Introduce PRIORITY_UPDATE frame and priority tracking per stream.

fixtures/protocol/http2/a_frame.rb

@@ -3,6 +3,7 @@
 # Released under the MIT License.
 # Copyright, 2019-2024, by Samuel Williams.
 
+require "socket"
 require "protocol/http2/framer"
 
 module Protocol

lib/protocol/http2/client.rb

@@ -29,15 +29,25 @@ def send_connection_preface(settings = [])
 					@framer.write_connection_preface
 
 					# We don't support RFC7540 priorities:
-					settings = settings.to_a
-					settings << [Settings::NO_RFC7540_PRIORITIES, 1]
+					if settings.is_a?(Hash)
+						settings = settings.dup
+					else
+						settings = settings.to_h
+					end
+
+					unless settings.key?(Settings::NO_RFC7540_PRIORITIES)
+						settings = settings.dup
+						settings[Settings::NO_RFC7540_PRIORITIES] = 1
+					end
 
 					send_settings(settings)
 
 					yield if block_given?
 
 					read_frame do |frame|
-						raise ProtocolError, "First frame must be #{SettingsFrame}, but got #{frame.class}" unless frame.is_a? SettingsFrame
+						unless frame.is_a? SettingsFrame
+							raise ProtocolError, "First frame must be #{SettingsFrame}, but got #{frame.class}"
+						end
 					end
 				else
 					raise ProtocolError, "Cannot send connection preface in state #{@state}"

lib/protocol/http2/connection.rb

@@ -8,6 +8,7 @@
 require_relative "flow_controlled"
 
 require "protocol/hpack"
+require "protocol/http/header/priority"
 
 module Protocol
 	module HTTP2
@@ -400,6 +401,19 @@ def receive_push_promise(frame)
 				raise ProtocolError, "Unable to receive push promise!"
 			end
 
+			def receive_priority_update(frame)
+				if frame.stream_id != 0
+					raise ProtocolError, "Invalid stream id: #{frame.stream_id}"
+				end
+
+				stream_id, value = frame.unpack
+
+				# Apparently you can set the priority of idle streams, but I'm not sure why that makes sense, so for now let's ignore it.
+				if stream = @streams[stream_id]
+					stream.priority = Protocol::HTTP::Header::Priority.new(value)
+				end
+			end
+
 			def client_stream_id?(id)
 				id.odd?
 			end

lib/protocol/http2/framer.rb

@@ -14,6 +14,7 @@
 require_relative "goaway_frame"
 require_relative "window_update_frame"
 require_relative "continuation_frame"
+require_relative "priority_update_frame"
 
 module Protocol
 	module HTTP2
@@ -29,6 +30,13 @@ module HTTP2
 			GoawayFrame,
 			WindowUpdateFrame,
 			ContinuationFrame,
+			nil,
+			nil,
+			nil,
+			nil,
+			nil,
+			nil,
+			PriorityUpdateFrame,
 		].freeze
 
 		# Default connection "fast-fail" preamble string as defined by the spec.

lib/protocol/http2/priority_update_frame.rb

@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+# Released under the MIT License.
+# Copyright, 2019-2024, by Samuel Williams.
+
+require_relative "frame"
+require_relative "padded"
+require_relative "continuation_frame"
+
+module Protocol
+	module HTTP2
+		# The PRIORITY_UPDATE frame is used by clients to signal the initial priority of a response, or to reprioritize a response or push stream. It carries the stream ID of the response and the priority in ASCII text, using the same representation as the Priority header field value.
+		# 
+		# +-+-------------+-----------------------------------------------+
+		# |R|                 Prioritized Stream ID (31)                  |
+		# +-+-----------------------------+-------------------------------+
+		# |                    Priority Field Value (*)                 ...
+		# +---------------------------------------------------------------+
+		#
+		class PriorityUpdateFrame < Frame
+			TYPE = 0x10
+			FORMAT = "N".freeze
+
+			def unpack
+				data = super
+
+				prioritized_stream_id = data.unpack1(FORMAT)
+
+				return prioritized_stream_id, data.byteslice(4, data.bytesize - 4)
+			end
+
+			def pack(prioritized_stream_id, data, **options)
+				super([prioritized_stream_id].pack(FORMAT) + data, **options)
+			end
+
+			def apply(connection)
+				connection.receive_priority_update(self)
+			end
+		end
+	end
+end

lib/protocol/http2/server.rb

@@ -29,8 +29,16 @@ def read_connection_preface(settings = [])
 					@framer.read_connection_preface
 
