Due: 16 April 2019 (Tuesday Week 8) by 23:59
COMP3221 Assignment 2: CS Blockchain
The goal of this project is to implement a Multi-threaded Client-Server (CS) Blockchain applica- tion in Java which can spread messages to multiple servers and accept connections from multiple clients at the same time.
1 Submission Details
The assignment comprises three tasks and each task can be submitted separately. The final version of your assignment should be submitted electronically via PASTA by 23:59 on the Wednesday of Week 8 (Hard Deadline). The project is an individual project, and each student has to submit his/her own version.
1.1 Program structure
For task 1, six java files must be submitted. It is recommended to submit by 23:59 on the Sunday of Week 6 (Soft Deadline).
• A Blockchain.java file.
• A Block.java file.
• A Transaction.java file.
• A BlockchainServer.java file.
• A BlockchainServerRunnable.java file. • A PeriodicCommitRunnable.java file.
For task 2, ten java files must be submitted. It is recommended to submit by 23:59 on the Sunday of Week 6 (Soft Deadline).
• A Blockchain.java file.
• A Block.java file.
• A Transaction.java file.
• A BlockchainServer.java file.
• A BlockchainServerRunnable.java file.
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COMP3221 Multithreaded Client-Server Blockchain
• A BlockchainClient.java file.
• A BlockchainClientRunnable.java file. • A ServerInfo.java file.
• A ServerInfoList.java file.
• A PeriodicCommitRunnable.java file.
For task 3, ten java files and ReliabilityReport.pdf file must be submitted. It is recom- mended to submit by 23:59 on the Sunday of Week 7 (Soft Deadline).
• A Blockchain.java file.
• A Block.java file.
• A Transaction.java file.
• A BlockchainServer.java file.
• A BlockchainServerRunnable.java file. • A BlockchainClient.java file.
• A BlockchainClientRunnable.java file. • A ServerInfo.java file.
• A ServerInfoList.java file.
• A PeriodicCommitRunnable.java file.
• A ReliabilityReport.pdf file.
Please use the skeleton code which is provided on elearning and ed as the base. All classes will be stored in the same default package (no package header in java files), and all files should be located in the same src folder with no subfolders. All present .java files should be correct and do not forget to remove any dummy files that do not count as source files (E.g. junit test cases, class files). Please zip the src folder and submit the resulting archive src.zip by the deadline given above. The program should compile with Java 8. No optional packages that are not part of the default Java 8 JDK can be used.
1.2 Submission system
PASTA will be used to assess that your program correctly implements the Multithread Client-Server Blockchain protocol. The archive src.zip should be submitted at https: //pastpd01191.srv.sydney.edu.au/PASTA. To access this website, you will have to be connected to the network of the University of Sydney (physically on campus or through VPN).
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COMP3221 Multithreaded Client-Server Blockchain
PASTA stands for “Programming Assessment Submission and Testing Application” and is a web-based application that automates the compilation, execution and testing of your pro- gram. When you submit your src.zip archive in PASTA, the system enqueues your submis- sion in the shared queue of all assignments to be tested. It may take more time close to the deadline as many students will try to submit at the same time.
1.3 Academic Honesty / Plagiarism
By uploading your submission to PASTA you implicitly agree to abide by the University policies regarding academic honesty, and in particular that all the work is original and not plagiarised from the work of others. If you believe that part of your submission is not your work you must bring this to the attention of your tutor or lecturer immediately. See the policy slides released in Week 1 for further details.
In assessing a piece of submitted work, the School of IT may reproduce it entirely, may provide a copy to another member of faculty, and/or communicate a copy of this assignment to a plagiarism checking service or in-house computer program. A copy of the assignment may be maintained by the service or the School of IT for the purpose of future plagiarism checking.
2 Marking
This assignment is worth 10% of your final grade for this unit of study.
The first category of tasks, called Blockchain: Multithreaded Server, assesses the behaviour of the server with respect to requirement. If you could pass all tests, two marks are given.
• Maximum 1 mark for server accepting multiple client connections at the same time.
• Maximum 1 mark for server processing multiple client requests at the same time with proper synchronisation.
The second category, called Blockchain: Multithreaded Client, assesses the behaviour of the client concerning requirement. If you could pass all tests, four marks are given.
