Socket, accept() function, Invalid argument - c

Question

I am getting an error "Invalid argument" when i call the accept() function on the server side of a client-server application. I don't get what is wrong and if you see what is wrong let me know please. Thanks.
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
int main(int argc, char* argv[])
{
int sockfd, newsockfd, portno, len;
struct sockaddr_in server, client;
if(argc < 2){
perror("Add more arguments");
}
sockfd = socket(AF_UNIX,SOCK_STREAM,0);
if(sockfd < 0){
perror("Error at socket()");
}
printf("Socketfd: %d\n",sockfd);
bzero((char *)&server, sizeof(server));
portno = atoi(argv[1]);
server.sin_family = AF_UNIX;
server.sin_addr.s_addr = INADDR_ANY;
server.sin_port = htons(portno);
if(bind (sockfd, (struct sockaddr *)&server, sizeof(server)) <0){
perror("Error at bind ()-server");
}
listen(sockfd,5);
int readval;
char buffer[256];
for(;;){
len = sizeof(client);
newsockfd = accept (sockfd, (struct sockaddr *)&server,&len);
if (newsockfd == -1){
perror("Erroare at accept()");
}
else do{
readval = (sockfd,buffer,sizeof(buffer));
if (readval < 0 ){
perror("Error at reading()");
}
else if (readval == 0){
printf("End conection");
}
else{
printf("Mesage is: %s\n", buffer);
}
}while (readval > 0);
close(newsockfd);
}
return 0;
}

Answer 1

You have to use sockaddr_un instead of sockaddr_in for Unix domain sockets OR substitute AF_UNIX with AF_INET.
Plus, check the return of listen.
Plus change this line
readval = (sockfd,buffer,sizeof(buffer));
with
readval = read(newsockfd,buffer,sizeof(buffer));
because data is going to be sent through the newly created socket and not on the listening one
Plus, as mentioned by #trojanfoe, subst the server with the client structure into the accept() call

Answer 2

This line:
newsockfd = accept (sockfd, (struct sockaddr *)&server, &len);
Should be:
newsockfd = accept (sockfd, (struct sockaddr *)&client, &len);
From the manpage:
The argument addr is a pointer to a sockaddr structure. This structure
is filled in with the address of the peer socket, as known to the
communications layer. The exact format of the address returned addr is
determined by the socket's address family (see socket(2) and the
respective protocol man pages). When addr is NULL, nothing is filled
in; in this case, addrlen is not used, and should also be NULL.
Also check the return value from listen().

Answer 3

I ran into a similar issue before and it was due to not having the read function in a loop. Here is an example I did before.
while (1) {
new_sockfd = accept(sockfd, (struct sockaddr *) &client_addr,
&sin_size);
if (new_sockfd == -1)
perror("accepting connection");
printf("server: got connection from %s port %d\n",
inet_ntoa(client_addr.sin_addr),
ntohs(client_addr.sin_port));
recv_length = recv(new_sockfd, &buffer, DATA, 0);
while (recv_length > 0) {
printf("RECV: %d bytes\n", recv_length);
dump(buffer, recv_length);
recv_length = recv(new_sockfd, &buffer, DATA, 0);
}
close(new_sockfd);
}