PCPP2 Network Programming — 20 Questions

Question 1

You are developing a TCP client using the socket module. After calling socket.connect(), which method should be invoked to ensure all buffered data is transmitted to the server before closing the connection?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

socket.shutdown(socket.SHUT_WR). The shutdown() method allows for fine-grained control over the socket connection state, ensuring graceful termination.

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socket.sendall()

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socket.flush()

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socket.close()

Question 2

In a Python TCP server, what is the primary purpose of the backlog parameter in the listen(backlog) method?

Accepted Answer

It defines the maximum length of the queue of pending connections.. The backlog defines the maximum number of queued connections allowed before the OS starts rejecting new ones.

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It sets the timeout for idle client sockets.

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It limits the total number of connected clients.

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It specifies the maximum number of bytes per packet.

Question 3

You are using socket.socket(socket.AF_INET, socket.SOCK_DGRAM). You attempt to send 10,000 bytes via sendto(). Why might the operation raise an OSError?

Accepted Answer

The datagram size exceeds the maximum packet size allowed by the network stack.. UDP packets are limited by the MTU of the network path; trying to send a datagram larger than the buffer/MTU limits can cause an OS-level error.

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The socket must be set to non-blocking mode to send large data.

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UDP is connection-oriented and requires connect() first.

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TCP handshaking is missing for UDP.

Question 4

When using socket.setsockopt(), which option is required to immediately reuse a port that is currently in a TIME_WAIT state after a server restart?

Accepted Answer

socket.SO_REUSEADDR. SO_REUSEADDR allows a socket to bind to an address/port that is currently in the TIME_WAIT state.

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socket.TCP_NODELAY

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socket.SO_LINGER

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socket.SO_KEEPALIVE

Question 5

You are designing a cross-platform network application. Why is it recommended to use socket.getaddrinfo() instead of socket.gethostbyname()?

Accepted Answer

It supports IPv6 and is more portable across different network stacks.. getaddrinfo() is protocol-agnostic (IPv4/IPv6) and returns structured information suitable for socket creation.

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It caches results to reduce DNS requests.

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It is faster than gethostbyname().

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It automatically resolves local hostnames.

Question 6

You are building an application using SSL/TLS. Which module must be used to wrap a standard socket to provide encrypted communication?

Accepted Answer

ssl. The ssl module provides the necessary wrappers to enable TLS/SSL over standard socket objects.

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cryptography

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hashlib

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socket.ssl

Question 7

You are configuring a server to handle high-concurrency requests. Why is it preferable to use the select.select() module over a simple blocking recv() loop?

Accepted Answer

It enables monitoring multiple socket descriptors for I/O readiness.. select.select() allows monitoring multiple sockets simultaneously, preventing the server from blocking on a single idle connection.

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It reduces the CPU usage of the Python interpreter during idle times.

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It automatically implements multi-threaded socket handling.

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It automatically handles TCP flow control packets.

Question 8

Which method should a developer use to retrieve the IP address and port of the remote peer connected to a TCP socket?

Accepted Answer

socket.getpeername(). getpeername() returns the address of the remote endpoint connected to the socket.

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socket.recvfrom()

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socket.getsockname()

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socket.getfqdn()

Question 9

Which socket method is used to bind a socket to a specific address and port?

Accepted Answer

socket.bind(). The bind() method associates a socket with a specific address and port tuple.

Answer

socket.accept()

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socket.connect()

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socket.listen()

Question 10

Which function in the socket module is used to convert a 32-bit integer from host byte order to network byte order?

Accepted Answer

socket.htonl(). htonl() stands for Host to Network Long, converting 32-bit integers for network transmission.

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socket.ntohl()

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socket.htons()

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socket.inet_aton()

Question 11

When handling TCP streams, why might recv(1024) return fewer than 1024 bytes even if the sender sent more?

Accepted Answer

TCP is a stream protocol; it does not guarantee message boundaries.. TCP is a stream-oriented protocol, not a message-oriented one. Data is delivered based on buffer availability and segmentation.

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The packet was dropped due to network congestion.

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The socket was set to non-blocking mode.

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The OS limited the receive window size.

Question 12

When implementing a custom application protocol over TCP, how should you handle message framing?

Accepted Answer

Use a unique delimiter or a length prefix header for each message.. Since TCP is a stream, you must implement a protocol layer (like length-prefixing) to know when one message ends and the next begins.

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Rely on recv() returning one complete message at a time.

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Call sleep() between sends to ensure packet separation.

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Use UDP instead for automatic framing.

Question 13

You need to detect if a client has disconnected from your TCP server. What is the standard behavior of recv() when the peer performs a clean shutdown?

Accepted Answer

It returns an empty string (b'').. A clean shutdown by the peer causes recv() to return an empty bytes object (b'').

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It raises a ConnectionResetError.

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It returns None.

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It blocks indefinitely.

Question 14

What is the effect of setting a socket to non-blocking mode using socket.setblocking(False)?

Accepted Answer

It raises an exception if an operation would block.. Non-blocking sockets cause operations like recv() and connect() to raise an exception if they cannot be completed immediately.

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It makes the socket perform asynchronous DNS lookups.

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It increases the throughput of the connection.

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It automatically closes the socket if it is idle.

Question 15

You are writing a UDP server. What is the main disadvantage of using UDP for high-volume data transmission compared to TCP?

Accepted Answer

UDP does not provide delivery guarantees or ordering.. UDP provides no guarantee of delivery, order, or congestion control, requiring the application to handle these issues.

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UDP packets are always larger than TCP packets.

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UDP requires more handshake overhead.

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UDP is not supported on all operating systems.

Question 16

In a multi-threaded Python server, why is it discouraged to share a single socket object across multiple threads without synchronization?

Accepted Answer

Concurrent access can lead to interleaved or corrupted data streams.. Socket operations are generally thread-safe in CPython, but overlapping operations on the same file descriptor can lead to interleaved data or corrupted state.

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Python's GIL prevents concurrent socket access.

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Sockets are not picklable.

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The socket module raises a RuntimeError for concurrent usage.

Question 17

What is the purpose of the socket.recvfrom() method?

Accepted Answer

It retrieves data and the sender's address in a single call.. recvfrom() is designed for connectionless protocols like UDP to receive data and return the address of the sender.

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It is for TCP servers to accept new connections.

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It forces a socket to switch to UDP mode.

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It is used to receive large files in chunks.

Question 18

Why is the socket.socket() constructor typically called with socket.AF_INET and socket.SOCK_STREAM for a standard web server?

Accepted Answer

To provide a reliable, connection-oriented byte stream.. AF_INET defines IPv4 and SOCK_STREAM defines the TCP protocol, which are standard for HTTP.

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To enable UDP broadcast.

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To reduce latency for real-time video.

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To support raw IP packet injection.

Question 19

Which of the following is the correct way to close a socket object in Python?

Accepted Answer

socket.close(). The close() method should be called on the socket object to release the underlying file descriptor.

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socket.destroy()

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socket.shutdown()

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del socket

Question 20

What is the significance of the SO_BROADCAST option in a UDP socket?

Accepted Answer

It enables the socket to send packets to a broadcast address.. SO_BROADCAST is a prerequisite for sending packets to the broadcast address on a network interface.

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It allows the socket to handle incoming multicast traffic.

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It allows the socket to listen to all ports on a machine.

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It makes the socket connection-oriented.