Question

I am trying to implement a simple chat program in linux using bsd sockets. Right now I am just trying to send and receive one message to the server from a client. Whenever I run the code, recv returns -1 and the errno code is 22.

Server code –

struct sockaddr name;
char buf[80];

int main(int agrc, char** argv) {

    int sock, new_sd;   //sock is this socket, new_sd is connection socket
    int adrlen, cnt;

    name.sa_family = AF_UNIX;
    strcpy(name.sa_data, "/tmp/servsock");
    adrlen = strlen(name.sa_data) + sizeof(name.sa_family);

    sock = socket(AF_UNIX, SOCK_STREAM, 0);

    if (sock < 0) {
        cout<<"\nserver socket failure "<<errno;
        cout<<"\nServer: ";
        exit(1);
    }

    unlink("/tmp/servsock");
    if(bind (sock, &name, adrlen) < 0)
        cout<<"\nBind failure "<<errno;

    if(listen(sock, 5) < 0)
        cout<<"\nlisten error "<<errno;

    while(1) {
        if( new_sd = accept(sock, &name, (socklen_t*)&adrlen) < 0) {
            cout<<"\nserver accept failure "<<errno;
            exit(1);
        }

        char* buf = new char[14];

        if(recv(sock, buf, 14, 0) < 0) {
            cout<<"\nError receiving data "<<errno;
            exit(1);
        }
    }   //end while
    return 0;
}

Client code –

struct sockaddr name;

int main(int agrc, char** argv) {

    int sock, new_sd, adrlen, cnt;
    sock = socket(AF_UNIX, SOCK_STREAM, 0);

    if (sock < 0) {
        cout<<"\nserver socket failure "<<errno;
        cout<<"\nServer: ";
        exit(1);
    }

    //stuff for server socket
    name.sa_family = AF_UNIX;
    strcpy(name.sa_data, "/tmp/servsock");
    adrlen = strlen(name.sa_data) + sizeof(name.sa_family);

    if(connect(sock, &name, adrlen) < 0) {
        cout<<"\nclient connection failure "<<errno;
        exit(1);
    }

    cout<<"\nSuccessful connection from client 1";

    std::string buf = "\nClient 1 Here";

    if(send(sock, buf.c_str(), strlen(buf.c_str()), 0) < 0) {
        cout<<"\nError sending data from client 1 "<<errno;
        exit(1);
    }
    cout<<"\nExiting normally";
    return 0;
}

Even though I get the error on the server side, I do not get the error message on the client side – it just exits normally.

According to – http://www.workers.com.br/manuais/53/html/tcp53/mu/mu-7.htm the errno 22 error message just means “Invalid argument”. But I don’t know how exactly to interpret that…if an argument was invalid why would it even compile?

If anyone can point out what I’m doing wrong here I would be very grateful. And any other small notes you feel like pointing out would be welcomed. Thanks for any help.

Answer 1

Aside from all other problems in your code, you are trying to read on the wrong file descriptor – it should be new_sd, not sock, which is a server socket and can only accept() new connections.

Edit 0:

Big boo-boo:

if( new_sd = accept(sock, &name, (socklen_t*)&adrlen) < 0) { ...

This is equivalent to:

if( new_sd = (accept(sock, &name, (socklen_t*)&adrlen) < 0)) {

So new_sd gets totally wrong value. General wisdom is not to put assignments into conditionals. Consider compiling with high warning levels, at least -Wall -pedantic.