LFTP

Source Code

Github

Group Member

Name(姓名)	Student Number(学号)	Major(专业)
Weiyuan Xu(徐伟元)	16340261	Software Engineering-Computer Application(软件工程-计算机应用)
Yongqi Xiong(熊永琦)	16340258	Software Engineering-Computer Application(软件工程-计算机应用)

LFTP, a network application, supports large file transfer between two computers in the Internet.

Dependency

Operating System: linux /macOS /windows

Environment: >= python 3.6

Usage

For macOS user, type the command in your terminal first to enable transferring the max size of the UDP packet:

sudo sysctl -w net.inet.udp.maxdgram=65535

Before you use this program, on the server-side, you should make a folder named data under code/ first to store the files to exchange with clients:

cd code
mkdir data

Then, you could run command below to run the program on the server:

# use python 3.x
python ./server.py [hostname port]
# default hostname: localhost
# default port: 8080

After that, you could run the command below to connect and exchange files with the server:

# use python 3.x
python ./client.py lget/lsend hostname[:port] filename
# default port: 8080

Hope you enjoy your time with it.

The technical requirements

• Programing language: Python;

• LFTP should use a client-server service model;

• LFTP must include a client side program and a server side program; Client side program can not only send a large file to the server but also download a file from the server.

  Sending file should use the following format: LFTP lsend myserver mylargefile Getting file should use the following format: LFTP lget myserver mylargefile The parameter myserver can be a url address or an IP address.

• LFTP should use UDP as the transport layer protocol.

• LFTP must realize 100% reliability as TCP;

• LFTP must implement flow control function similar as TCP;

• LFTP must implement congestion control function similar as TCP;

• LFTP server side must be able to support multiple clients at the same time;

• LFTP should provide meaningful debug information when programs are executed.

The Design Doc

Detail Design Doc are here

Simple introduction of design are shown below:

• Transport Layer: RDP Protocol

  • Packet Structure

    UDP packet data field
    Sequence Number
    Acknowledgement Number
    Flag Field (ACK, SYN, RST, FIN, WRW)
    rwnd
    Data

  • Fundament According to the Application layer requests, send data and receive data function are fundamental and application needn't know the implementation. Thus, we first design two functions: rdp_send(data) to send data and rdp_recv(size) to get data. Furthermore, these two function should act like TCP, which means application just invokes functions and knows where it get/send data. So we need to make connection between server and client before invoking these functions with handshake behavior. makeConnection(targetAddress) is needed.

  • Multiple Client Since server must support multiple client, the server application(host) must handle the clients at the same time. So multiple thread is needed. We provide each connected client a server program running in different port. So we design listen(num) function to listen the connection requests from clients and maximum number of client for server to serve is num. The listen function provides the listening and helps make connection between server and client. Hence, sockets are created when connection successfully made in listen, we must export the serving socket for server application. accept() retrieve a serving socket and server application must run the socket in a thread and handle it.

  • Summary rdp_send(data),rdp_recv(size),makeConnection(targetAddress),listen(num) and accept() are the most important function designed in RDP. Following, we will introduce the implementation and the detail design of them.

The Testing Doc

Detail Test Doc