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<?php
namespace bandwidthThrottle\tokenBucket;
use malkusch\lock\exception\MutexException;
use bandwidthThrottle\tokenBucket\storage\Storage;
use bandwidthThrottle\tokenBucket\storage\StorageException;
use bandwidthThrottle\tokenBucket\util\TokenConverter;
/**
* Token Bucket algorithm.
*
* The token bucket algorithm can be used for controlling the usage rate
* of a resource. The scope of that rate is determined by the underlying
* storage.
*
* Example:
* <code>
* 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();
* }
* </code>
*
* @author Markus Malkusch <[email protected]>
* @link bitcoin:1335STSwu9hST4vcMRppEPgENMHD2r1REK Donations
* @license WTFPL
*/
final class TokenBucket
{
/**
* @var Rate The rate.
*/
private $rate;
/**
* @var int Token capacity of this bucket.
*/
private $capacity;
/**
* @var Storage The storage.
*/
private $storage;
/**
* @var TokenConverter Token converter.
*/
private $tokenConverter;
/**
* Initializes the Token bucket.
*
* The storage determines the scope of the bucket.
*
* @param int $capacity positive capacity of the bucket
* @param Rate $rate rate
* @param Storage $storage storage
*/
public function __construct($capacity, Rate $rate, Storage $storage)
{
if ($capacity <= 0) {
throw new \InvalidArgumentException("Capacity should be greater than 0.");
}
$this->capacity = $capacity;
$this->rate = $rate;
$this->storage = $storage;
$this->tokenConverter = new TokenConverter($rate);
}
/**
* Bootstraps the storage with an initial amount of tokens.
*
* If the storage was already bootstrapped this method returns silently.
*
* While you could call bootstrap() on each request, you should not do that!
* This method will do unnecessary storage communications just to see that
* bootstrapping was performed already. You therefore should call that
* method in your application's bootstrap or deploy process.
*
* This method is threadsafe.
*
* @param int $tokens Initial amount of tokens, default is 0.
*
* @throws StorageException Bootstrapping failed.
* @throws \LengthException The initial amount of tokens is larger than the capacity.
*/
public function bootstrap($tokens = 0)
{
try {
if ($tokens > $this->capacity) {
throw new \LengthException(
"Initial token amount ($tokens) is larger than the capacity ($this->capacity)."
);
}
if ($tokens < 0) {
throw new \InvalidArgumentException(
"Initial token amount ($tokens) should be greater than 0."
);
}
$this->storage->getMutex()
->check(function () {
return !$this->storage->isBootstrapped();
})
->then(function () use ($tokens) {
$this->storage->bootstrap($this->tokenConverter->convertTokensToMicrotime($tokens));
});
} catch (MutexException $e) {
throw new StorageException("Could not lock bootstrapping", 0, $e);
}
}
/**
* Consumes tokens from the bucket.
*
* This method consumes only tokens if there are sufficient tokens available.
* If there aren't sufficient tokens, no tokens will be removed and the
* remaining seconds to wait are written to $seconds.
*
* This method is threadsafe.
*
* @param int $tokens The token amount.
* @param double &$seconds The seconds to wait.
*
* @return bool If tokens were consumed.
* @SuppressWarnings(PHPMD)
*
* @throws \LengthException The token amount is larger than the capacity.
* @throws StorageException The stored microtime could not be accessed.
*/
public function consume($tokens, &$seconds = 0)
{
try {
if ($tokens > $this->capacity) {
throw new \LengthException("Token amount ($tokens) is larger than the capacity ($this->capacity).");
}
if ($tokens <= 0) {
throw new \InvalidArgumentException("Token amount ($tokens) should be greater than 0.");
}
return $this->storage->getMutex()->synchronized(
function () use ($tokens, &$seconds) {
$tokensAndMicrotime = $this->loadTokensAndTimestamp();
$microtime = $tokensAndMicrotime["microtime"];
$availableTokens = $tokensAndMicrotime["tokens"];
$delta = $availableTokens - $tokens;
if ($delta < 0) {
$this->storage->letMicrotimeUnchanged();
$passed = microtime(true) - $microtime;
$seconds = max(0, $this->tokenConverter->convertTokensToSeconds($tokens) - $passed);
return false;
} else {
$microtime += $this->tokenConverter->convertTokensToSeconds($tokens);
$this->storage->setMicrotime($microtime);
$seconds = 0;
return true;
}
}
);
} catch (MutexException $e) {
throw new StorageException("Could not lock token consumption.", 0, $e);
}
}
/**
* Returns the token add rate.
*
* @return Rate The rate.
*/
public function getRate()
{
return $this->rate;
}
/**
* The token capacity of this bucket.
*
* @return int The capacity.
*/
public function getCapacity()
{
return $this->capacity;
}
/**
* Returns the currently available tokens of this bucket.
*
* This is a purely informative method. Use this method if you are
* interested in the amount of remaining tokens. Those tokens
* could be consumed instantly. This method will not consume any token.
* Use {@link consume()} to do so.
*
* This method will never return more than the capacity of the bucket.
*
* @return int amount of currently available tokens
* @throws StorageException The stored microtime could not be accessed.
*/
public function getTokens()
{
return $this->loadTokensAndTimestamp()["tokens"];
}
/**
* Loads the stored timestamp and its respective amount of tokens.
*
* This method is a convenience method to allow sharing code in
* {@link TokenBucket::getTokens()} and {@link TokenBucket::consume()}
* while accessing the storage only once.
*
* @throws StorageException The stored microtime could not be accessed.
* @return array tokens and microtime
*/
private function loadTokensAndTimestamp()
{
$microtime = $this->storage->getMicrotime();
// Drop overflowing tokens
$minMicrotime = $this->tokenConverter->convertTokensToMicrotime($this->capacity);
if ($minMicrotime > $microtime) {
$microtime = $minMicrotime;
}
$tokens = $this->tokenConverter->convertMicrotimeToTokens($microtime);
return [
"tokens" => $tokens,
"microtime" => $microtime
];
}
}