I want to listen to SSDP multicasts on port 1900. The port is already opened by Windows Discovery Service. I fail to bind my socket despite using SO_REUSEADDR socket option. I'm starting my application as administrator.
If I stop the service, start my application and then restart the service, then both get messages. What am I doing wrong?
static SOCKET CreateSocket(const char *ccAddress, unsigned short ulPort, struct IfPoolItem *item) {
struct sockaddr_in sAddr;
struct ip_mreq mc_req;
SOCKET sRet;
char cSockParam = TRUE;
/* create a socket */
if((sRet = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == INVALID_SOCKET)
{
return(INVALID_SOCKET);
}
item->s = sRet;
if (setsockopt(sRet, IPPROTO_IP, SO_REUSEADDR, &cSockParam, sizeof(cSockParam)) == -1) {
int iTmp = WSAGetLastError();
return (INVALID_SOCKET);
}
/* bind the socket to the given port */
memset(&sAddr, 0, sizeof(sAddr));
sAddr.sin_family = AF_INET;
sAddr.sin_addr.s_addr = inet_addr(item->szIP);
sAddr.sin_port = htons(ulPort);
if(bind(sRet, (struct sockaddr *)&sAddr, sizeof(sAddr)) == SOCKET_ERROR)
{
int iTmp = WSAGetLastError();
closesocket(sRet);
return(INVALID_SOCKET);
}
cSockParam = 4;
if (setsockopt(sRet, IPPROTO_IP, IP_MULTICAST_TTL, &cSockParam, sizeof(cSockParam)) == -1) {
int iTmp = WSAGetLastError();
return (INVALID_SOCKET);
}
/* Construct an IGMP join request structure */
mc_req.imr_multiaddr.s_addr = inet_addr(ccAddress);
mc_req.imr_interface.s_addr = inet_addr(item->szIP);
/* Send an ADD_MEMBERSHIP message via setsockopt */
if((setsockopt(sRet, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char FAR *) &mc_req, sizeof(mc_req))) == -1) {
int iTmp = WSAGetLastError();
return (INVALID_SOCKET);
}
/* Return the created socket. */
return(sRet);
}
I am not an expert with sockets but if you look at this msdn page it says that SO_REUSEADDR should be used with level = SOL_SOCKET parameter. So probably you call should be something like
setsockopt(sRet, SOL_SOCKET, SO_REUSEADDR,&cSockParam, sizeof(cSockParam))
Please try this and let meknow if it made any difference
I am not exactly sure if this is your problem, but the WDS may be using SO_EXCLUSIVEADDRUSE which is preventing your bind(). The docs in this link would seem to describe the behavior you are reporting.
Related
Now I am testing rdma-core with fork.
In server I use rselect and raccept to receive rsocket connection from client.
Server can rrecv the msg from client successfully.
But server cannot rsend to client. It return -1 and errno 13 permission denied.
THe same code without rsocket, it will send OK.
For rdma-core/librdmacm rsocket, how support fork?
