WSAConnect

The Windows Sockets WSAConnect function establishes a connection to another socket application, exchanges connect data, and specifies needed quality of service based on the supplied FLOWSPEC structure.

int  WSAConnect (
  SOCKET s,                          
  const struct sockaddr FAR * name,  
  int namelen,                       
  LPWSABUF lpCallerData,             
  LPWSABUF lpCalleeData,             
  LPQOS lpSQOS,                      
  LPQOS lpGQOS                       
);

Parameters

s: [in] A descriptor identifying an unconnected socket.
name: [in] The name of the socket in the other application to which to connect.
namelen: [in] The length of the name.
lpCallerData: [in] A pointer to the user data that is to be transferred to the other socket during connection establishment.
lpCalleeData: [out] A pointer to the user data that is to be transferred back from the other socket during connection establishment.
lpSQOS: [in] A pointer to the FLOWSPEC structures for socket s, one for each direction.
lpGQOS: [in] Reserved for future use with socket groups. A pointer to the FLOWSPEC structures for the socket group (if applicable).

Remarks

The WSAConnect function is used to create a connection to the specified destination, and to perform a number of other ancillary operations that occur at connect time. If the socket, s, is unbound, unique values are assigned to the local association by the system, and the socket is marked as bound.

For connection-oriented sockets (for example, type SOCK_STREAM), an active connection is initiated to the foreign host using name (an address in the name space of the socket; for a detailed description, please see bind). When this call completes successfully, the socket is ready to send/receive data. If the address field of the name structure is all zeroes, WSAConnect will return the error WSAEADDRNOTAVAIL. Any attempt to reconnect an active connection will fail with the error code WSAEISCONN.

For connection-oriented, nonblocking sockets, it is often not possible to complete the connection immediately. In such cases, this function returns the error WSAEWOULDBLOCK. However, the operation proceeds. When the success or failure outcome becomes known, it may be reported in one of several ways depending on how the client registers for notification. If the client uses select, success is reported in the writefds set and failure is reported in the exceptfds set. If the client uses WSAAsyncSelect or WSAEventSelect, the notification is announced with FD_CONNECT and the error code associated with the FD_CONNECT indicates either success or a specific reason for failure.

For a connectionless socket (for example, type SOCK_DGRAM), the operation erformed by WSAConnect is merely to establish a default destination address so that the socket can be used on subsequent connection-oriented send and receive operations (send, WSASend, recv, and WSARecv). Any datagrams received from an address other than the destination address specified will be discarded. If the address field of the name structure is all zeroes, the socket will be disconnected. Then, the default remote address will be indeterminate, so send/WSASend and recv/WSARecv calls will return the error code WSAENOTCONN. However, sendto/WSASendTo and recvfrom/WSARecvFrom can still be used. The default destination can be changed by simply calling WSAConnect again, even if the socket is already "connected". Any datagrams queued for receipt are discarded if name is different from the previous WSAConnect.

For connectionless sockets, name can indicate any valid address, including a broadcast address. However, to connect to a broadcast address, a socket must have setsockopt SO_BROADCAST enabled. Otherwise, WSAConnect will fail with the error code WSAEACCES.

On connectionless sockets, exchange of user-to-user data is not possible and the corresponding parameters will be silently ignored.

The application is responsible for allocating any memory space pointed to directly or indirectly by any of the parameters it specifies.

The lpCallerData is a value parameter that contains any user data that is to be sent along with the connection request. If lpCallerData is NULL, no user data will be passed to the peer. The lpCalleeData is a result parameter that will contain any user data passed back from the other socket as part of the connection establishment in a WSABUF structure. The member lpCalleeData->len initially contains the length of the buffer allocated by the application and pointed to by lpCalleeData->buf. lpCalleeData->len will be set to zero if no user data has been passed back. The lpCalleeData information will be valid when the connection operation is complete. For blocking sockets, the connection operation completes when the WSAConnect function returns. For nonblocking sockets, completion will be after the FD_CONNECT notification has occurred. If lpCalleeData is NULL, no user data will be passed back. The exact format of the user data is specific to the address family to which the socket belongs.

