket_fd,(struct sockaddr*)&name_cliente,(socklen_t*)&cliente_name_len))
{
pthread_t thread;
new_sock = malloc(1);
*new_sock = cliente_socket_fd;
if(i <= nThreads) // nThreads is the maximum of threads permitted
{
if(pthread_create(&thread, NULL, connectionSocket, (void*)new_sock) < 0)
{
perror("Error");
return 1;
}
i++;
}
}
Function that recives information from create thread:
void *connectionSocket(void *sockR)
{
int sock = *(int*)sockR;
int x;
char buffer[1024];
do{
x = strlen(buffer) + 1;
read(sock,buffer, x);
readSocket(sock, buffer);
}while(1 || strcmp(buffer,"end") != 0);
close(sock);
return 0;
}
Server read socket function:
int readSocket(int sock, const char* buffer)
{
//char buffer[1024];
//char message[1024] ;
int ssize;
ssize = strlen(buffer);
if(ssize == 0)
return 0;
char* message = (char*) malloc(ssize);
//memset(buffer, 0, sizeof buffer);
memset(message, 0, sizeof message);
strcat(message, buffer);
...
writeSocket(sock, message);
...
Function that writes in the socket:
void writeSocket(int sock, const char* mensagem)
{
int ssize = strlen(message) + 1;
write(sock, &ssize, sizeof(ssize));
write(sock, message, ssize);
}
Again sorry if i'm being a noob or asking too much but any help is greatly appreciated. Thanks.

Answer 1

in function: connectionSocket()
this line
x = strlen(buffer) + 1;
is garbage because strlen() stops when it finds a NUL byte.
However, the buffer has not been set to a known condition so there may or may not be a NUL byte in the buffer. I.E. undefined behavior.
the accept() function returns -1 when an error occurs, However the posted code will blindly continue into the body of the loop
Suggest writing that line similar to:
while( 1 )
{
cliente_socket_fd = accept(socket_fd,(struct sockaddr*)&name_cliente, (socklen_t*)&cliente_name_len) );
if( -1 == cliente_socket_fd )
{
perror( "accept failed" );
break; // exit loop
}
// implied else, accept successful
then, to be able to access those threads, later, this line:
if(pthread_create(&thread, NULL, connectionSocket, (void*)new_sock) < 0)
should be setting a 'unique' 'thread' rather than the only 'thread' Suggest:
pthread_t thread[ nThreads ] = {0};
if(pthread_create(&thread[i], NULL, connectionSocket, (void*)new_sock) < 0)
then, a socket is (effectively) an integer, which, depending on the underlying hardware architecture is 4 or 8 bytes So this line:
new_sock = malloc(1);
does not allocate enough bytes, it should be:
new_sock = malloc( sizeof( int ) );
if( !new_sock )
{ // then, malloc failed
perror( "malloc failed" );
break; // exit loop
}
// implied else, malloc successful
*new_sock = cliente_socket_fd;
this line:
}while(1 || strcmp(buffer,"end") != 0);
will never exit the loop. Suggest:
}while( strcmp(buffer,"end") != 0 );
this line:
read(sock,buffer, x);
will try to read some random number of bytes because the value in 'x' is not valid. Suggest;
read(sock,buffer, sizeof( buffer ));
the above are the most obvious problems in the posted code. If you had posted a cleanly compiles, short, example that can be run and still shows the problems, I could have helped you more.