Improve flow control handling allowing connection local window to have desired high water mark.

Author: ioquatix

lib/protocol/http2/connection.rb

@@ -55,8 +55,8 @@ def initialize(framer, local_stream_id)
 				@decoder = HPACK::Context.new
 				@encoder = HPACK::Context.new
 
-				@local_window = Window.new(@local_settings.initial_window_size)
-				@remote_window = Window.new(@remote_settings.initial_window_size)
+				@local_window = LocalWindow.new
+				@remote_window = Window.new
 			end
 
 			def id
@@ -183,13 +183,6 @@ def send_settings(changes)
 				frame.pack(changes)
 
 				write_frame(frame)
-				
-				# If the initial window size is set to something bigger than the default, we want to increase it.
-				difference = @local_settings.pending.initial_window_size - @local_window.capacity
-				
-				if difference > 0
-					send_window_update(difference)
-				end
 			end
 
 			# Transition the connection into the closed state.
@@ -235,6 +228,8 @@ def update_local_settings(changes)
 				@streams.each_value do |stream|
 					stream.local_window.capacity = capacity
 				end
+				
+				@local_window.desired = capacity
 			end
 
 			def update_remote_settings(changes)

lib/protocol/http2/flow_controlled.rb

@@ -60,13 +60,14 @@ def update_local_window(frame)
 			end
 
 			def consume_local_window(frame)
+				# For flow-control calculations, the 9-octet frame header is not counted.
 				amount = frame.length
 				@local_window.consume(amount)
 			end
 
 			def request_window_update
 				if @local_window.limited?
-					self.send_window_update(@local_window.used)
+					self.send_window_update(@local_window.wanted)
 				end
 			end
 

lib/protocol/http2/window_update_frame.rb

@@ -33,10 +33,6 @@ def initialize(capacity = 0xFFFF)
 				@capacity = capacity
 			end
 
-			def dup
-				return self.class.new(@capacity)
-			end
-			
 			# The window is completely full?
 			def full?
 				@available <= 0
@@ -73,6 +69,10 @@ def expand(amount)
 				end
 			end
 
+			def wanted
+				@used
+			end
+			
 			def limited?
 				@available < (@capacity / 2)
 			end
@@ -82,6 +82,30 @@ def to_s
 			end
 		end
 
+		# This is a window which efficiently maintains a desired capacity.
+		class LocalWindow < Window
+			def initialize(capacity = 0xFFFF, desired: nil)
+				super(capacity)
+				
+				@desired = desired
+			end
+			
+			attr_accessor :desired
+			
+			def wanted
+				if @desired
+					# We must send an update which allows at least @desired bytes to be sent.
+					(@desired - @capacity) + @used
+				else
+					@used
+				end
+			end
+			
+			def limited?
+				@available < ((@desired || @capacity) / 2)
+			end
+		end
+		
 		# The WINDOW_UPDATE frame is used to implement flow control.
 		#
 		# +-+-------------------------------------------------------------+

spec/protocol/http2/window_spec.rb

@@ -87,7 +87,7 @@
 		expect(frame.unpack).to eq 120
 	end
 
-	context '#receive_window_update' do
+	describe '#receive_window_update' do
 		it "should be invoked when window update is received" do
 			# Write 200 bytes of data (client -> server) which exhausts server local window
 			stream.send_data("*" * 200)