 					# We don't support RFC7540 priorities:
-					settings = settings.to_a
-					settings << [Settings::NO_RFC7540_PRIORITIES, 1]
+					if settings.is_a?(Hash)
+						settings = settings.dup
+					else
+						settings = settings.to_h
+					end
+
+					unless settings.key?(Settings::NO_RFC7540_PRIORITIES)
+						settings = settings.dup
+						settings[Settings::NO_RFC7540_PRIORITIES] = 1
+					end
 
 					send_settings(settings)
 

lib/protocol/http2/settings_frame.rb

@@ -27,8 +27,22 @@ class Settings
 				:maximum_header_list_size=,
 				nil,
 				:enable_connect_protocol=,
+				:no_rfc7540_priorities=,
 			]
 
+			def initialize
+				# These limits are taken from the RFC:
+				# https://tools.ietf.org/html/rfc7540#section-6.5.2
+				@header_table_size = 4096
+				@enable_push = 1
+				@maximum_concurrent_streams = 0xFFFFFFFF
+				@initial_window_size = 0xFFFF # 2**16 - 1
+				@maximum_frame_size = 0x4000 # 2**14
+				@maximum_header_list_size = 0xFFFFFFFF
+				@enable_connect_protocol = 0
+				@no_rfc7540_priorities = 0
+			end
+
 			# Allows the sender to inform the remote endpoint of the maximum size of the header compression table used to decode header blocks, in octets.
 			attr_accessor :header_table_size
 
@@ -91,16 +105,18 @@ def enable_connect_protocol?
 				@enable_connect_protocol == 1
 			end
 
-			def initialize
-				# These limits are taken from the RFC:
-				# https://tools.ietf.org/html/rfc7540#section-6.5.2
-				@header_table_size = 4096
-				@enable_push = 1
-				@maximum_concurrent_streams = 0xFFFFFFFF
-				@initial_window_size = 0xFFFF # 2**16 - 1
-				@maximum_frame_size = 0x4000 # 2**14
-				@maximum_header_list_size = 0xFFFFFFFF
-				@enable_connect_protocol = 0
+			attr :no_rfc7540_priorities
+
+			def no_rfc7540_priorities= value
+				if value == 0 or value == 1
+					@no_rfc7540_priorities = value
+				else
+					raise ProtocolError, "Invalid value for no_rfc7540_priorities: #{value}"
+				end
+			end
+
+			def no_rfc7540_priorities?
+				@no_rfc7540_priorities == 1
 			end
 
 			def update(changes)
@@ -110,40 +126,6 @@ def update(changes)
 					end
 				end
 			end
-
-			def difference(other)
-				changes = []
-
-				if @header_table_size != other.header_table_size
-					changes << [HEADER_TABLE_SIZE, @header_table_size]
-				end
-
-				if @enable_push != other.enable_push
-					changes << [ENABLE_PUSH, @enable_push]
-				end
-
-				if @maximum_concurrent_streams != other.maximum_concurrent_streams
-					changes << [MAXIMUM_CONCURRENT_STREAMS, @maximum_concurrent_streams]
-				end
-
-				if @initial_window_size != other.initial_window_size
-					changes << [INITIAL_WINDOW_SIZE, @initial_window_size]
-				end
-
-				if @maximum_frame_size != other.maximum_frame_size
-					changes << [MAXIMUM_FRAME_SIZE, @maximum_frame_size]
-				end
-
-				if @maximum_header_list_size != other.maximum_header_list_size
-					changes << [MAXIMUM_HEADER_LIST_SIZE, @maximum_header_list_size]
-				end
-
-				if @enable_connect_protocol != other.enable_connect_protocol
-					changes << [ENABLE_CONNECT_PROTOCOL, @enable_connect_protocol]
-				end
-
-				return changes
-			end
 		end
 
 		class PendingSettings

lib/protocol/http2/stream.rb

@@ -76,6 +76,8 @@ def initialize(connection, id, state = :idle)
 
 				@local_window = Window.new(@connection.local_settings.initial_window_size)
 				@remote_window = Window.new(@connection.remote_settings.initial_window_size)
+
+				@priority = nil
 			end
 
