Request size limits in Express - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of setting request size limits in Express?

Request size limits help protect your server from very large requests that can slow down or crash your app. They stop clients from sending too much data at once.

beginner

How do you set a request size limit for JSON bodies in Express using built-in middleware?

Use express.json({ limit: 'size' }) where 'size' is a string like '100kb' or '1mb'. Example: app.use(express.json({ limit: '100kb' })) limits JSON body size to 100 kilobytes.

beginner

What happens if a client sends a request body larger than the set limit in Express?

Express will reject the request and send an error response (usually 413 Payload Too Large). This prevents the server from processing oversized data.

beginner

Which Express middleware can you use to limit URL-encoded form data size?

Use express.urlencoded({ limit: 'size' }) to limit the size of URL-encoded form data. For example, app.use(express.urlencoded({ limit: '50kb', extended: true })) limits form data to 50 kilobytes.

beginner

Why is it important to set request size limits in a real-world Express app?

Setting limits helps keep your app safe from attacks like denial of service, avoids memory overload, and improves performance by rejecting too large requests early.

Which Express middleware option sets the maximum size for JSON request bodies?

A express.limit({ size: '100kb' })

B express.static({ maxSize: '100kb' })

C express.json({ limit: '100kb' })

D express.urlencoded({ maxLength: '100kb' })

express.json({ limit: '100kb' }) correctly sets the max size for JSON bodies.

What HTTP status code does Express usually send when a request body is too large?

A 400 Bad Request

B 413 Payload Too Large

C 404 Not Found

D 500 Internal Server Error

413 Payload Too Large is the standard response when request size exceeds limits.

Which middleware limits URL-encoded form data size in Express?

A express.urlencoded()

B express.static()

C express.json()

D express.limit()

express.urlencoded() is used to parse and limit URL-encoded form data.

Why should you set request size limits in your Express app?

A To disable JSON parsing

B To allow unlimited data uploads

C To speed up client downloads

D To protect server from large requests that can cause crashes

Limits protect the server from very large requests that can slow or crash it.

How do you set a 1MB limit for JSON bodies in Express?

A app.use(express.json({ limit: '1mb' }))

B app.use(express.json({ maxSize: 1 }))

C app.use(express.urlencoded({ limit: '1mb' }))

D app.use(express.limit({ size: '1mb' }))

express.json({ limit: '1mb' }) sets the JSON body size limit to 1 megabyte.

Explain how to set request size limits for JSON and URL-encoded data in Express and why it matters.

Think about middleware options and server safety.

Describe what happens when a client sends a request larger than the allowed size limit in Express.

Focus on server response and behavior.

Practice

1. What is the main purpose of setting a request size limit in Express middleware like express.json()?

easy

A. To increase the speed of the server by caching requests

B. To prevent very large requests from slowing down or crashing the server

C. To automatically compress large requests for faster processing

D. To allow unlimited request sizes for flexibility

Solution

1. Step 1: Understand the role of request size limits

   Request size limits help protect the server from very large requests that can slow it down or cause crashes.

2. Step 2: Identify the correct purpose in Express middleware

   The limit option in express.json() sets this size limit to keep the server safe and responsive.

3. Final Answer:

   To prevent very large requests from slowing down or crashing the server -> Option B

4. Quick Check:

   Request size limit = prevent server overload [OK]

Hint: Request size limits protect server from overload [OK]

Common Mistakes:

• Thinking it speeds up requests by caching
• Confusing size limit with compression
• Assuming unlimited size is better

2. Which of the following is the correct way to set a 10kb limit on JSON request bodies in Express?

easy

A. app.use(express.json({ sizeLimit: 10 }))

B. app.use(express.json(limit = 10))

C. app.use(express.json({ maxSize: '10kb' }))

D. app.use(express.json({ limit: '10kb' }))

Solution

1. Step 1: Recall the correct option name for size limit

   The correct option to set request size limit in express.json() is limit.

