feat(rate-limiter): add Prism and RateLimiter

lib/prism/rate_limiter/memory_store.rb

@@ -0,0 +1,57 @@
+require 'monitor'
+
+module Prism
+  module RateLimiter
+    # In-process fixed-window counter + ban list, guarded by a Monitor so
+    # concurrent requests (threaded server, parallel test threads) do not
+    # race on the same key. Lost on process restart - use PStoreStore when
+    # limits need to survive that.
+    class MemoryStore
+      include MonitorMixin
+
+      Window = Struct.new(:started_at, :count)
+
+      def initialize
+        super()
+        @windows = {}
+        @bans = {}
+      end
+
+      def count(key, period)
+        synchronize do
+          now = Time.now
+          window = @windows[key]
+          if window.nil? || now - window.started_at >= period
+            window = Window.new(now, 0)
+            @windows[key] = window
+          end
+          window.count += 1
+        end
+      end
+
+      def banned?(key)
+        synchronize do
+          expires_at = @bans[key]
+          next false unless expires_at
+          if Time.now >= expires_at
+            @bans.delete(key)
+            false
+          else
+            true
+          end
+        end
+      end
+
+      def ban!(key, duration)
+        synchronize { @bans[key] = Time.now + duration }
+      end
+
+      def reset!
+        synchronize do
+          @windows.clear
+          @bans.clear
+        end
+      end
+    end
+  end
+end

lib/prism/rate_limiter/pstore_store.rb

@@ -0,0 +1,62 @@
+require 'pstore'
+require 'fileutils'
+
+module Prism
+  module RateLimiter
+    # PStore-backed fixed-window counter + ban list, same contract as
+    # MemoryStore, but durable: limits and bans survive a process
+    # restart, and multiple processes sharing one file share state
+    # (each PStore#transaction takes an exclusive flock on the file).
+    class PStoreStore
+      def initialize(path)
+        @path = path
+        directory = File.dirname(path)
+        FileUtils.mkdir_p(directory) unless directory == '.' || Dir.exist?(directory)
+        @pstore = PStore.new(path)
+        @pstore.transaction do
+          @pstore[:windows] ||= {}
+          @pstore[:bans] ||= {}
+        end
+      end
+
+      def count(key, period)
+        @pstore.transaction do
+          now = Time.now
+          started_at, current = @pstore[:windows][key]
+          if started_at.nil? || now - started_at >= period
+            started_at = now
+            current = 0
+          end
+          current += 1
+          @pstore[:windows][key] = [started_at, current]
+          current
+        end
+      end
+
+      def banned?(key)
+        @pstore.transaction do
+          expires_at = @pstore[:bans][key]
+          if expires_at.nil?
+            false
+          elsif Time.now >= expires_at
+            @pstore[:bans].delete(key)
+            false
+          else
+            true
+          end
+        end
+      end
+
+      def ban!(key, duration)
+        @pstore.transaction { @pstore[:bans][key] = Time.now + duration }
+      end
+
+      def reset!
+        @pstore.transaction do
+          @pstore[:windows] = {}
+          @pstore[:bans] = {}
+        end
+      end
+    end
+  end
+end