Question

I am learning socket programming for use in an upcoming project, and I have researched the issue pretty extensively. Basically, all this program needs to is on a client computer (locally, i.e. my computer) needs to connect to a remote server and send a command (which it has done, I have gotten it to read back Apache server stats to me).

What is happening is this: I believe I have the socket set right, but the server receives random garbage buffers (one of which consisted of ” ‘>Z”). I have tried various socket settings, different bindings, etc.

I have in the process of starting it will initialize winsock, create a socket, bind the network, and then do a listen loop and while(1) recv data.

I have yet to get the server (on a remote computer, hosted at a datacenter) to output the message. This is my only goal for the time being. I appreciate everyone’s help in advance, and the code is before (this is the entire code, sorry for the length).

Client Code:

char *host = "127.0.0.1";
        SOCKET clientsock;
        struct sockaddr_in server_address;

        struct hostent *host_info;

        WSADATA WSAData;
        if(WSAStartup(MAKEWORD(2,2), &WSAData) != -1) {
            cout << "WINSOCK2 Initialized" << endl;         
            if((clientsock = socket(AF_INET, SOCK_STREAM, 0)) != SOCKET_ERROR) {
                cout << "Socket Created" << endl;

                char opt[2];
                opt[0] = 0;
                opt[1] = 1;

                //setsockopt(clientsock, SOL_SOCKET, SO_BROADCAST, opt, sizeof(opt));

                host_info = gethostbyname(host);                    

                server_address.sin_family = AF_INET;
                server_address.sin_addr = *((struct in_addr *)host_info->h_addr);                   
                server_address.sin_port = htons(80);

                if(connect(clientsock, (struct sockaddr *)&server_address, sizeof(struct sockaddr)) == 0) {
                    cout << "Connected to host" << endl;
                    char COMMAND[22] = "SVR --WINSOCK-VERIFY\0";
                    if(send(clientsock, COMMAND, sizeof(COMMAND), 0)) {
                        cout << "Command Sent" << endl;                         
                        closesocket(clientsock);
                    }
                    else {
                        cout << "ERROR - Could not send command. " << "Error: " << WSAGetLastError() << endl;
                        closesocket(clientsock);
                        WSACleanup();
                    }
                }
                else {
                    cout << "ERROR - Could not connect to host. " << "Error: " << WSAGetLastError() << endl;
                    closesocket(clientsock);
                    WSACleanup();
                }                   
            }
            else {
                cout << "ERROR - Could not create the socket. " << "Error: " << WSAGetLastError() << endl;                  
                WSACleanup();
            }               
        }
        else {
            cout << "ERROR - Could not initialize WINSOCK2. " << "Error: " << WSAGetLastError() << endl;                                
            WSACleanup();
        }

Server Code:

SOCKET serversock;
        char *server = "127.0.0.1";     
        //char *server = "50.31.1.180"; 
        struct sockaddr_in server_address;

        WSADATA WSAData;
        if(WSAStartup(MAKEWORD(2,2), &WSAData) != -1) {
            cout << "WINSOCK2 Initialized" << endl;

            if((serversock = socket(PF_INET, SOCK_DGRAM, PF_UNSPEC)) != SOCKET_ERROR) {
                cout << "Socket Created" << endl;

                unsigned long NB = 1;
                ioctlsocket(serversock, FIONBIO, &NB);

                server_address.sin_family = AF_INET;
                server_address.sin_addr = *((struct in_addr *)server);
                server_address.sin_port = htons(21578); 

                if(bind(serversock, (struct sockaddr*)&server_address, sizeof(struct sockaddr) == 0)) {
                    cout << "Network bound" << endl;                    

                    cout << "Listening..." << endl;
                    listen(serversock, 5);                      
                    while(1) {                  
                        int size = sizeof((struct sockaddr *)server);
                        SOCKET clientsock = accept(serversock, (struct sockaddr *)server, &size);
                        char INCOMMAND[20];
                        if(clientsock >= 0) { 
                            if(recv(clientsock, INCOMMAND, sizeof(INCOMMAND), 0)) {                             
                                int i = 0;  
                                if(INCOMMAND == "SVR --WINSOCK-VERIFY\0") {
                                    cout << "SVR receieved" << endl;
                                }
                                while(INCOMMAND[i] != '\0') {
                                    cout << INCOMMAND[i];                                       
                                    i++;                                                                            
                                }                                   
                                cout << endl;                                   
                            }
                            else {
                                cout << "ERROR - Could not receive command" << endl;
                                break;
                            }
                        }
                    }                       
                }
                else {
                    cout << "ERROR - Could not bind network. " << "Error: " << WSAGetLastError() << endl;
                    closesocket(serversock);
                    WSACleanup();
                }
            }
            else {
                cout << "ERROR - Could not create the socket. " << "Error: " << WSAGetLastError() << endl;                  
                WSACleanup();
            }
        }
        else {
            cout << "ERROR - Could not initialize WINSOCK2. " << "Error: " << WSAGetLastError() << endl;                                
            WSACleanup();
        }

Answer 1

Calls to send/recv may not send/receive the amount of bytes you indicate in their third argument, in fact, most of the time they will send/receive less bytes than you expect. You usually have to loop until the entire data has been sent/received. Also note that doing this:

char buffer[100];
recv(clientsock, buffer, sizeof(buffer), 0);
cout << buffer;

Will most surelly print garbage, since you don’t have a null terminator in your char array(whatch out for buffer overflows when appending it), and you’re not checking the return value of recv. It might be reading 1 byte only(or none if an error ocurred). You’re printing your buffer the same way in your server app.

In this case, you are actually sending the null-terminator, but since you might read less bytes than you expect, this character might not be received by the other application, thus printing it will print garbage chars.

Edit: You should have a look at the structure of a sockaddr struct. You can have a look at it here. In your code you are using this convertion:

int size = sizeof((struct sockaddr *)"127.0.0.1");

const char *, which is the type of “127.0.0.1”, cannot be casted to a sockaddr pointer, they’re incompatible. Here you should use getaddrinfo in order to resolve the IP address(note that you could use a domain name, and this function would resolve it). There are lots of tutorials online on how to use this function, just search for “getaddrinfo”.