COMPSCI 711 Assignment A1
Due date: 23:59 1st October

The purpose of this assignment is to understand the techniques used by the CDN in
reducing the amount of data transmission and practice developing distributed applications.

The system consists of three components as shown in the figure below.
client cache server


The server provides a service that allows users to browse and download files. The cache
caches the data previously downloaded by the client. It should be assumed that the three
components reside at different locations. The client program interacts with the server
through the cache. That is, when the client wants to browse the list of files available on
the server or to download a file from the server, the client’s requests are sent to the cache
first and the cache forwards the requests to the server. Similarly, the server also sends the
replies to the clients through the cache.
Your implementation should be in C# or Java. Client, cache and server MUST be
implemented as separate programs. You must provide a batch file to run your program.
There are two options for this assignment. They differ in their difficulty. Option 1 is
relatively easy. You should only do ONE of the options. However, the maximum mark
for option 1 is 11 while the maximum mark for option 2 is 17. If you do both options,
your mark is the mark of the option that you gain higher mark.


Option 1 (11 marks)

Programming (10 marks)
In this option, you are required to implement the client program, the cache and the server.
The requirements for the three programs are as below:
? The client program should provide a GUI interface that (a) allows the user to display
the list of files that are available on the server, (b) allows the user to select a file from
the list of available files to download, and, (c) allows the user to display the contents
of the downloaded file. In this option, you can assume the files to be downloaded are
text files.
? The cache should cache the files previously downloaded by the client.
o If the user requests for a file that has the same name as a previously
downloaded file, the cached copy of the file should be returned to the user.
o The cache should keep a log to record of the activities of the cache. For each
user’s file downloading request, the log should indicate whether the request is
satisfied by a cached file or the requested file needs to be downloaded from
the server. For example, when a user’s request is received, the following log
entry might be created:
user request: file xyz at 10:27:00 2021-07-01
response: cached file xyz
or
user request: file xyz at 10:27:00 2021-07-01
response: file xyz downloaded from the server
o The cache should provide a GUI interface that allows the user to view the
contents of the cache’s log and the list of files that are cached on the server.
o The interface should provide a function (e.g. a clear button) that allows the
files in the cache to be cleared (i.e. deleted).
o It should be assumed that the cache has sufficient space to hold all the
downloaded files. That is, you do not need to consider cache replacement
policy.
? The server program should provide (a) an operation that allows the user to download
a file with a given name, and, (b) an operation that lists the names of the files
available on the server.

Report (1 mark)
Write a report about your implementation. Your report should include the following.
(a) Which option you have implemented.
(b) Instructions on how to run your programs.
Save your report as a PDF file. Name it as report.pdf.

Option 2 (17 marks)

Programming (14 marks)
In this option, you are required to implement the client program, the cache and the server.
The cache and the server should allow fragments of the files to be cached. In your
implementation, the fragmentation of the files should be carried out automatically. That is,
the users do not need to rewrite the files for caching purpose. The files to be downloaded
are image files.
? The client program should provide a GUI interface that (a) allows the user to display
the list of files that are available on the server, (b) allows the user to select a file from
the list of available files to download, and, (c) allows the user to display the contents
of the downloaded file (i.e., display the downloaded image).

The requirements for the cache are as below:
o When a user requests for a file, if there are some cached data that can be used to
construct the requested file, the cached data should be used, and, only the data that do
not exist on the cache should be downloaded from the server.
o The cache should keep a log to record of the activities of the cache. For each user’s
file downloading request, the log should indicate the percentage of the file that is
constructed using the data cached on the server. The percentage is defined as “the size
of the cached data used to construct the file / the size of the file” where the size is
measured in bytes. For example, when a user’s request is received, the following log
entry might be created:
user request: file xyz at 10:27:00 2021-07-01
response: 82% of file xyz was constructed with the cached data
o The cache should provide a GUI interface that allows the user to view the contents of
the cache’s log, the list of cached data fragments and the contents of the selected data
fragment cached on the cache server. The contents of the data should be displayed as
a sequence of bytes in hexadecimal numbers. Each byte consists of two hexadecimal
digits. For example, the contents of a data segment might be “1F02…” where “…”
denotes more hexadecimal digits. Your program must display the exact contents. That
is, you cannot display “…” as output.
o The size of each data fragment should be around 2KB. Otherwise, your programs
might not work properly for the test cases used by the marker.
o The interface should provide a function (e.g. a clear button) that allows the files in the
cache to be cleared (i.e. deleted).
o It should be assumed that the cache has sufficient space.

The server program should provide the following:
? An operation that allows the user to download a file with a given name.
? An operation that lists the names of the files available on the server.
? Operations that are necessary to allow the cache to download fragments of the
files.

The mark that you gain depends on whether the scheme that you use can maximize the
reusable data on the cache. Two example files that differ in 3 bytes are given as an
example. You should test your programs thoroughly with more test data.

Report (3 marks)
Write a report about your implementation. Your report should include the following.
(a) Which option you have implemented.
(b) Instructions on how to run your programs.
(c) Describe the techniques that you use to determine which portions of a file need to be
downloaded from the server.
Save your report as a PDF file. Name it as report.pdf.


Submission
Please zip your Visual Studio project in a file after deleting the "bin" and "obj" folders.
Name this zip file as upi.zip where upi is your university login ID, e.g. jbon007.zip.
Submit the file through http://adb.auckland.ac.nz/.
NO email submission will be accepted.
Marking Schedule

Option 1
Programming
mark
a batch file for running the program 1
Client & Server
A GUI interface that allows the user to display the list of files that are available
on the server
1
A GUI interface that allows the user to select a file from the list of available
files to download
1
A GUI interface that allows the user to display the contents of the downloaded
file.
1
Cache
If the user requests for a file that has the same name as a previously
downloaded file, the cached copy of the file should be returned to the user.
3
A GUI interface for viewing the cache's log and the log is kept correctly. 1
A GUI interface for clearing the contents of the cache and the content can be
cleared correctly.
1
A GUI interface for viewing the list of cached files and the list is kept correctly. 1

Report
Mark
Instructions on how to run your programs 1

Option 2
Programming
mark
a batch file for running the program 0.5
Client & Server
A GUI interface that allows the user to display the list of files that are available
on the server
0.5
A GUI interface that allows the user to select a file from the list of available
files to download
0.5
A GUI interface that allows the user to display the contents of the downloaded
file.
0.5
Cache
If there are some cached data that can be used to construct the requested file,
only the data that do not exist on the cache should be downloaded from the
server

Case 1: Download files with different names but similar contents. 4
Case 2: Download files with the same name but slightly different contents. 4
A GUI interface for viewing the cache's log and the log is kept correctly. 1
A GUI interface for clearing the contents of the cache and the content can be
cleared correctly.
1
A GUI interface for viewing the list of cached files and the list is kept correctly. 1
A GUI interface for viewing the contents of the selected data fragment cached
on the cache server.
1

Report
Mark
Instructions on how to run your programs 0.5
Describe the techniques that you use to determine which portions of a file need
to be downloaded from the server
2.5