Use of WinSockAPI
1.WSAStartup function
In order to call any Winsock API function in your application, the first thing you need to do is to initialize Winsock service through WSAStartup function, so you need to call WSAStartup function.
Declare the function WSA Startup Lib "WS2 _ 32.dll" _
(ByVal wversionlong，lpWSAData As WSAData)Long
This function has two parameters: wVersionRequired and lpWSAData. The wVersionRequired parameter defines the highest version that Windows sockets can provide. Its upper byte defines the minor version number, and its lower byte defines the major version number. The following are two examples of Winsock versions used in VB:
Initialization version 1. 1.
lngRetVal = wsa startup(h 10 1，udtWinsockData)
Initialize version 2.2
lngRetVal = WSAStartup(H202，udtWinsockData)
The second parameter is the data structure of WSADATA, which receives data when executing Windows Sockets.
Sign WSAData
WVersion in integer form
WHighVersion in integer form
SZ description As String * wsa description _ LEN
szSystemStatus As String * wsa sys _ STATUS _ LEN
IMaxSockets in integer form
IMaxUdpDg is an integer
LpVendorInfo is Long.
End type
The following table describes the data members:
Field description
Windows socket version information.
WHighVersion is the highest version that supports Winsock by loading library files.
It is usually the same as the wVersion value.
SZ describes a detailed SZ describing the Windows socket when it is executed.
SzSystemStatus contains related status and configuration information.
IMaxSockets indicates the maximum number of sockets open at the same time, and 0 indicates no limit.
IMaxUdpDg means the maximum number of datagrams that can be opened at the same time, and 0 means there is no limit.
Information retention specified by LpVendorInfo supplier
There is no return value of lpVendorInfo in Winsock version 1. 1 and 2.2. Because winsock 2 supports multiple transmission protocols, iMaxSockets and iMaxUdpDg can only be used in winsock 1. 1 which only supports TCP/TP. To get these values in Winsock 2, you can use the WSAEnumProtocols function.
If it succeeds or returns an error code, the function returns 0.
Error code meaning
WSASYSNOTREADY pointed out that the network is not ready for transmission.
WSAVERNOTSUPPORTED The current WinSock implementation does not support the Windows Socket specification version specified by the application.
WSAEINPROGRESS is blocking WinSock calls.
The protocol requested by WSAEPROCLIM is not configured in the system, or its implementation is not supported.
WSAEFAULT lpWSAData is not a valid pointer.
2.WSACleanup function
Every time you call WSAStartup function, you need to call WSACleanup function to inform the system to unload the library file and empty the allocated resources. This function is very simple, with no parameters:
Declare the function wsacleanuplib "ws2 _ 32.dll" () as Long.
3. Establish socket function
Declare the function socket library "ws2 _ 32.dll" (byval af as long, _
ByVal s_type is Long,
ByVal protocol is as long)
This function has three parameters that define what kind of socket to create. These three parameters are:
Parameter describes enumeration type.
Af address series specification. Address family
S _ s_typeThe type specification of the new socket. SocketType
Protocol used for socket socket protocol.
It is specific to the indicated address.
Family.