• Maximum 1 mark for client being able to read config file properly.
• Maximum1markforclientbeingabletoadd,remove,update,listservers’infocorrectly.
• Maximum 1 mark for client unicasting, multicasting and broadcasting messages to servers correctly.
• Maximum 1 mark for client printing replies accurately.
The third category, called Blockchain: Reliability, assesses the resilience level of client / server to exceptions and crashes. Maximum four marks are given if all corner cases are handled and documented properly.
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COMP3221 Multithreaded Client-Server Blockchain
• Maximum 1 mark for client resilient to exceptions and crashes.
• Maximum 1 mark for server resilient to exceptions and crashes.
• Maximum 1 mark for implementing test cases and dummy client / server properly. • Maximum 1 mark for documenting exceptions precisely.
Please make sure previous tasks are implemented correctly, before moving to next task. You may face cascading failures due to incomplete implementation of previous tasks.
2.1 Feedback
PASTA provides feedback about each individual submission, one at a time. It will output a list of tests and outcomes indicating whether your program passed each visible test successfully or failed. The feedback provided is indicative, intentionally high-level and will not precisely identify the nature of any bug of your program. Please write your personal test cases and thoroughly test all your code before submission.
3 Functionalities of a Client-Server Blockchain
The goal of this project is to implement a Reliable Multithreaded Client-Server (CS) Blockchain application. The previous blockchain completed in assignment 1 can only manage one client and one server running at the same time, At this stage, we are going to extend as- signment 1 with multithreading support. Many clients can talk to a single server concurrently, and a client can talk to multiple servers concurrently as well. The following tasks indicate the features that should be achieved, one solution for each task is expected to be submitted.
Task 0 Blockchain: Proof-of-Work Simulation
This task is designed to let you familarise yourself with multithreading. No coding is required, and no mark is assigned to this task.
Previously, our method to build a block is pretty simple, where every three transactions gen- erate a new block. In reality, blockchain employs a different way to create a block. Each miner (server) who mines (create) the block, are competing to commit the correct block under some specific rules. An example of such a rule is to build blocks with a hash value starting from character “A”. However, the transactions cannot be altered to make hash value beginning with “A”. Therefore, we need to introduce an extra random variable called nonce when calculating the hash. By changing the nonce value, the hash of the block gets changed as well. The lucky miner who gets the nonce correct is the owner of the block, who can claim the mining reward.
To realise this periodic mining behaviour, we need a separate execution line who mines the block every few seconds. This is the place where multithreading could help us.
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} }
}
COMP3221 Multithreaded Client-Server Blockchain
A quick recap, multithreading enables a single program (process) with multiple lines of exe- cution. This execution unit is named as a thread (In contrast to process, which is the resource unit). In Java, we can quickly implement thread concept by creating a custom class which extends Thread class or implements the Runnable interface. To pass the raw inputs into the thread, you could use the constructor. To fetch the processed output back, you could create a getter method. The thread can be started by invoking start() method, and the main thread can wait for the child thread to finish by calling the join() method. Those information was provided in lectures and labs.
Below is a concrete implementation which achieves the functionality described above. Please do not modify this class.
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import java.security.SecureRandom;
public class PeriodicCommitRunnable implements Runnable{
private volatile boolean isRunning; private int nonce;
private Blockchain blockchain; private SecureRandom randomGenerator;
public PeriodicCommitRunnable(Blockchain blockchain) { isRunning = true;
this.blockchain = blockchain;
randomGenerator = new SecureRandom();
nonce = randomGenerator.nextInt(); }
public void setRunning(boolean isRunning) { this.isRunning = isRunning; } public boolean getRunning() { return isRunning; }
@Override
public void run() {
while (isRunning) { blockchain.commit(nonce);
nonce = randomGenerator.nextInt(); try {
Thread.sleep(400);
} catch (InterruptedException e) {
System.err.println(“PeriodicCommitterInterrupted.”); }
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COMP3221 Multithreaded Client-Server Blockchain
Task 1 Blockchain: Multithreaded Server
In task 1, you are required to extend the Blockchain’s server, which can process client requests like tx
In this case, each client socket being created by ServerSocket should be handled by one of the worker thread BlockchainServerRunnable. BlockchainServerRunnable class’s constructor accepts two parameters. The first is the client socket, and the second is the blockchain. Since all worker threads modify the same blockchain, you are also required to improve the blockchain class provided to you with proper synchronisation support as taught in week 2’s tutorial.
