Winsock echo server port - c

Question

I'm trying to port this simple TCP echo program (https://github.com/mafintosh/echo-servers.c/blob/master/tcp-echo-server.c) under Windows for teaching purposes.
My adaptation compiles and run, but it doesn't work:
**** EDIT: The listen call was somehow cut out. Thank to Remy ****
The client connects, but doen't get any echo.
Ported code is as follows (error messages are in Italian, but they should be clear nevertheless):
#include <stdio.h>
#include <stdlib.h>
#include <winsock.h>
#define BUFFER_SIZE 1024
void on_error(char *s) { fprintf(stderr,"%s\n",s); fflush(stderr); exit(1); }
int main(int argc, char *argv[]) {
WSADATA wsadata;
int server_fd, client_fd, err;
struct sockaddr_in server, client;
char buf[BUFFER_SIZE];
int port = 6666;
int risultato = WSAStartup(MAKEWORD(2,2),&wsadata);
if (risultato != NO_ERROR)
{fprintf(stderr,"Errore in WSAStartup");fflush(stderr); exit(1);}
server_fd = socket(AF_INET, SOCK_STREAM, 0);
if (server_fd < 0) on_error("Non ho potuto creare il socket\n");
server.sin_family = AF_INET;
server.sin_port = htons(port);
server.sin_addr.s_addr = htonl(INADDR_ANY);
const char opt_val = 1;
setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR, &opt_val, sizeof opt_val);
/** bind & listen **/
err = bind(server_fd, (struct sockaddr *) &server, sizeof(server));
if (err < 0) on_error("Non ho potuto fare il bind del socket\n");
err = listen(server_fd, 128);
if (err < 0) on_error("Non ho potuto mettermi in ascolto sul socket\n");
printf("SERVER LISTENING ON PORT %d\n", port);
while (1) {
int client_len = sizeof(client);
do {
client_fd = accept(server_fd, (struct sockaddr *) &client, &client_len);
} while ( client_fd = SOCKET_ERROR);
if (client_fd < 0) on_error("Non riesco a stabilire una nuova connessione\n");
while (1) {
int read = recv(client_fd, buf, BUFFER_SIZE, 0);
if (!read) break;
if (read < 0) on_error("Errore nella lettura dal client\n");
err = send(client_fd, buf, read, 0);
if (err < 0) on_error("Errore nella scrittura verso il client\n");
}
}
WSACleanup();
return 0;
}

Answer 1

You are calling bind() to set up the listening port, but you are not calling listen() to actually start listening on the port before entering your accept() loop.
Once you fix that mistake, your accept() loop is broken anyway because it is forcing client_fd to SOCKET_ERROR even if accept() is successful. Your while() condition is using the = assignment operator when it needs to use the == comparison operator instead. And you should be checking for INVALID_SOCKET instead of SOCKET_ERROR.
Now with that said, there are some other things to consider:
WinSock does not use int to represent sockets, it uses SOCKET instead, which is a UINT_PTR. When checking for an invalid socket handle, don't use < 0, use == INVALID_SOCKET instead.
Most socket functions return error codes via WSAGetLastError() (WSAStartup() being an exception to that). Get in the habit of using it, and reporting error codes in your output messages, so you know why things are failing.
SO_REUSEADDR expects a BOOL value, not a char value. A BOOL is a typedef for int and thus is 4 bytes.
not all socket errors are fatal, so you should not kill your entire server if a recv()/send() operation fails on a non-fatal error.
send() is not guaranteed to send everything you ask it to send, so you should account for that.
don't forget to close the accepted client socket when you are done using it.
Try this:
#include <stdio.h>
#include <stdlib.h>
#include <winsock.h>
#define BUFFER_SIZE 1024
void on_error(char *s, int *errCode = NULL)
{
int err = (errCode) ? *errCode : WSAGetLastError();
fprintf(stderr, "%s: %d\n", s, err);
fflush(stderr);
exit(1);
}
int main(int argc, char *argv[])
{
WSADATA wsadata;
SOCKET server_fd, client_fd;
struct sockaddr_in server, client;
int port = 6666, err;
char buf[BUFFER_SIZE];
err = WSAStartup(MAKEWORD(2,2), &wsadata);
if (err != 0)
on_error("Errore in WSAStartup", &err);
server_fd = socket(AF_INET, SOCK_STREAM, 0);
if (server_fd == INVALID_SOCKET)
on_error("Non ho potuto creare il socket");
memset(&server, 0, sizeof(server));
server.sin_family = AF_INET;
server.sin_port = htons(port);
server.sin_addr.s_addr = INADDR_ANY;
/** bind & listen **/
const BOOL opt_val = TRUE;
setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR, (char*)&opt_val, sizeof(opt_val));
err = bind(server_fd, (struct sockaddr *) &server, sizeof(server));
if (err == SOCKET_ERROR)
on_error("Non ho potuto fare il bind del socket");
err = listen(server_fd, 1);
if (err == SOCKET_ERROR)
on_error("Non ho potuto mettermi in ascolto sul socket");
printf("SERVER LISTENING ON PORT %d\n", port);
while (1)
{
int client_len = sizeof(client);
client_fd = accept(server_fd, (struct sockaddr *) &client, &client_len);
if (client_fd == INVALID_SOCKET)
on_error("Non riesco a stabilire una nuova connessione");
bool keepLooping = true;
do
{
int read = recv(client_fd, buf, BUFFER_SIZE, 0);
if (read == 0)
break;
if (read == SOCKET_ERROR)
{
err = WSAGetLastError();
if ((err != WSAENOTCONN) && (err != WSAECONNABORTED) && (err == WSAECONNRESET))
on_error("Errore nella lettura dal client", &err);
break;
}
char *pbuf = buf;
do
{
int sent = send(client_fd, pbuf, read, 0);
if (sent == SOCKET_ERROR)
{
err = WSAGetLastError();
if ((err != WSAENOTCONN) && (err != WSAECONNABORTED) && (err == WSAECONNRESET))
on_error("Errore nella scrittura verso il client", &err);
keepLooping = false;
break;
}
pbuf += sent;
read -= sent;
}
while (read > 0);
}
while (keepLooping);
closesocket(client_fd);
}
WSACleanup();
return 0;
}

Answer 2

I'm sorry, but
while (client_fd = SOCKET_ERROR)
don't you mean?
(client_fd == SOCKET_ERROR)