How to get client real ip-address and port using IOCP?

Question

I need to take ip-address and port of clients in server. Server written on C++ using IOCP, so I don't accept clients, I create new socket and then accept (AcceptEx) client on this ready socket. And because of it struct sockaddr_in is not correct.

How can I do this?

Thanks!

Answer 1

AcceptEx may return you both your and peer addresses (ip+port of TCP sockets).

BOOL AcceptEx(
  __in   SOCKET sListenSocket,
  __in   SOCKET sAcceptSocket,
  __in   PVOID lpOutputBuffer,
  __in   DWORD dwReceiveDataLength,
  __in   DWORD dwLocalAddressLength,
  __in   DWORD dwRemoteAddressLength,
  __out  LPDWORD lpdwBytesReceived,
  __in   LPOVERLAPPED lpOverlapped
);

You should specify lpOutputBuffer to point on a buffer with enough size to hold 2 returned addresses, then . dwLocalAddressLength and dwRemoteAddressLength should be set to the address size reserved in the buffer.

According to MSDN the buffer size required for a single address (for AcceptEx function) is sizeof(SOCKADDR_IN) + 16:

dwLocalAddressLength [in]

The number of bytes reserved for the local address information. This value must be at least 16 bytes more than the maximum address

length for the transport protocol in use.

Of course the buffer must be valid for the I/O duration. You may put it inside your OVERLAPPED structure. Something like this:

struct OverlappedAccept
    :public OVERLAPPED
{
    // some context information that you need
    // ...

    // Buffer for addresses
    struct {
        BYTE m_pLocal[sizeof(SOCKADDR_IN) + 16];
        BYTE m_pRemote[sizeof(SOCKADDR_IN) + 16];
    } m_Bufs;
};


// start accept operation
OverlappedAccept* pOver = /* ... */;

BOOL bRet = AcceptEx(
    hSockListen,
    hSockNew,
    &pOver->m_Bufs,
    0,
    sizeof(pOver->m_Bufs.m_pLocal),
    sizeof(pOver->m_Bufs.m_pRemote),
    &dwBytes,
    pOver);

After the I/O has (successfully) completed you may get the addresses:

sockaddr *pLocal = NULL, *pRemote = NULL;
int nLocal = 0, nRemote = 0;
GetAcceptExSockAddrs(
    &pOver->m_Bufs,
    0,
    sizeof(pOver->m_Bufs.m_pLocal),
    sizeof(pOver->m_Bufs.m_pRemote),
    &pLocal,
    &nLocal,
    &pRemote,
    &nRemote);