Rate limit headers (X-RateLimit) in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this rate limit header parsing code?

Given this HTTP response header string, what will the printed output be?

Rest API

headers = {
    'X-RateLimit-Limit': '1000',
    'X-RateLimit-Remaining': '250',
    'X-RateLimit-Reset': '1672531200'
}

limit = int(headers.get('X-RateLimit-Limit', 0))
remaining = int(headers.get('X-RateLimit-Remaining', 0))
reset = int(headers.get('X-RateLimit-Reset', 0))

print(f"Limit: {limit}, Remaining: {remaining}, Reset: {reset}")

A Limit: 1000, Remaining: 0, Reset: 1672531200

B Limit: 1000, Remaining: 250, Reset: 1672531200

C Limit: 0, Remaining: 0, Reset: 0

D Limit: 1000, Remaining: 250, Reset: 0

💡 Hint

Check how the get method retrieves values and the default values used.

The code extracts the three rate limit headers and converts them to integers. Since all headers exist, the values are parsed correctly.

🧠 Conceptual

intermediate

What does the X-RateLimit-Reset header represent?

In REST APIs, what does the X-RateLimit-Reset header usually indicate?

A The time when the rate limit window resets, usually as a UNIX timestamp

B The total number of allowed requests in the current window

C The duration in seconds until the rate limit resets

D The number of requests remaining before the limit is reached

💡 Hint

Think about what a timestamp represents compared to a duration.

X-RateLimit-Reset typically gives the exact time (UNIX timestamp) when the rate limit window resets, not a count or duration.

🔧 Debug

advanced

Why does this code raise a ValueError when parsing rate limit headers?

Consider this code snippet that parses rate limit headers:

limit = int(headers['X-RateLimit-Limit'])
remaining = int(headers['X-RateLimit-Remaining'])
reset = int(headers['X-RateLimit-Reset'])

Sometimes it raises ValueError. Why?

A The headers dictionary is immutable, so int() cannot convert values

B Headers might be missing, causing a KeyError, not ValueError

C Header values might be empty strings or non-numeric, causing int() to fail

D The int() function cannot convert string numbers to integers

💡 Hint

Check what happens if the header value is not a valid number string.

If a header value is an empty string or contains letters, int() raises ValueError. This is common if the server sends malformed headers.

📝 Syntax

advanced

Which option correctly sets rate limit headers in a Flask response?

You want to add rate limit headers to a Flask HTTP response. Which code snippet is correct?

Rest API

from flask import Flask, jsonify
app = Flask(__name__)

@app.route('/')
def index():
    response = jsonify(message='Hello')
    # Add headers here
    return response

A

response.headers['X-RateLimit-Limit'] = '500'
response.headers['X-RateLimit-Remaining'] = '100'
response.headers['X-RateLimit-Reset'] = '1672531200'

B

response.set_header('X-RateLimit-Limit', '500')
response.set_header('X-RateLimit-Remaining', '100')
response.set_header('X-RateLimit-Reset', '1672531200')

C

response.headers.add('X-RateLimit-Limit', 500)
response.headers.add('X-RateLimit-Remaining', 100)
response.headers.add('X-RateLimit-Reset', 1672531200)

D

response.headers = {
    'X-RateLimit-Limit': 500,
    'X-RateLimit-Remaining': 100,
    'X-RateLimit-Reset': 1672531200
}

💡 Hint

Check how to assign headers in Flask response objects.

Flask response headers are a dictionary-like object. You assign string values by key. Methods like set_header or add do not exist. Replacing the entire headers dict is not allowed.

🚀 Application

expert

How many requests remain after this sequence of API calls with rate limit headers?

An API returns these headers on each call:

X-RateLimit-Limit: 10
X-RateLimit-Remaining: 7
X-RateLimit-Reset: 1700000000

You make 3 calls in a row, each returning the same headers but with X-RateLimit-Remaining decreasing by 1 each time. What is the X-RateLimit-Remaining value after the third call?

A 0

B 7

C 10

D 4

💡 Hint

Subtract one remaining request per call from the initial remaining count.

Starting with 7 remaining, after 3 calls each reducing remaining by 1, the remaining is 7 - 3 = 4.