int main(int argc,char *argv[])
{
int ret;
int server_sockfd, client_sockfd;
int server_len, client_len;
struct sockaddr_in server_address;
struct sockaddr_in client_address;
memset(&server_address,0,sizeof(server_address));
memset(&client_address,0,sizeof(client_address));
int result;
fd_set readfds, testfds;
int maxfd;
int on=1;
server_sockfd = rsocket(AF_INET, SOCK_STREAM, 0);
setsockopt(server_sockfd, SOL_SOCKET, SO_BROADCAST, &on, sizeof(on));
server_address.sin_family = AF_INET;
server_address.sin_port = htons(8888);
server_address.sin_addr.s_addr = htonl(INADDR_ANY);
ret = rbind(server_sockfd,(struct sockaddr *)&server_address,sizeof(server_address));
printf("rbind retunr %d\n", ret);
ret = rlisten(server_sockfd,5);
printf("rlisten retunr %d\n", ret);
//set fd_set
FD_ZERO(&readfds);
FD_SET(server_sockfd,&readfds);
maxfd = server_sockfd + 1;
while(1)
{
char ch;
int fd,i;
int nread;
testfds = readfds;
result = rselect(FD_SETSIZE, &testfds, NULL, NULL, NULL);
printf("rselect retunr %d\n", result);
if(result < 1)
{
printf("server5\n");
exit(1);
}
for( fd = 1; fd < maxfd; fd++)
{
if(FD_ISSET(fd,&testfds))
{
if(fd == server_sockfd)
{
memset(&client_address,0,sizeof(client_address));
client_len = sizeof(client_address);
client_sockfd = raccept(server_sockfd,(struct sockaddr *)&client_address,&client_len);
if(fork()==0)
{
setsockopt(client_sockfd, SOL_SOCKET, SO_BROADCAST, &on, sizeof(on));
rclose(server_sockfd);
ret = rrecv(client_sockfd,&ch,1,0);
printf("recv from client : %c, ret %d\n",ch, ret);
sleep(2);
ch++;
ret = rsend(client_sockfd,&ch,1,0);
printf("rsend to client : %c, ret %d, erro %d\n",ch, ret, errno);
}
}
}
}
}
}
As you can see from the rsocket man page:
The preload library can be used by setting LD_PRELOAD when running. Note that not all applications will work with rsockets. Support is limited based on the socket options used by the application. Support for fork() is limited, but available. To use rsockets with the preload library for applications that call fork, users must set the environment variable RDMAV_FORK_SAFE=1 on both the client and server side of the connection. In general, fork is supportable for server applications that accept a connection, then fork off a process to handle the new connection.
As far as I can see, to use rsockets with fork, you have to:
Use sockets API in both your client and your servers (rather than using rsocket calls directly).
Run both the client and your server with these environment variables: RDMAV_FORK_SAFE=1 LD_PRELOAD=/usr/lib/x86_64-linux-gnu/rsocket/librspreload.so (or change the path according to where librspreload.so is installed on your system).
Without using LD_PRELOAD it seems like fork is not supported, meaning that a child process can't use rsockets that the parent has created.
I'm facing an issue doing a select() call waiting on a socket + pipe.
I know there are already some topics on that but I have read lots of things and their opposite and I can't figure out what is the best solution for my problem.
The best for me would be to use WaitForMultipleObjects() listening on these two objects but when I try to call it only on the WSAEvent object, it fails and last error catch is code 6 (Invalid Handle).
WSAEVENT sockEvent = WSACreateEvent();
sockEvent = WSAEventSelect(fd, sockEvent, FD_WRITE);
HANDLE *pHandles = &sockEvent;
DWORD dwEvent = WaitForMultipleObjects(1, pHandles, FALSE, amqp_time_ms_until(deadline));
switch (dwEvent)
{
// ghEvents[0] was signaled
case WAIT_OBJECT_0 + 0:
// TODO: Perform tasks required by this event
return AMQP_STATUS_OK;
// ghEvents[1] was signaled
case WAIT_OBJECT_0 + 1:
// TODO: Perform tasks required by this event
return AMQP_STATUS_POLL_EXTERNAL_WAKE;
case WAIT_TIMEOUT:
return AMQP_STATUS_TIMEOUT;
// Return value is invalid.
default:
return AMQP_STATUS_SOCKET_ERROR;
}
So WaitForMultipleObjects doesn't seems to Work with WinSocks events, however I have already seen some examples on the net working with it.
And the of WSACreateEvent documentation (https://msdn.microsoft.com/en-us/library/windows/desktop/ms741561%28v=vs.85%29.aspx) says this :
Windows Sockets 2 event objects are system objects in Windows
environments. Therefore, if a Windows application wants to use an
auto-reset event rather than a manual-reset event, the application can
call the CreateEvent function directly.
This doesn't mean that WSAEvent are based on regular windows events ? If it's the case why it doesn't work with WaitForMultipleObjects ? The doc says it can handle regular events.
Thanks for helping.