To test it, try to connect to your server with multiple clients developed in the previous assign- ment at the same time, you should make sure all your clients can see the same result, and no race condition occurs.
Please use the skeleton code below to implement your BlockchainServer class.
if (args.length != 1) { return;
public class BlockchainServer {
public static void main(String[] args) {
9 int portNumber = Integer.parseInt(args[0]);
10 Blockchain blockchain = new Blockchain();
11
12 PeriodicCommitRunnable pcr = new PeriodicCommitRunnable(blockchain);
13 Thread pct = new Thread(pcr);
14 pct.start();
15
16 // implement your code here. 17
18 pcr.setRunning(false);
19 pct.join();
20 }
21
22 // implement any helper method here if you need any
23 }
please use the skeleton code below to implement your BlockchainServerRunnable class.
public class BlockchainServerRunnable implements Runnable{
public BlockchainServerRunnable(Socket clientSocket, Blockchain blockchain) {
// implement your code here
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4 5}
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7 public void run() {
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9} 10
// implement your code here
11 // implement any helper method here if you need any 12 }
Task 2
Blockchain: Client
COMP3221 Multithreaded Client-Server Blockchain
Previously, our client just worked as a simple repeater sitting between the user and server. Whatever the user types in, the client directly forward it to the server. Whatever the server replies, it just gets popped back to the client. At this stage, we redesign our client to make it support more routing mechanisms. So it can provide multicast and broadcast functionalities.
Here is a list of commands your client must handle properly.
• ls command. “ls”
• ad command. “ad|
• rm command. “rm|
• up command. “up|
• tx command. “tx|
• pb command. “pb”
• pb command. “pb|
• pb command. “pb|
To maintain a list of known server, we create two separate classes to store server information. The first is the ServerInfo class which records individual server information like host name and port number. Another is the ServerInfoList class, which stores a list of ServerInfo objects. Some methods of those two classes are already implemented for you. Your first job here is to implement the InitialiseFromFile() method. In this method, your client should be able to read a config file where each line (entry) follows the
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public class ServerInfo { private String host;
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8 9}
public ServerInfo(String host, int port) { this.host = host;
this.port = port;
10 public String getHost() { return host; }
11 public int getPort() { return port; }
12 public void setHost(String host) { this.host = host; }
13 public void setPort(int port) { this.port = port; }
14
15 // implement any helper method here if you need any
16 }
please use the skeleton code below to implement your ServerInfoList class.
ArrayList
9 public void initialiseFromFile(String filename) { 10 // implement your code here
public class ServerInfoList {
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public ServerInfoList() { serverInfos = new ArrayList<>();
COMP3221 Multithreaded Client-Server Blockchain
value in the server info list. Any entries with server index above or equal to servers.num should be ignored. If there are multiple entries with the same key, the latest value is used.
In the following example. The ServerInfoList will be initialised to size three, with elements null, null, serverinfo(localhost, 8333).
1 servers.num=2 # same key, first entry will be ingored.
2 servers.num=3
3
4 server0.host=localhost # port number is missing, null value will be added to the list. 5
6 server1.host=localhost
7 server1.port=123456 # port number is greater than 65535, null value will be added to the list.
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9 server2.host=localhost
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11 server2.port=8333 12
13 server3.host=localhost # server index equals to servers.num, this entry will be ignored.
14 server3.port=8334
please use the skeleton code below to implement your ServerInfo class.
