Refactor Reactor and Client request buffering

Refactor Reactor into a more generic IO-with-timeout monitor,
using a Queue to simplify the implementation.
Move request-buffering logic into Server#reactor_wakeup.
Fixes bug in managing timeouts on clients.
Move, update and rewrite documentation to match updated class structure.

History.md

@@ -8,6 +8,7 @@
 
 * Refactor
   * Consolidate option handling in Server, Server small refactors, doc chang (#2389)
+  * Refactor Reactor and Client request buffering (#2279)
 
 ## 5.0.2 / 2020-09-28
 

lib/puma/client.rb

@@ -103,7 +103,12 @@ def in_data_phase
     end
 
     def set_timeout(val)
-      @timeout_at = Time.now + val
+      @timeout_at = Process.clock_gettime(Process::CLOCK_MONOTONIC) + val
+    end
+
+    # Number of seconds until the timeout elapses.
+    def timeout
+      [@timeout_at - Process.clock_gettime(Process::CLOCK_MONOTONIC), 0].max
     end
 
     def reset(fast_check=true)
@@ -255,14 +260,16 @@ def finish(timeout)
         rescue ThreadPool::ForceShutdown
           nil
         end
-        unless can_read
-          write_error(408) if in_data_phase
-          raise ConnectionError
-        end
+        timeout! unless can_read
       end
       true
     end
 
+    def timeout!
+      write_error(408) if in_data_phase
+      raise ConnectionError
+    end
+
     def write_error(status_code)
       begin
         @io << ERROR_RESPONSE[status_code]

lib/puma/queue_close.rb

@@ -0,0 +1,24 @@
+# Queue#close was added in Ruby 2.3.
+# Add a simple implementation for earlier Ruby versions.
+unless Queue.instance_methods.include?(:close)
+  class ClosedQueueError < StandardError; end
+  module Puma
+    module QueueClose
+      def initialize
+        @closed = false
+        super
+      end
+      def close
+        @closed = true
+      end
+      def closed?
+        @closed
+      end
+      def push(object)
+        raise ClosedQueueError if @closed
+        super
+      end
+    end
+    Queue.prepend QueueClose
+  end
+end