WSAConnectByNameA function (winsock2.h)

The WSAConnectByName function establishes a connection to a specified host and port. This function is provided to allow a quick connection to a network endpoint given a host name and port.

This function supports both IPv4 and IPv6 addresses.

Syntax

BOOL WSAConnectByNameA(
  [in]      SOCKET          s,
  [in]      LPCSTR          nodename,
  [in]      LPCSTR          servicename,
  [in, out] LPDWORD         LocalAddressLength,
  [out]     LPSOCKADDR      LocalAddress,
  [in, out] LPDWORD         RemoteAddressLength,
  [out]     LPSOCKADDR      RemoteAddress,
  [in]      const timeval   *timeout,
            LPWSAOVERLAPPED Reserved
);

Parameters

[in] s

A descriptor that identifies an unconnected socket.

[in] nodename

A NULL-terminated string that contains the name of the host or the IP address of the host on which to connect for IPv4 or IPv6.

[in] servicename

A NULL-terminated string that contains the service name or destination port of the host on which to connect for IPv4 or IPv6.

A service name is a string alias for a port number. For example, “http” is an alias for port 80 defined by the Internet Engineering Task Force (IETF) as the default port used by web servers for the HTTP protocol. Possible values for the servicename parameter when a port number is not specified are listed in the following file:

%WINDIR%\system32\drivers\etc\services

[in, out] LocalAddressLength

On input, a pointer to the size, in bytes, of the LocalAddress buffer provided by the caller. On output, a pointer to the size, in bytes, of the SOCKADDR for the local address stored in the LocalAddress buffer filled in by the system upon successful completion of the call.

[out] LocalAddress

A pointer to the SOCKADDR structure that receives the local address of the connection. The size of the parameter is exactly the size returned in LocalAddressLength. This is the same information that would be returned by the getsockname function. This parameter can be NULL, in which case, the LocalAddressLength parameter is ignored.

[in, out] RemoteAddressLength

On input, a pointer to the size, in bytes, of the RemoteAddress buffer provided by the caller. On output, a pointer to the size, in bytes, of the SOCKADDR for the remote address stored in RemoteAddress buffer filled-in by the system upon successful completion of the call.

[out] RemoteAddress

A pointer to the SOCKADDR structure that receives the remote address of the connection. This is the same information that would be returned by the getpeername function. This parameter can be NULL, in which case, the RemoteAddressLength is ignored.

[in] timeout

The time, in milliseconds, to wait for a response from the remote application before aborting the call.

Reserved

Reserved for future implementation. This parameter must be set to NULL.

Return value

If a connection is established, WSAConnectByName returns TRUE and LocalAddress and RemoteAddress parameters are filled in if these buffers were supplied by the caller.

If the call fails, FALSE is returned. WSAGetLastError can then be called to get extended error information.

Remarks

WSAConnectByName is provided to enable quick and transparent connections to remote hosts on specific ports. It is compatible with both IPv6 and IPv4 versions.

To enable both IPv6 and IPv4 communications, use the following method:

• The setsockopt function must be called on a socket created for the AF_INET6 address family to disable the IPV6_V6ONLY socket option before calling WSAConnectByName. This is accomplished by calling the setsockopt function on the socket with the level parameter set to IPPROTO_IPV6 (see IPPROTO_IPV6 Socket Options), the optname parameter set to IPV6_V6ONLY, and the optvalue parameter value set to zero .

WSAConnectByName has limitations: It works only for connection-oriented sockets, such as those of type SOCK_STREAM. The function does not support overlapped I/O or non-blocking behavior. WSAConnectByName will block even if the socket is in non-blocking mode.

WSAConnectByName does not support user-provided data during the establishment of a connection. This call does not support FLOWSPEC structures, either. In cases where these features are required, WSAConnect must be used instead.

In versions before Windows 10, if an application needs to bind to a specific local address or port, then WSAConnectByName cannot be used since the socket parameter to WSAConnectByName must be an unbound socket.

This restriction was removed Windows 10.

The RemoteAddress and the LocalAddress parameters point to a SOCKADDR structure, which is a generic data type. When WSAConnectByName is called, it is expected that a socket address type specific to the network protocol or address family being used will actually be passed in these parameters. So for IPv4 addresses, a pointer to a sockaddr_in structure would be cast to a pointer to SOCKADDR as the RemoteAddress and LocalAddress parameters. For IPv6 addresses, a pointer to a sockaddr_in6 structure would be cast to a pointer to SOCKADDR as the RemoteAddress and LocalAddress parameters.

When the WSAConnectByName function returns TRUE, the socket s is in the default state for a connected socket. The socket s does not enable previously set properties or options until SO_UPDATE_CONNECT_CONTEXT is set on the socket. Use the setsockopt function to set the SO_UPDATE_CONNECT_CONTEXT option.

