Why can't people connect to my server app? - winapi

Question

I have a server written in C under Windows, but I can only seem to connect to it from machines that are also connected to the router my computer is connected to. Any ideas why? Here's my code:
#ifndef WIN32_LEAN_AND_MEAN
#define WIN32_LEAN_AND_MEAN
#endif
#include <windows.h>
#include <winsock2.h>
#include <ws2tcpip.h>
#include <iphlpapi.h>
#include <stdio.h>
#pragma comment(lib,"Ws2_32.lib")
#define PORT "1234"
#define BUFLEN 512
DWORD ErrorMessage(char* msg, int error)
{
printf("ErrorMessage: %s\nCodErr: %d\n", msg, error);
return -1;
}
void PrintArray(char* v, unsigned int len)
{
for(unsigned int i = 0 ; i < len ; i++)
printf("%c",v[i]);
printf("\n");
}
DWORD WINAPI ClientHandler(LPVOID lpParam)
{
SOCKET ClientSocket = *((SOCKET*)lpParam);
char recvbuf[BUFLEN];
int iResult,iSendResult;
do
{
iResult = recv(ClientSocket, recvbuf, BUFLEN, 0);
if(iResult > 0)
{
PrintArray(recvbuf,iResult);
iSendResult = send(ClientSocket, recvbuf, iResult, 0);
if(iSendResult == SOCKET_ERROR)
{
closesocket(ClientSocket);
WSACleanup();
return ErrorMessage("send",WSAGetLastError());
}
}
else if(iResult == 0)
printf("Connection closing...\n");
else
{
closesocket(ClientSocket);
WSACleanup();
return ErrorMessage("recv",WSAGetLastError());
}
}
while(iResult > 0);
return 0;
}
int main()
{
WSADATA wsaData;
int iResult;
iResult = WSAStartup(MAKEWORD(2,2),&wsaData);
if(iResult != 0)
{
printf("WSAStartup failed and with error code: %d\n",iResult);
return ErrorMessage("WSAStartup",GetLastError());
}
struct addrinfo *result = NULL, *ptr = NULL, hints;
memset(&hints,0,sizeof(hints));
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_STREAM;
hints.ai_protocol = IPPROTO_TCP;
hints.ai_flags = AI_PASSIVE;
iResult = getaddrinfo(NULL,PORT,&hints,&result);
if(iResult != 0)
{
printf("getaddrinfo failed %d\n",iResult);
WSACleanup();
return -1;
}
SOCKET ListenSocket = INVALID_SOCKET;
ListenSocket = socket(result->ai_family, result->ai_socktype, result->ai_protocol);
if(ListenSocket == INVALID_SOCKET)
{
freeaddrinfo(result);
WSACleanup();
return ErrorMessage("socket",WSAGetLastError());
}
iResult = bind(ListenSocket, result->ai_addr, (int)result->ai_addrlen);
if(iResult == SOCKET_ERROR)
{
freeaddrinfo(result);
closesocket(ListenSocket);
WSACleanup();
return ErrorMessage("bind", WSAGetLastError());
}
freeaddrinfo(result);
if(listen(ListenSocket,5) == SOCKET_ERROR)
{
closesocket(ListenSocket);
WSACleanup();
return ErrorMessage("listen",WSAGetLastError());
}
SOCKET ClientSocket = INVALID_SOCKET;
sockaddr sa;
while(true)
{
ClientSocket = accept(ListenSocket, &sa /*NULL*/, NULL);
if(ClientSocket == INVALID_SOCKET)
{
closesocket(ListenSocket);
WSACleanup();
return ErrorMessage("accept",WSAGetLastError());
}
printf("New client arrived...\n");
if(CreateThread(NULL, 0, ClientHandler, &ClientSocket, 0, NULL) == NULL)
ErrorMessage("CreateThread",GetLastError());
}
iResult = shutdown(ClientSocket,SD_BOTH);
if(iResult == SOCKET_ERROR)
{
closesocket(ClientSocket);
closesocket(ListenSocket);
WSACleanup();
return ErrorMessage("shutsown",WSAGetLastError());
}
closesocket(ListenSocket);
WSACleanup();
return 0;
}

Answer 1

I can't follow your code, but usually I use bind with htons. In your code, it's not obvious how you convert your string "1234" into a numeric value. I wrote a very crude simple Web Server on port 1234 that just serves out a dummy "Hello World" page. All validation has been removed to keep the example short:
#include "stdafx.h"
#include <tchar.h>
#include <windows.h>
#include <winsock.h>
#pragma comment(lib, "wsock32.lib")
int _tmain(int argc, _TCHAR* argv[])
{
WSADATA wsaData = {0};
WSAStartup(0x202, &wsaData);
SOCKET serverSocket = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
SOCKADDR_IN sin = {0};
sin.sin_family = PF_INET;
sin.sin_port = htons(1234);
sin.sin_addr.s_addr = INADDR_ANY;
bind(serverSocket, (LPSOCKADDR) &sin, sizeof(sin));
listen(serverSocket, 1);
SOCKET clientSocket = accept(serverSocket, NULL, NULL);
while (clientSocket != INVALID_SOCKET)
{
char request[1024] = {0};
recv(clientSocket, request, 1024, 0);
static char html[] =
"HTTP/1.1 200 OK\n"
"Content-Type: text/html\n"
"\n"
"<HTML><HEAD><TITLE>Hello World!</TITLE></HEAD><BODY>Hello World!</BODY></HTML>\n\n";
send(clientSocket, html, sizeof(html), 0);
closesocket(clientSocket);
clientSocket = accept(serverSocket, NULL, NULL);
}
closesocket(serverSocket);
WSACleanup();
return 0;
}

Answer 2

The problem is not in your program. The problem is in the configuration of your router.
Try to connect to some other TCP/IP service on your computer from outside.