Web server implementation of File transfer programming

As a general rule, the process of designing a Web server is divided into simple steps, each step being implemented as a module.

1. Overall design

The server program sends the file to the client or receives the file from the client, each communication can only do one file transfer, after the transfer is ready to process the next communication. The client program can exit after receiving or sending a file. Therefore, the server short program is a dead loop, after processing once do not exit, continue to listen. The client program handles a connection.

2. Client program Design

The client program has 3 main tasks,

(1) Analysis of commands entered by the user

(2) Make a request to the server based on the command

(3) The result of waiting for the server to return the request

The first task is to parse the command, this FTP program client provides the user with 8 kinds of commands, as shown in the following table:

Commands entered by the user	Command meaning
Get	Getting files from the server
Put	Transferring files to the server
Cd	Directory to enter the client
!cd	Enter the server-side directory
Ls	List the contents of the client's current directory
!ls	List the contents of the current directory on the server side
Connect	Connecting to a server
Bye	Exit program

The client obtains a string from the standard input, parses the string to get commands and arguments, and therefore requires a fixed string input. After the input format is fixed, the client will split the string to determine the function to complete. Each command entered by the user will send a request code to the server through the client, which can be processed by identifying the request code to determine the client's request. The following is a table of commands and corresponding requests entered by the user:

Commands entered by the user	The corresponding request
Get	GET
Put	PUT
Cd	No need to communicate with server, no request
!cd	Cd
Ls	No need to communicate with server, no request
!ls	Ls
Connect	The connection request is made and no additional processing is required on the server side, so no request code
Bye	BYE

3. Server-side programming

The server program is similar to a client program and has 3 tasks.

(1) Analysis Request code

(2) According to the request code to make corresponding processing

(3) Wait for the return result or answer message

According to the design of the top client we know that there are only 5 request codes to be processed on the server side, as shown in the following table:

request code	corresponding processing
get	transfer files to client
put	Accept client Files
cd	Enter directory
ls
bye	disconnect

After dividing the task, there are two main links need to be clear, is the communication protocol and server model, the communication protocol of this program is divided into two kinds. One is a get command, a put command and a command that!LS commands need to transfer the contents of a file, a communication protocol with a "four-time handshake", and a "two-time handshake" for a command that does not need to transfer the contents of a file.

The server side uses the model of the concurrent server, and if the client is blocked, the server can still handle the other connections.

Web server implementation of File transfer programming