Transport layer protocol: TCP/UDP protocol
TCP : Transmission Control Protocol, connection-oriented, reliable transmission, byte stream-oriented;
——Applied to scenarios that require more security than real-time performance (file transfer, etc.);
UDP : User Datagram Protocol, connectionless, unreliable, datagram-oriented;
——Applied to scenarios that require real-time performance more than security (video, audio, etc.);
UDP operation process:
Server:
① Create a socket:
Create a socket structure in the kernel to associate the process with the network card;
② Bind address information for the socket:
Describe the source address information for the created socket structure;
③ Receive data:
Take out data from the socket receiving buffer;
④ Send data to the server:
Put the data to be sent into the send buffer;
⑤ Close the socket;
client:
① Create a socket;
② Bind address information for the socket:
The client does not recommend actively binding addresses . After binding, the program can only start one and the client does not need to use a fixed address;
③Send data to the server:
If the socket is not bound to the specified address before sending data, the system will automatically select the appropriate address information for binding;
④ Receive data;
⑤ Close the socket;
TCP operation process
Listening socket (only for handling new connection requests) & communication socket (only for communication);
Need to connect first and then communicate, so there is no broadcast operation;
Server
① Create a socket:
Create a socket structure in the kernel to associate the process with the network card;
② Bind address information for the socket:
Describe the source address information for the created socket structure;
③Start monitoring:
Tell the server that the current socket can handle the connection request (the listening socket is converted to the listen state);
If a client sends a connection request, the service will create a new socket for it to communicate with the specified client (the socket is a communication socket, and the state is established—ready state);
④ Obtain a new connection:
Take out a new socket descriptor from the completed connection queue, which corresponds to the communication between the specified socket and the specified client;
⑤ send and receive data;
⑥Close the socket;
client
① Create a socket;
②Bind address information for the socket (not recommended);
③Initiate a connection to the server:
After the connection, the client tcp will also save the complete quintuple;
④ send and receive data;
⑤ Close the socket;
Interface introduction
#include<sys/socket.h>
#include<netinet/in.h>
create socket
int socket(int domain, int type, int protocol);
//domain:地址域类型——AF_INET & AF_INET6;
//type:套接字类型——SOCK_STREAM & SOCK_DGRAM;
//protocol:协议类型——IPPROTO_TCP & IPPROTO_UDP (可以默认给0);
//返回值:成功返回一个套接字描述符，失败返沪-1;
Bind address information
int bind(int sockfd, const struct sockaddr* addr, socklen_t addrlen);
//sockfd:创建套接字返回的描述符;
//addr:要绑定的地址信息(这是一个通用描述，根据前两个字节的内容使用统一的接口绑定不同的地址结构,还有端口信息、IP地址,IPV4为struct sockaddr_in, IPV6为struct sockaddr_in6);
//addrlen:地址信息长度,防止访问越界;
eg:
struct sockaddr_in addr;
addr.sin_family = AF_INET;//前两个字节代表IPV4地址结构，IPV6为AF_INET6
addr.sin_port = htons(9000);//端口信息,需要转化为网络字节序
addr.sin_addr.s_addr = inet_addr("192.168.2.2");//本机有的IP地址,inet_addr可将点分十进制转化为长整型数字
bind(sockfd, (struct sockaddr*)&addr, sizeof(struct sockaddr_in));
close socket
int close(int sockfd);
//实际情况下在TCP通信中，监听套接字基本不关闭，一般只关闭通信套接字
UDP send data
ssize_t sendto(int sockfd,char* data,int data_len,int flag,struct socket* dest_addr,socket_t addr_len);
//sockfd:套接字描述符
//data:要发送的数据首地址
//data_len:要发送的数据长度
//flag:选项标志，默认为0----表示当前操作是阻塞操作
//dest_addr:对端地址信息
//addr_len:地址信息结构长度
//返回值:成功返回实际发送数据长度，失败返回-1
UDP receiving data
ssize_t recvfrom(int sockfd,void* buf,size_t len,int flag,struct socket* src_addr,socket_t *addrlen);
//sockfd:套接字描述符
//buf:一块空间首地址，用于存放从内核获取到的数据
//len:要获取的数据长度
//flag:选项标志，默认为0----表示当前操作是阻塞操作
//src_addr:源端地址信息
//*addrlen:这是输入输出型参数,指定想要多长地址，返回实际长度地址
The TCP client initiates a connection to the server
int connect(int socket, struct sockaddr* srvaddr, socklen_t addrlen);
//srvaddr:服务器地址信息
//返回值:成功返回0，失败返回-1；
The TCP server listens to the connection sent by the client (parameters will be asked)
int listen(int socket, int backlog);
//backlog:同一时间最大并发连接数，当socket连接队列被放满之后，如果有新的连接请求到来则丢弃，以此限制同一时间所处理的新建连接请求数量;
//该操作将服务器端状态置为listen;
TCP get new connection
Take out a socket t that has been connected from the socket queue of the kernel that has completed the connection , and return the descriptor;
int accept(int listen_socket, struct sockaddr* addr, socklen_t *addrlen);
//listen_socket:监听套接字,决定了获取的是哪个套接字的新建连接;
//addr:一个地址结构的空间首地址,用于接收新连接的客户端地址信息;
//*addr:用于指定想要获取的地址长度以及返回的实际长度;
//返回值:成功返回新建连接的描述符,失败返回-1;
TCP sends data
ssize_t send(int sockfd, char *buf, int len, int flag);
//sockfd:新建套接字描述符;
//data:要发送的数据的空间首地址;
//len:要发送的数据长度;
//flag:0,默认阻塞接收;
//返回值:成功返回实际发送的数据长度,出错返回-1,
TCP receives data
The TCP communication socket saves the complete five-tuple ;
ssize_t recv(int sockfd, char *buf, int len, int flag);
//sockfd:新建套接字描述符;
//buf:空间首地址用于存放接收的数据;
//len:要获取的数据长度;
//flag:0,默认阻塞接收;
//返回值:成功返回实际获取到的数据长度,出错返回-1,连接断开返回0;