Internet Programming in Microsoft WinSock API

by Chin-Shiuh Shieh on

Introduction

• API, abbreviation of Application Program Interface, a set of routines, protocols, and tools for building software applications.
• Winsock is a collection of API for the communication between applications and the TCP/IP stack.
  
• Winsock is originated from Socket API of Berkeley Unix (1983).

TCP Socket versus UDP Socket

• Transmission Control Protocaol Socket
  • Client-Server architecture
  • Connection-oriented with error control
  • 
• User Datagram Protocol Socket
  • Peer-to-Peer architecture
  • Connectionless without error control
  • 

Winsock API

• Refer to the Win32 Developer's Reference/Micorsoft Windows Socket 2 Reference shipped with Borland C++ Buider 5.0 Professional for detail syntax and usage of the following Winsock API.

  Winsock 2.0 API

  BSD Socket API	Winsocket Extended API	Functionality
  accept	WSAAccept	Let listening socket accepts connection request from remote socket and establish the connection.
  bind		Set local socket's IP address and port number.
  closesocket		Close connection and socket, and release system resource.
  connect	WSAConnect	Establish connect to a remote socket.
  getpeername		Get remote socket's IP address and port number.
  getsockname		Get local socket's IP address and port number.
  getsocketopt		Get socket's options.
  ioctlsocket		Set or get socket's parameters.
  listen		Let socket listen to incoming request.
  recv	WSARecv	Receive data from socket.
  recvfrom	WSARecvFrom	Receive data and source information.
  select		Set socket's read/write status and execute synchrnous I/O.
  	WSASelect	Set socket's read/write status and execute asynchrnous I/O.
  send	WSASend	Send data to connected socket.
  sendto	WSASendTo	Send data to specified IP address/Port number.
  setsockopt		Set socket's options.
  shutdown		Disable socket's send and receive.
  socket	WSASocket	Create socket.
  BSD Socket API	Winsocket Extended API	Functionality (Winsock Control Related)
  	WSACleanup	Terminate use of the Windows Sockets DLL.
  	WSADuplicateSocket	Return a WSAPROTOCOL_INFO structure that can be used to create a new socket descriptor for a shared socket.
  	WSAEnumProtocols	Get information about available transport protocols.
  	WSAGetLastError	Get the error status for the last operation which failed.
  	WSASetLastError	Set the error code which can be retrieved through the WSAGetLastError function.
  	WSAStartup	Initiate use of the Windows Sockets DLL by a process.
  BSD Socket API	Winsocket Extended API	Functionality (Windows Event Related)
  	WSACloseEnevt	Close an open event object.
  	WSACreateEvent	Create a new event object.
  	WSAEnumNetworkEvents	Discover occurrences of network events for the indicated socket.
  	WSAResetEvent	Reset the state of the specified event object to nonsignaled.
  	WSASetEvent	Set the state of the specified event object to signaled.
  	WSAWaitForMultipleEvents	Return either when one or all of the specified event objects are in the signaled state, or when the time-out interval expires.
  BSD Socket API	Winsocket Extended API	Functionality (Conversion API)
  htonl	WSAHtonl	Convert an u_long from host to TCP/IP network byte order.
  htons	WSAHtons	Convert an u_short from host to TCP/IP network byte order.
  ntohl	WSANtohl	Convert an u_long from TCP/IP network order to host byte order.
  ntohs	WSANtohs	Convert an u_short from TCP/IP network byte order to host byte order.
  inet_addr		Convert a string containing an Internet Protocol dotted address into an in_addr.
  inet_ntoa		Convert a network address into a string in dotted format.
  BSD Socket API	Winsocket Extended API	Functionality (Database(DNS) API)
  gethostbyaddr		Get host information corresponding to an address.
  gethostbyname		Get host information corresponding to a hostname.
  gethostname		Return the standard host name for the local machine.
  getprotobyname		Get protocol information corresponding to a protocol name.
  getprotobynumber		Get protocol information corresponding to a protocol number.
  getservbyname		Get service information corresponding to a service name and protocol.
  getservbyport		Get service information corresponding to a port and protocol.
  	WSAAsyncGetHostByAddr	Get host information corresponding to an address asynchronusly.
  	WSAAsyncGetHostByName	Get host information corresponding to a hostname asynchronusly.
  	WSAAsyncGetProtoByName	Get protocol information corresponding to a protocol name asynchronusly.
  	WSAAsyncGetProtoByNumber	Get protocol information corresponding to a protocol number asynchronusly.
  	WSAAsyncGetServByName	Get service information corresponding to a service name and protocol asynchronusly.
  	WSAAsyncGetServByPort	Get service information corresponding to a port and protocol asynchronusly.