For example:

//Need to #include <mswsock.h> for SO_UPDATE_CONNECT_CONTEXT

int iResult = 0;

iResult = setsockopt( s, SOL_SOCKET, SO_UPDATE_CONNECT_CONTEXT, NULL, 0 );

Windows 8.1 and Windows Server 2012 R2: The WSAConnectByNameW function is supported for Windows Store apps on Windows 8.1, Windows Server 2012 R2, and later.

Examples

Establish a connection using WSAConnectByName.

#ifndef UNICODE
#define UNICODE
#endif

#define WIN32_LEAN_AND_MEAN

#include <winsock2.h>
#include <Ws2tcpip.h>
#include <mswsock.h>   // Need for SO_UPDATE_CONNECT_CONTEXT
#include <stdio.h>

// Link with ws2_32.lib
#pragma comment(lib, "Ws2_32.lib")

SOCKET
OpenAndConnect(LPWSTR NodeName, LPWSTR PortName) 
{
    SOCKET ConnSocket = INVALID_SOCKET;
    int ipv6only = 0;
    int iResult;
    BOOL bSuccess;
    SOCKADDR_STORAGE LocalAddr = {0};
    SOCKADDR_STORAGE RemoteAddr = {0};
    DWORD dwLocalAddr = sizeof(LocalAddr);
    DWORD dwRemoteAddr = sizeof(RemoteAddr);
  
    ConnSocket = socket(AF_INET6, SOCK_STREAM, 0);
    if (ConnSocket == INVALID_SOCKET){
        wprintf(L"socket failed with error: %d\n", WSAGetLastError());
        return INVALID_SOCKET;
    }

    iResult = setsockopt(ConnSocket, IPPROTO_IPV6,
        IPV6_V6ONLY, (char*)&ipv6only, sizeof(ipv6only) );
    if (iResult == SOCKET_ERROR){
        wprintf(L"setsockopt for IPV6_V6ONLY failed with error: %d\n",
            WSAGetLastError());
        closesocket(ConnSocket);
        return INVALID_SOCKET;       
    }

    bSuccess = WSAConnectByName(ConnSocket, NodeName, 
            PortName, &dwLocalAddr,
            (SOCKADDR*)&LocalAddr,
            &dwRemoteAddr,
            (SOCKADDR*)&RemoteAddr,
            NULL,
            NULL);
    if (!bSuccess){
        wprintf(L"WsaConnectByName failed with error: %d\n", WSAGetLastError());
        closesocket(ConnSocket);
        return INVALID_SOCKET;       

    
    }

    iResult = setsockopt(ConnSocket, SOL_SOCKET,
        SO_UPDATE_CONNECT_CONTEXT, NULL, 0);
    if (iResult == SOCKET_ERROR){
        wprintf(L"setsockopt for SO_UPDATE_CONNECT_CONTEXT failed with error: %d\n",
            WSAGetLastError());
        closesocket(ConnSocket);
        return INVALID_SOCKET;       
    }

    return ConnSocket;
}

int __cdecl wmain(int argc, wchar_t **argv)
{
   //-----------------------------------------
    // Declare and initialize variables
    WSADATA wsaData;
    int iResult;

    SOCKET s = INVALID_SOCKET;

    // Validate the parameters
    if (argc != 3) {
        wprintf(L"usage: %ws <Nodename> <Portname>\n", argv[0]);
        wprintf(L"wsaconnectbyname establishes a connection to a specified host and port.\n");
        wprintf(L"%ws www.contoso.com 8080\n", argv[0]);
        return 1;
    }

    // Initialize Winsock
    iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
    if (iResult != 0) {
        wprintf(L"WSAStartup failed: %d\n", iResult);
        return 1;
    }

    wprintf(L"WsaConnectByName with following parameters:\n");
    wprintf(L"\tNodename = %ws\n", argv[1]);
    wprintf(L"\tPortname (or port) = %ws\n\n", argv[2]);

    //--------------------------------
    // Call our function that uses the WsaConnectByName. 
    
    s = OpenAndConnect(argv[1], argv[2]);
    if ( s == INVALID_SOCKET ) {
        wprintf(L"WsaConnectByName failed with error: %d\n", WSAGetLastError());
        WSACleanup();
        return 1;
    }
    else
    {
        wprintf(L"WsaConnectByName succeeded\n");
        
        closesocket(s);
        WSACleanup();
        return 0;
    }
}

Requirements

See also

IPPROTO_IPV6 Socket Options

SOCKADDR

WSAConnect

WSAConnectByList

WSAGetLastError

getaddrinfo

getpeername

getsockname

setsockopt