Extract Adapters, add Redis adapter (#18)

This also adds a Redis adapter and a Memory adapter. The Redis adapter is useful since it can be a continuation of Prorate in a way - but with conditional fillup added in.

The memory store is useful in a different way - it can be used as a reference implementation to test other adapters against. Also make the adapter configurable on the `Pecorino` module.

.github/workflows/ci.yml

@@ -2,37 +2,11 @@ name: CI
 
 on:
   - push
-  - pull_request
 
 env:
   BUNDLE_PATH: vendor/bundle
 
 jobs:
-  # lint:
-  #   name: Code Style
-  #   runs-on: ubuntu-22.04
-  #   if: github.event_name == 'push' || github.event.pull_request.head.repo.full_name != github.repository
-  #   strategy:
-  #     matrix:
-  #       ruby:
-  #         - '2.7'
-  #   steps:
-  #     - name: Checkout
-  #       uses: actions/checkout@v4
-  #     - name: Setup Ruby
-  #       uses: ruby/setup-ruby@v1
-  #       with:
-  #         ruby-version: ${{ matrix.ruby }}
-  #         bundler-cache: true
-  #     - name: Rubocop Cache
-  #       uses: actions/cache@v3
-  #       with:
-  #         path: ~/.cache/rubocop_cache
-  #         key: ${{ runner.os }}-rubocop-${{ hashFiles('.rubocop.yml') }}
-  #         restore-keys: |
-  #           ${{ runner.os }}-rubocop-
-  #     - name: Rubocop
-  #       run: bundle exec rubocop
   test:
     name: Tests
     runs-on: ubuntu-22.04
@@ -50,6 +24,11 @@ jobs:
         options: --health-cmd pg_isready --health-interval 10s --health-timeout 5s --health-retries 5
         ports:
           - 5432:5432
+      redis:
+        image: redis
+        options: --health-cmd "redis-cli ping" --health-interval 10s --health-timeout 5s --health-retries 5
+        ports:
+          - 6379:6379
     steps:
       - name: Checkout
         uses: actions/checkout@v4

CHANGELOG.md

@@ -1,3 +1,10 @@
+## 0.7.0
+
+- Allow `Pecorino.adapter` to be assigned, and add `adapter:` to all classes. This allows the adapter for Pecorino to be configured manually and overridden in an initializer.
+- Add Redis-based adapter derived from Prorate
+- Formalize and test the adapter API
+- Add a memory-based adapter for single-process applications (and as a reference)
+
 ## 0.6.0
 
 - Add `Pecorino::Block` for setting blocks directly. These are available both to `Throttle` with the same key and on their own. This can be used to set arbitrary blocks without having to configure a `Throttle` first.

README.md

@@ -2,7 +2,11 @@
 
 Pecorino is a rate limiter based on the concept of leaky buckets, or more specifically - based on the [generic cell rate](https://brandur.org/rate-limiting) algorithm. It uses your DB as the storage backend for the throttles. It is compact, easy to install, and does not require additional infrastructure. The approach used by Pecorino has been previously used by [prorate](https://github.com/WeTransfer/prorate) with Redis, and that approach has proven itself.
 
-Pecorino is designed to integrate seamlessly into any Rails application using a PostgreSQL or SQLite database (at the moment there is no MySQL support, we would be delighted if you could add it).
+Pecorino is designed to integrate seamlessly into any Rails application, and will use either:
+
+* A memory store (good enough if you have just 1 process)
+* A PostgreSQL or SQLite database (at the moment there is no MySQL support, we would be delighted if you could add it)
+* A Redis instance
 
 If you would like to know more about the leaky bucket algorithm: [this article](http://live.julik.nl/2022/08/the-unreasonable-effectiveness-of-leaky-buckets) or the [Wikipedia article](https://en.wikipedia.org/wiki/Leaky_bucket) are both good starting points. [This Wikipedia article](https://en.wikipedia.org/wiki/Generic_cell_rate_algorithm) describes the generic cell rate algorithm in more detail as well.
 

