Client-server architecture in Unity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start the server in Unity.

Unity

NetworkManager.singleton.Start[1]();

Drag options to blanks, or click blank then click option'

AClient

BConnect

CHost

DServer

Attempts:

3 left

💡 Hint

Common Mistakes

Using StartClient() instead of StartServer()

Using StartHost() which starts both client and server

To start the server in Unity's networking, you call StartServer() on the NetworkManager singleton.

2fill in blank

medium

Complete the code to send a message from client to server.

Unity

client.Send[1](message);

Drag options to blanks, or click blank then click option'

ACommand

BMessage

CRpc

DEvent

Attempts:

3 left

💡 Hint

Common Mistakes

Using Rpc which is server to client

Using Event which is not a Unity networking method

In Unity networking, clients send commands to the server using methods marked with [Command].

3fill in blank

hard

Fix the error in the server callback method declaration.

Unity

[[1]]
void CmdSendData(string data) {
    // server logic
}

Drag options to blanks, or click blank then click option'

AServerCallback

BClientRpc

CCommand

DServerRpc

Attempts:

3 left

💡 Hint

Common Mistakes

Using ClientRpc attribute instead of Command

Using ServerRpc which is not a Unity HLAPI attribute

The correct attribute to mark a method as a command from client to server is [Command].

4fill in blank

hard

Fill both blanks to create a dictionary of player scores where keys are player IDs and values are scores greater than 10.

Unity

var highScores = new Dictionary<int, int> { { [1], [2] } };

Drag options to blanks, or click blank then click option'

AplayerId

Bscore

C15

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using score as key instead of playerId

Using 5 as score which is not greater than 10

The dictionary key is the player ID and the value is the score. We want scores greater than 10, so 15 fits.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps player names to their scores if the score is above 50.

Unity

var topPlayers = new Dictionary<string, int> { { [1], [2] } }; // Only if [3] > 50

Drag options to blanks, or click blank then click option'

AplayerName

Bscore

DplayerId

Attempts:

3 left

💡 Hint

Common Mistakes

Using playerId instead of playerName as key

Using playerId in the condition instead of score

The dictionary maps player names to scores, and the condition checks if the score is above 50.

Practice

1. In Unity's client-server architecture, what is the main role of the client?

easy

A. Send requests to the server and receive responses

B. Store all game data permanently

C. Control the server hardware

D. Manage other clients directly

Solution

1. Step 1: Understand client role in client-server

   The client initiates communication by sending requests to the server.

2. Step 2: Understand server response

   The server processes requests and sends back responses to the client.

3. Final Answer:

   Send requests to the server and receive responses -> Option A

4. Quick Check:

   Client = Request sender [OK]

Hint: Clients always ask; servers always answer [OK]

Common Mistakes:

• Thinking client stores all data permanently
• Confusing client with server hardware control
• Assuming clients manage other clients

2. Which of the following is the correct way to create a TcpClient in Unity C#?

easy

A. TcpClient client = TcpClient("127.0.0.1", 8080);

B. TcpClient client = new TcpClient.connectTo("127.0.0.1", 8080);

C. TcpClient client = new TcpClient.connect("127.0.0.1", 8080);

D. TcpClient client = new TcpClient("127.0.0.1", 8080);

Solution

1. Step 1: Recall TcpClient constructor syntax

   In C#, creating a new TcpClient requires the 'new' keyword and constructor with IP and port.

2. Step 2: Check each option's syntax

   Only TcpClient client = new TcpClient("127.0.0.1", 8080); uses 'new TcpClient("127.0.0.1", 8080);' correctly.

3. Final Answer:

   TcpClient client = new TcpClient("127.0.0.1", 8080); -> Option D

4. Quick Check:

   Use 'new' keyword with constructor [OK]

Hint: Always use 'new' to create objects in C# [OK]

Common Mistakes:

• Omitting 'new' keyword
• Using incorrect method names like connect or connectTo
• Wrong constructor call syntax

3. What will the following Unity C# code output if the server sends back the string "Hello Client"?

using System;
using System.Net.Sockets;
using System.Text;

TcpClient client = new TcpClient("127.0.0.1", 9000);
NetworkStream stream = client.GetStream();
byte[] data = new byte[256];
int bytes = stream.Read(data, 0, data.Length);
string response = Encoding.ASCII.GetString(data, 0, bytes);
Console.WriteLine(response);

medium

A. System.Byte[]

B. Hello Client

C. null

D. Exception thrown

Solution

1. Step 1: Understand data reading from NetworkStream

   The code reads bytes from the stream into a byte array and counts bytes read.

