Client server communication project 1

1、 functional requirement ：

1、 Realize the basic communication between client and server
2、 The client can read the file list of the server , And print on the client
3、 After the client enters the corresponding file name , The server can transfer the corresponding file to the client
4、 The server is transferring files , The client can open 、 Pause and terminate file transfers
5、 The client can obtain the configuration parameters of the server , Include the server name and the maximum number of client connections supported
6、 The client can modify the configuration parameters of the server , And save , Still effective after restart
7、 Implement multithreading processing mechanism , Parallel processing of multi client access
notes ： Use static link libraries and Makefile Script Compilation project

2、socket Communication process

Socket That is what we call socket , It is one or a way of communication between computers . Through this Agreement , A computer can receive data from other computers , You can also send data to other computers .
The server is initialized first socket() function , And then bind to the port bind() function , Listen to the port listen() function , call accept() function , Wait for the client to connect . At this time, if a client initializes a socket() function , And then connect to the server connect() function , If the connection is successful , At this time, the connection between the client and the server is established . The client sends the request , The server receives the request and processes it , Then send the response data to the client , Client reads data , Finally, close the connection , An interaction ends .

3、socket Related functions

3.1、socket() function

int socket(int domain, int type, int protocol);
socket() Function to create a socket The descriptor , Take it as a parameter , You can perform some read and write operations , The parameters are defined as follows ：
1、domain: Protocol family （AF_INET(IPv4)、AF_INET6(IPv6)）
2、type:sockset type ,SOCK_STREAM(TCP)、SOCK_DGRAM(UDP)
3、protocol: Designated agreement , Specified as 0

3.2、bind() function

int bind(int sockfd, const struct sockaddr* addr, socklen_t addrlen);
bind() The function assigns a specific address in an address family to socket, The parameters are as follows ：
1、sockfd：socket The descriptor , adopt socket() establish 
2、addr： Point to bind to sockfd Agreement address for 
3、addrlen： The size of the corresponding address structure 

3.3、listen() function

int listen(int sockfd, int backlog);
socket() Function created socket The default is an active type ,listen() Function will socket Become passive , Waiting for the client to connect , The parameters are as follows ：
1、sockfd：socket The descriptor , adopt socket() establish 
2、backlog：socket The maximum number of connections that can be monitored at the same time 

3.4、connect() function

int connect(int sockfd, const struct sockaddr* addr, socklen_t addrlen);
 The client calls connect() Function to establish TCP Server connection , The parameters are as follows ：
1、sockfd：socket The descriptor , adopt socket() establish 
2、addr： Server's socket Pointer address structure 
3、addrlen： Corresponding socket Length of address structure 

3.5、accept() function

int accept(int sockfd, const struct sockaddr* addr, socklen_t addrlen);
 The server calls... In turn socket()、bind()、listen() after , Will monitor the designated socket Address 
 The client calls... In turn socket()、connect() after , Sent a connection request to the server 
 After the server receives the request , Will call accept() Receiving request , And establish a connection , Return connected socket Description words 
1、sockfd：socket The descriptor , adopt socket() establish 
2、addr： Client's socket Pointer address structure 
3、addrlen： Corresponding socket Length of address structure 

notes ： A server usually creates only one socket Description words , It exists throughout the life of the server . The kernel creates a connected connection for each client connection received by the server process socket Description words , When the server completes the service to a client , Corresponding connected socket Description word is closed .
3.6、write()/read() function

ssize_t write(int fd, const void *buf, size_t count);
ssize_t read(int fd, const void *buf, size_t count);
 explain ：
write Function will buf Data write in socket Data flow . Returns the number of bytes written on success , Return... On failure -1, And at the same time set error Variable 
read The function can be derived from fd Read content in , Returns the number of bytes actually read when successful , return 0 Read to the end of the file , Less than 0 Indicates that there is a mistake 
 These two functions do not actually transmit data directly to the network , Instead, write the data to the cache first , Read again 
1、fd：socket The descriptor , adopt socket() establish 
2、buf： Address of the data buffer to be written or read 
3、count： Number of data bytes written or read 

3.7、close() function

int close(int fd);
 After the read / write operation is completed, you need to close the socket, At this time, it can no longer be used as a read-write descriptor