Computer network --Socket

Socket Programming

Socket programming - Application Programming Interface (API)

Network Programming Interface

Application programming interface API (Application Programming Interface)

Application Programming Interface API: is the control and control of the operating system application process will be a transition system call interface.

Some typical application programming interface :

• Berkeley UNIX operating system defines an API, called socket interface (socket interface), referred to as a socket (socket).
• Microsoft operating system uses its interface to the socket API, a slightly different form of API, and called Windows Socket Interface, WINSOCK.
• AT & T UNIX System V for a defined API, abbreviated as TLI (Transport Layer Interface)

Socket Programming -Socket API Overview

• Originally designed: for BSD UNIX-Berkley, for the TCP / IP protocol stack interfaces
• Currently: de facto industry standard, the vast majority of operating systems support
• The most typical Internet network application API interface
• Communication Model: Client / Server (C / S)
• Inter-application communication process abstraction

Identify communication endpoints (External): IP address + port number

How to operate the system / process management socket (internal)? A: socket descriptor (socket descriptor), a small integer

Socket abstract

Similar to the abstract file when the application process creates a socket, the operating system allocates a data structure to store information about the socket, returned socket descriptor

Address structure

Defined structure sockaddr_in:

structsockaddr_in
{
    u_charsin_len;       /*地址长度*/
    u_charsin_family;    /*地址族(TCP/IP：AF_INET)*/
    u_shortsin_port;  /*端口号*/
    structin_addrsin_addr;/*IP地址*/
    char sin_zero[8]; /*未用(置0)*/
}

Using TCP / IP protocol suite of network applications endpoint address variable declaration, using the structure sockaddr_in

Socket Programming -Socket API function

Socket API function (WinSock)

//WSAStartup
intWSAStartup(WORD wVersionRequested, LPWSADATA lpWSAData);
//WSACleanup
intWSACleanup(void);

Use Socket application must first call the WSAStartup function before using Socket

• The first parameter indicates the version WinSock program request, wherein the high byte indicate the minor version, the lower byte indicates the major version.
  • Hexadecimal integer, for example 0x102 represents version 2.1
• The second argument returns the version information of the actual WinSock
  • Structure pointer WSADATA

//使用2.1版本的WinSock的程序代码段
wVersionRequested= MAKEWORD( 2, 1 );
err = WSAStartup( wVersionRequested, &wsaData);

Upon completion of the application using the Socket library request, and finally to call WSACleanup function, unbind and Socket library release system resources occupied Socket Library

sd= socket(protofamily,type,proto);

Create a socket, the operating system returns socket descriptor (SD), the first parameter (protocol family): protofamily = PF_INET (TCP / IP), the second parameter (socket type): type = SOCK_STREAM,SOCK_DGRAM orSOCK_RAW（TCP/IPthe third parameters (protocol number): 0 is the default

//创建一个流套接字的代码段
structprotoent*p;
p=getprotobyname("tcp");
SOCKET sd=socket(PF_INET,SOCK_STREAM,p->p_proto);

Socket service-oriented type of TCP / IP

• TCP: reliable, connection-oriented, byte-stream transmission, point
• UDP: unreliable, connectionless datagram transport

int closesocket(SOCKET sd);

Close a socket descriptor sd, if a plurality of processes share a socket, the socket closesocket reference count by 1, is reduced to 0 is not closed, a process of a multi-threaded socket no use counting, if a thread calls closesocket process will shut down a socket, other threads in the process will not be able to access the socket, the return value: 0: success, SOCKET_ERROR: failure

int bind(sd,localaddr,addrlen);

Binding of a socket local endpoint address: IP address + port number

Parameter: socket descriptor (sd), endpoint address (the localaddr)

Clients generally do not have to call bind function

Server: well-known port number, IP address

int listen(sd,queuesize);

Opposite side stream socket server in listening state, only the server calls, only for connection-oriented stream socket

Setting a connection request queue size (QUEUESIZE)

Return value: 0: Successful SOCKET_ERROR: Failed

connect(sd,saddr,saddrlen);

Call connect the client to make the client socket function (SD) with a specific port socket particular computer (the saddr) a (service) connection, only for the client, the client may be used for TCP UDP client may also be used end, TCP client: establish a TCP connection, UDP client: specify the server endpoint address

newsock= accept(sd,caddr,caddrlen);

Service program function call accept a connection queue taken was at the top of the client request from a client requests a stream socket in a listening state sd, and creates a new socket to create a socket connection channel with the client, only to TCP socket, only for server

The use of the newly created sockets (newsock) to communicate with customers

send(sd,*buf,len,flags);

TCP socket function send (client and server), or call the connect function of UDP client socket

sendto(sd,*buf,len,flags,destaddr,addrlen);

sendto function for the UDP server socket and connect the function is not called UDP client socket

recv(sd,*buffer,len,flags);

