Buffer and streams relationship in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the role of a Buffer in Node.js streams?

In Node.js, when working with streams, what is the main purpose of a Buffer?

A It temporarily holds chunks of data to manage flow between fast and slow streams.

B It permanently stores all data from a stream for later use.

C It converts streams into JSON objects automatically.

D It encrypts data passing through the stream for security.

💡 Hint

Think about how data flows smoothly between parts that work at different speeds.

A Buffer in Node.js streams temporarily stores chunks of data to help manage the flow between fast data producers and slower consumers. This prevents data loss or overload.

❓ component_behavior

intermediate

What happens when a readable stream's internal buffer is full?

Consider a readable stream in Node.js. What occurs when its internal buffer reaches its highWaterMark limit?

A The stream discards new incoming data until space is available.

B The stream throws an error and closes immediately.

C The stream pauses reading from the source until the buffer is drained.

D The stream automatically increases the buffer size without pausing.

💡 Hint

Think about how streams prevent memory overload by controlling reading speed.

When the internal buffer hits the highWaterMark, the readable stream pauses reading from the source to prevent memory overload until some data is consumed and the buffer has space again.

📝 Syntax

advanced

Identify the correct way to create a Buffer from a stream chunk

Given a chunk of data from a readable stream, which code correctly creates a Buffer from it in Node.js?

Node.js

stream.on('data', (chunk) => {
  // create buffer here
});

A const buf = new Buffer(chunk);

B const buf = Buffer.from(chunk);

C const buf = Buffer.alloc(chunk);

D const buf = Buffer.create(chunk);

💡 Hint

Use the modern, safe method to create buffers from data.

Buffer.from() is the recommended way to create a Buffer from existing data like a stream chunk. The new Buffer() constructor is deprecated, and Buffer.alloc() creates an empty buffer of a specified size.

❓ state_output

advanced

What is the output when piping a readable stream to a writable stream with backpressure?

Consider this Node.js code snippet: const { Readable, Writable } = require('stream'); const readable = Readable.from(['a', 'b', 'c']); const writable = new Writable({ write(chunk, encoding, callback) { setTimeout(() => { console.log(chunk.toString()); callback(); }, 100); } }); readable.pipe(writable); What will be the order and timing of the console output?

A The letters 'a', 'b', 'c' print in order with about 100ms delay between each.

B All letters print immediately at once without delay.

C Only 'a' prints, then the program stops due to backpressure.

D The letters print in reverse order: 'c', 'b', 'a'.

💡 Hint

Think about how backpressure slows down writing but keeps order.

The writable stream simulates slow writing with a 100ms delay per chunk. Backpressure causes the readable stream to wait, so chunks print in order with delays.

🔧 Debug

expert

Why does this stream pipeline cause a memory leak?

Examine this Node.js code: const fs = require('fs'); const { Transform } = require('stream'); const readStream = fs.createReadStream('largefile.txt'); const transformStream = new Transform({ transform(chunk, encoding, callback) { // process chunk callback(null, chunk); } }); readStream.pipe(transformStream); // No pipe to writable stream or data event listener Why might this code cause a memory leak?

A Because the pipe method requires a third argument to work properly.

B Because the transform stream is missing the flush method.

C Because the file 'largefile.txt' does not exist, causing an error.

D Because the readable stream's data is not consumed, its internal buffer fills up indefinitely.

💡 Hint

Think about what happens if data is produced but never read or consumed.

If a readable stream pipes into a transform stream but the transform stream's output is not consumed (no pipe or data listener), the internal buffers fill up, causing a memory leak.