Provides a generic rate limiter for node.js. Useful for API clients, web crawling, or other tasks that need to be throttled. Two classes are exposed, RateLimiter and TokenBucket. TokenBucket provides a lower level interface to rate limiting with a configurable burst rate and drip rate. RateLimiter sits on top of the token bucket and adds a restriction on the maximum number of tokens that can be removed each interval to comply with common API restrictions like "150 requests per hour maximum".
Use NPM to install:
npm install limiter
A simple example allowing 150 requests per hour:
var RateLimiter = RateLimiter;// Allow 150 requests per hour (the Twitter search limit). Also understands// 'second', 'minute', 'day', or a number of millisecondsvar limiter = 150 'hour';// Throttle requestslimiter;
Another example allowing one message to be sent every 250ms:
var RateLimiter = RateLimiter;var limiter = 1 250;limiter;
The default behaviour is to wait for the duration of the rate limiting
that’s currently in effect before the callback is fired, but if you
true as the third parameter, the callback will be fired
immediately with remainingRequests set to -1:
var RateLimiter = RateLimiter;var limiter = 150 'hour' true; // fire CB immediately// Immediately send 429 header to client when rate limiting is in effectlimiter;
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.
var RateLimiter = RateLimiter;var limiter = 10 'second';if limiterconsole;elseconsole;
To get the number of remaining tokens outside the
simply use the
var RateLimiter = RateLimiter;var limiter = 1 250;// returns 1 since we did not remove a token and our number of tokens per interval is 1limiter;
Using the token bucket directly to throttle at the byte level:
var BURST_RATE = 1024 * 1024 * 150; // 150KB/sec burst ratevar FILL_RATE = 1024 * 1024 * 50; // 50KB/sec sustained ratevar TokenBucket = TokenBucket;// We could also pass a parent token bucket in as the last parameter to// create a hierarchical token bucketvar bucket = BURST_RATE FILL_RATE 'second' null;bucket;
Both the token bucket and rate limiter should be used with a message queue or some way of preventing multiple simultaneous calls to removeTokens(). Otherwise, earlier messages may get held up for long periods of time if more recent messages are continually draining the token bucket. This can lead to out of order messages or the appearance of "lost" messages under heavy load.
(The MIT License)
Copyright (c) 2013 John Hurliman. <email@example.com>
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
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