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https://github.com/bandwidth-throttle/token-bucket

Implementation of the Token Bucket algorithm in PHP.
https://github.com/bandwidth-throttle/token-bucket

Last synced: 14 days ago
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Implementation of the Token Bucket algorithm in PHP.

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# Token Bucket



This is a threadsafe implementation of the [Token Bucket algorithm](https://en.wikipedia.org/wiki/Token_bucket)

in PHP. You can use a token bucket to limit an usage rate for a resource 

(e.g. a stream bandwidth or an API usage).



The token bucket is an abstract metaphor which doesn't have a direction of

the resource consumption. I.e. you can limit a rate for consuming or producing.

E.g. you can limit the consumption rate of a third party API service, or you

can limit the usage rate of your own API service.



# Installation



Use [Composer](https://getcomposer.org/):



```sh

composer require bandwidth-throttle/token-bucket

```



# Usage



The package is in the namespace

[`bandwidthThrottle\tokenBucket`](http://bandwidth-throttle.github.io/token-bucket/api/namespace-bandwidthThrottle.tokenBucket.html).



## Example



This example will limit the rate of a global resource to 10 requests per second

for all requests.



```php

use bandwidthThrottle\tokenBucket\Rate;

use bandwidthThrottle\tokenBucket\TokenBucket;

use bandwidthThrottle\tokenBucket\storage\FileStorage;



$storage = new FileStorage(__DIR__ . "/api.bucket");

$rate    = new Rate(10, Rate::SECOND);

$bucket  = new TokenBucket(10, $rate, $storage);

$bucket->bootstrap(10);



if (!$bucket->consume(1, $seconds)) {

    http_response_code(429);

    header(sprintf("Retry-After: %d", floor($seconds)));

    exit();

}



echo "API response";

```



Note: In this example `TokenBucket::bootstrap()` is part of the code. This is

not recommended for production, as this is producing unnecessary storage

communication. `TokenBucket::bootstrap()` should be part of the application's

bootstrap or deploy process.



## Scope of the storage



First you need to decide the scope of your resource. I.e. do you want to limit

it per request, per user or amongst all requests? You can do this by choosing a

[`Storage`](http://bandwidth-throttle.github.io/token-bucket/api/class-bandwidthThrottle.tokenBucket.storage.Storage.html)

implementation of the desired scope:



- The [`RequestScope`](http://bandwidth-throttle.github.io/token-bucket/api/class-bandwidthThrottle.tokenBucket.storage.scope.RequestScope.html)

limits the rate only within one request. E.g. to limit the bandwidth of a download.

Each requests will have the same bandwidth limit.



- The [`SessionScope`](http://bandwidth-throttle.github.io/token-bucket/api/class-bandwidthThrottle.tokenBucket.storage.scope.SessionScope.html)

limits the rate of a resource within a session. The rate is controlled over

all requests of one session. E.g. to limit the API usage per user.



- The [`GlobalScope`](http://bandwidth-throttle.github.io/token-bucket/api/class-bandwidthThrottle.tokenBucket.storage.scope.GlobalScope.html)

limits the rate of a resource for all processes (i.e. requests). E.g. to limit

the aggregated download bandwidth of a resource over all processes. This scope

permits race conditions between processes. The TokenBucket is therefore

synchronized on a shared mutex.



## TokenBucket



When you have your storage you can finally instantiate a

[`TokenBucket`](http://bandwidth-throttle.github.io/token-bucket/api/class-bandwidthThrottle.tokenBucket.TokenBucket.html).

The first parameter is the capacity of the bucket. I.e. there will be never

more tokens available. This also means that consuming more tokens than the

capacity is invalid.



The second parameter is the token-add-[`Rate`](http://bandwidth-throttle.github.io/token-bucket/api/class-bandwidthThrottle.tokenBucket.Rate.html).

It determines the speed for filling the bucket with tokens. The rate is the

amount of tokens added per unit, e.g. `new Rate(100, Rate::SECOND)`

would add 100 tokens per second.



The third parameter is the storage, which is used to persist the token amount

of the bucket. The storage does determine the scope of the bucket.



### Bootstrapping



A token bucket needs to be bootstrapped. While the method

[`TokenBucket::bootstrap()`](http://bandwidth-throttle.github.io/token-bucket/api/class-bandwidthThrottle.tokenBucket.TokenBucket.html#_bootstrap)

doesn't have any side effects on an already bootstrapped bucket, it is not

recommended do call it for every request. Better include that in your

application's bootstrap or deploy process.



### Consuming



Now that you have a bootstrapped bucket, you can start consuming tokens. The

method [`TokenBucket::consume()`](http://bandwidth-throttle.github.io/token-bucket/api/class-bandwidthThrottle.tokenBucket.TokenBucket.html#_consume)

will either return `true` if the tokens were consumed or `false` else.

If the tokens were consumed your application can continue to serve the resource.



Else if the tokens were not consumed you should not serve the resource.

In that case `consume()` did write a duration of seconds into its second parameter

(which was passed by reference). This is the duration until sufficient

tokens would be available.



## BlockingConsumer



In the first example we did either serve the request or fail with the HTTP status

code 429. This is actually a very resource efficient way of throtteling API

requests as it doesn't reserve resources on your server.



However sometimes

it is desirable not to fail but instead wait a little bit and then continue

serving the requests. You can do this by consuming the token bucket with

a [`BlockingConsumer`](http://bandwidth-throttle.github.io/token-bucket/api/class-bandwidthThrottle.tokenBucket.BlockingConsumer.html).



```php

use bandwidthThrottle\tokenBucket\Rate;

use bandwidthThrottle\tokenBucket\TokenBucket;

use bandwidthThrottle\tokenBucket\BlockingConsumer;

use bandwidthThrottle\tokenBucket\storage\FileStorage;



$storage  = new FileStorage(__DIR__ . "/api.bucket");

$rate     = new Rate(10, Rate::SECOND);

$bucket   = new TokenBucket(10, $rate, $storage);

$consumer = new BlockingConsumer($bucket);

$bucket->bootstrap(10);



// This will block until one token is available.

$consumer->consume(1);



echo "API response";

```



This will effectively limit the rate to 10 requests per seconds as well. But

in this case the client has not to bother with the 429 error. Instead the

connection is just delayed to the desired rate.



# License and authors



This project is free and under the WTFPL.

Responsible for this project is Markus Malkusch [email protected].



## Donations



If you like this project and feel generous donate a few Bitcoins here:

[1335STSwu9hST4vcMRppEPgENMHD2r1REK](bitcoin:1335STSwu9hST4vcMRppEPgENMHD2r1REK)



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