TCP client-server programming model

1. The client calls sequence

Client programming sequence is as follows:

1. Call the socket function to create a socket
2. Call connect server connections
3. Call the I / O functions (read / write) and server-side communications
4. Calling close socket is closed

2. The server-side call sequence

Server programming sequence is as follows:

1. Call the socket function to create a socket
2. Call bind bind local address and port
3. Start calling listen listening
4. A call to accept client connections extracted from the connected queue
5. Call the I / O functions (read / write) to communicate with clients
6. Call the close function closes the socket

3. Common Functions

3.1. Socket and address binding function

(1) bind address

#include <sys/socket.h>

int bind(int sockfd, const struct sockaddr *addr, socklen_t len);

Returns: the successful return 0, -1 error

Special bind address Introduction

A host can have multiple network interfaces and multiple IP addresses, if we only care about the connection request for an address, we can specify a specific local IP address, if you want to respond to connection requests on all interfaces necessary to use a special address INADDR_ANY

#define INADDR_ANY (uint32_t)0x00000000

Listen for connection requests on the server for all IP obtained

struct sockaddr_in servaddr;

memset(&servaddr, 0, sizeof(servaddr));

servaddr.sin_addr.s_addr = INADDR_ANY;

3.2. Find an address bound to the socket

#include <sys/socket.h>

int getsockname(int sockfd, struct sockaddr *restrict_addr, socklen_t *restrict_alenp);

Returns: the successful return 0, -1 error

3.3. Getting the other address

int getpeername(int sockfd, struct sockaddr *restrict_addr, socklen_t *restrict_alenp);

Returns: the successful return 0, -1 error

3.4. To establish a connection on the server side

#include <sys/socket.h>

int listen(int sockfd, int backlog);

返回：成功返回0，出错返回-1。

backlog指定进行客户端连接排队的队列长度。

int accept(int sockfd, struct sockaddr *restrict_addr, socklen_t *restrict_len);

返回：成功返回一个新的sockfd（客户端的）。

3.5.客户端请求连接

#include <sys/socket.h>

int connect(int sockfd, const struct sockaddr *addr, socklen_t len);

返回：成功返回0，出错返回-1

3.6.IO操作函数

read和write函数默认都是阻塞性的读写函数。此时需要考虑服务器的并发处理。

4.服务器端并发性处理

4.1.多进程模型

弊端：进程占用系统资源，当子进程过多将占用过多的系统资源，难以处理大并发的场景。

4.2.多线程模型

以分离状态去启动子线程，子线程运行完后自动释放空间。