discourse/lib/rate_limiter.rb

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require_dependency 'rate_limiter/limit_exceeded'
require_dependency 'rate_limiter/on_create_record'
# A redis backed rate limiter.
class RateLimiter
def self.key_prefix
"l-rate-limit:"
end
def self.disable
@disabled = true
end
def self.enable
@disabled = false
end
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# We don't observe rate limits in test mode
def self.disabled?
@disabled || Rails.env.test?
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end
def self.clear_all!
$redis.delete_prefixed(RateLimiter.key_prefix)
end
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def initialize(user, key, max, secs)
@user = user
@key = "#{RateLimiter.key_prefix}:#{@user && @user.id}:#{key}"
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@max = max
@secs = secs
end
def clear!
$redis.del(@key)
end
def can_perform?
rate_unlimited? || is_under_limit?
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end
def performed!
return if rate_unlimited?
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if is_under_limit?
# simple ring buffer.
$redis.lpush(@key, Time.now.to_i)
$redis.ltrim(@key, 0, @max - 1)
# let's ensure we expire this key at some point, otherwise we have leaks
$redis.expire(@key, @secs * 2)
else
raise LimitExceeded.new(seconds_to_wait)
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end
end
def rollback!
return if RateLimiter.disabled?
$redis.lpop(@key)
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end
private
def seconds_to_wait
@secs - age_of_oldest
end
def age_of_oldest
# age of oldest event in buffer, in seconds
Time.now.to_i - $redis.lrange(@key, -1, -1).first.to_i
end
def is_under_limit?
# number of events in buffer less than max allowed? OR
($redis.llen(@key) < @max) ||
# age bigger than silding window size?
(age_of_oldest > @secs)
end
def rate_unlimited?
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!!(RateLimiter.disabled? || (@user && @user.staff?))
end
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end