private int port;
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COMP3221 Multithreaded Client-Server Blockchain
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}
public ArrayList
this.serverInfos = serverInfos; }
public boolean addServerInfo(ServerInfo newServerInfo) { // implement your code here
}
public boolean updateServerInfo(int index, ServerInfo newServer) { // implement your code here
}
public boolean removeServerInfo(int index) { // implement your code here
}
public boolean clearServerInfo() { // implement your code here
}
public String toString() { String s = “”;
for (int i = 0; i < serverInfos.size(); i++) { if (serverInfos.get(i) != null) {
s += "Server" + i + ": " + serverInfos.get(i).getHost() + " " + serverInfos.get(i).getPort() + "\n";
} }
return s; }
// implement any helper method here if you need any
}
Before moving to the next stage, we suggest everyone implement three helper methods first. unicast(), broadcast() and multicast().Incomputernetworking,thesearethethree most common ways to route messages. Typically, those three casting methods are imple- mented in the network layer supported by the IP protocol. Here we are trying to do a simu- lation at the application layer, where we define unicast as a one-to-one communication with one thread, broadcast as a one-to-all communication with multiple threads, and multicast is a one-to-many communication with multiple threads. The BlockchainClientRunnable class is the thread that is used to send the message to the server. It should create a connection first, and then forward the message via the socket to the server. The reply from the server should be stored to the variable reply. The socket connection should close immediately after the response comes back by sending cc to the server. At this stage, socket connects and the fol- lowing reads and writes operation should have a timeout of 2 seconds. Once all threads termi- nate, all replies should be printed on the screen. If the connected server does not reply or any
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COMP3221 Multithreaded Client-Server Blockchain exception has been raised, it should print "Server is not available\n\n" to the screen.
All replies should prepend a header like "Server
• ls (List) command, print the server info list, using toString() method provided. (toString() + “\n”)
• ad (Add) command, append the new ServerInfo to the ServerInfoList if the ServerInfo is valid.
• rm (Remove) command, remove the ServerInfo indexed by the server index from the list (set to null) if the server index is a valid index.
• up (Update) command, update the ServerInfo indexed by server index to be the new ServerInfo provided if the new ServerInfo is valid and the server index is valid as well.
• cl (Clear) command, remove all null values from the ServerInfoList if null value exists.
• tx (Transact) command, broadcast the transaction message to all servers and print the reply one by one in the terminal.
• pb (PrintBlockchain) command, broadcast pb request to all servers, if no server index specified. Unicast to that specific server, if there is one server index given. Multicast to those specified server, if there is more than one server index given.
• sd (ShutDown) command, shut down your client.
For ad, rm, up and cl command, if the operation succeeded, please print “Succeeded\n\n” to the terminal. Otherwise, please print “Failed\n\n” to the terminal. For pb command, if the index specified is invalid, or if the value at that index is null, simply ignore that index and printnothing.Foranyotherundefinedcommands,pleaseprint”Unknown Command\n\n”to the terminal.
To test it, firstly, test it with two servers running on the same machine, then try to migrate you server to different machines in the same local network (same LAN or same WLAN), finally move to the WAN network.
Make sure you can reproduce the following transcript locally. Assume the config file is the example above, and there are two servers running at localhost port 8333, 8334.
1 ls
2 Server2: localhost 8333
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4 ad|localhost|8334
5 Succeeded
6
7 ls
8 Server2: localhost 8333
9 Server3: localhost 8334
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COMP3221 Multithreaded Client-Server Blockchain
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11 rm|3
12 Succeeded
13
14 ls
15 Server2: localhost 8333
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17 rm|-1
18 Failed
19
20 ls
21 Server2: localhost 8333
22
23 up|1|localhost|8334
24 Succeeded
25
26 up|3|localhost|8335
27 Succeeded
28
29 ls
30 Server1: localhost 8334
31 Server2: localhost 8333
32 Server3: localhost 8335
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34 cl
35 Succeeded
36
37 ls
38 Server0: localhost 8334
39 Server1: localhost 8333
40 Server2: localhost 8335
41
42 clear
43 Unknown Command
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45 tx|test0001|1
46 Server0: localhost 8334
47 Accepted
48
49 Server1: localhost 8333
50 Accepted
51
52 Server2: localhost 8335
53 Server is not available
54
55 pb
56 Server0: localhost 8334
57 Pool:
58 ———————————————————————————
59 |test0001| 1|
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if (args.length != 1) { return;
10 ServerInfoList sil = new ServerInfoList();
11 sil.initialiseFromFile(configFileName);
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13 Scanner sc = new Scanner(System.in);
14
15 while (true) {
16
String message = sc.nextLine();
COMP3221 Multithreaded Client-Server Blockchain
60 ——————————————————————————— 61
62 Server1: localhost 8333
63 Pool:
64 ———————————————————————————
65 |test0001| 1|
66 ———————————————————————————
67
68 Server2: localhost 8335
69 Server is not available
70
71 pb|0|1
72 Server0: localhost 8334
73 Pool:
74 ———————————————————————————
75 |test0001| 1|
76 ———————————————————————————
77
78 Server1: localhost 8333
79 Pool:
80 ———————————————————————————
81 |test0001| 1|
82 ———————————————————————————
83
84 pb|0
85 Server0: localhost 8334
86 Pool:
87 ———————————————————————————
88 |test0001| 1|
89 ———————————————————————————
90
91 sd
Please use the skeleton code below to implement your BlockchainClient class.
