学习网址：
什么是 socket 编程？
Socket programming is a way of connecting two nodes on a network to communicate with each other. One socket(node) listens on a particular port at an IP, while other socket reaches out to the other to form a connection. Server forms the listener socket while client reaches out to the server.
服务端
示例代码
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| // Server side C/C++ program to demonstrate Socket programming
#include <unistd.h>
#include <stdio.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <string.h>
#define PORT 8080
int main(int argc, char const *argv[])
{
int server_fd, new_socket, valread;
struct sockaddr_in address;
int opt = 1;
int addrlen = sizeof(address);
char buffer[1024] = {0};
char *hello = "Hello from server";
// Creating socket file descriptor
if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0)
{
perror("socket failed");
exit(EXIT_FAILURE);
}
// Forcefully attaching socket to the port 8080
if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, &opt, sizeof(opt)))
{
perror("setsockopt");
exit(EXIT_FAILURE);
}
address.sin_family = AF_INET;
address.sin_addr.s_addr = INADDR_ANY;
address.sin_port = htons( PORT );
// Forcefully attaching socket to the port 8080
if (bind(server_fd, (struct sockaddr *)&address, sizeof(address)) < 0)
{
perror("bind failed");
exit(EXIT_FAILURE);
}
if (listen(server_fd, 3) < 0)
{
perror("listen");
exit(EXIT_FAILURE);
}
if ((new_socket = accept(server_fd, (struct sockaddr *)&address, (socklen_t*)&addrlen))<0)
{
perror("accept");
exit(EXIT_FAILURE);
}
valread = read( new_socket , buffer, 1024);
printf("%s\n",buffer );
send(new_socket , hello , strlen(hello) , 0 );
printf("Hello message sent\n");
return 0;
}
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接口的创建
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| int socketfd = socket(domain, type, protocol);
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绑定
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| int bind(int sockfd, const struct sockaddr *addr, socklen_t addrlen);
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创建接口之后，上面的 bind 函数会将 sockfd 这个接口绑定到 addr 这个自定义数据结构对象中指定的地址和端口。
在上面的示例代码中我们使用 INADDR_ANY 来指定 IP 地址，因为我们将服务绑定到了本地的端口。
监听
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| int listen(int sockfd, int backlog);
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该语句令服务器接口处于被动接收消息的模式，也就是说，它开始等待客户端向服务器建立连接。
backlog 定义了 socket 在连接时，连接等待队列中可以增长到的最大长度。如果有客户端在最大长度时连接到服务器时，客户端会收到一个 ECONNREFUSED 的错误信息。
接收
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| int new_socket= accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen);
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它将 sockfd 等待队列中最靠前的连接请求解压出来，创建一个新的 socket 连接，返回一个新的描述符。
到此为止，服务器和和客户端已经建立了连接，可以传送数据。
客户端
示例代码
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| // Client side C/C++ program to demonstrate Socket programming
#include <stdio.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <string.h>
#define PORT 8080
int main(int argc, char const *argv[])
{
struct sockaddr_in address;
int sock = 0, valread;
struct sockaddr_in serv_addr;
char *hello = "Hello from client";
char buffer[1024] = {0};
if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0)
{
printf("\n Socket creation error \n");
return -1;
}
memset(&serv_addr, '0', sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(PORT);
// Convert IPv4 and IPv6 addresses from text to binary form
if(inet_pton(AF_INET, "127.0.0.1", &serv_addr.sin_addr)<=0)
{
printf("\nInvalid address/ Address not supported \n");
return -1;
}
if (connect(sock, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0)
{
printf("\nConnection Failed \n");
return -1;
}
send(sock , hello , strlen(hello) , 0 );
printf("Hello message sent\n");
valread = read( sock , buffer, 1024);
printf("%s\n",buffer );
return 0;
}
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接口的创建
与服务器端接口的创建过程相同。
连接的建立
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| int connect(int sockfd, const struct sockaddr *addr, socklen_t addrlen);
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connect 这个系统函数调用，将描述符 sockfd 与由 addr 参数确定的地址和端口连接起来。
总结
TCP-IP 协议下流程大致如下：