This is your problem:
sockEvent = WSAEventSelect(fd, sockEvent, FD_WRITE);
You're overwriting the event handle! (As documented, the return value for WSAEventSelect is either 0 or SOCKET_ERROR. It is not a new event handle.)
Try something like
if (WSAEventSelect(fd, sockEvent, FD_WRITE) != 0) return SOCKET_ERROR;
Looking at the declaration of WSAEVENT revealed that WSAEVENT is simply an alias for HANDLE. This explains the note of the WSACreateEvent documentation you added to your post. So WSACreateEvent simply creates a manual reset event by calling CreateEvent(..., TRUE, FALSE, ...);.
Therefore an event returned by WSACreateEvent has to work along with WaitForMultipleObjects(..).
According to the code you've posted I cannot see any reason why WaitForMultipleObjects(..) should return "invalid handle" when supplied with an event returned by WSACreateEvent...
It may be though that pipes do not work with WaitForMultipleObjects(..). I remember having problems with that a long time ago but I cannot remember the details right now. But maybe it is another place to start digging...
Here is the code of my little test application which creates two threads (one event thread signalling a normal event and a simple TCP/IP server sending data). In the main loop a connection to the server is established and signalled events are processed.
#include <winsock2.h>
#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#pragma comment(lib, "Ws2_32.lib");
#define SERVER_PORT 5000
HANDLE hSomeEvent;
HANDLE hSocketEvent;
DWORD WINAPI eventThread(LPVOID pData)
{
while (1)
{
SleepEx(2250, FALSE);
SetEvent(hSomeEvent);
}
return (0);
}
DWORD WINAPI serverThread(LPVOID pData)
{
SOCKET listener;
struct sockaddr_in sockaddr;
int size;
SOCKET client;
listener = socket(AF_INET, SOCK_STREAM, 0);
if (listener == INVALID_SOCKET)
{
printf("Could not create socket : %d" , WSAGetLastError());
}
sockaddr.sin_family = AF_INET;
sockaddr.sin_addr.s_addr = INADDR_ANY;
sockaddr.sin_port = htons(SERVER_PORT);
if (bind(listener, (struct sockaddr *)&sockaddr , sizeof(sockaddr)) == SOCKET_ERROR)
{
printf("Bind failed with error code : %d" , WSAGetLastError());
}
listen(listener, 1);
while (listener)
{
size = sizeof(struct sockaddr_in);
client = accept(listener, (struct sockaddr *)&sockaddr, &size);
printf("client connected\n");
while (client != INVALID_SOCKET)
{
SleepEx(5000, FALSE);
if (send(client, "hello\0", 6, 0) != 6)
{
closesocket(client);
shutdown(client, 2);
client = INVALID_SOCKET;
}
}
SetEvent(hSomeEvent);
}
return (0);
}
int main()
{
WSADATA wsaData;
HANDLE events[2];
DWORD result;
SOCKET s;
struct hostent *hp;
struct sockaddr_in sockaddr;
int len;
char buff[1024 * 16];
HANDLE *evtPtr;
WSAStartup(MAKEWORD(2, 2), &wsaData);
hSocketEvent = WSACreateEvent();
//hSocketEvent = CreateEvent(NULL, FALSE, FALSE, "socket_event");
hSomeEvent = CreateEvent(NULL, FALSE, FALSE, "some_event");
CreateThread(NULL, 0, eventThread, NULL, 0, &result);
CreateThread(NULL, 0, serverThread, NULL, 0, &result);
s = socket(AF_INET, SOCK_STREAM, 0);
if (s == INVALID_SOCKET)
{
printf("Could not create socket : %d" , WSAGetLastError());
}
hp = gethostbyname("127.0.0.1");
sockaddr.sin_addr.s_addr = *((unsigned long*)hp->h_addr);
sockaddr.sin_family = AF_INET;
sockaddr.sin_port = htons(SERVER_PORT);
if (connect(s, (struct sockaddr*)&sockaddr, sizeof(sockaddr)))
{
closesocket(s);
printf("Could not connect socket : %d" , WSAGetLastError());
}
WSAEventSelect(s, hSocketEvent, FD_READ);
do
{
//events[0] = hSocketEvent;
//events[1] = hSomeEvent;
//result = WaitForMultipleObjects(2, events, FALSE, 1000);
evtPtr = &hSocketEvent;
result = WaitForMultipleObjects(1, evtPtr, FALSE, 1000);
switch (result)
{
case WAIT_OBJECT_0 + 0:
printf("hSocketEvent is signalled!\n");
len = recv(s, buff, sizeof(buff), 0);
printf(" %d bytes received\n", len);
WSAResetEvent(hSocketEvent);
break;
case WAIT_OBJECT_0 + 1:
printf("hSomeEvent is signalled!\n");
break;
case WAIT_TIMEOUT:
printf("timeout\n");
break;
default:
printf("error = %d\n", GetLastError());
break;
}
}
while (1);
printf("\n\nend.");
getch();
return (0);
}
Note that if you use WSACreateEvent you have to manually reset the event after readinng the data (otherwise WaitForMultipleObjects(..) will go nuts).