At connect time, an application can use the lpSQOS and lpGQOS parameters to override any previous quality of service specification made for the socket through WSAIoctl with either the SIO_SET_QOS or SIO_SET_GROUP_QOS opcodes.

lpSQOS specifies the FLOWSPEC structures for socket s, one for each direction, followed by any additional provider-specific parameters. If either the associated transport provider in general or the specific type of socket in particular cannot honor the quality of service request, an error will be returned as indicated below. The sending or receiving flow specification values will be ignored, respectively, for any unidirectional sockets. If no provider-specific parameters are supplied, the buf and len fields of lpSQOS->ProviderSpecific should be set to NULL and zero, respectively. A NULL value for lpSQOS indicates no application supplied quaility of service.

Reserved for future use with socket groups, lpGQOS specifies the FLOWSPEC structures for the socket group (if applicable), one for each direction, followed by any additional provider-specific parameters. If no provider-specific parameters are supplied, the buf and len fields of lpGQOS->ProviderSpecific should be set to NULL and zero, respectively. A NULL value for lpGQOS indicates no application-supplied group quality of service. This parameter will be ignored if s is not the creator of the socket group.

When connected sockets become closed for whatever reason, they should be discarded and recreated. It is safest to assume that when things go awry for any reason on a connected socket, the application must discard and recreate the needed sockets in order to return to a stable point.

Return Values

If no error occurs, WSAConnect returns zero. Otherwise, it returns SOCKET_ERROR, and a specific error code can be retrieved by calling WSAGetLastError. On a blocking socket, the return value indicates success or failure of the connection attempt.

With a nonblocking socket, the connection attempt can not be completed immediately. In this case, WSAConnect will return SOCKET_ERROR, and WSAGetLastError will return WSAEWOULDBLOCK. In this case, the application can:

Use select to determine the completion of the connection request by checking if the socket is writeable.
If your application is using WSAAsyncSelect to indicate interest in connection events, then your application will receive an FD_CONNECT notification when the connect operation is complete(successful or not).
If your application is using WSAEventSelect to indicate interest in connection events, then the associated event object will be signaled when the connect operation is complete (successful or not).

For a nonblocking socket, until the connection attempt completes all subsequent calls to WSAConnect on the same socket will fail with the error code WSAEALREADY.

If the return error code indicates the connection attempt failed (that is, WSAECONNREFUSED, WSAENETUNREACH, WSAETIMEDOUT) the application can call WSAConnect again for the same socket.

Error Codes

WSANOTINITIALISED	A successful WSAStartup must occur before using this function.
WSAENETDOWN	The network subsystem has failed.
WSAEADDRINUSE	The local address of the socket is already in use and the socket was not marked to allow address reuse with SO_REUSEADDR. This error usually occurs during the execution of bind, but could be delayed until this function if the bind function operates on a partially wild-card address (involving ADDR_ANY) and if a specific address needs to be "committed" at the time of this function.
WSAEINTR	The (blocking) Windows Socket 1.1 call was canceled through WSACancelBlockingCall.
WSAEINPROGRESS	A blocking Windows Sockets 1.1 call is in progress, or the service provider is still processing a callback function.
WSAEALREADY	A nonblocking connect/WSAConnect call is in progress on the specified socket.
WSAEADDRNOTAVAIL	The remote address is not a valid address (such as ADDR_ANY).
WSAEAFNOSUPPORT	Addresses in the specified family cannot be used with this socket.
WSAECONNREFUSED	The attempt to connect was rejected.
WSAEFAULT	The name or the namelen parameter is not a valid part of the user address space, the namelen parameter is too small, the buffer length for lpCalleeData, lpSQOS, and lpGQOS are too small, or the buffer length for lpCallerData is too large.
WSAEINVAL	The parameter s is a listening socket, or the destination address specified is not consistent with that of the constrained group the socket belongs to.
WSAEISCONN	The socket is already connected (connection-oriented sockets only).
WSAENETUNREACH	The network cannot be reached from this host at this time.
WSAENOBUFS	No buffer space is available. The socket cannot be connected.
WSAENOTSOCK	The descriptor is not a socket.
WSAEOPNOTSUPP	The FLOWSPEC structures specified in lpSQOS and lpGQOS cannot be satisfied.
WSAEPROTONOSUPPORT	The lpCallerData argument is not supported by the service provider.
WSAETIMEDOUT	Attempt to connect timed out without establishing a connection.
WSAEWOULDBLOCK	The socket is marked as nonblocking and the connection cannot be completed immediately.
WSAEACCES	Attempt to connect datagram socket to broadcast address failed because setsockopt SO_BROADCAST is not enabled.

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