lib/pecorino.rb

@@ -7,24 +7,24 @@
 require_relative "pecorino/railtie" if defined?(Rails::Railtie)
 
 module Pecorino
-  autoload :Postgres, "pecorino/postgres"
-  autoload :Sqlite, "pecorino/sqlite"
   autoload :LeakyBucket, "pecorino/leaky_bucket"
   autoload :Block, "pecorino/block"
   autoload :Throttle, "pecorino/throttle"
   autoload :CachedThrottle, "pecorino/cached_throttle"
 
+  module Adapters
+    autoload :MemoryAdapter, "pecorino/adapters/memory_adapter"
+    autoload :PostgresAdapter, "pecorino/adapters/postgres_adapter"
+    autoload :SqliteAdapter, "pecorino/adapters/sqlite_adapter"
+    autoload :RedisAdapter, "pecorino/adapters/redis_adapter"
+  end
+
   # Deletes stale leaky buckets and blocks which have expired. Run this method regularly to
   # avoid accumulating too many unused rows in your tables.
   #
   # @return void
   def self.prune!
-    # Delete all the old blocks here (if we are under a heavy swarm of requests which are all
-    # blocked it is probably better to avoid the big delete)
-    ActiveRecord::Base.connection.execute("DELETE FROM pecorino_blocks WHERE blocked_until < NOW()")
-
-    # Prune buckets which are no longer used. No "uncached" needed here since we are using "execute"
-    ActiveRecord::Base.connection.execute("DELETE FROM pecorino_leaky_buckets WHERE may_be_deleted_after < NOW()")
+    adapter.prune
   end
 
   # Creates the tables and indexes needed for Pecorino. Call this from your migrations like so:
@@ -38,36 +38,41 @@ def self.prune!
   # @param active_record_schema[ActiveRecord::SchemaMigration] the migration through which we will create the tables
   # @return void
   def self.create_tables(active_record_schema)
-    active_record_schema.create_table :pecorino_leaky_buckets, id: :uuid do |t|
-      t.string :key, null: false
-      t.float :level, null: false
-      t.datetime :last_touched_at, null: false
-      t.datetime :may_be_deleted_after, null: false
-    end
-    active_record_schema.add_index :pecorino_leaky_buckets, [:key], unique: true
-    active_record_schema.add_index :pecorino_leaky_buckets, [:may_be_deleted_after]
+    adapter.create_tables(active_record_schema)
+  end
 
-    active_record_schema.create_table :pecorino_blocks, id: :uuid do |t|
-      t.string :key, null: false
-      t.datetime :blocked_until, null: false
-    end
-    active_record_schema.add_index :pecorino_blocks, [:key], unique: true
-    active_record_schema.add_index :pecorino_blocks, [:blocked_until]
+  # Allows assignment of an adapter for storing throttles. Normally this would be a subclass of `Pecorino::Adapters::BaseAdapter`, but
+  # you can assign anything you like. Set this in an initializer. By default Pecorino will use the adapter configured from your main
+  # database, but you can also create a separate database for it - or use Redis or memory storage.
+  #
+  # @param adapter[Pecorino::Adapters::BaseAdapter]
+  # @return [Pecorino::Adapters::BaseAdapter]
+  def self.adapter=(adapter)
+    @adapter = adapter
+  end
+
+  # Returns the currently configured adapter, or the default adapter from the main database
+  #
+  # @return [Pecorino::Adapters::BaseAdapter]
+  def self.adapter
+    @adapter || default_adapter_from_main_database
   end
 
   # Returns the database implementation for setting the values atomically. Since the implementation
   # differs per database, this method will return a different adapter depending on which database is
   # being used
-  def self.adapter
+  #
+  # @param adapter[Pecorino::Adapters::BaseAdapter]
+  def self.default_adapter_from_main_database
     model_class = ActiveRecord::Base
     adapter_name = model_class.connection.adapter_name
     case adapter_name
     when /postgres/i
-      Pecorino::Postgres.new(model_class)
+      Pecorino::Adapters::PostgresAdapter.new(model_class)
     when /sqlite/i
-      Pecorino::Sqlite.new(model_class)
+      Pecorino::Adapters::SqliteAdapter.new(model_class)
     else
-      raise "Pecorino does not support #{adapter_name} just yet"
+      raise "Pecorino does not support the #{adapter_name} database just yet"
     end
   end
 end

