C # compile FTP client software

1 Introduction

I know. There are many ready-made FTP software on the Internet. However. We also want to know some underlying FTP institutions. This open-source project may be helpful to you when you learn FTP knowledge.ProgramThe interface looks like filezilla. Although filezilla is popular, it has some bugs. When I open my blog, there is always a problem. I need to connect to my server through FTP. Send and download files. Because. I decided to write my own software to handle all the situations. Filezilla is good enough. But it is not mine.

 

2 Background

 

Let's see what we already know. We know that FTP is a standard TCP-based network protocol. Transfers files from one host to another. It is a C/S architecture.

 

Figure 2

 

FTP programs were once Based on command lines. We can still connect to the FTP server through cmd.exe. Because FTP can indeed be operated through commands. For example. We can use the "stor" command on the command line to send files. To complete these requests. The FTP server must always run and wait for client requests to come. We can better understand FTP from Wikipedia:

 

The client computer can communicate with the server through port 21 of the server. It is called a control connection. It remains open during a session. The first connection. A data connection is called a data connection. The server can open port 20 (active mode) to the client, establish a data path, and connect to the client to transmit data. Or the client opens a random port (passive mode) to connect to the server to transmit data. The control connection uses a telnet-like Protocol and is used for client and server session management (commands, identifiers, and passwords ).. For example. "RetrFilename"The file will be downloaded from the server.

Figure 3

Two types of connections are required for a complete FTP file transfer. One is a file transfer command called a control connection, and the other is a real file transfer called a data connection.

The server sends a response to the control connection through a three-digit ASCII status code that may contain optional descriptions. For example. "200" or "200 OK" indicates that the previous command was successful. Numbers represent numbers. The description provides instructions (such as "OK"), or some required parameters (such as the need for an account to store files). What should we do. Obviously. Send commands, receive "OK" responses, and send data. Receive data. Finished. But first, the server is ready. The FTP server can run in active and passive modes. The active mode is server-based connection, while the passive mode is the connection of the client. Continue.

In active connection, the client sends its own IP address and port to the server. Then the server tries to connect to the client, but may be rejected for firewall reasons. We use anti-virus/built-in firewall on Windows. Right. Let's look at the passive mode.

In a passive connection. The server sends its IP address and port to the client through a "PASV" command. Then the client tries to connect to the server through this IP address. It is very useful for sending files. When we send a file. The "PASV" mode is preferred, as you said. Most protocols. For example, FTP/HTTP uses ASCII encoding because it is globally available. So we will use this encoding. You can get the FTP command list from below

Both active and passive are for the server.

3. Use Code

Now we are ready for writing software. Let's write some useful code. :) First. The "Open File Dialog Box" is integrated into our form.

3.1 Resource Manager Components

We need a Resource Manager component to view all our files on the software interface. In this way, we can select the files to be sent to the FTP server and create a Windows form control library (provided in the download package)

Figure 4

It looks like the above. First add a Treeview, some buttons, and a search function

 
Treeview. nodes. Clear (); treenode noded=NewTreenode (); noded. Tag=Environment. getfolderpath (environment. specialfolder. desktop); noded. Text="Desktop"; Noded. imageindex=10; Noded. selectedimageindex=10; Treeview. nodes. Add (noded );
 

As shown in the code above. We need to add a master node. My documents. My computer and so on. Then obtain the subdirectory.

 String  [] Dirlist; dirlist = Directory. getdirectories (parentnode. Tag. tostring (); array. Sort (dirlist );  If (Dirlist. Length = Parentnode. nodes. Count)  Return  ;  For ( Int I = 0 ; I <dirlist. length; I ++ ) {Node = New  Treenode (); node. Tag = Dirlist [I]; node. Text = Dirlist [I]. substring (dirlist [I]. lastindexof ( @"  \  " ) + 1  ); Node. imageindex = 1  ; Parentnode. nodes. Add (node );} 

 

You can see the complete code from the downloaded package. We should also handle the mouse click event.

Now we have a resource manager. And all the information required by FTP and.

First, we connect to the server. What should we do?

