Connect() function in C, invalid argument - c

Question

I'm coding a client/server, the client simply sends a message to the server that he will print the message.
To do this I used sockets and localhost. Here is the code:
server:
#include <unistd.h>
#include <stdio.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <string.h>
#include <sys/un.h>
#include <sys/socket.h>
#include"thpool.h"
#include"functions.h"
#define N 7
#define SERVER_PATH "/tmp/server"
int main(void){
unlink(SERVER_PATH);
struct sockaddr_un stru;
int sock_serv, new_sock;
int opt = 1;
struct sockaddr* cliaddr;
char buff[N];
cliaddr = malloc(sizeof(struct sockaddr));
socklen_t addrlen = strlen((char* )cliaddr);
if((sock_serv = socket(AF_UNIX, SOCK_STREAM, 0)) < 0){
printf("socket creation error");
exit(-1);
}
bzero(&stru, sizeof(struct sockaddr_in));
stru.sun_family = AF_UNIX ;
strncpy (stru.sun_path, SERVER_PATH, sizeof(stru.sun_path));
if((bind(sock_serv, (struct sockaddr*) &stru , sizeof(struct sockaddr_un ))) < 0){
perror("bind failed");
exit(EXIT_FAILURE);
}
if(listen(sock_serv, SOMAXCONN) < 0){
perror("listen error\n");
exit(EXIT_FAILURE);
}
if((new_sock = accept(sock_serv, NULL, 0)) < 0){
perror("accept error\n");
exit(EXIT_FAILURE);
}
read(new_sock , buff, N) ;
printf("Server got: %s\n" , buff);
close(sock_serv);
close(new_sock);
unlink(SERVER_PATH);
return 0;
}
and here is the client:
#include <unistd.h>
#include <stdio.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <string.h>
#include <sys/un.h>
#include <sys/socket.h>
#include<errno.h>
#include"thpool.h"
#include"functions.h"
#define SERVER_PATH "/tmp/server"
int main(void){
int sock_cl;
struct sockaddr* sa;
socklen_t sa_lenght;
sa = malloc(sizeof(struct sockaddr));
sa_lenght = strlen((char* )sa);
if((sock_cl = socket(AF_UNIX, SOCK_STREAM, 0)) < 0){
perror("socket creation error");
exit(EXIT_FAILURE);
}
sa->sa_family = AF_UNIX ;
strncpy (sa->sa_data, SERVER_PATH, sizeof(sa->sa_data));
while (connect(sock_cl , (struct sockaddr*)&sa , (socklen_t)sa_lenght) == -1) {
perror("connection to the server failed");
exit(EXIT_FAILURE);
}
write (sock_cl, "Hello!", 7);
printf("message sended\n");
close(sock_cl);
return 0;
}
I have a problem with the connect() function, the error is "invalid argument". Note that I first executed the server and then the client, so is not that the problem.

Answer 1

This is how you define sa, as a pointer to struct sockaddr.
struct sockaddr* sa;
Here you take the address of the variable sa and cast it to the type of sa.
(struct sockaddr*)&sa
The result is a pointer to pointer to struct sockaddr, which gets brute force cast to pointer to struct sockaddr.
Type-casting is a trap and you got caught in it.
To solve, I recommend using a tutorial on sockets.
I think that when comparing your client and the example client in this tutorial especially the pointer level issue you have created becomes nicely visible:
https://www.cs.rpi.edu/~moorthy/Courses/os98/Pgms/socket.html

Answer 2

Your server and client are both misusing the sockaddr... structures. The error on the server side doesn't affect anything because it is not actually using the faulty sockaddr it allocates, it just leaks. But your client is completely misusing the sockaddr that is passed to connect(), which is why connect() fails.
Try this instead:
server
#include <unistd.h>
#include <stdio.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <string.h>
#include <sys/un.h>
#include <sys/socket.h>
#include "thpool.h"
#include "functions.h"
#define N 7
#define SERVER_PATH "/tmp/server"
int main(void){
unlink(SERVER_PATH);
struct sockaddr_un stru;
int sock_serv, new_sock;
ssize_t bufflen;
char buff[N];
if((sock_serv = socket(AF_UNIX, SOCK_STREAM, 0)) < 0){
printf("socket creation error");
exit(-1);
}
bzero(&stru, sizeof(stru));
stru.sun_family = AF_UNIX;
strncpy (stru.sun_path, SERVER_PATH, sizeof(stru.sun_path));
if((bind(sock_serv, (struct sockaddr*) &stru, sizeof(stru))) < 0){
perror("bind error");
exit(EXIT_FAILURE);
}
if(listen(sock_serv, SOMAXCONN) < 0){
perror("listen error");
exit(EXIT_FAILURE);
}
if((new_sock = accept(sock_serv, NULL, 0)) < 0){
perror("accept error");
exit(EXIT_FAILURE);
}
bufflen = read(new_sock, buff, N);
if (bufflen < 0) {
perror("read error");
}
else if (bufflen == 0) {
printf("Client disconnected\n");
}
else {
printf("Server got: %.*s\n", (int) bufflen, buff);
}
close(new_sock);
close(sock_serv);
unlink(SERVER_PATH);
return 0;
}
client
#include <unistd.h>
#include <stdio.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <string.h>
#include <sys/un.h>
#include <sys/socket.h>
#include <errno.h>
#include "thpool.h"
#include "functions.h"
#define SERVER_PATH "/tmp/server"
const char *msg = "Hello!";
int main(void){
int sock_cl;
struct sockaddr_un sa;
ssize_t sent;
if((sock_cl = socket(AF_UNIX, SOCK_STREAM, 0)) < 0){
perror("socket creation error");
exit(EXIT_FAILURE);
}
bzero(&s, sizeof(sa));
sa.sa_family = AF_UNIX;
strncpy (sa.sa_data, SERVER_PATH, sizeof(sa.sa_data));
if (connect(sock_cl, (struct sockaddr*) &sa, (socklen_t) sizeof(sa)) < 0) {
perror("connect error");
exit(EXIT_FAILURE);
}
sent = write(sock_cl, msg, strlen(msg)+1);
if (sent < 0) {
perror("write error");
}
else {
printf("Message sent: %.*s\n", (int) sent, msg);
}
close(sock_cl);
return 0;
}