 			# The connection this stream belongs to.
@@ -90,6 +92,9 @@ def initialize(connection, id, state = :idle)
 			attr :local_window
 			attr :remote_window
 
+			# @attribute [Protocol::HTTP::Header::Priority | Nil] the priority of the stream.
+			attr_accessor :priority
+
 			def maximum_frame_size
 				@connection.available_frame_size
 			end

test/protocol/http2/client.rb

@@ -34,7 +34,7 @@
 
 			client_settings_frame = framer.read_frame
 			expect(client_settings_frame).to be_a Protocol::HTTP2::SettingsFrame
-			expect(client_settings_frame.unpack).to be == settings
+			expect(client_settings_frame.unpack).to be == settings + [[Protocol::HTTP2::Settings::NO_RFC7540_PRIORITIES, 1]]
 
 			# Fake (empty) server settings:
 			server_settings_frame = Protocol::HTTP2::SettingsFrame.new
@@ -52,6 +52,27 @@
 		expect(client.local_settings.header_table_size).to be == 1024
 	end
 
+	it "should fail if the server does not reply with settings frame" do
+		data_frame = Protocol::HTTP2::DataFrame.new
+		data_frame.pack("Hello, World!")
+
+		expect do
+			client.send_connection_preface(settings) do
+				framer.write_frame(data_frame)
+			end
+		end.to raise_exception(Protocol::HTTP2::ProtocolError, message: be =~ /First frame must be Protocol::HTTP2::SettingsFrame/)
+	end
+
+	it "should send connection preface with no RFC7540 priorities" do
+		server_settings_frame = client.send_connection_preface({}) do
+			client_settings_frame = server.read_connection_preface({})
+
+			expect(client_settings_frame.unpack).to be == [[Protocol::HTTP2::Settings::NO_RFC7540_PRIORITIES, 1]]
+		end
+
+		expect(server_settings_frame.unpack).to be == [[Protocol::HTTP2::Settings::NO_RFC7540_PRIORITIES, 1]]
+	end
+
 	it "can generate a stream id" do
 		id = client.next_stream_id
 		expect(id).to be == 1

test/protocol/http2/priority_update_frame.rb

@@ -0,0 +1,65 @@
+# frozen_string_literal: true
+# Released under the MIT License.
+# Copyright, 2019-2024, by Samuel Williams.
+
+require "protocol/http2/priority_update_frame"
+
+require "protocol/http2/a_frame"
+require "protocol/http2/connection_context"
+
+describe Protocol::HTTP2::PriorityUpdateFrame do
+	let(:frame) {subject.new}
+
+	it_behaves_like Protocol::HTTP2::AFrame do
+		before do
+			frame.pack 1, "u=1, i"
+		end
+
+		it "applies to the connection" do
+			expect(frame).to be(:connection?)
+		end
+	end
+
+	with "client/server connection" do
+		include_context Protocol::HTTP2::ConnectionContext
+
+		def before
+			client.open!
+			server.open!
+
+			super
+		end
+
+		it "fails with protocol error if stream id is not zero" do
+			# This isn't a valid for the frame stream_id:
+			frame.stream_id = 1
+
+			# This is a valid stream payload:
+			frame.pack stream.id, "u=1, i"
+
+			expect do
+				frame.apply(server)
+			end.to raise_exception(Protocol::HTTP2::ProtocolError)
+		end
+
+		let(:stream) {client.create_stream}
+
+		it "updates the priority of a stream" do
+			stream.send_headers [["content-type", "text/plain"]]
+			server.read_frame
+
+			expect(server).to receive(:receive_priority_update)
+			expect(stream.priority).to be_nil
+
+			frame.pack stream.id, "u=1, i"
+			client.write_frame(frame)
+
+			inform server.read_frame
+
+			server_stream = server.streams[stream.id]
+			expect(server_stream).not.to be_nil
+
+			expect(server_stream.priority).to be == ["u=1", "i"]
+		end
+	end
+end

test/protocol/http2/server.rb

@@ -78,7 +78,7 @@
 		# The server immediately sends its own settings frame...
 		frame = framer.read_frame
 		expect(frame).to be_a Protocol::HTTP2::SettingsFrame
-		expect(frame.unpack).to be == server_settings
+		expect(frame.unpack).to be == server_settings + [[Protocol::HTTP2::Settings::NO_RFC7540_PRIORITIES, 1]]
 
 		# And then it acknowledges the client settings:
 		frame = framer.read_frame