WINDOWS C: TCP Socket send&recv at the same time - c

Question

I'm trying to make two-way communication over a TCP socket between server and client on Windows. I've tried using threads, but it doesn't work, and I don't know why.
If I try putting this in the while loop, it waits for the user to type something (because of fgets()) before it prints the next message.
while(1) {
bzero(message, 2000);
if (recv(sock, message, 2000, 0) < 0) {
printf("Connection lost!\n");
getch();
}
else {
strcat(message, "\0");
fprintf(stdout, "%s", message);
};
bzero(client, 2000);
fgets(sednmesg, sizeof(sednmesg), stdin);
strcat(client, sednmesg);
strcat(client, "\0");
send(sock, client, strlen(client), 0);
}
My disastrous attempt with threads:
Server.c:
#include <stdio.h>
#include <winsock.h>
#include <stdlib.h>
#include "stdafx.h"
#include <conio.h>
#include <io.h>
#define bzero(b,len) (memset((b), '\0', (len)), (void) 0)
#pragma comment(lib,"ws2_32.lib") //Winsock Library
char message[4040];
DWORD WINAPI thrd() {
WSADATA wsa;
SOCKET sock, newsock;
int c;
struct sockaddr_in server, client;
char smesg[155];
printf("\nInitialising Winsock...");
if (WSAStartup(MAKEWORD(2, 2), &wsa) != 0)
{
printf("Failed. Error Code : %d", WSAGetLastError());
return 1;
}
printf("Initialised.\n");
if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == INVALID_SOCKET) {
printf("Could not create socket! Error: %d", WSAGetLastError());
return 1;
}
//textcolor(2);
printf("Socket Created!\n");
server.sin_family = AF_INET;
server.sin_addr.s_addr = INADDR_ANY;
server.sin_port = htons(8989);
//bind
if (bind(sock, (struct sockaddr *)&server, sizeof(server)) == SOCKET_ERROR) {
printf("Bind failed! Error Code: %d", WSAGetLastError());
}
puts("Binded!");
printf("\nNow Listening...\n");
listen(sock, 1);
//Accept!
c = sizeof(struct sockaddr_in);
newsock = accept(sock, (struct sockaddr *)&client, &c);
if (newsock == INVALID_SOCKET) {
printf("Couldn't Accept connection!");
}
printf("Accepted Connection!\n");
u_long iMode = 1;
ioctlsocket(newsock, FIONBIO, &iMode);
Sleep(99);
system("cls");
printf("Writer Thread has been started!");
//char *client_ip = inet_ntoa(client.sin_addr);
//int client_port = ntohs(client.sin_port);
while (1) {
bzero(smesg, sizeof(smesg));
fgets(smesg, sizeof(smesg), stdin);
strcat(smesg, "\0");
send(newsock, smesg, strlen(smesg), 0);
}
}
int main()
{
WSADATA wsa;
FILE * fp;
unsigned long on = 1;
const char *file = "fout.txt";
SOCKET sock, newsock;
int c;
struct sockaddr_in server, client;
char smesg[155];
printf("\nInitialising Winsock...");
if (WSAStartup(MAKEWORD(2, 2), &wsa) != 0)
{
printf("Failed. Error Code : %d", WSAGetLastError());
return 1;
}
printf("Initialised.\n");
if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == INVALID_SOCKET) {
printf("Could not create socket! Error: %d", WSAGetLastError());
return 1;
}
//textcolor(2);
printf("Socket Created!\n");
server.sin_family = AF_INET;
server.sin_addr.s_addr = INADDR_ANY;
server.sin_port = htons(3939);
//bind
if (bind(sock, (struct sockaddr *)&server, sizeof(server)) == SOCKET_ERROR) {
printf("Bind failed! Error Code: %d", WSAGetLastError());
}
puts("Binded!");
printf("\nNow Listening...\n");
listen(sock, 1);
//Accept!