2. Step 2: Convert bytes to string

   It converts the bytes read to a string using ASCII encoding, which matches the server's sent string.

3. Final Answer:

   Hello Client -> Option B

4. Quick Check:

   Read bytes + decode = server message [OK]

Hint: Decode bytes read from stream to get server message [OK]

Common Mistakes:

• Printing byte array directly instead of decoding
• Ignoring number of bytes read
• Assuming null if no data

4. Identify the error in this Unity C# client code snippet:

TcpClient client = new TcpClient();
client.Connect("192.168.1.10", 7000);
NetworkStream stream = client.GetStream();
byte[] message = Encoding.ASCII.GetBytes("Ping");
stream.Write(message, 0, message.Length);
stream.Close();
client.Close();

medium

A. Missing try-catch block for network exceptions

B. Calling stream.Close() before client.Close() causes error

C. TcpClient must be created with IP and port in constructor

D. No error; code is correct

Solution

1. Step 1: Review TcpClient creation and connection

   Creating TcpClient with default constructor and then calling Connect is valid.

2. Step 2: Check for error handling

   Network operations can fail; missing try-catch means exceptions are unhandled.

3. Final Answer:

   Missing try-catch block for network exceptions -> Option A

4. Quick Check:

   Always handle network exceptions [OK]

Hint: Always wrap network calls in try-catch [OK]

Common Mistakes:

• Assuming stream.Close() before client.Close() is wrong
• Thinking TcpClient must have IP in constructor
• Ignoring exception handling

5. You want to build a Unity client that connects to a server and sends a player's score only if it is above 1000. Which code snippet correctly implements this logic using TcpClient and NetworkStream?

hard

A. if(score > 1000) {
TcpClient client = new TcpClient("server.com");
NetworkStream stream = client.GetStream();
byte[] data = Encoding.ASCII.GetBytes(score.ToString());
stream.Write(data, 0, data.Length);
stream.Close();
client.Close();
}

B. TcpClient client = new TcpClient("server.com", 5000);
NetworkStream stream = client.GetStream();
if(score > 1000) {
byte[] data = Encoding.ASCII.GetBytes(score.ToString());
stream.Write(data, 0, data.Length);
}
stream.Close();
client.Close();

C. TcpClient client = new TcpClient();
if(score > 1000) {
client.Connect("server.com", 5000);
NetworkStream stream = client.GetStream();
byte[] data = Encoding.ASCII.GetBytes(score.ToString());
stream.Write(data, 0, data.Length);
stream.Close();
client.Close();
}

D. if(score > 1000) {
TcpClient client = new TcpClient();
client.Connect("server.com", 5000);
NetworkStream stream = client.GetStream();
byte[] data = Encoding.ASCII.GetBytes(score);
stream.Write(data, 0, data.Length);
stream.Close();
client.Close();
}

Solution

1. Step 1: Check conditional connection and sending

   TcpClient client = new TcpClient(); if(score > 1000) { client.Connect("server.com", 5000); NetworkStream stream = client.GetStream(); byte[] data = Encoding.ASCII.GetBytes(score.ToString()); stream.Write(data, 0, data.Length); stream.Close(); client.Close(); } creates TcpClient without parameters, connects only if score > 1000, then sends data.

2. Step 2: Verify data conversion and method calls

   Converts score to string before encoding to bytes, uses correct Connect() and stream methods.

3. Final Answer:

   new TcpClient(); client.Connect() inside if(score > 1000) -> Option C

4. Quick Check:

   Connect and send inside if condition [OK]

Hint: Connect and send only inside the if block [OK]

Common Mistakes:

• Sending data without converting score to string
• Connecting outside the if condition
• Using score directly as bytes without encoding