Sending/receiving strings with sockets - c

Question

Here's a simple code tcp client/server where the server sends "Hello from Server" after connection established. My problems are:
1) client writes the string after i close the server.exe window and don't know why;
2) client prints strange characters and not "Hello from server". I miss something in the output format.
SERVER
#if defined WIN32
#include <winsock2.h>
#else
#define closesocket close
#include <sys/socket.h>
#include <arpa/inet.h>
#include <unistd.h>
#endif
#include <stdio.h>
#include <stdlib.h>
#define PROTOPORT 5193 //default protocol port number
#define QLEN 6 // size of request queue
#define BUFFERSIZE 10
void ErrorHandler (char *errorMessage) {
printf (errorMessage);
}
void ClearWinSock() {
#if defined WIN32
WSACleanup ();
#endif
}
int main(void) {
#if defined WIN32
WSADATA wsaData;
int iResult = WSAStartup (MAKEWORD(2,2), &wsaData);
if (iResult != 0) {
ErrorHandler ("Error at WSAStartup()\n");
return 0;
}
#endif
// CREAZIONE DELLA SOCKET
int MySocket;
MySocket = socket (PF_INET, SOCK_STREAM, IPPROTO_TCP);
if (MySocket < 0) {
ErrorHandler ("socket creation failed.\n");
ClearWinSock();
return 0;
}
// ASSEGNAZIONE DI UN INDIRIZZO ALLA SOCKET
struct sockaddr_in sad;
memset (&sad, 0, sizeof (sad)); //ensures that extra bytes contain 0
sad.sin_family = AF_INET;
sad.sin_addr.s_addr = inet_addr ("127.0.0.1"); //ip del server con conversione
//da notazione dotted-decimal in un numero a 32 bit
//espresso nella rappresentazione della rete
sad.sin_port = htons (5193); //host to network short
//Assegnazione porta e ip alla socket e verifica presenza di eventuali errori
if (bind (MySocket, (struct sockaddr*) & sad, sizeof (sad)) < 0) {
ErrorHandler ("bind() failed.\n");
closesocket (MySocket);
ClearWinSock ();
return 0;
}
// SETTAGGIO DELLA SOCKET ALL'ASCOLTO
if (listen (MySocket, QLEN) < 0) {
ErrorHandler ("listen() failed.\n");
closesocket (MySocket);
ClearWinSock ();
return 0;
}
// ACCETTARE UNA NUOVA CONNESSIONE - e creazione di una nuova socket per comunicare con il client
struct sockaddr_in cad; //structure for the client address
int clientSocket; // socket descriptor for the client
int clientLen; //the size of the client address
printf ("Waiting for a client to connect...");
while (1) {
clientLen = sizeof (cad); //set the size of the client address
if ((clientSocket = accept (MySocket, (struct sockaddr*) &cad, &clientLen)) < 0) {
ErrorHandler ("accept() failed.\n");
// CHIUSURA DELLA CONNESSIONE
closesocket (MySocket);
ClearWinSock ();
return 0;
}
printf ("Handling client %s\n", inet_ntoa (cad.sin_addr));
}
char* inputString = "Hello from server"; // Stringa da inviare
int stringLen = strlen (inputString); // Determina la lunghezza
// INVIARE DATI AL CLIENT
if (send (clientSocket, inputString, stringLen, 0) != stringLen) {
ErrorHandler ("send () sent a different number of bytes than expected");
closesocket (clientSocket);
ClearWinSock();
system("pause");
return 0;
}
closesocket(MySocket);
ClearWinSock ();
return 0;
}
CLIENT
#if defined WIN32
#include <winsock2.h>
#else
#define closesocket close
#include <sys/socket.h>
#include <arpa/inet.h>
#include <unistd.h>
#endif
#include <stdio.h>
#include <stdlib.h>
#define BUFFERSIZE 20 // Dimensione buffer che riceve dati dal server
#define PROTOPORT 5193 // Numero di porta di default
void ErrorHandler (char *errorMessage) {
printf (errorMessage);
}
void ClearWinSock () {
#if defined WIN32
WSACleanup();
#endif
}
int main (void) {
#if defined WIN32
WSADATA wsaData;
int iResult = WSAStartup (MAKEWORD (2,2), &wsaData);
if (iResult !=0) {
printf ("error at WSASturtup\n");
return 0;
}
#endif
// CREAZIONE DELLA SOCKET
int Csocket;
Csocket = socket (PF_INET, SOCK_STREAM, IPPROTO_TCP);
if (Csocket < 0) {
ErrorHandler ("socket creation failed.\n");
closesocket (Csocket);
ClearWinSock ();
return 0;
}
// COSTRUZIONE DELL'INDIRIZZO DEL SERVER
struct sockaddr_in sad;
memset (&sad, 0, sizeof (sad));
sad.sin_family = AF_INET;
sad.sin_addr.s_addr = inet_addr ("127.0.0.1"); //ip del server con conversione
//da notazione dotted-decimal in un numero a 32 bit
//espresso nella rappresentazione della rete
sad.sin_port = htons (5193); // Server port
//CONNESSIONE AL SERVER
if (connect (Csocket, (struct sockaddr*) &sad, sizeof (sad)) < 0) {
ErrorHandler ("Failed to connect.\n");
closesocket (Csocket);
ClearWinSock();
return 0;
}
char buf[BUFFERSIZE];
recv (Csocket, buf, BUFFERSIZE - 1, 0);
printf("Server scrive: %s\n",buf);
// CHIUSURA DELLA CONNESSIONE
closesocket (Csocket);
ClearWinSock();
printf ("\n");
system ("pause");
return 0;
}
In the end: If I would to send more strings, have I to use one send() and one recv() for each of them?

Answer 1

The biggest issue is that you do not break out of the server loop. This is why you don't see anything on the client until you quit the server. The socket gets closed when the program terminates, so the recv call in client no longer blocks. Also, in client you don't check return val from recv and print junk.
Server fix:
while (1) {
clientLen = sizeof (cad); //set the size of the client address
if ((clientSocket = accept (MySocket, (struct sockaddr*) &cad, &clientLen)) < 0) {
....
}
printf ("Handling client %s\n", inet_ntoa (cad.sin_addr));
break; // <- terminate loop,
// or just get rid of the loop altogether as there
// is no real need for it I can see
}
Client fix:
int read = recv (Csocket, buf, BUFFERSIZE - 1, 0);
if (read <= 0) {
// Not successful
}
else {
buf[read] = 0; // Add eos
printf("%s", buf);
}