Socket programming basics in Computer Networks - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a socket using IPv4 and TCP protocols.

Computer Networks

sock = socket.socket(socket.[1], socket.SOCK_STREAM)

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

AAF_INET6

BAF_INET

CSOCK_DGRAM

DSOCK_RAW

Attempts:

3 left

💡 Hint

Common Mistakes

Using AF_INET6 instead of AF_INET for IPv4 sockets.

Confusing socket types with address families.

The AF_INET constant specifies the IPv4 address family, which is commonly used for TCP sockets.

2fill in blank

medium

Complete the code to bind the socket to all interfaces on port 8080.

Computer Networks

sock.bind(([1], 8080))

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

A"0.0.0.0"

B"localhost"

C"127.0.0.1"

D"255.255.255.255"

Attempts:

3 left

💡 Hint

Common Mistakes

Binding to 'localhost' limits connections to local only.

Using broadcast address '255.255.255.255' is incorrect for binding.

The IP address "0.0.0.0" means binding to all available network interfaces on the machine.

3fill in blank

hard

Fix the error in the code to listen for incoming connections with a backlog of 5.

Computer Networks

sock.[1](5)

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

Aconnect

Bbind

Clisten

Daccept

Attempts:

3 left

💡 Hint

Common Mistakes

Using accept() before listen().

Using bind() or connect() incorrectly here.

The listen() method enables the socket to accept incoming connections, with the argument specifying the maximum queued connections.

4fill in blank

hard

Fill both blanks to accept a connection and receive data from the client.

Computer Networks

conn, addr = sock.[1]()
data = conn.[2](1024)

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

Aaccept

Brecv

Csend

Dconnect

Attempts:

3 left

💡 Hint

Common Mistakes

Using send() instead of recv() to receive data.

Using connect() on server side instead of accept().

The accept() method waits for an incoming connection and returns a new socket and address. The recv() method reads data from the connection.

5fill in blank

hard

Fill all three blanks to send a response and close the connection properly.

Computer Networks

conn.[1](b"HTTP/1.1 200 OK\r\nContent-Type: text/plain\r\n\r\nHello")
conn.[2](socket.SHUT_RDWR)
sock.[3]()

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

Asend

Bclose

Cshutdown

Drecv

Attempts:

3 left

💡 Hint

Common Mistakes

Calling close() before shutdown(), which may cause data loss.

Using recv() instead of send() to send data.

First, send() sends the response bytes. Then shutdown() disables further sends and receives on the connection. Finally, close() releases the socket resources.

Practice

1. What is the primary purpose of a socket in computer networks?

easy

A. To enable communication between two programs over a network

B. To store files on a server

C. To encrypt data before sending

D. To manage user permissions on a device

Solution

1. Step 1: Understand what a socket does

   A socket is an endpoint for sending or receiving data across a network connection.

2. Step 2: Identify the main function

   Its main role is to allow two programs on different devices to communicate.

3. Final Answer:

   To enable communication between two programs over a network -> Option A

4. Quick Check:

   Socket = communication endpoint [OK]

Hint: Remember sockets connect programs for data exchange [OK]

Common Mistakes:

• Confusing sockets with file storage
• Thinking sockets encrypt data
• Assuming sockets manage user permissions

2. Which of the following is the correct order of steps in basic socket programming?

easy

A. Bind, create socket, listen, accept, send/receive, close

B. Create socket, bind, listen, accept, send/receive, close

C. Create socket, listen, bind, accept, send/receive, close

D. Accept, create socket, bind, listen, send/receive, close

Solution

1. Step 1: Recall the socket programming sequence

   The correct sequence starts by creating a socket, then binding it to an address and port.

2. Step 2: Follow the connection steps

   After binding, the server listens for connections, accepts them, then sends/receives data, and finally closes the socket.

3. Final Answer:

   Create socket, bind, listen, accept, send/receive, close -> Option B

4. Quick Check:

   Socket steps = create, bind, listen, accept, send/receive, close [OK]

Hint: Remember: Create, Bind, Listen, Accept, Communicate, Close [OK]

Common Mistakes:

• Binding before creating socket
• Listening before binding
• Accepting before listening

3. Consider this Python server code snippet:

import socket
s = socket.socket()
s.bind(('localhost', 12345))
s.listen(1)
conn, addr = s.accept()
data = conn.recv(1024)
print(data.decode())
conn.close()
s.close()

What will be printed if the client sends the message "Hello"?

medium

A. Error: decode() not found

B. b'Hello'

C. Hello

D. None

Solution

1. Step 1: Understand data reception

   The server receives bytes data from the client using conn.recv(1024).

2. Step 2: Decode bytes to string

   The data.decode() converts bytes to a readable string, so printing it shows "Hello".

3. Final Answer:

   Hello -> Option C

4. Quick Check:

   Bytes decoded to string = Hello [OK]

Hint: recv() returns bytes; decode() converts to string [OK]

Common Mistakes:

• Expecting bytes output without decoding
• Assuming decode() causes error
• Thinking recv() returns None

4. Identify the error in this socket server code snippet:

import socket
s = socket.socket()
s.listen(1)
s.bind(('localhost', 12345))
conn, addr = s.accept()

medium

A. Calling listen() before bind()

B. Missing socket creation

C. accept() called without listen()

D. bind() called after accept()

Solution

1. Step 1: Check the order of socket calls

   The socket must be bound to an address before it starts listening.

2. Step 2: Identify the incorrect sequence

   Here, listen() is called before bind(), which is incorrect and will cause an error.

3. Final Answer:

   Calling listen() before bind() -> Option A

4. Quick Check:

   Bind before listen [OK]

Hint: Always bind socket before listen() [OK]

Common Mistakes:

• Calling listen() before bind()
• Confusing accept() and listen() order
• Forgetting to create socket

5. You want to write a server that handles multiple clients one after another using sockets. Which approach correctly applies socket programming basics?

hard

A. Create socket, accept client without binding or listening, communicate, close socket

B. Bind socket, create socket, listen, accept client, communicate, close socket

C. Create socket, bind, accept client, listen, communicate, close socket

D. Create socket, bind, listen, accept client, communicate, close client socket, then accept next client

Solution

1. Step 1: Understand sequential client handling

   The server must create a socket, bind it, and listen before accepting clients one by one.

2. Step 2: Follow correct order for each client

   For each client, accept the connection, communicate, close the client socket, then accept the next client.

3. Final Answer:

   Create socket, bind, listen, accept client, communicate, close client socket, then accept next client -> Option D

4. Quick Check:

   Correct socket lifecycle for multiple clients = Create socket, bind, listen, accept client, communicate, close client socket, then accept next client [OK]

Hint: Bind and listen once; accept and close per client [OK]

Common Mistakes:

• Accepting without binding or listening
• Calling listen after accept
• Binding before creating socket