Advanced Computer Communication (CNCO3002)
CURTIN UNIVERSITY
School of Electrical Engineering, Computing and Mathematical Sciences
Discipline of Computing
Assignment 1: Anonymous Storage Server.
Due Date: 4.00 p.m. Monday, 14 September 2020
The objective of this network programming assignment is to develop two complementary programs, a client and a server, that implement an anonymous storage server.
The server stores user files anonymously. A user, via client, sends a file to the server. The server stores the file in a folder, and returns a hash key to the client. The user can retrieve the stored file using the key. The key is sufficiently long and complex to guarantee that nobody, except the user, can guess the key of each file.
A key is generated as follows. When the server receives a file, it creates a new name, i.e., file_n for the file, generates a hash key for the file_n, stores the file in a folder storage, and returns the key to the client. Note, the server can use a global counter to create a unique file name, i.e., the value of n is positive integer {1, 2, 3, … }. The key is an MD5 hash, which is a 128-bits value usually printed as 32 hexadecimal numbers created by Unix function md5sum. You may use popen() function to call md5sum in your program, and pclose() function to close the created stream.
The client and server recognize the following five user commands. Each command is not case sensitive.
1) STORE local_file: A user asks the server to store a file local_file that is located at client.
The client sends command STORE and the content of file local_file to the server, waits for reply from the server, i.e., the file’s key, shows the reply on the screen, and waits for another user command. Note that the name of the file, i.e., local_file, is not sent to the server.
Receiving this request, the server creates a unique file name, e.g., file_100, generates the hash key for file_100, writes the content of local_file in file_100, which is stored in a directory storage, records this transaction in the file’s history, sends a message “STORE: File has been stored with hash key”, and waits for another client request.
2) GET key file_name: A user wants to retrieve from the server a file whose hash is key, and writes its content in file_name located at client.
The client sends this request to the server, waits for the file sent by the server, stores its content in a file file_name in client’s directory, and waits for another user command. Note that file_name is not sent to the server.
Receiving this request, the server sends the file whose hash is key to the client, records this transaction in the file’s history, and waits for another client request.
If the received key does not correspond to hash of any file on the server, the server sends a message “GET: Error! Hash key is not valid” and waits for another client request.
A client is given k chances to send a valid key. The kth time a client provides an invalid key, the client is disconnected and no new connection will be accepted from the same IP address within t1 seconds. Let t1 = 1 and k = 1 be command line arguments when you run server.
3) DELETE key: A user wants to delete a file whose hash is key from the server.
The client sends this request to the server, waits for a reply, shows the reply on the screen, and waits for another user command.
Receiving this request, the server deletes a file from folder storage whose hash is key, records this transaction to the file’s history, and replies with “DELETE: File with hash key has been deleted”, and waits for another client request.
If the received key does not correspond to the hash of any file on the server, the server sends a message “DELETE: Error! Hash key is not valid” and waits for another client request.
A client is given k chances to send a valid key. The kth time a client provides an invalid key, the client is disconnected and no new connection will be accepted from the same IP address within t1 seconds. Let t1 = 1 and k = 1 be command line arguments when you run server.
4) HISTORY key: A user wants to read the recorded history of the file whose hash is key.
The client sends the request to the server, waits for a reply, shows the reply on the screen, and waits for another user command.
Receiving this request, the server sends to the client the history records for key, and waits for another client request.
If there is no entry for key, the server sends a message “HISTORY: Error! There is no history for hash key” and wait for another client request.
A client is given k chances to send a valid key. The kth time a client provides an invalid key, the client is disconnected and no new connection will be accepted from the same IP address within t1 seconds. Let t1 = 1 and k = 1 be command line arguments when you run server.
5) QUIT: A user wants to disconnect from the server.
The client sends the request to the server, waits for an acknowledgement, and closes the connection.
Receiving this request, the server sends a message “Thank you for using our anonymous storage”, and closes the connection.
A. Requirements
1. A client should be started with:
./client IP_address port
or
./client host_name port
Note, IP_address is the server’s IP address (in dotted decimal notation), host_name is the name of the server’s host computer, and port is the port number of the server. For the port number, use the first of the ten ephemeral port numbers assigned to you.
Once a client is connected to the server, the client waits for user command, and a prompt ID is shown on the screen, where ID is your student ID.
2. A server creates a new process for each connecting client.
3. A server disconnects a client if it does not receive any request from the client within t2 seconds. Let t2 = 1 be a command line argument when you run the server. Thus, the server is run as:
./server k t1 t2
4. A server maintains a history of each file it stores. This history is kept in memory and is updated for every operation on the file. The history of a file contains the following information: the file’s key, time of each operation, type of each operation, i.e., store, get, delete, history, and the IP address of the client that requests for each operation.
Note: the history of each file is shared among all child servers, and thus a shared memory should be created, and a proper synchronization/mutual exclusion handling is required.
5. A client must check the syntax and validity of each user command. Similarly, each child server must check the validity and syntax of its client’s request.
B. Implementation
1. Your program must be written in C, and must run on our department’s laboratory computers.
2. You are allowed to use any existing functions/codes. However, you are responsible for the correctness of the functions, and you have to mention/cite the sources.
3. Make sure to check for error return from each system call, and to close every socket created.
4. Your main program for the server should be in server.c, and that for your client program should be in client.c. You must provide files makeserver and makeclient for the server and client, respectively.
5. While developing your program, make sure that you kill all your (possibly run-away) processes using ‘kill –9’, and release any unused resources, e.g., shared memory.
6. You MAY make your own justifiable assumptions/requirements other than those already given. However, YOU HAVE TO DOCUMENT ANY ADDITIONAL ASSUMPTIONS/LIMITATIONS FOR YOUR IMPLEMENTATIONS.
C. Instruction for submission and demo
1. Assignment submission is compulsory. Students will be penalized by a deduction of ten percent per calendar day for a late submission. An assessment more than seven calendar days overdue will not be marked and will receive a mark of 0.
Due dates and other arrangements may only be altered with the consent of the majority of the students enrolled in the unit and with the consent of the lecturer.
2. You must (i) put your program files, i.e., client.c, server.c, makeclient, makeserver, and other required files, in your home directory named ACC/assignment1, (ii) submit the soft copy of assignment report to the unit Blackboard (in one zip file), i.e., ID_Assignment1.zip, where ID is your student ID.
3. The soft copy of your report, as stated in 2(ii), MUST include:
• A signed cover page that explicitly states the submitted assignment is your own work. The cover includes the words “Advanced Computer Communication Assignment 1”, and your name in the form: family, other names. Your name should be as recorded in the student database.
• Software solution of your assignment that MUST include (i) all source code for the programs with proper in-line and header documentation. Use proper indentation so that your code can be easily read. Make sure that you use meaningful variable names, and delete all unnecessary comments that you created while debugging your program;
and (ii) readme file that, among others, explains how to compile your program and how to run the program.
• Detailed discussion on how any mutual exclusion is achieved on shared resources,
e.g., memory, and what processes access the shared resources.
• Description of any cases for which your program is not working correctly or how you test your program that make you believe it works perfectly.
• Sample inputs and outputs from running your programs.
Your report will be assessed (worth 20% of the overall mark for Assignment 1).
4. Demo requirements:
• You will be required to demonstrate and explained your programs.
• You MUST keep the source code for your programs in your home directory, and the source code MUST be that submitted.
• The programs MUST run on our Department’s computer system.
Failure to meet these requirements may result in the assignment not being marked.