c = sizeof(struct sockaddr_in);
newsock = accept(sock, (struct sockaddr *)&client, &c);
ioctlsocket(newsock, FIONBIO, &on);
if (newsock == INVALID_SOCKET) {
printf("Couldn't Accept connection!");
}
printf("Accepted Connection!\n");
//char *client_ip = inet_ntoa(client.sin_addr);
//int client_port = ntohs(client.sin_port);
HANDLE thread = CreateThread(NULL, 0, thrd, NULL, 0, NULL);
fp = fopen(file, "r+");
while (1) {
/*
bzero(smesg, sizeof(smesg));
printf("Command: ");
fgets(smesg, 155, stdin);
strcat(smesg, "\0");
send(newsock, smesg, strlen(smesg), 0);
*/
bzero(message, sizeof(message));
recv(newsock, message, 2000, 0);
fprintf(stdout, "%s", message);
fprintf(fp, "%s", message);
}
fclose(fp);
return 0;
}
Client.c:
#include <stdio.h>
#include <winsock.h>
#include <stdlib.h>
#include "stdafx.h"
#include <conio.h>
#define bzero(b,len) (memset((b), '\0', (len)), (void) 0)
#pragma comment(lib,"ws2_32.lib") //Winsock Library
DWORD WINAPI thrd() {
char client[2050] = "Client: ";
WSADATA wsa;
SOCKET sock;
struct sockaddr_in server;
char sednmesg[2000];
printf("\nInitialising Winsock...");
if (WSAStartup(MAKEWORD(2, 2), &wsa) != 0)
{
printf("Failed. Error Code : %d", WSAGetLastError());
getch();
return 1;
}
printf("Initialised.\n");
if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == INVALID_SOCKET) {
printf("Could not create socket! Error: %d", WSAGetLastError());
getch();
return 1;
}
//textcolor(2);
printf("Socket Created!\n");
//ioctlsocket(sock, FIONBIO, &on);
server.sin_addr.s_addr = inet_addr("127.0.0.1");
server.sin_family = AF_INET;
server.sin_port = htons(8989);
//Connect
if (connect(sock, (struct sockaddr *)&server, sizeof(server)) < 0) {
puts("Connect Error");
getch();
return 1;
}
puts("Connected\n");
// If iMode!=0, non-blocking mode is enabled.
u_long iMode = 1;
ioctlsocket(sock, FIONBIO, &iMode);
Sleep(99);
system("cls");
printf("Writer Thread has been started!");
//We'll be running this one on port 8989 if this doesn't work!
while (1) {
bzero(client, 2000);
fgets(sednmesg, sizeof(sednmesg), stdin);
strcat(client, sednmesg);
strcat(client, "\0");
send(sock, client, strlen(client), 0);
}
}
int main(int argc, char *argv[])
{
char *msg = "a";
char client[2050] = "Client: ";
unsigned long on = 1;
int reader;
WSADATA wsa;
int sent = 0;
SOCKET sock;
struct sockaddr_in server;
char message[2000];
char sednmesg[2000];
printf("\nInitialising Winsock...");
if (WSAStartup(MAKEWORD(2, 2), &wsa) != 0)
{
printf("Failed. Error Code : %d", WSAGetLastError());
getch();
return 1;
}
printf("Initialised.\n");
if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == INVALID_SOCKET) {
printf("Could not create socket! Error: %d", WSAGetLastError());
getch();
return 1;
}
//textcolor(2);
printf("Socket Created!\n");
//ioctlsocket(sock, FIONBIO, &on);
server.sin_addr.s_addr = inet_addr("127.0.0.1");
server.sin_family = AF_INET;
server.sin_port = htons(3939);
//Connect
if (connect(sock, (struct sockaddr *)&server, sizeof(server)) < 0) {
puts("Connect Error");
getch();
return 1;
}
puts("Connected\n");
// If iMode!=0, non-blocking mode is enabled.
u_long iMode = 1;
ioctlsocket(sock, FIONBIO, &iMode);
//Creating writer thread.