The SELinux module sends out a netlink broadcast to any listening sockets. I'm wondering if it's possible to listen for netlink broadcast from within another kernel module?
From SELinux netlink code:
netlink_broadcast(selnl, skb, 0, SELNLGRP_AVC, GFP_USER);
I found that you can listen for netlink data through the use of regular sockets. And, yes, it's possible in kernel-space.
You basically need to create and bind to a socket:
struct sock *sock = NULL;
struct sockaddr_nl addr = { 0 };
/* Create a netlink socket for SELinux traffic */
int rc = sock_create_kern(AF_NETLINK, SOCK_RAW, NETLINK_SELINUX,
&ctx.sock);
if (rc)
return rc;
addr.nl_family = AF_NETLINK;
addr.nl_pid = 0;
addr.nl_groups = SELNLGRP_AVC;
rc = kernel_bind(ctx.sock, (struct sockaddr *) &addr, sizeof(addr));
if (rc)
return rc;
/* Setup socket callback */
sock = ctx.sock->sk;
sock->sk_data_ready = netlink_data_ready;
sock->sk_allocation = GFP_KERNEL;
To receive the data:
static void netlink_data_ready(struct sock *sk, int bytes)
{
struct sk_buff *skb = NULL;
struct nlmsghdr *nlh = NULL;
int rc = 0;
/* Receive the data packet (blocking) */
skb = skb_recv_datagram(sk, 0, 0, &rc);
if (rc) {
printk(KERN_ERROR "Failed on skb_recv_datagram(). rc=%d.", -rc);
return;
}
nlh = (struct nlmsghdr *) skb->data;
if (!nlh || !NLMSG_OK(nlh, bytes)) {
printk(KERN_ERROR "Invalid netlink header data.");
return;
}
if (nlh->nlmsg_type == SELNL_MSG_POLICYLOAD ||
nlh->nlmsg_type == SELNL_MSG_SETENFORCE) {
/* Insert code here */
}
}
I have created single Server and Single Client echo application. It works fine for single server and single client. But now I want to make it more practical by handling multiple clients for a single Server. I came accross the idea of using listen() function at Server side to handle multiple client connections but then I came to know that listen is only used for TCP. Kindly help me with this. below is my functional code for single Server and Single Client. Help me with how can I modify it to make a Single Server Multiple Client application.
