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