lib/pecorino/adapters/base_adapter.rb

@@ -0,0 +1,66 @@
+# frozen_string_literal: true
+
+# An adapter allows Pecorino throttles, leaky buckets and other
+# resources to interfact to a data storage backend - a database, usually.
+class Pecorino::Adapters::BaseAdapter
+  # Returns the state of a leaky bucket. The state should be a tuple of two
+  # values: the current level (Float) and whether the bucket is now at capacity (Boolean)
+  #
+  # @param key[String] the key of the leaky bucket
+  # @param capacity[Float] the capacity of the leaky bucket to limit to
+  # @param leak_rate[Float] how many tokens leak out of the bucket per second
+  # @return [Array]
+  def state(key:, capacity:, leak_rate:)
+    [0, false]
+  end
+
+  # Adds tokens to the leaky bucket. The return value is a tuple of two
+  # values: the current level (Float) and whether the bucket is now at capacity (Boolean)
+  #
+  # @param key[String] the key of the leaky bucket
+  # @param capacity[Float] the capacity of the leaky bucket to limit to
+  # @param leak_rate[Float] how many tokens leak out of the bucket per second
+  # @param n_tokens[Float] how many tokens to add
+  # @return [Array]
+  def add_tokens(key:, capacity:, leak_rate:, n_tokens:)
+    [0, false]
+  end
+
+  # Adds tokens to the leaky bucket conditionally. If there is capacity, the tokens will
+  # be added. If there isn't - the fillup will be rejected. The return value is a triplet of
+  # the current level (Float), whether the bucket is now at capacity (Boolean)
+  # and whether the fillup was accepted (Boolean)
+  #
+  # @param key[String] the key of the leaky bucket
+  # @param capacity[Float] the capacity of the leaky bucket to limit to
+  # @param leak_rate[Float] how many tokens leak out of the bucket per second
+  # @param n_tokens[Float] how many tokens to add
+  # @return [Array]
+  def add_tokens_conditionally(key:, capacity:, leak_rate:, n_tokens:)
+    [0, false, false]
+  end
+
+  # Sets a timed block for the given key - this is used when a throttle fires. The return value
+  # is not defined - the call should always succeed.
+  # @param key[String] the key of the block
+  # @param block_for[#to_f, Active Support Duration] the duration of the block, in seconds
+  def set_block(key:, block_for:)
+  end
+
+  # Returns the time until which a block for a given key is in effect. If there is no block in
+  # effect, the method should return `nil`. The return value is either a `Time` or `nil`
+  # @param key[String] the key of the block
+  def blocked_until(key:)
+  end
+
+  # Deletes leaky buckets which have an expiry value prior to now and throttle blocks which have
+  # now lapsed
+  # @return [void]
+  def prune
+  end
+
+  # Creates the database tables for Pecorino to operate, or initializes other
+  # schema-like resources the adapter needs to operate
+  def create_tables(active_record_schema)
+  end
+end

