Socket (Socket) is an abstraction layer, the application can send or receive data through it, it can be the same as file open, close, and write operations.
1. socke classification
- 1.1 Stream Sockets
it provides a reliable, bidirectional data transmission connection-oriented services, achieve error-free data, duplicate-free transmission. In the TCP / IP protocol suite, to realize the transmission of a byte stream using the TCP protocol.
- 1.2 datagram socket
it provides a connectionless, reliable two-way data transmission services. Packets are sent in a separate form, and retains a record boundaries, does not provide reliable guarantee. In the TCP / IP protocol suite to achieve datagram sockets use UDP protocol.
- 1.3 raw socket
The socket allows for lower layer protocol (such as IP or ICMP) direct access.
2. Basic Operation Function
- Create socket socket ()
socket () function call format:
socket（int af，int type，int protocol）；
parameter af protocol family use the specified socket
type parameter to specify the type of communication required. Comprising a data stream , datagram , primitive type .
Parameter Description protocol socket protocol family used in the particular protocol. If the caller does not want to use the specified protocol is set to 0, the default connection mode.
- bind (): bind local address
after a socket with socket () to create, in fact, it has not been associated with any particular local or destination address
- connect (): Connects the socket to the destination address of the
socket is initially created is not associated with any foreign destination address. The client can call connect () binds a permanent destination address for the socket, place it in a connected state.
- listen (): set the wait connect state
program to a server program, when applying to the socket, and call bind () bound to a local address, you should wait for a client to request connection. listen () is the function of a socket is set to such a state.
- accept (): accept connection requests
server process using the system call socket, bind and listen to create a socket, bind it to a well-known port, and specify the length of the queue connection requests. Then, the server calls accept enters a wait state until it reaches a connection request.- send () / recv () and a sendto () / recvfrom ()
for transmitting and receiving data.
3. c implemented network chat program]
- client encoding process
#
#pragma comment(lib,"ws2_32.lib")
#include<Winsock2.h>
#include <stdio.h>
#include <stdlib.h>
#define DATA_BUFFER 1024
int main(int argc, char * argv[]){
WSADATA wsaData;
SOCKET sClient;
int i =5;
int iSend;
int iPort = 5050;
int iLen;
char buf[DATA_BUFFER];
struct sockaddr_in ser;
if(argc<2)
{
printf("Usage: client [server IP address]\n");
return -1;
}
memset(buf,0,sizeof(buf));
if(WSAStartup(MAKEWORD(2,2),&wsaData)!=0)
{
printf("Failed to load Winsock.\n");
return -1;
}
ser.sin_family = AF_INET;
ser.sin_port = htons(iPort);
ser.sin_addr.s_addr = inet_addr(argv[1]);
sClient = socket(AF_INET,SOCK_STREAM,0);
if(sClient == INVALID_SOCKET)
{
printf("socket() Failed: %d\n",WSAGetLastError());
return -1;
}
if(connect(sClient,(struct sockaddr *)&ser,sizeof(ser)) == INVALID_SOCKET)
{
printf("connect() Failed: %d\n",WSAGetLastError());
return -1;
}
else
{
while(i-->0)
{
iLen = recv(sClient,buf,sizeof(buf),0);
if(iLen == 0)
return -1;
else if(iLen == SOCKET_ERROR)
{
printf("recv() Failed: %d\n",WSAGetLastError());
return -1;
}
else
printf("recv() data from server: %s\n",buf); // 输出接收数据
printf("输入：");
scanf("%s",buf);
iSend = send(sClient,buf,sizeof(buf),0);
if(iSend == SOCKET_ERROR) //错误处理
{
printf("send() Failed: %d\n",WSAGetLastError());
break;
}
else if(iSend == 0)
{
break;
}
else
{
printf("send() byte: %d\n",iSend); //输出发送成功字节数
}
}
}
closesocket(sClient); //关闭 socket
WSACleanup();
return 0;}
- sever coding process
#include <Winsock2.h>
#include <stdio.h>
#include <stdlib.h>
#define DEFAULT_PORT 5050 //服务端默认端口
int main(){
int iPort = DEFAULT_PORT; //输入端口号
WSADATA wsaData; //数据结构，用来存储被 WSAStartup()调用返回的socket
SOCKET sListen,sAccept; //
int i =5;
int iLen; //客户机地址长度
int iSend; //发送数据长度
char buf[] = "I am a server"; //要发送给客户的信息
struct sockaddr_in ser,cli; //服务器和客户的地址
if(WSAStartup(MAKEWORD(2,2),&wsaData)!=0)
{
printf("Failed to load Winsock.\n"); //Winsock 初始化错误
return -1;
}
sListen = socket(AF_INET,SOCK_STREAM,0); //创建服务器端套接字 ，SOCK_STREAM面向连接
if(sListen == INVALID_SOCKET) // INVALID_SOCKET= -1
{
printf("socket() Failed: %d\n",WSAGetLastError()); //返回上次发生的网络错误 ,INVALID_SOCKET =-1
return -1;
}
//以下初始化服务器端地址
ser.sin_family = AF_INET; //使用 IP 地址族
ser.sin_port = htons(iPort); //主机序端口号转换为网络字节序端口号
ser.sin_addr.s_addr = htonl(INADDR_ANY); //主机序 IP 地址转换为网络字节序主机地址 INADDR_ANY ：0x00000000
//使用系统指定的 IP 地址 INADDR_ANY
if(bind(sListen,(LPSOCKADDR)&ser,sizeof(ser)) == SOCKET_ERROR) //套接定与地址的绑定
{
printf("bind() Failed: %d\n",WSAGetLastError());
return -1;
}
if(listen(sListen,5) == SOCKET_ERROR) //进入监听状态,listen的第二个参数为可以排队的最大连接个数 SOCKET_ERROR =-1
{
printf("lisiten() Failed: %d\n",WSAGetLastError());
return -1;
}
iLen = sizeof(cli); //初始化客户端地址长度参数 16B
while(1) //进入循环等待客户的连接请求
{
sAccept = accept(sListen,(struct sockaddr *)&cli,&iLen); //第一个参数：服务器的socket描述字，2： 指针，用于返回客户端的协议地址，3：协议地址的长度
if(sAccept == INVALID_SOCKET)
{
printf("accept() Failed: %d\n",WSAGetLastError());
return -1;
}
printf("Accepted client IP:[%s],port:[%d]\n",inet_ntoa(cli.sin_addr),ntohs(cli.sin_port));
//输出客户端 IP 地址和端口号
while(i-->0)
{
iSend = send(sAccept,buf,sizeof(buf),0); //1指定发送端套接字描述符2存放应用程序要发送数据的缓冲区3发送的数据的字节数 4一般置0
if(iSend == SOCKET_ERROR) //错误处理
{
printf("send() Failed: %d\n",WSAGetLastError());
break;
}
else if(iSend == 0)
{
break;
}
else
{
printf("send() byte: %d\n",iSend); //输出发送成功字节数
}
iLen = recv(sAccept,buf,sizeof(buf),0);
if(iLen == 0)
return -1;
else if(iLen == SOCKET_ERROR)
{
printf("recv() Failed: %d\n",WSAGetLastError());
return -1;
}
else
printf("recv() data from server: %s\n",buf); // 输出接收数据
printf("输入：");
scanf("%s",buf);
}
closesocket(sAccept);
}
closesocket(sListen); //关闭 socket
WSACleanup(); //输出发送成功字节数
return 0;}
Output
Client
Service-Terminal