SERVER:
#define PORT 8888 //The port on which to listen for incoming data
int main()
{
SOCKET s;
struct sockaddr_in serverSocket, clientSocket;
char receiveBuffer[1000];
//int receiveBufferLength=1000;
int clientSocketLength;
int recv_len;
clientSocketLength = sizeof(clientSocket) ;
WSADATA wsa;
//Initialise winsock
printf("\nInitialising Winsock...");
if (WSAStartup(MAKEWORD(2,2),&wsa) != 0)
{
printf("Failed. Error Code : %d",WSAGetLastError());
exit(EXIT_FAILURE);
}
printf("Socket Initialised.\n");
//Create a socket
if((s = socket(AF_INET , SOCK_DGRAM , 0 )) == INVALID_SOCKET)
{
printf("Could not create socket : %d" , WSAGetLastError());
}
printf("Socket created.\n");
//Prepare the sockaddr_in structure
serverSocket.sin_family = AF_INET;
serverSocket.sin_addr.s_addr = INADDR_ANY;
serverSocket.sin_port = htons( PORT );
//Bind
if( bind(s ,(struct sockaddr *)&serverSocket , sizeof(serverSocket)) == SOCKET_ERROR)
{
printf("\nBind failed with error code : %d" , WSAGetLastError());
exit(EXIT_FAILURE);
}
printf("Bind done\n\n");
//keep listening for data
while(1)
{
printf("\n\t\t\tWaiting for data...\n");
fflush(stdout);
//receiveBuffer[2000]=NULL;
if((recv_len = recvfrom(s, receiveBuffer, 1000, 0, (struct sockaddr *) &clientSocket, &clientSocketLength)) == SOCKET_ERROR)
{
printf("\n\nrecvfrom() failed with error code : %d" , WSAGetLastError());
//exit(EXIT_FAILURE);
while(1);
}
//print details of the client/peer and the data received
printf("\n\nReceived packet from %s:%d\n", inet_ntoa(clientSocket.sin_addr), ntohs(clientSocket.sin_port));
printf("\nClient Says: " );
printf(receiveBuffer,recv_len);
//now reply the client with the same data
if (sendto(s, receiveBuffer, recv_len, 0, (struct sockaddr*) &clientSocket, clientSocketLength) == SOCKET_ERROR)
{
printf("\nsendto() failed with error code : %d" , WSAGetLastError());
// exit(EXIT_FAILURE);
while(1);
}
else
printf("\nMessage Sent Back to Client");
}
closesocket(s);
WSACleanup();
return 0;
}
CLIENT:
#define PORT 8888 //The port on which to listen for incoming data
#define SERVER "10.0.1.25" //ip address of udp server
//#define PORT 8888 //The port on which to listen for incoming data
int main(void)
{
struct sockaddr_in connectedSocket;
int s;
int length=sizeof(connectedSocket);
char receiveBuffer[1000];
char message[1000];
//clear the buffer by filling null, it might have previously received data
memset(receiveBuffer,'\0', 1000);
WSADATA wsa;
//Initialise winsock
printf("\nInitialising Winsock...\n");
if (WSAStartup(MAKEWORD(2,2),&wsa) != 0)
{
printf("\nFailed. Error Code : %d",WSAGetLastError());
exit(EXIT_FAILURE);
}
printf("\n.........Initialised.\n");
//create socket
if ( (s=socket(AF_INET, SOCK_DGRAM, 0)) == SOCKET_ERROR)
{
printf("\n\nsocket() failed with error code : %d" , WSAGetLastError());
exit(EXIT_FAILURE);
}
//setup address structure
memset((char *) &connectedSocket, 0, sizeof(connectedSocket));
connectedSocket.sin_family = AF_INET;
connectedSocket.sin_port = htons(PORT);
//connectedSocket.sin_port = INADDR_BROADCAST;
connectedSocket.sin_addr.S_un.S_addr = inet_addr(SERVER);
while(1)
{
printf("\n\n\nEnter message : ");
gets(message);
//send the message
if (sendto(s, message,sizeof(message) , 0 , (struct sockaddr *) &connectedSocket, sizeof(connectedSocket)) == SOCKET_ERROR)
{
printf("\nsendto() failed with error code : %d" , WSAGetLastError());
exit(EXIT_FAILURE);
}
printf("\nMessage Successfully sent to Server");
// fflush(stdout);
if (recvfrom(s, receiveBuffer, 1000, 0, (struct sockaddr *) &connectedSocket,&length) == SOCKET_ERROR)
{
printf("\nrecvfrom() failed with error code : %d" , WSAGetLastError());
exit(EXIT_FAILURE);
}
printf("\nServer Says : ");
printf(receiveBuffer,sizeof(receiveBuffer));
}
closesocket(s);
WSACleanup();
return 0;
}
Let me explain a few things for you that might be confusing.