HANDLE thread = CreateThread(NULL, 0, thrd, NULL, 0, NULL);
while (1) {
bzero(message, 2000);
if (recv(sock, message, 2000, 0) < 0) {
printf("Connection lost!\n");
getch();
}
else {
strcat(message, "\0");
fprintf(stdout, "%s", message);
};
//bzero(client, 2000);
/*
fgets(sednmesg, sizeof(sednmesg), stdin);
strcat(client, sednmesg);
strcat(client, "\0");
send(sock, client, strlen(client), 0);
*/
}
return 0;
}

Answer 1

You don't need to open/connect 2 separate listening ports in order to implementing bi-directional communication. TCP is bi-directional, you only need one connection. However, you are enabling non-blocking socket I/O on both ends, but you are not actually using non-blocking I/O correctly. In particular, you are not handling the WSAEWOULDBLOCK error code at all, which is reported by recv() when there is no data available to read, and by send() when the receiver has too much data to read and cannot receive new data yet.
If you want to use threads, then use separate threads for reading and sending, and forget non-blocking I/O altogether. But make sure you are defining your threads correctly (you thread procedure is missing a required input parameter!).
Try something more like this:
Server.c:
#include "stdafx.h"
#include <stdio.h>
#include <winsock.h>
#include <stdlib.h>
#include <conio.h>
#pragma comment(lib,"ws2_32.lib") //Winsock Library
DWORD WINAPI sendThrd(LPVOID lpParam)
{
SOCKET sock = * (SOCKET*) lpParam;
char smesg[155], *pdata;
int len, ret;
do
{
if (!fgets(smesg, sizeof(smesg), stdin))
break;
len = strlen(smesg);
pdata = smesg;
while (len > 0)
{
ret = send(sock, pdata, len, 0);
if (ret == SOCKET_ERROR)
{
printf("Send failed. Error: %d", WSAGetLastError());
break;
}
pdata += ret;
len -= ret;
}
}
while (true);
shutdown(sock, SD_SEND);
return 0;
}
DWORD WINAPI recvThrd(LPVOID lpParam)
{
SOCKET sock = * (SOCKET*) lpParam;
char smesg[256];
int ret;
FILE *fp = fopen("fout.txt", "w+");
do
{
ret = recv(sock, smesg, sizeof(smesg), 0);
if (ret <= 0)
{
if (ret == 0)
printf("Client disconnected\n");
else
printf("Connection lost! Error: %d\n", WSAGetLastError());
break;
}
printf("%.*s", ret, smesg);
if (fp)
fprintf(fp, "%.*s", ret, smesg);
}
while (true);
if (fp)
fclose(fp);
shutdown(sock, SD_RECEIVE);
return 0;
}
int main()
{
WSADATA wsa;
SOCKET sock, newsock;
int c;
struct sockaddr_in server;
printf("Initializing Winsock...\n");
int ret = WSAStartup(MAKEWORD(2, 2), &wsa);
if (ret != 0)
{
printf("Initialization Failed. Error: %d", ret);
return 1;
}
printf("Initialized.\n");
sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (sock == INVALID_SOCKET) {
printf("Could not create socket! Error: %d\n", WSAGetLastError());
return 1;
}
//textcolor(2);
printf("Socket Created!\n");
memset(&server, 0, sizeof(server));
server.sin_family = AF_INET;
server.sin_addr.s_addr = INADDR_ANY;
server.sin_port = htons(3939);
//bind
if (bind(sock, (struct sockaddr *)&server, sizeof(server)) == SOCKET_ERROR) {
printf("Bind failed! Error: %d\n", WSAGetLastError());
closesocket(sock);
return 1;
}
printf("Binded!\n");
// listen
if (listen(sock, 1) == SOCKET_ERROR) {
printf("Listen failed! Error: %d\n", WSAGetLastError());
closesocket(sock);
return 1;
}
printf("Now Listening...\n");
//Accept!
