Memcached::RateLimit

Sliding window rate limiting with Memcached

SYNOPSIS

use Memcached::RateLimit;

my $rl = Memcached::RateLimit->new("memcache://localhost:11211");
$rl->error_handler(sub ($rl, $message) {
  warn "rate limit error: $message";
});

# allow 30 requests per minute
if($rl->rate_limit("resource", 1, 30, 60))
{
  # rate limit exceeded
}

DESCRIPTION

This module implements rate limiting logic. It is intended for high volume websites that require limits on the access or modification to resources. It is implemented using Rust and FFI::Platypus, so you will need the rust toolchain in order to install this module.

Why Rust? Well none of the Perl Memcache clients I found supported TLS, and the Rust memcache crate did. Also Rust is fast and has a number of safety checks that give me confidence that it won't crash our app.

The actual algorithm is based one used by Bugzilla, and by default it will "fail open", meaning if for some reason the client cannot connect to the Memcached server, it will allow the request.

CONSTRUCTOR

new

my $rl = Memcached::RateLimit->new($url);
my $rl = Memcached::RateLimit->new(\%config);

Create a new instance of Memcached::RateLimit. The URL should be of the form shown in the synopsis above.

The following schemes are supported:

• memcache
• memcache+tcp
• memcache+tls
• memcache+udp
• memcache+unix

You can append these query parameters to the URL:

• connect_timeout

  Connect timeout in seconds. May be specified as a floating point, that is 0.2 is 20 milliseconds.

• protocol

  If set to ascii this will use the ASCII protocol instead of binary.

• tcp_nodelay

  Boolean true or false.

• timeout

  IO timeout in seconds. May be specified as a floating point, that is 0.2 is 20 milliseconds.

• verify_mode

  For TLS, this can be set to none or peer.

[version 0.03]

You can provide a %Config hash instead of a URL. All of the query parameters mentioned above can be provided in addition to these:

• scheme

  The scheme (example: memcache or memcache+tls).

• host

  The server hostname or IPv4/IPv6 address.

• port

  The TCP or UDP port to connect to.

• read_timeout

  The read timeout in seconds. May be specified as a floating point, that is 0.2 is 20 milliseconds.

• write_timeout

  The write timeout in seconds. May be specified as a floating point, that is 0.2 is 20 milliseconds.

• retry

  [version 0.04]

  The default instance number of retries.

METHODS

rate_limit

my $limited = $rl->rate_limt($name, $size, $rate_max, $rate_seconds);
my $limited = $rl->rate_limt($name, $size, $rate_max, $rate_seconds, $retry);

This method returns a boolean true, if a request of $size exceeds the rate limit of $rate_max over the past $rate_seconds. If you only want to rate limit the number of requests then you can set $size to 1.

This method will return a boolean false, and increment the appropriate counters if the requests fits within the rate limit.

This method will also return boolean false, if it is unable to connect to or otherwise experiences an error talking to the memcached server. In this case it will also call the error handler.

[version 0.04]

If $retry is provided then if there are errors talking to memcached, it will be attempted $retry times. If this parameter is not provided, then the default instance retry limit will be used, and if there is not instance default the class default of 1 will be used.

set_read_timeout

$rl->set_read_timeout($secs);

Sets the IO Read timeout to $secs, may be fractional.

set_write_timeout

$rl->set_write_timeout($secs);

Sets the IO Write timeout to $secs, may be fractional.

error_handler

$rl->error_handler(sub ($rl, $message) {
  ...
});

This method will set the error handler, to be called in the case of an error with the memcached server. It will pass in the instance of Memcached::RateLimit as $rl and a diagnostic as $message. Since this module will fail open, it is probably useful to increment error counters and provide diagnostics with this method to your monitoring system.

final_error_handler

[version 0.04]

$rl->final_error_handler(sub ($rl, $message) {
});

This method is like the error_handler method, but it only gets called at the end if none of the retry attempts succeed. The last error message is passed in.

SEE ALSO

• Cache::Memcached::Fast
• Redis::RateLimit

AUTHOR

Author: Graham Ollis [email protected]

Contributors:

Dylan Hardison (DHARDISON)

COPYRIGHT AND LICENSE

This software is copyright (c) 2022 by Graham Ollis.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.