Sockets Interface

You access the winsock API by inserting, at the beginning of your code, the statement:

#include <winsock2.h>

The winsock API conforms to a sockets standard, functional on both UNIX and Windows platforms, so a sockets-based program written for a UNIX platform should be able to communicate with a sockets-based program running on a Windows platform.

Win32 Sockets API

• int WSAStartup(WORD wVersionRequested, LPWSADATA lpWSAData)
  • Loads the winsock library version requested in wVersionRequested.
  • Returns zero if successful.
  • wVersionRequested is the winsock version, either 1.1 or 2.2, written with major version in the low part of a DWORD and minor version in the high part.
  • lpwSAData is a WSAData structure, filled by WSAStartup.
  • Example:

    WSAData wsaData;
    WSAStartup(MAKEWORD(2,2), wsaData);

• SOCKET socket(int af, int type, int protocol)
  • creates a socket that is bound to a specific service provider.
  • returned value is a valid socket if no error, otherwise INVALID_SOCKET.
  • af is the address family of the protocol. AF_INET is the address family of the internet protocol (IP).
  • type is the socket type. SOCK_STREAM is the type we will use.
  • protocol input qualifies the specific transport. IPPROTO_IP is used for IP protocol.
  • Example:

    SOCKET s = socket(AF_INET, SOCK_STREAM, IPPROTO_IP);

• int bind(SOCKET s, const struct sockaddr name, int namelen)
  • bind associates a socket with a specific port.
  • returned value is 0 if no error, otherwise SOCKET_ERROR.
  • s is a socket used for listening for incoming connection requests.
  • sockaddr is an address buffer specific to the protocol used.
  • namelen is the length of the address buffer
  • Example:

    SOCKET S;
    struct sockaddr_in tcpaddr;
    int port = 5150;
    s = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    tcpaddr.sin_family = AF_INET;
    tcpaddr.sin_port = htons(port);
    tcpaddr.sin_addr.s_addr = htonl(INADDR_ANY) // accepts any incoming
    bind(s, (SOCKADDR*)&tcpaddr, sizeof(tcpaddr));
    

• int listen(SOCKET s, int backlog)
  • Starts socket s listening for incoming requrests.
  • returned value is 0 if no error, otherwise SOCKET_ERROR.
  • s is the listener socket.
  • backlog is the maximum queue length for pending connections.
• SOCKET accept(SOCKET s, struct sockaddr addr, int addrlen)
• Accepts an incoming request for a connection.
• Return value of type SOCKET is the server socket to use for this connection, if successful, otherwise INVALID_SOCKET.
• s is the listening socket.
• addr is an address buffer, specific to the protocol used.
• addrlen is length of addr.
• int connect(SOCKET s, const struct sockaddr name, int namelen)
• Request to connect to a listener socket specified in name.
• s is a valid socket you want to use to make a connection.
• name is a tcp socketaddr structure that identifies the server you want to connect to.
• namelen is the length of the socket address structure.
• Example:

  SOCKET sClient;
  int iPort = 4040;
  char szServer = "127.0.0.1";
  struct sockaddr_in server;
  server.sin_family = AF_INET;
  server.sin_port = htons(iPort);
  server.sin_addr.s_addr = inet_addr(szServer);
  connect(sClient, (struct sockaddr*)&server, sizeof(server));

• int send(SOCKET s, const char *buf, int len, int flags)
  • Send a buffer of len bytes to a connected socket.
  • returns the number of bytes actually sent.
  • s is the sender's socket.
  • buf is the buffer of characters to be sent.
  • len is the number of buffer characters to send.
  • flags is zero for a routed message.
• int recv(SOCKET s, char *buf, int len, int flags)
  • Accept incoming data on a valid socket s.
  • Returns the number of bytes received if successful. Returns 0 if the connection has been closed by sender. Otherwise, returns -1 to indicate an error.
  • s is the receiving socket.
  • buf is a character buffer you provide to receive data.
  • flags should be zero.