c = sizeof(client);
newsock = accept(sock, (struct sockaddr *)&client, &c);
if (newsock == INVALID_SOCKET) {
printf("Couldn't Accept connection! Error: %d\n", WSAGetLastError());
closesocket(sock);
return 1;
}
//char *client_ip = inet_ntoa(client.sin_addr);
//int client_port = ntohs(client.sin_port);
printf("Accepted Connection!\n");
printf("Starting Reader/Writer Threads...\n");
HANDLE threads[2];
threads[0] = CreateThread(NULL, 0, sendThrd, &newsock, 0, NULL);
threads[1] = CreateThread(NULL, 0, recvThrd, &newsock, 0, NULL);
WaitForMultipleObjects(2, threads, TRUE, INFINITE);
CloseHandle(threads[0]);
CloseHandle(threads[1]);
closesocket(newsock);
closesocket(sock);
return 0;
}
Client.c:
#include "stdafx.h"
#include <stdio.h>
#include <winsock.h>
#include <stdlib.h>
#include <conio.h>
#pragma comment(lib,"ws2_32.lib") //Winsock Library
DWORD WINAPI sendThrd(LPVOID lpParam)
{
SOCKET sock = * (SOCKET*) lpParam;
char smesg[155], *pdata;
int len, ret;
do
{
if (!fgets(smesg, sizeof(smesg), stdin))
break;
len = strlen(smesg);
pdata = smesg;
while (len > 0)
{
ret = send(sock, pdata, len, 0);
if (ret == SOCKET_ERROR)
{
printf("Send failed. Error: %d\n", WSAGetLastError());
break;
}
pdata += ret;
len -= ret;
}
}
while (true);
shutdown(sock, SD_SEND);
return 0;
}
DWORD WINAPI recvThrd(LPVOID lpParam)
{
SOCKET sock = * (SOCKET*) lpParam;
char smesg[256];
int ret;
do
{
ret = recv(sock, smesg, sizeof(smesg), 0);
if (ret <= 0)
{
if (ret == 0)
printf("Server disconnected\n");
else
printf("Connection lost! Error: %d\n", WSAGetLastError());
break;
}
printf("%.*s", ret, smesg);
}
while (true);
shutdown(sock, SD_RECEIVE);
return 0;
}
int main(int argc, char *argv[])
{
WSADATA wsa;
SOCKET sock;
struct sockaddr_in server;
printf("Initializing Winsock...\n");
int ret = WSAStartup(MAKEWORD(2, 2), &wsa);
if (ret != 0)
{
printf("Initialization Failed. Error: %d", ret);
return 1;
}
printf("Initialized.\n");
sock = socket(AF_INET, SOCK_STREAM, 0);
if (sock == INVALID_SOCKET) {
printf("Could not create socket! Error: %d", WSAGetLastError());
getch();
return 1;
}
//textcolor(2);
printf("Socket Created!\n");
memset(&server, 0, sizeof(server));
server.sin_addr.s_addr = inet_addr("127.0.0.1");
server.sin_family = AF_INET;
server.sin_port = htons(3939);
//Connect
if (connect(sock, (struct sockaddr *)&server, sizeof(server)) == SOCKET_ERROR) {
printf("Connect failed! Error: %d", WSAGetLastError());
closesocket(sock);
getch();
return 1;
}
printf("Connected\n");
//Creating reader/writer threads.
printf("Starting Reader/Writer Threads...\n");
HANDLE threads[2];
threads[0] = CreateThread(NULL, 0, sendThrd, &sock, 0, NULL);
threads[1] = CreateThread(NULL, 0, recvThrd, &sock, 0, NULL);
WaitForMultipleObjects(2, threads, TRUE, INFINITE);
CloseHandle(threads[0]);
CloseHandle(threads[1]);
closesocket(sock);
getch();
return 0;
}