FTP

A client-server Implementation of the File Transfer Protocol closely following RFC-959 and Beej's Guide.

Demo

The developer was too lazy to make a screencast. You may want checkout the logs.

Features

• Closely follows the official spec for FTP : RFC-959
• Provides basic authentication with multiuser support.
• Supports multiple client connections.
• Handles control connection (PI) and data connection (DTP) separately.
• Supports switching of data connection port with PORT command.
• Works over localhost, local network and over the internet.

Click here to know about all the supported commands.

Supported commands

All command mentioned below are case insensitive unless otherwise specified.

Command	Usage	Action
HELP	help	Show all the available commands
!<cmd>	!pwd !cd .. !mkdir clientDir	Execute a command on the client itself. Because they are directly executed on client system, these are case sensitive.
NOOP	noop	Execute No operation. Serves as a dummy command.
USER	USER <username> user root	Provide username for login
PASS	PASS <password> pass root	Provide password for login
SYS	sys	Get System Details Of server
PWD	pwd	Print working directory
LIST	LIST ls ls serverDir	List directory contents
CWD	cwd .. cd .. cd serverDir	Change working directory
CDUP	cdup	Change to parent directory
MKD	mkd dirName mkdir dirName	Make directory
RMD	rmd dirName rmdir dirName	Remove directory
STOR	STOR putFileOnServer.txt put putFileOnServer.txt	Send File to Server
RETR	RETR getFileFromServer.txt get getFileFromServer.txt	Retrive File from Server
PORT	PORT <IP> <Port> PORT CURRENT_MACHINE_IP 5643 PORT localhost 9584 PORT 200.212.111.32 8868	Switch data connection IP, Port
QUIT	quit exit	Quit the application
ABORT	abort abor	Abort the last command and related data transfer
PASV	pasv	Switch to Passive Receive Mode
TYPE	TYPE A E	Switch the representation type. Default is ASCII Non Print.
MODE	MODE S	Switch the transfer mode. Default is Stream.
STRU	STRU F	Switch the File structure Type. Default is File.

How to make

• git clone and cd in the folder
• make sure you have make installed, then run make -s
• it will create a bin folder with two executables client and server

How to Run

• go to where executables live cd ./bin
• server needs to be started first. Usage is as follows.
  • ./server This uses port=9000 as default.
  • ./server <portNumber> in case you want to supply custom port number.
• client can be started as follows.
  • ./client This uses host=localhost and port=9000 as defaults.
  • ./client <serverIP> <serverPort> in case server is on different machine.

Testing

The code has been tested in all three cases mentioned above. The maximum file size tested is 190 MB over the internet and 2.5 GB over localhost. In theory, it should work for even bigger file sizes. File integrity is intact, no corruption occurs during the transfer.

Click here to know more about the testing details.

Localhost

• Both client and server are on same machine.
• Use 127.0.0.1 or localhost as Server IP

LAN

• Both system are on Local Network
• use localIPs like 192.168.0.9. You must know server's local IP for this.

Internet

• Both systems want to transfer files over the internet.
• Internet Testing has been done with VM instances for below 2 scenarios.
  • Scenario 1 : Server and client are both on different VMs. Both have static IP.
  • scenario 2 : Server is on VM with static IP. Client is my machine (behind a router).
  • VM-1 on Google cloud ssh jatin@ftp-tester-1 : acts as server
  • VM-2 on Google cloud ssh jatin@ftp-tester-2 : acts as client
• Ensure that server has static IP. The easiest way to know if a machine has a static internet IP is :
  • Run the server program on the machine you wish to test for static IP
  • From any other machine telnet <machineInternetIP> <portOnWhichServerIsRUnning=9000>
  • To obtain a machine's internet IP, use curl ifconfig.me
  • It should ideally establish connection, because FTP is based on the telnet protocol. If however, it says No route to Host, then it means the machine is behind a router and NAT is your enemy.
• Things to keep in mind while creating your VMs for testing -
  • First, create some VM instances on google cloud. Make sure you have free credits.
  • Server needs to have a static IP. In your project, go to VPC network > External IP addresses and reserve static IP address for your machines.
  • On google cloud, all ports are blocked by default. But our ftp-server should be allowed to use ports freely. So we have to add two Firewall rules to allow ingress and egress traffic on all ports on all protocols accessible by all IPs i.e. 0.0.0.0/0
  • Setup ssh login. Then login using ssh <username>@<external-IP>
  • If you don't want to remember external IP's you can also add custom hostnames and resolve them in your /etc/hosts file
  • Then clone the project, make it, and run
  • To connect to server, client needs to know server's static internet ip. That's a pre-requisite.

General Questions

How to analyse what's happening behind the scenes ?

How to analyse

• Monitoring system calls with strace
  • strace will allow you to monitor relevant system calls as they happen.
  • go to where executable live cd ./bin
  • strace -fe trace=process,network,signal ./bin/server 9000
  • strace -fe trace=process,network,signal ./bin/client 127.0.0.1 9000
• Monitoring processes, their children, pid, ppid, pgid with ps
  • Use ps fj to see the tree format of all the forks, along with their pid's and ppid's.
• Generating logs with tee. This is very unpredictable for interactive programs.
  • make | tee logs/makelog.txt
  • ./bin/server | tee logs/serverlog.txt
  • ./bin/client | tee logs/clientlog.txt
• Hiding all the server logs with output redirection
  • To hide all output from server, send it to the null device
  • ./server &>/dev/null

How is the code in the project formatted ?

How to Format code

• a chromium based, opinionated .clang-format file is present in project root.
• This has been used for all the formatting in this project.
• Set your IDE format settings to file.
• For VS Code, add these in your setting.json

  "C_Cpp.clang_format_path": "/usr/bin/clang-format-3.8",
  "C_Cpp.clang_format_style": "file",
  "C_Cpp.clang_format_fallbackStyle": "Chromium",

• Build your own formatter file here
• Know more about unified formatting across IDE's here

How much work was involved in the project? What's the future scope?

• The project was divided into a lot of small tasks.
• The tasks belonged either of the three categories -
  • Must have features,
  • Good to have features, and
  • Future scope.
• You can find all these details in the extended todo list