Address series:
AF_UNSPEC = 0 '/* Not specified */
AF_UNIX = 1 '/* Host local (pipeline, portal) */
AF_INET = 2 '/* Internet: UDP, TCP, etc. */
Af _ implicit = 3'/* ARPANET IMP address */
AF_PUP = 4 '/* pup protocol: for example, BSP */
AF_CHAOS = 5 '/* mit chaos protocol */
AF_NS = 6 '/* XEROX NS protocol */
AF_IPX = AF_NS '/* IPX protocols: IPX, SPX, etc. */
AF_ISO = 7 '/* ISO protocol */
AF_OSI = AF_ISO '/* OSI is ISO */
AF_ECMA = 8 '/* European computer manufacturers */
AF_DATAKIT = 9 '/* datakit protocol */
AF_CCITT = 10 '/* CCITT protocol, X.25, etc. */
AF _ SNA = 1 1 '/* IBM SNA */
AF_DECnet = 12 '/* DECnet */
AF_DLI = 13 '/* direct data link interface */
AF_LAT = 14 '/* LAT */
AF _ hy link = 15 '/* NSC Hyperchannel */
AF _ apple talk = 16 '/* apple talk */
AF_NETBIOS = 17 '/* NetBios style address */
AF _ voice view = 18 '/* voice view */
AF_FIREFOX = 19 '/* Protocol from FIREFOX */
AF_UNKNOWN 1 = 20 '/* Someone is using this! */
AF_BAN = 2 1 '/* Banyan */
AF_ATM = 22 '/* local ATM service */
AF_INET6 = 23 '/* Internet version 6 */
AF _ CLUSTER = 24 '/* Microsoft wolf pack */
AF _ 12844 = 25 '/* IEEE 1284.4 WG AF */
AF_MAX = 26
Socket type:
SOCK_STREAM = 1' /* stream socket */
SOCK_DGRAM = 2' /* datagram socket */
SOCK _ RAW = 3 '/* RAW- protocol interface */
SOCK_RDM = 4' /* Reliable delivered message */
SOCK_SEQPACKET = 5' /* Ordered packet flow */
Agreement:
IPPROTO_IP = 0 '/* Virtual IP */
IPPROTO_ICMP = 1 '/* control message protocol */
IPPROTO_IGMP = 2 '/* Internet Group Management Protocol */
Ipproto _ GGP = 3'/* Gateway 2 (deprecated) */
IPPROTO_TCP = 6 '/* tcp */
IPPROTO_PUP = 12 '/* pup */
IPPROTO_UDP = 17 '/* User Datagram Protocol */
IPPROTO_IDP = 22 '/* xns idp */
IPPROTO_ND = 77 '/* unofficial network disk proto */
IPPROTO_RAW = 255 '/* Original IP packet */
IPPROTO_MAX = 256
This function can establish a network socket using a specific protocol. For example, for UDP protocol, it can be written as follows:
S = socket (AF_INET, SOCK_DGRAM, IPPROTO_UDP)
S = socket (AF_INET, SOCK_STREAM, IPPROTO_TCP)
4. Turn off the socket function
Declare the function closesocket lib "ws2 _ 32.dll" (byvals as Long) as long.
When the socket is created, the function has a Handle parameter.
5. Connection function
Declare the function connection library "ws2 _ 32.dll" (byvals as long, _
ByRef name is sockaddr_in, _
As long as, as long as
parameter
Socket handle for s connection.
Name the address where the connection is established.
The length of the namelen connection address.
Return value
Returns 0 on success. Otherwise, it returns SOCKET_ERROR and the corresponding error number err. lastteller error.
Obviously, when calling this function, we need to know the socket handle, port number and host name (or host IP address) of the computer to be connected. We know that the Connect method of Winsock control depends on two variables: RemoteHost and RemotePort. This method does not need a socket handle because it is already encapsulated in a COM object. You might think that the connect function should also accept the same variable settings, however, this is not the case. The transmission of the host address and port number of the connect function depends on the sockaddr_in structure.
Public type sockaddr_in
Sin_family is an integer
Sin_port is an integer
As long as sin_addr.
Sin_zero( 1 to 8) as bytes.
End type
6. Socket helper function
Declare the function binding library "ws2 _ 32.dll" (byvals as long, _
ByRef name is sockaddr_in, _
ByRef namelen is the same length.
S is a Socket created by using the socket function, name is a pointer to the structure describing the communication object, and namelen is the length of the structure. knot
Components in this structure include:
IP address: corresponding to name.sin _ addr.s _ addr
Port number: corresponding to name.sin_port.
Port numbers are used to represent different processes (i.e. applications) on the same computer, and there are two ways to assign them:
The first allocation method is that the process allows the system to automatically allocate a port number for the socket, and only needs to specify the port number as 0 before calling bind. The port number automatically assigned by the system is between 1024 and 5000, and any TCP or UDP port between 1 and 1023 is reserved. The system does not allow any process to use the reserved port unless its valid user ID is zero (that is, superuser).
The second allocation method is that the process specifies a specific port for the socket. This is very useful for servers that need to allocate a well-known port for sockets. The specified range is between 1024 and 65536.
Address type: corresponding to name.sin_family, generally assigned as AF_INET, indicating an Internet address (i.e. IP address). IP address is usually represented by dot, but it is actually a long integer of 32 bits, which can be converted by inet_addr () function.
7. Socket listener function
Declare the function listenlib "ws2 _ 32.dll" (byvals is Long, ByVal backlog is Long) as Long.
The listen function is used to set the socket to listening state, which means that the socket is ready to connect. Note that this function is generally used in service programs, where s is a Socket created by using the socket function, and the backlog parameter is used to set the number of clients waiting to connect.