Function Prototypes

• int WSAStartup(WORD wVersionRequested,LPWSADATA lpWSAData);
• int WSACleanup(void);
• int gethostname(char FAR * name,int namelen);
• struct hostent FAR * gethostbyaddr(const char FAR * addr,int len,int type);
• struct hostent FAR * gethostbyname(const char FAR * name);
• char FAR * inet_ntoa(struct in_addr in);
• unsigned long inet_addr(const char FAR * cp);
• u_short htons(u_short hostshort);
• SOCKET socket(int af,int type,int protocol);
• int closesocket(SOCKET s);
• int bind(SOCKET s,const struct sockaddr FAR* name,int namelen);
• int WSAAsyncSelect(SOCKET s,HWND hWnd,unsigned int wMsg,long lEvent);
• int sendto(SOCKET s,const char FAR * buf,int len,int flags,const struct sockaddr FAR * to,int tolen);
• int recvfrom(SOCKET s,char FAR* buf,int len,int flags,struct sockaddr FAR* from,int FAR* fromlen);
• int connect(SOCKET s,const struct sockaddr FAR* name,int namelen);
• int send(SOCKET s,const char FAR * buf,int len,int flags);
• int recv(SOCKET s,char FAR* buf,int len,int flags);
• int listen(SOCKET s,int backlog);
• SOCKET accept(SOCKET s,struct sockaddr FAR* addr,int FAR* addrlen);

Data Structures

• struct WSAData {
      WORD            wVersion;
      WORD            wHighVersion;
      char            szDescription[WSADESCRIPTION_LEN+1];
      char            szSystemStatus[WSASYSSTATUS_LEN+1];
      unsigned short  iMaxSockets;
      unsigned short  iMaxUdpDg; 
      char FAR *      lpVendorInfo;
  };
  

• struct hostent {
      char FAR *          h_name;
      char FAR * FAR *    h_aliases;
      short               h_addrtype;
      short               h_length;
      char FAR * FAR *    h_addr_list;
  };
  

• struct in_addr {
      union {
          struct { u_char s_b1,s_b2,s_b3,s_b4; } S_un_b;
          struct { u_short s_w1,s_w2; } S_un_w;
          u_long S_addr;
      } S_un;
  };
  #define s_addr  S_un.S_addr
  

• struct sockaddr_in {
      short   sin_family;
      u_short sin_port;
      struct  in_addr sin_addr;
      char    sin_zero[8];
  };
  

Using Winsock API

• Have "#include <winsock.h>" in source programs.
• 

Sample Programs

• Get Winsock Version Information
• Get Local Host Information
• DNS Look Up
• UDP Message Sender
• UDP Message Receiver
• TCP Message Client

Useful C++ Builder Functions

• extern PACKAGE int __fastcall MessageDlg(const AnsiString Msg, TMsgDlgType DlgType, TMsgDlgButtons Buttons, int HelpCtx);
• extern PACKAGE AnsiString __fastcall IntToStr(int Value);
• extern PACKAGE int __fastcall StrToInt(const AnsiString S);
• char* __fastcall AnsiString::c_str() const;
• extern PACKAGE AnsiString __fastcall StrPas(const char * Str);
• void __fastcall Refresh(void);
• HANDLE CreateThread(LPSECURITY_ATTRIBUTES lpThreadAttributes,DWORD dwStackSize,LPTHREAD_START_ROUTINE lpStartAddress,DWORD dwCreationFlags,LPDWORD lpThreadId);