First, in your server you need to set serverSocket.sin_addr.s_addr to INADDR_ANY even if you want to broadcast. You don't want to make it INADDR_BROADCAST. This is simply telling the server to bind on any IP address your computer has, cause a single computer can have more than 1 IP. Which you are doing correctly.
But how can you broadcast from the server? You need to use setsockopt with SO_BROADCAST parameter like this ...
int options = 1;
if ((setsockopt(s, SOL_SOCKET, SO_BROADCAST,(char *)&options,sizeof(options))) < 0){
printf("%d",WSAGetLastError());
}
This will make your server listens for broadcasts, but how can you send broadcasts? You need to set INADDR_BROADCAST in the s_addr field in the sockaddr structure before calling sendto function.
clientSocket.sin_addr.s_addr = INADDR_BROADCAST;
Then use sendto with clientSocket to boardcast your messsage back.
Second, in your client code, you have two options depending on your application.
If you want your clients to send message first to the server (direct without broadcast) then you are doing it right, by setting inet_addr(SERVER) so the client send the message to your server only.
But, if you want the client to broadcast the message, then you need to use setsockopt again in your client, same as in your server, and set the address in connectSocketstructure to INADDR_BROADCAST.
Finally, it would be better if you tell us what are you trying to accomplish here. If you want clients to connect to server first, then the server announce the client to other clients, then you might take TCP instead of UDP.
The ConnectEx function requires an "unconnected, previously bound socket". Indeed, if I omit the bind step in my example (see below), ConnectEx fails with WSAEINVAL.
Here's my current understanding: before calling ConnectEx, bind the socket to INADDR_ANY and port 0 (unless it is already bound):
struct sockaddr_in addr;
ZeroMemory(&addr, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = INADDR_ANY;
addr.sin_port = 0;
rc = bind(sock, (SOCKADDR*) &addr, sizeof(addr));
if (rc != 0) { ... bind failed; call WSAGetLastError to see why ... }
Or for an IPv6 socket:
struct sockaddr_in6 addr;
ZeroMemory(&addr, sizeof(addr));
addr.sin6_family = AF_INET6;
addr.sin6_addr = in6addr_any;
addr.sin6_port = 0;
rc = bind(sock, (SOCKADDR*) &addr, sizeof(addr));
if (rc != 0) { ... bind failed; call WSAGetLastError to see why ... }
This lets the operating system assign a local address to our socket (as opposed to the remote address we are connecting to). connect does this step automatically, but ConnectEx does not.
My questions are:
Is my assessment correct?
Is there a way to do this automatic bind that is agnostic to the address family, or will I have to handle each of AF_INET, AF_INET6, AF_BTH (Bluetooth), etc. manually?
