141 lines
5.2 KiB
Markdown
141 lines
5.2 KiB
Markdown
# limiter #
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[](https://travis-ci.org/jhurliman/node-rate-limiter)
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[](https://www.npmjs.com/package/limiter)
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Provides a generic rate limiter for node.js. Useful for API clients, web
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crawling, or other tasks that need to be throttled. Two classes are exposed,
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RateLimiter and TokenBucket. TokenBucket provides a lower level interface to
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rate limiting with a configurable burst rate and drip rate. RateLimiter sits
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on top of the token bucket and adds a restriction on the maximum number of
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tokens that can be removed each interval to comply with common API
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restrictions like "150 requests per hour maximum".
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## Installation ##
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Use NPM to install:
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npm install limiter
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## Usage ##
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A simple example allowing 150 requests per hour:
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```javascript
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var RateLimiter = require('limiter').RateLimiter;
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// Allow 150 requests per hour (the Twitter search limit). Also understands
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// 'second', 'minute', 'day', or a number of milliseconds
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var limiter = new RateLimiter(150, 'hour');
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// Throttle requests
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limiter.removeTokens(1, function(err, remainingRequests) {
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// err will only be set if we request more than the maximum number of
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// requests we set in the constructor
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// remainingRequests tells us how many additional requests could be sent
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// right this moment
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callMyRequestSendingFunction(...);
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});
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```
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Another example allowing one message to be sent every 250ms:
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```javascript
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var RateLimiter = require('limiter').RateLimiter;
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var limiter = new RateLimiter(1, 250);
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limiter.removeTokens(1, function() {
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callMyMessageSendingFunction(...);
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});
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```
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The default behaviour is to wait for the duration of the rate limiting
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that’s currently in effect before the callback is fired, but if you
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pass in ```true``` as the third parameter, the callback will be fired
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immediately with remainingRequests set to -1:
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```javascript
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var RateLimiter = require('limiter').RateLimiter;
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var limiter = new RateLimiter(150, 'hour', true); // fire CB immediately
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// Immediately send 429 header to client when rate limiting is in effect
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limiter.removeTokens(1, function(err, remainingRequests) {
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if (remainingRequests < 0) {
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response.writeHead(429, {'Content-Type': 'text/plain;charset=UTF-8'});
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response.end('429 Too Many Requests - your IP is being rate limited');
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} else {
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callMyMessageSendingFunction(...);
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}
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});
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```
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A synchronous method, tryRemoveTokens(), is available in both RateLimiter and TokenBucket. This will return immediately with a boolean value indicating if the token removal was successful.
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```javascript
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var RateLimiter = require('limiter').RateLimiter;
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var limiter = new RateLimiter(10, 'second');
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if (limiter.tryRemoveTokens(5))
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console.log('Tokens removed');
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else
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console.log('No tokens removed');
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```
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To get the number of remaining tokens **outside** the `removeTokens`-callback
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simply use the `getTokensRemaining`-method.
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```javascript
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var RateLimiter = require('limiter').RateLimiter;
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var limiter = new RateLimiter(1, 250);
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// returns 1 since we did not remove a token and our number of tokens per interval is 1
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limiter.getTokensRemaining();
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```
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Using the token bucket directly to throttle at the byte level:
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```javascript
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var BURST_RATE = 1024 * 1024 * 150; // 150KB/sec burst rate
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var FILL_RATE = 1024 * 1024 * 50; // 50KB/sec sustained rate
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var TokenBucket = require('limiter').TokenBucket;
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// We could also pass a parent token bucket in as the last parameter to
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// create a hierarchical token bucket
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var bucket = new TokenBucket(BURST_RATE, FILL_RATE, 'second', null);
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bucket.removeTokens(myData.byteLength, function() {
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sendMyData(myData);
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});
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```
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## Additional Notes ##
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Both the token bucket and rate limiter should be used with a message queue or
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some way of preventing multiple simultaneous calls to removeTokens().
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Otherwise, earlier messages may get held up for long periods of time if more
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recent messages are continually draining the token bucket. This can lead to
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out of order messages or the appearance of "lost" messages under heavy load.
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## License ##
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(The MIT License)
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Copyright (c) 2013 John Hurliman. <jhurliman@jhurliman.org>
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Permission is hereby granted, free of charge, to any person obtaining
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a copy of this software and associated documentation files (the
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'Software'), to deal in the Software without restriction, including
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without limitation the rights to use, copy, modify, merge, publish,
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distribute, sublicense, and/or sell copies of the Software, and to
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permit persons to whom the Software is furnished to do so, subject to
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the following conditions:
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The above copyright notice and this permission notice shall be
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included in all copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND,
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EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
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CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
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TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
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SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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