lib/pecorino/adapters/memory_adapter.rb

@@ -0,0 +1,147 @@
+# frozen_string_literal: true
+
+# A memory store for leaky buckets and blocks
+class Pecorino::Adapters::MemoryAdapter
+  class KeyedLock
+    def initialize
+      @locked_keys = Set.new
+      @lock_mutex = Mutex.new
+    end
+
+    def lock(key)
+      loop do
+        @lock_mutex.synchronize do
+          next if @locked_keys.include?(key)
+          @locked_keys << key
+          return
+        end
+      end
+    end
+
+    def unlock(key)
+      @lock_mutex.synchronize do
+        @locked_keys.delete(key)
+      end
+    end
+
+    def with(key)
+      lock(key)
+      yield
+    ensure
+      unlock(key)
+    end
+  end
+
+  def initialize
+    @buckets = {}
+    @blocks = {}
+    @lock = KeyedLock.new
+  end
+
+  # Returns the state of a leaky bucket. The state should be a tuple of two
+  # values: the current level (Float) and whether the bucket is now at capacity (Boolean)
+  def state(key:, capacity:, leak_rate:)
+    @lock.lock(key)
+    level, ts = @buckets[key]
+    @lock.unlock(key)
+
+    return [0, false] unless level
+
+    dt = get_mono_time - ts
+    level_after_leak = [0, level - (leak_rate * dt)].max
+    [level_after_leak.to_f, (level_after_leak - capacity) >= 0]
+  end
+
+  # Adds tokens to the leaky bucket. The return value is a tuple of two
+  # values: the current level (Float) and whether the bucket is now at capacity (Boolean)
+  def add_tokens(key:, capacity:, leak_rate:, n_tokens:)
+    add_tokens_with_lock(key, capacity, leak_rate, n_tokens, _conditionally = false)
+  end
+
+  # Adds tokens to the leaky bucket conditionally. If there is capacity, the tokens will
+  # be added. If there isn't - the fillup will be rejected. The return value is a triplet of
+  # the current level (Float), whether the bucket is now at capacity (Boolean)
+  # and whether the fillup was accepted (Boolean)
+  def add_tokens_conditionally(key:, capacity:, leak_rate:, n_tokens:)
+    add_tokens_with_lock(key, capacity, leak_rate, n_tokens, _conditionally = true)
+  end
+
+  # Sets a timed block for the given key - this is used when a throttle fires. The return value
+  # is not defined - the call should always succeed.
+  def set_block(key:, block_for:)
+    raise ArgumentError, "block_for must be positive" unless block_for > 0
+    @lock.lock(key)
+    @blocks[key] = get_mono_time + block_for.to_f
+    Time.now + block_for.to_f
+  ensure
+    @lock.unlock(key)
+  end
+
+  # Returns the time until which a block for a given key is in effect. If there is no block in
+  # effect, the method should return `nil`. The return value is either a `Time` or `nil`
+  def blocked_until(key:)
+    blocked_until_monotonic = @blocks[key]
+    return unless blocked_until_monotonic
+
+    now_monotonic = get_mono_time
+    return unless blocked_until_monotonic > now_monotonic
+
+    Time.now + (blocked_until_monotonic - now_monotonic)
+  end
+
+  # Deletes leaky buckets which have an expiry value prior to now and throttle blocks which have
+  # now lapsed
+  def prune
+    now_monotonic = get_mono_time
+
+    @blocks.keys.each do |key|
+      @lock.with(key) do
+        @blocks.delete(key) if @blocks[key] && @blocks[key] < now_monotonic
+      end
+    end
+
+    @buckets.keys.each do |key|
+      @lock.with(key) do
+        _level, expire_at_monotonic = @buckets[key]
+        @buckets.delete(key) if expire_at_monotonic && expire_at_monotonic < now_monotonic
+      end
+    end
+  end
+
+  # No-op
+  def create_tables(active_record_schema)
+  end
+
+  private
+
+  def add_tokens_with_lock(key, capacity, leak_rate, n_tokens, conditionally)
+    @lock.lock(key)
+    now = get_mono_time
+    level, ts, _ = @buckets[key] || [0.0, now]
+
+    dt = now - ts
+    level_after_leak = clamp(0, level - (leak_rate * dt), capacity)
+    level_after_fillup = level_after_leak + n_tokens
+    if level_after_fillup > capacity && conditionally
+      return [level_after_leak, level_after_leak >= capacity, _did_accept = false]
+    end
+
+    clamped_level_after_fillup = clamp(0, level_after_fillup, capacity)
+    expire_after = now + (level_after_fillup / leak_rate)
+    @buckets[key] = [clamped_level_after_fillup, now, expire_after]
+
+    [clamped_level_after_fillup, clamped_level_after_fillup == capacity, _did_accept = true]
+  ensure
+    @lock.unlock(key)
+  end
+
+  def get_mono_time
+    Process.clock_gettime(Process::CLOCK_MONOTONIC)
+  end
+
+  def clamp(min, value, max)
+    return min if value < min
+    return max if value > max
+    value
+  end
+end