UDP server receives client socket recv function receives data from the other end of the TCP connection, or from a function call connect data sent by

recvfrom(sd,*buf,len,flags,senderaddr,saddrlen);

recvfrom function terminal for receiving data from the UDP socket with the server does not call connect function UDP client socket

int setsockopt(intsd, intlevel, intoptname, *optval, intoptlen);

setsockopt () function is used to set the option parameter of the socket sd

int getsockopt(intsd, intlevel, intoptname, *optval, socklen_t*optlen);

a getsockopt () function is used to obtain any type, any state of the current value of the option sockets, and stores the result optval

WSAStartup: initialize the socket library (only WinSock)
WSACleanup: clear / terminate the use of socket library (only WinSock)
socket: create socket connect: "Connect" remote server (client-only)
closesocket: release / Close the socket bind: bind a socket local IP address and port number (typically the client does not)
the listen: opposite side TCP server socket is listening mode, and set the queue size (only TCP server socket)
Accept: accept / extracting a connection request, a new socket is created, the new socket (only for server-side TCP socket)
the recv: receiving data (a TCP client socket or connected mode the UDP socket)
recvfrom: receiving data packets (UDP socket used for non-connected mode)
send: sends data (TCP socket for the client or the UDP socket connected mode)
the sendto: sending data packets (UDP socket used for non-connected mode)
the setsockopt: set socket option parameters
getsockopt: Get socket option parameter

Network byte order

TCP / IP defines a standard binary integer representation of a protocol header: network byte order (network byte order), some parameters Socket API function needs to be stored in network byte order (such as IP address, port number, etc.)

Native byte order can be achieved between the network byte order conversion function

htons: native byte order → network byte order (16bits)
ntohs: → local network byte order byte order (16bits)
htonl: native byte order → network byte order (32bits)
ntohl: local network byte order → byte order (32bits)

Network applications Socket API (TCP) to call basic flow

Socket Programming - Client software design

Resolve the server IP address

The client may use the domain name (e.g.: study.163.com) or IP address (eg: 123.58.180.121) identifies the server, using the IP protocol requires a 32 bit binary IP address, it is necessary to convert the domain name or IP address is a 32-bit IP address

The inet_addr function () dotted-decimal IP address to the IP address conversion 32

Function gethostbyname () domain to achieve IP address conversion 32, it returns a pointer to a pointer structure hostent

Resolution server (well-known) port number

The client may also use the service name (e.g., HTTP) server port identifier, service name needs to be converted to well-known port number, function The getservbyname () returns a pointer to a pointer structure servent

Resolution Protocol No.

The client may use the protocol name (eg: the TCP) specify the protocol, the protocol needs to be converted to name resolution protocol (eg: 6), with getprotobyname function () implement protocol name conversion protocol number, returns a pointer to a pointer structure protoent

TCP Client Software Process

1. Determine the server IP address and port number

2. Create a socket

3. Assign local endpoint address (IP address + port number)

4. Connect server (socket)

5. Follow the application layer protocol for communication

6. Close / releasable connection

UDP Client Software Process

1. Determine the server IP address and port number

2. Create a socket

3. Assign local endpoint address (IP address + port number)

4. Specify the server endpoint address, UDP datagram structure

5. Follow the application layer protocol for communication

6. Close / releasing the socket

Socket programming - server software design

4 types of basic server

• No connection loop (Iterative connectionless) server
• Loop connection-oriented (Iterative connection-oriented) server
• No concurrent connections (Concurrent connectionless) server
• Concurrent connection-oriented (Concurrent connection-oriented) basic types of servers server 4

Connectionless server basic flow loop

1. Create a socket

2. Binding endpoint address (INADDR_ANY + port number)

3 repeatedly receives a request from a client

4. Follow the application layer protocol configuration response message transmitted to the client

Data transmission:

The server can not use the connect () function, connectionless server using the sendto () function to send data packets

Access to customer endpoint address: Call recvfrom () function when receiving data, automatically extract

Connection-oriented server processes the basic cycle

1. Create a (main) socket, bind and well-known port number;

2. Set (main) passive socket listening mode, ready for the server;

3. The call accept () function takes the next connection request (through the main socket), creates a new socket for establishing a connection with the client;

4. Follow the application layer protocol, the client receives the repeated request, constructs and sends a response (via the new socket);

5. After service for a particular client, closes the connection between the client and returns to step 3. The loop connection-oriented server processes the basic

Concurrent basic flow connectionless server

The main thread 1: create a socket, bind and well-known port number;

The main thread 2: repeatedly calls recvfrom () function to receive the next client request, and creates a new thread in response to the client process;

1 child thread: receiving a particular request;

Child thread 2: According to the application layer protocol configuration response message, and calls the sendto () transmission;

Child thread 3: Exit (a sub-thread processing a request after termination)

Concurrent connection-oriented server processes the basic

The main thread 1: Create the (main) socket, bind and well-known port number;

The main thread 2: Set (main) passive socket listening mode, ready for the server;

The main thread 3: repeatedly call accept () function takes the next connection request (through the main socket), and creates a new child thread in response to the client process;

1 child thread: receiving a customer service request (by the newly created socket);

Child thread 2: Following the application layer protocol to interact with a particular customer;

Child thread 3: Turn off / release the connection and exit (thread termination)

example

Connectionless server cycle DAYTIME

Connection-oriented servers concurrently DAYTIME