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b86127ad12
Currently, Discourse rate limits all incoming requests by the IP address they originate from regardless of the user making the request. This can be frustrating if there are multiple users using Discourse simultaneously while sharing the same IP address (e.g. employees in an office). This commit implements a new feature to make Discourse apply rate limits by user id rather than IP address for users at or higher than the configured trust level (1 is the default). For example, let's say a Discourse instance is configured to allow 200 requests per minute per IP address, and we have 10 users at trust level 4 using Discourse simultaneously from the same IP address. Before this feature, the 10 users could only make a total of 200 requests per minute before they got rate limited. But with the new feature, each user is allowed to make 200 requests per minute because the rate limits are applied on user id rather than the IP address. The minimum trust level for applying user-id-based rate limits can be configured by the `skip_per_ip_rate_limit_trust_level` global setting. The default is 1, but it can be changed by either adding the `DISCOURSE_SKIP_PER_IP_RATE_LIMIT_TRUST_LEVEL` environment variable with the desired value to your `app.yml`, or changing the setting's value in the `discourse.conf` file. Requests made with API keys are still rate limited by IP address and the relevant global settings that control API keys rate limits. Before this commit, Discourse's auth cookie (`_t`) was simply a 32 characters string that Discourse used to lookup the current user from the database and the cookie contained no additional information about the user. However, we had to change the cookie content in this commit so we could identify the user from the cookie without making a database query before the rate limits logic and avoid introducing a bottleneck on busy sites. Besides the 32 characters auth token, the cookie now includes the user id, trust level and the cookie's generation date, and we encrypt/sign the cookie to prevent tampering. Internal ticket number: t54739.
209 lines
4.5 KiB
Ruby
209 lines
4.5 KiB
Ruby
# frozen_string_literal: true
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# A redis backed rate limiter.
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class RateLimiter
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attr_reader :max, :secs, :user, :key, :error_code
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def self.key_prefix
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"l-rate-limit3:"
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end
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def self.disable
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@disabled = true
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end
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def self.enable
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@disabled = false
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end
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# We don't observe rate limits in test mode
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def self.disabled?
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@disabled
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end
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# Only used in test, only clears current namespace, does not clear globals
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def self.clear_all!
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Discourse.redis.delete_prefixed(RateLimiter.key_prefix)
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end
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def self.clear_all_global!
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Discourse.redis.without_namespace.keys("GLOBAL::#{key_prefix}*").each do |k|
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Discourse.redis.without_namespace.del k
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end
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end
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def build_key(type)
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"#{RateLimiter.key_prefix}:#{@user && @user.id}:#{type}"
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end
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def initialize(user, type, max, secs, global: false, aggressive: false, error_code: nil)
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@user = user
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@type = type
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@key = build_key(type)
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@max = max
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@secs = secs
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@global = global
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@aggressive = aggressive
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@error_code = error_code
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end
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def clear!
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redis.del(prefixed_key)
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end
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def can_perform?
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rate_unlimited? || is_under_limit?
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end
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def seconds_to_wait(now = Time.now.to_i)
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@secs - age_of_oldest(now)
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end
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# reloader friendly
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unless defined? PERFORM_LUA
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PERFORM_LUA = <<~LUA
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local now = tonumber(ARGV[1])
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local secs = tonumber(ARGV[2])
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local max = tonumber(ARGV[3])
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local key = KEYS[1]
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if ((tonumber(redis.call("LLEN", key)) < max) or
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(now - tonumber(redis.call("LRANGE", key, -1, -1)[1])) >= secs) then
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redis.call("LPUSH", key, now)
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redis.call("LTRIM", key, 0, max - 1)
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redis.call("EXPIRE", key, secs * 2)
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return 1
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else
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return 0
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end
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LUA
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PERFORM_LUA_SHA = Digest::SHA1.hexdigest(PERFORM_LUA)
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end
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unless defined? PERFORM_LUA_AGGRESSIVE
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PERFORM_LUA_AGGRESSIVE = <<~LUA
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local now = tonumber(ARGV[1])
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local secs = tonumber(ARGV[2])
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local max = tonumber(ARGV[3])
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local key = KEYS[1]
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local return_val = 0
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if ((tonumber(redis.call("LLEN", key)) < max) or
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(now - tonumber(redis.call("LRANGE", key, -1, -1)[1])) >= secs) then
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return_val = 1
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else
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return_val = 0
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end
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redis.call("LPUSH", key, now)
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redis.call("LTRIM", key, 0, max - 1)
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redis.call("EXPIRE", key, secs * 2)
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return return_val
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LUA
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PERFORM_LUA_AGGRESSIVE_SHA = Digest::SHA1.hexdigest(PERFORM_LUA_AGGRESSIVE)
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end
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def performed!(raise_error: true)
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return true if rate_unlimited?
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now = Time.now.to_i
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if ((max || 0) <= 0) || rate_limiter_allowed?(now)
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raise RateLimiter::LimitExceeded.new(seconds_to_wait(now), @type, @error_code) if raise_error
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false
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else
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true
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end
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rescue Redis::CommandError => e
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if e.message =~ /READONLY/
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# TODO,switch to in-memory rate limiter
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else
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raise
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end
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end
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def rollback!
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return if RateLimiter.disabled?
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redis.lpop(prefixed_key)
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rescue Redis::CommandError => e
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if e.message =~ /READONLY/
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# TODO,switch to in-memory rate limiter
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else
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raise
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end
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end
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def remaining
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return @max if @user && @user.staff?
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arr = redis.lrange(prefixed_key, 0, @max) || []
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t0 = Time.now.to_i
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arr.reject! { |a| (t0 - a.to_i) > @secs }
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@max - arr.size
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end
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private
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def rate_limiter_allowed?(now)
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lua, lua_sha = nil
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if @aggressive
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lua = PERFORM_LUA_AGGRESSIVE
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lua_sha = PERFORM_LUA_AGGRESSIVE_SHA
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else
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lua = PERFORM_LUA
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lua_sha = PERFORM_LUA_SHA
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end
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eval_lua(lua, lua_sha, [prefixed_key], [now, @secs, @max]) == 0
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end
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def prefixed_key
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if @global
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"GLOBAL::#{key}"
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else
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Discourse.redis.namespace_key(key)
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end
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end
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def redis
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Discourse.redis.without_namespace
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end
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def age_of_oldest(now)
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# age of oldest event in buffer, in seconds
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now - redis.lrange(prefixed_key, -1, -1).first.to_i
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end
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def is_under_limit?
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now = Time.now.to_i
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# number of events in buffer less than max allowed? OR
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(redis.llen(prefixed_key) < @max) ||
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# age bigger than sliding window size?
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(age_of_oldest(now) >= @secs)
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end
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def rate_unlimited?
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!!(RateLimiter.disabled? || (@user && @user.staff?))
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end
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def eval_lua(lua, sha, keys, args)
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redis.evalsha(sha, keys, args)
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rescue Redis::CommandError => e
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if e.to_s =~ /^NOSCRIPT/
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redis.eval(lua, keys, args)
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else
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raise
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end
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end
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end
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