public class BlockchainClient {
public static void main(String[] args) {
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8 String configFileName = args[0]; 9
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// implement your code here
} }
COMP3221 Multithreaded Client-Server Blockchain
public static void unicast (int serverIndex, ServerInfo serverInfo, String message) {
public static void broadcast (ServerInfoList serverInfoList, String message) { // implement your code here
}
public static void multicast (ServerInfoList serverInfoList, ArrayList
// implement your code here
}
// implement any helper method here if you need any
}
// implement your code here
}
Please use the skeleton code below to implement your BlockchainClientRunnable class.
public class BlockchainClientRunnable implements Runnable { private String reply;
public BlockchainClientRunnable(int serverIndex, String serverName, int portNumber, String message) {
// header string
this.reply = “Server” + serverIndex + “: ” + serverName
+ ” ” + portNumber + “\n”; }
public void run() {
// implement your code here
}
public String getReply() { return reply;
}
// implement any helper method here if you need any
}
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COMP3221 Multithreaded Client-Server Blockchain
Task 3 Blockchain: Reliability
For this task, we would like you to thoroughly test your Blockchain system and its reliability by implementing unit testing, integration testing and acceptance testing. We would like your Blockchain to be as robust and stable as possible. You should first test its functionalities then identify as many vulnerabilities as possible.
Evaluation Procedure: To find vulnerabilities, we are going to test our code as much as pos- sible to look specifically for corner cases. The ultimate goal here is to make our client/server resilient to all kinds of exceptions (which lead to crashes). Exceptions should be handled properly with a meaningful error message instead of throwing it to public or simply print the stack trace on the screen. We propose a three phase testing procedure as a guidance.
Step 1. (Unit Testing) Write general unit tests that should test functionalities and find possible errors in your code. You should document which error the test case is targeting at, what the input is, what the expected output is and what the actual output is. This should be demonstrated with code and comments and also included in documentation.
Step 2. (Integration Testing) For this step, you should test the whole system of Blockchain- Server and BlockchainClient by testing the server with valid and invalid client requests and the client with valid and invalid server responses. The goal of this test is to illustrate how your blockchain cope with malicious clients/servers.
Check out this ED tutorial on how to perform unit and integration testing: https:// edstem.org/courses/3215/discussion/121758
Step 3. (Acceptance Testing) Now, it’s time to turn to actual people. Since people break things quite easily, your task is to go and find a friend that is outside of this course and has little to no knowledge of networking. Let your friend write a config file and use your client and server (with no help from you). You should document your testing procedure, E.g., when, with whom, under which testing environment, do you find any new exceptions, etc.
For task 3’s marking, 2 marks are given based on the resilience level of your client/server. This part is assessed by PASTA automatically. Therefore, after you successfully figure out all exceptions, and handle them properly, do not forget to submit your final version to PASTA. Another 2 marks are given based on the quality of your test cases and documentation. This part is assessed by your tutor. Hence, please contact them for help if you have any question.
Document Format
• Unit Testing
– Purpose of the Test – Input
– Expected Output
– Actual Output
• Integration Testing – Test Cases
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COMP3221 Multithreaded Client-Server Blockchain
– Input
– Expected Output – Actual Output
• Acceptance Testing
– Test Cases: User and System Setup
– Testing Procedure
– User’s Config File
– Test Outcomes: Successful Operations and Errors
General Tips for Getting Good Marks
• Set up IDEs to help you find errors and debug.
• Try not to throw exceptions across multiple methods, catch and handle them as soon as possible.
• Write the most specific exception. For example: Don’t just catch IOException, try to catch ConnectException which is a subclass of IOException.
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