Working ConnectEx example (also on Gist: https://gist.github.com/4158972):
#include <stdio.h>
#include <WinSock2.h>
#include <MSWSock.h>
#include <WS2tcpip.h>
#pragma comment(lib, "Ws2_32.lib")
struct mswsock_s {
LPFN_CONNECTEX ConnectEx;
} mswsock;
static BOOL load_mswsock(void)
{
SOCKET sock;
DWORD dwBytes;
int rc;
/* Dummy socket needed for WSAIoctl */
sock = socket(AF_INET, SOCK_STREAM, 0);
if (sock == INVALID_SOCKET)
return FALSE;
{
GUID guid = WSAID_CONNECTEX;
rc = WSAIoctl(sock, SIO_GET_EXTENSION_FUNCTION_POINTER,
&guid, sizeof(guid),
&mswsock.ConnectEx, sizeof(mswsock.ConnectEx),
&dwBytes, NULL, NULL);
if (rc != 0)
return FALSE;
}
rc = closesocket(sock);
if (rc != 0)
return FALSE;
return TRUE;
}
int main(int argc, char *argv[])
{
int rc;
BOOL ok;
WSADATA wsaData;
SOCKET sock;
rc = WSAStartup(MAKEWORD(2,2), &wsaData);
if (rc != 0) {
printf("WSAStartup failed: %d\n", rc);
return 1;
}
if (LOBYTE(wsaData.wVersion) != 2 || HIBYTE(wsaData.wVersion) != 2) {
printf("Your computer is from the wrong millenium.\n");
WSACleanup();
return 1;
}
if (!load_mswsock()) {
printf("Error loading mswsock functions: %d\n", WSAGetLastError());
return 1;
}
sock = socket(AF_INET, SOCK_STREAM, 0);
if (sock == INVALID_SOCKET) {
printf("socket: %d\n", WSAGetLastError());
return 1;
}
/* ConnectEx requires the socket to be initially bound. */
{
struct sockaddr_in addr;
ZeroMemory(&addr, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = INADDR_ANY;
addr.sin_port = 0;
rc = bind(sock, (SOCKADDR*) &addr, sizeof(addr));
if (rc != 0) {
printf("bind failed: %d\n", WSAGetLastError());
return 1;
}
}
/* Issue ConnectEx and wait for the operation to complete. */
{
OVERLAPPED ol;
ZeroMemory(&ol, sizeof(ol));
sockaddr_in addr;
ZeroMemory(&addr, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = inet_addr("173.194.37.36"); // google.com
addr.sin_port = htons(80);
ok = mswsock.ConnectEx(sock, (SOCKADDR*) &addr, sizeof(addr), NULL, 0, NULL, &ol);
if (ok) {
printf("ConnectEx succeeded immediately\n");
} else if (WSAGetLastError() == ERROR_IO_PENDING) {
printf("ConnectEx pending\n");
DWORD numBytes;
ok = GetOverlappedResult((HANDLE) sock, &ol, &numBytes, TRUE);
if (ok)
printf("ConnectEx succeeded\n");
else
printf("ConnectEx failed: %d\n", WSAGetLastError());
} else {
printf("ConnectEx failed: %d\n", WSAGetLastError());
return 1;
}
}
/* Make the socket more well-behaved. */
rc = setsockopt(sock, SOL_SOCKET, SO_UPDATE_CONNECT_CONTEXT, NULL, 0);
if (rc != 0) {
printf("SO_UPDATE_CONNECT_CONTEXT failed: %d\n", WSAGetLastError());
return 1;
}
/* This will fail if SO_UPDATE_CONNECT_CONTEXT was not performed. */
rc = shutdown(sock, SD_BOTH);
if (rc != 0) {
printf("shutdown failed: %d\n", WSAGetLastError());
return 1;
}
printf("Done\n");
return 0;
}
connect does this step automatically, but ConnectEx does not.
Correct.
Is my assessment correct?
Yes.
Is there a way to do this automatic bind that is agnostic to the address family, or will I have to handle each of AF_INET, AF_INET6, AF_BTH (Bluetooth), etc. manually?
I believe that INADDR_ANY is a bunch of zeros in all address families, so you could just try using the memset() and omitting the assignment to addr.sin_addr.s_addr completely. Whether this is kosher, portable, politically correct etc. is another question into which I will not enter.
It seems pretty curious that Microsoft didn't manage to have ConnectEx() call bind() internally, considering that saving system calls is the motivation for its existence, and also considering that most programs never bind an outbound socket at all.
It is possible to get the bind address for ConnectEx in an address family independent way.
Solution 1
Call getaddrinfo with the following options:
pServiceName = "0"
hints.ai_flags = AI_PASSIVE
hints.ai_family = address family of the socket
Then use the first result of the returned address list.
To get the address family of the socket you can use getsockopt with SO_PROTOCOL_INFOW.
Solution 2
Use SOCKADDR_STORAGE for the address structure and call INETADDR_SETANY which is defined in MSTcpIP.h. It supports AF_INET and AF_INET6.