Buffer allocation and encoding in Node.js - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Buffer in Node.js?

A Buffer is a special object in Node.js used to store raw binary data. It helps handle data like files, network packets, or streams efficiently.

beginner

How do you allocate a Buffer of 10 bytes filled with zeros?

Use Buffer.alloc(10). This creates a Buffer of length 10 filled with zeros safely.

intermediate

What is the difference between Buffer.alloc() and Buffer.allocUnsafe()?

Buffer.alloc() creates a zero-filled Buffer for safety. Buffer.allocUnsafe() creates a Buffer faster but with old data inside, so you must overwrite it before use.

beginner

How do you convert a string to a Buffer with UTF-8 encoding?

Use Buffer.from('your string', 'utf8'). This encodes the string into bytes using UTF-8.

intermediate

What encoding options can you use when creating or converting Buffers?

Common encodings include 'utf8', 'ascii', 'base64', 'hex', and 'latin1'. They tell Node.js how to interpret or convert the bytes.

Which method creates a Buffer filled with zeros?

A Buffer.create(size)

B Buffer.allocUnsafe(size)

C Buffer.from(size)

D Buffer.alloc(size)

Buffer.alloc(size) creates a zero-filled Buffer safely.

What does Buffer.allocUnsafe(size) do?

A Creates a Buffer with uninitialized memory (old data)

B Creates a Buffer filled with zeros

C Creates a Buffer from a string

D Throws an error

Buffer.allocUnsafe(size) creates a Buffer quickly but with old data inside, so it is unsafe until overwritten.

How do you convert a string 'hello' to a Buffer with UTF-8 encoding?

A Buffer.alloc('hello')

B Buffer.encode('hello')

C Buffer.from('hello', 'utf8')

D Buffer.toString('hello')

Buffer.from('hello', 'utf8') converts the string to a Buffer using UTF-8 encoding.

Which encoding is NOT commonly used with Buffers?

A json

B base64

C utf8

D hex

'json' is not an encoding for Buffers; common encodings are utf8, base64, hex, ascii, and latin1.

Why should you be careful using Buffer.allocUnsafe()?

A It fills Buffer with zeros

B It may contain old sensitive data until overwritten

C It is slower than Buffer.alloc()

D It does not create a Buffer

Buffer.allocUnsafe() may contain old data, so you must overwrite it before use to avoid leaks.

Explain how to create a Buffer in Node.js and why encoding matters.

Think about how raw data and strings differ and how encoding helps convert between them.

Describe the risks and benefits of using Buffer.allocUnsafe() compared to Buffer.alloc().

Consider safety versus performance trade-offs.

Practice

1. What does Buffer.alloc(5) do in Node.js?

easy

A. Creates a buffer of length 5 filled with zeros

B. Creates a buffer of length 5 filled with random data

C. Creates a buffer from a string of length 5

D. Allocates memory but does not initialize the buffer

Solution

1. Step 1: Understand Buffer.alloc behavior

   Buffer.alloc(size) creates a buffer of the given size and fills it with zeros for safety.

2. Step 2: Apply to size 5

   Calling Buffer.alloc(5) creates a buffer of length 5 filled with zeros.

3. Final Answer:

   Creates a buffer of length 5 filled with zeros -> Option A

4. Quick Check:

   Buffer.alloc(5) = zero-filled buffer [OK]

Hint: Buffer.alloc always zero-fills the buffer size [OK]

Common Mistakes:

• Thinking Buffer.alloc fills with random data
• Confusing Buffer.alloc with Buffer.from
• Assuming buffer is uninitialized

2. Which of the following is the correct syntax to create a buffer from the string 'hello' using UTF-8 encoding?

easy

A. Buffer.alloc('hello', 'utf8')

B. Buffer.create('hello', 'utf8')

C. new Buffer('hello', 'utf8')

D. Buffer.from('hello', 'utf8')

Solution

1. Step 1: Identify correct Buffer creation method

   In modern Node.js, Buffer.from() creates a buffer from a string with encoding.

2. Step 2: Check syntax correctness

   Buffer.from('hello', 'utf8') is correct syntax; Buffer.alloc does not accept string input, and Buffer.create does not exist. new Buffer() is deprecated.

3. Final Answer:

   Buffer.from('hello', 'utf8') -> Option D

4. Quick Check:

   Use Buffer.from for string buffers [OK]

Hint: Use Buffer.from for strings, Buffer.alloc for size [OK]

Common Mistakes:

• Using Buffer.alloc with string input
• Using deprecated new Buffer()
• Using non-existent Buffer.create()

3. What will be the output of the following code?

const buf = Buffer.from('abc', 'utf8');
console.log(buf.length);

medium

A. 3

B. 6

C. 1

D. Error

Solution

1. Step 1: Understand Buffer.from with UTF-8 string

   The string 'abc' has 3 characters, each encoded as 1 byte in UTF-8.

2. Step 2: Check buffer length property

   The buffer length equals the number of bytes, so buf.length is 3.

3. Final Answer:

   3 -> Option A

4. Quick Check:

   UTF-8 'abc' length = 3 bytes [OK]

Hint: Buffer length equals byte count of string encoding [OK]

Common Mistakes:

• Assuming length is character count for multi-byte chars
• Expecting length to be string length property
• Confusing bytes with characters

4. Identify the error in this code snippet:

const buf = Buffer.alloc(5, 'abc');
console.log(buf.toString());

medium

A. Buffer.alloc cannot take a string as fill

B. toString() is not a Buffer method

C. No error, prints 'abcab'

D. Buffer.alloc size must be a string

Solution

1. Step 1: Check Buffer.alloc parameters

   Buffer.alloc(size, fill) accepts a size and a fill value. The fill can be a string, which repeats to fill the buffer.

2. Step 2: Understand fill behavior and toString()

   Filling 5 bytes with 'abc' repeats 'abcab'. toString() converts buffer back to string.

3. Final Answer:

   No error, prints 'abcab' -> Option C

4. Quick Check:

   Buffer.alloc fills string repeatedly [OK]

Hint: Buffer.alloc fills string repeatedly if fill is string [OK]

Common Mistakes:

• Thinking Buffer.alloc fill cannot be string
• Assuming toString() is invalid on Buffer
• Expecting error due to fill length mismatch

5. You want to create a buffer from the string 'café' and then convert it back to a string. Which encoding should you use to preserve the accented character correctly?

hard

A. 'ascii'

B. 'utf8'

C. 'base64'

D. 'hex'

Solution

1. Step 1: Understand character encoding for accented characters

   ASCII encoding cannot represent accented characters like 'é'. UTF-8 supports all Unicode characters including accented ones.

2. Step 2: Choose encoding for buffer creation and conversion

   Using 'utf8' ensures the accented character is preserved when converting to and from buffer.

3. Final Answer:

   'utf8' -> Option B

4. Quick Check:

   Use UTF-8 for accented characters [OK]

Hint: Use UTF-8 to handle accented characters correctly [OK]

Common Mistakes:

• Using ASCII which drops accents
• Using base64 or hex which are encoding formats, not text encodings
• Confusing base64 with UTF-8