Ftpsocket = New  Socket (addressfamily. InterNetwork, sockettype. Stream, protocoltype. TCP); appendtext (rchlog,  " Status: Resolving IP address \ n  "  , Color. Red); remoteaddress = DNS. gethostentry (server). Addresslist [ 0  ]; Appendtext (rchlog,  "  Status: IP address found->  " + Remoteaddress. tostring () + "  \ N  "  , Color. Red); addrendpoint = New Ipendpoint (remoteaddress, Port); appendtext (rchlog,  "  Status: endpoint found->  " + Addrendpoint. tostring () + "  \ N  "  , Color. Red); ftpsocket. Connect (addrendpoint ); 

 

 
Yes. We need a socket to connect to the server and then send the command
 

Appendtext (rchlog,"Command:"+ MSG +"\ N", Color. Blue); byte [] commandbytes= Encoding. ASCII. getbytes (MSG +"\ R \ n"). Tochararray (); ftpsocket. Send (commandbytes, commandbytes. length,0);//Read responseReadresponse ();
 

We send commands to the server. The server responds in its own language. We need to understand him. The response includes three digits and some explanations.

 

 Private   String Splitresponse (){  Try  {  While ( True  ) {Bytes = Ftpsocket. Receive (buffer, buffer. length, 0 ); //  Number of bytes (count) Statusmessage + = encoding. ASCII. getstring (buffer, 0 , Bytes ); //  Convert to string              If (Bytes <buffer. length) //  End of response                  Break  ;}  String [] MSG = statusmessage. Split ( '  \ N  '  );  If (Statusmessage. length> 2  ) Statusmessage = MSG [MSG. Length- 2 ]; // Remove last \ n          Else  Statusmessage = MSG [ 0  ];  If (! Statusmessage. substring ( 3 , 1 ). Equals ( "   "  ))  Return  Splitresponse ();  For ( Int I = 0 ; I <MSG. Length- 1 ; I ++ ) Appendtext (rchlog,  "  Response:  " + MSG [I] + "  \ N  "  , Color. Green );  Return  Statusmessage ;}  Catch  (Exception ex) {appendtext (rchlog, "  Status: error.  " + Ex. Message + "  \ N  "  , Color. Red); ftpsocket. Close ();  Return   ""  ;}} 

 

Finished. Now we can download, upload, and rename. Or deleted.

4. FTP command list

Command	Description
Abor	Interrupts the transmission of an active file.
Acct	System Account Information
Adat	Authentication/security data
Allo	Allocate space to receive files
Appe	Add files to the server
Auth	Authentication/Security Mechanism
CCC	Clear command channel
Cdup	Go to parent directory
Conf	Confidentiality Protection Command
CWD	Change the working directory on the server
Dele	Deletes a specified file on the server.
ENC	Confidential protection channel
Eprt	Specify the extended address and port that a server should connect
Epsv	Enter the extended Passive Mode
Feat	Obtain the function list provided by the server.
Help	Returns the specified command information.
Lang	Returned Language Information
List	If the file name is used to list file information, if the file name is a directory, the file list is listed.
Lprt	Specify the long address and port that a server should connect
Lpsv	Enter long Passive Mode
MDTM	Returns the last file modification time.
Mic	Complete protection commands
MKD	Create directory
MLSD	Lists the contents of a specified directory.
Mlst	List precise object information on the command line
Mode	Transmission Mode (S = stream mode, B = block mode, c = compression mode)
NLST	List contents of a specified directory
Noop	No action, (Virtual package, from frequent connection)
Opts	Select a feature Option
Pass	Verify Password
PASV	Enter passive mode
Pbsz	Protection buffer size
Port	Specify the address and port that the server should connect
Prot	Data Channel Protection Level
PWD	Display current working directory
Quit	Log out from the FTP server
Rein	Reinitialize the logon status connection
Rest	Restart the file at a specified point for transfer
RETR	Transfer file copies
RMD	Delete a specified directory on the server
RNFR	Rename from old name
RNTO	To new name
Site	Send the specified command to the remote server
Size	Returned File Size
SMNT	Mount the specified file structure
Stat	Returns the current status.
Stor	Store (copy) the file to the server
STOU	Store files to specified files on the server
Stru	Set the structure (F = file, r = record, P = page)
Syst	Back to the operating system used by the server
Type	Transmission Mode (A = ASCII, E = ebcdic, I = binary)
User	Verify user
Xcup	Jump to the parent directory of the current working path
Xmkd	Create directory
Xpwd	Output current working directory
Xrmd	Delete directory

 

5. Return code list

• 2XX-success returned
• 4xx or 5xx-return failure
• 1xx or 3xx-incorrect or incomplete reply

The second field defines the error type.

• X0z-syntax error.
• X1z-information-Request Information
• X2z-connection-indicates a problem with the control or data connection
• X3z-account authentication-Logon or account authentication problems.
• X4z-undefined
• X5z-file system-it may be a problem with the Server File System.

 

Download demo

C # compile an FTP Client

6. License

This article includesSource codeAnd file authorization under cpol.

 

Original article address: file-transfer-Protocol-ftp-Client

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