2. Step 2: Check the correct syntax for setting 10kb

   The value should be a string with units, like '10kb'. So { limit: '10kb' } is correct.

3. Final Answer:

   app.use(express.json({ limit: '10kb' })) -> Option D

4. Quick Check:

   Use limit: '10kb' option [OK]

Hint: Use limit option with string size like '10kb' [OK]

Common Mistakes:

• Using wrong option names like sizeLimit or maxSize
• Passing number without units
• Using assignment inside options object

3. Given this Express setup:

app.use(express.json({ limit: '5kb' }));
app.post('/data', (req, res) => {
  res.send('Received');
});

What happens if a client sends a JSON body of 10kb to /data?

medium

A. The server rejects the request with a 413 Payload Too Large error

B. The server ignores the body and responds with an empty object

C. The server crashes due to memory overflow

D. The server accepts the request and responds with 'Received'

Solution

1. Step 1: Understand the limit setting effect

   The limit is set to 5kb, so any request body larger than 5kb will be rejected.

2. Step 2: Identify Express behavior on large requests

   Express responds with a 413 Payload Too Large error when the body exceeds the limit.

3. Final Answer:

   The server rejects the request with a 413 Payload Too Large error -> Option A

4. Quick Check:

   Request > limit = 413 error [OK]

Hint: Requests over limit get 413 error response [OK]

Common Mistakes:

• Assuming server accepts large requests anyway
• Thinking server crashes instead of error response
• Believing server ignores body silently

4. Consider this Express code snippet:

app.use(express.json({ limit: 10000 }));

What is the problem with this code regarding request size limits?

medium

A. There is no problem; this code sets a 10kb limit correctly

B. The limit option is not supported by express.json()

C. The limit value is too small and will reject all requests

D. The limit value should be a string with units like '10kb', not a number

Solution

1. Step 1: Check the type of the limit option value

   The limit option accepts both numbers (in bytes) and strings with units like '10kb'.

2. Step 2: Understand the effect of passing a number

   Passing 10000 sets the limit to 10000 bytes (approximately 10kb), which works correctly.

3. Final Answer:

   There is no problem; this code sets a 10kb limit correctly -> Option A

4. Quick Check:

   limit: number = bytes [OK]

Hint: Limit accepts number (bytes) or string with units [OK]

Common Mistakes:

• Thinking it must be string with units only
• Thinking limit option is unsupported
• Assuming number means bytes automatically is wrong

5. You want to accept JSON requests up to 1mb but URL-encoded form data only up to 100kb in your Express app. Which setup correctly applies these limits?

hard

A. app.use(express.json({ limit: 100 * 1024 }));\napp.use(express.urlencoded({ limit: 1 * 1024 * 1024, extended: false }));

B. app.use(express.json({ maxSize: '1mb' }));\napp.use(express.urlencoded({ maxSize: '100kb', extended: true }));

C. app.use(express.json({ limit: '1mb' }));\napp.use(express.urlencoded({ limit: '100kb', extended: true }));

D. app.use(express.json({ limit: '100kb' }));\napp.use(express.urlencoded({ limit: '1mb', extended: true }));

Solution

1. Step 1: Set JSON request limit to 1mb correctly

   Use express.json({ limit: '1mb' }) to set JSON body limit to 1 megabyte.

2. Step 2: Set URL-encoded form data limit to 100kb correctly

   Use express.urlencoded({ limit: '100kb', extended: true }) to set form data limit to 100 kilobytes.

3. Step 3: Verify option names and values

   Both use the correct limit option with string sizes and proper extended flag for URL-encoded.

4. Final Answer:

   app.use(express.json({ limit: '1mb' })); app.use(express.urlencoded({ limit: '100kb', extended: true })); -> Option C

5. Quick Check:

   Use limit strings per middleware type [OK]

Hint: Set limits separately with correct units and options [OK]

Common Mistakes:

• Swapping limits between JSON and URL-encoded
• Using numbers instead of strings for limits
• Using wrong option names like maxSize