NodeJS Program to In-Memory Rate Limiter with Explanation
NodeJS
Hard
HTTP & APIs
31 views
1 min read
79 words
This problem helps you practice core NodeJS fundamentals in a practical way. It builds intuition around in-memory, rate, limiter. Let’s break it down step by step so you can implement it confidently.
Problem Statement
Limit to 3 requests per minute per key (demo counter).
Input Format
No input.
Output Format
Start server code.
Constraints
Use Map for counts.
Code Solution
This explanation is written for learning purposes and to help beginners understand the concept clearly.
const http = require('http');
const hits = new Map();
function allow(key) {
const now = Date.now();
const win = 60 * 1000;
const rec = hits.get(key) || { count: 0, start: now };
if (now - rec.start > win) {
rec.count = 0;
rec.start = now;
}
rec.count += 1;
hits.set(key, rec);
return rec.count <= 3;
}
const server = http.createServer((req, res) => {
const key = (req.socket.remoteAddress || 'local') + '|meetcode';
if (!allow(key)) {
res.writeHead(429, { 'Content-Type': 'text/plain' });
return res.end('Too many');
}
res.writeHead(200, { 'Content-Type': 'text/plain' });
res.end('OK');
});
server.listen(3006, () => console.log('http://localhost:3006'));
Output Example
No sample I/O is provided for this question.
Common Mistakes
- Misreading input/output format.
- Not handling constraints and edge cases.
- Off-by-one errors in loops.
- Forgetting to reset variables between test cases (if any).
Solution Guide
Problem
Limit to 3 requests per minute per key (demo counter).
Input / Output
Output
Start server code.
Constraints
Use Map for counts.
Details
Common Mistakes
- Misreading input/output format.
- Not handling constraints and edge cases.
- Off-by-one errors in loops.
- Forgetting to reset variables between test cases (if any).
Official Solution
const http = require('http');
const hits = new Map();
function allow(key) {
const now = Date.now();
const win = 60 * 1000;
const rec = hits.get(key) || { count: 0, start: now };
if (now - rec.start > win) {
rec.count = 0;
rec.start = now;
}
rec.count += 1;
hits.set(key, rec);
return rec.count <= 3;
}
const server = http.createServer((req, res) => {
const key = (req.socket.remoteAddress || 'local') + '|meetcode';
if (!allow(key)) {
res.writeHead(429, { 'Content-Type': 'text/plain' });
return res.end('Too many');
}
res.writeHead(200, { 'Content-Type': 'text/plain' });
res.end('OK');
});
server.listen(3006, () => console.log('http://localhost:3006'));
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