Protocol::HTTP2SourceProtocolHTTP2Connection

class Connection

This is the core connection class that handles HTTP/2 protocol semantics including stream management, settings negotiation, and frame processing.

Definitions

def initialize(framer, local_stream_id)

Initialize a new HTTP/2 connection.

Signature

parameter framer Framer

The frame handler for reading/writing HTTP/2 frames.

parameter local_stream_id Integer

The starting stream ID for locally-initiated streams.

Implementation

def initialize(framer, local_stream_id)
	super()
	
	@state = :new
	
	# Hash(Integer, Stream)
	@streams = {}
	
	@framer = framer
	
	# The next stream id to use:
	@local_stream_id = local_stream_id
	
	# The biggest remote stream id seen thus far:
	@remote_stream_id = 0
	
	@local_settings = PendingSettings.new
	@remote_settings = Settings.new
	
	@decoder = HPACK::Context.new
	@encoder = HPACK::Context.new
	
	@local_window = LocalWindow.new
	@remote_window = Window.new
end

def id

The connection stream ID (always 0 for connection-level operations).

Signature

returns Integer

Always returns 0 for the connection itself.

Implementation

def id
	0
end

def [](id)

Access streams by ID, with 0 returning the connection itself.

Signature

parameter id Integer

The stream ID to look up.

returns Connection | Stream | Nil

The connection (if id=0), stream, or nil.

Implementation

def [] id
	if id.zero?
		self
	else
		@streams[id]
	end
end

def maximum_frame_size

The size of a frame payload is limited by the maximum size that a receiver advertises in the SETTINGS_MAX_FRAME_SIZE setting.

Implementation

def maximum_frame_size
	@remote_settings.maximum_frame_size
end

def maximum_concurrent_streams

The maximum number of concurrent streams that this connection can initiate. This is a setting that can be changed by the remote peer.

It is not the same as the number of streams that can be accepted by the connection. The number of streams that can be accepted is determined by the local settings, and the number of streams that can be initiated is determined by the remote settings.

Implementation

def maximum_concurrent_streams
	@remote_settings.maximum_concurrent_streams
end

attr_accessor :state

Connection state (:new, :open, :closed).

attr_accessor :local_settings

Current settings value for local and peer

attr :local_window

Our window for receiving data. When we receive data, it reduces this window. If the window gets too small, we must send a window update.

attr :remote_window

Our window for sending data. When we send data, it reduces this window.

attr :remote_stream_id

The highest stream_id that has been successfully accepted by this connection.

def closed?

Whether the connection is effectively or actually closed.

Implementation

def closed?
	@state == :closed || @framer.nil?
end

def delete(id)

Remove a stream from the active streams collection.

Signature

parameter id Integer

The stream ID to remove.

returns Stream | Nil

The removed stream, or nil if not found.

Implementation

def delete(id)
	@streams.delete(id)
end

def close(error = nil)

Close the underlying framer and all streams.

Implementation

def close(error = nil)
	# The underlying socket may already be closed by this point.
	@streams.each_value{|stream| stream.close(error)}
	@streams.clear
	
ensure
	if @framer
		@framer.close
		@framer = nil
	end
end

def encode_headers(headers, buffer = String.new.b)

Encode headers using HPACK compression.

Signature

parameter headers Array

The headers to encode.

parameter buffer String

Optional buffer for encoding output.

returns String

The encoded header block.

Implementation

def encode_headers(headers, buffer = String.new.b)
	HPACK::Compressor.new(buffer, @encoder, table_size_limit: @remote_settings.header_table_size).encode(headers)
end

def decode_headers(data)

Decode headers using HPACK decompression.

Signature

parameter data String

The encoded header block data.

returns Array

The decoded headers.

Implementation

def decode_headers(data)
	HPACK::Decompressor.new(data, @decoder, table_size_limit: @local_settings.header_table_size).decode
end

def next_stream_id

Streams are identified with an unsigned 31-bit integer. Streams initiated by a client MUST use odd-numbered stream identifiers; those initiated by the server MUST use even-numbered stream identifiers. A stream identifier of zero (0x0) is used for connection control messages; the stream identifier of zero cannot be used to establish a new stream.

Implementation

def next_stream_id
	id = @local_stream_id
	
	@local_stream_id += 2
	
	return id
end

def ignore_frame?(frame)

6.8. GOAWAY There is an inherent race condition between an endpoint starting new streams and the remote sending a GOAWAY frame. To deal with this case, the GOAWAY contains the stream identifier of the last peer-initiated stream that was or might be processed on the sending endpoint in this connection. For instance, if the server sends a GOAWAY frame, the identified stream is the highest-numbered stream initiated by the client. Once sent, the sender will ignore frames sent on streams initiated by the receiver if the stream has an identifier higher than the included last stream identifier. Receivers of a GOAWAY frame MUST NOT open additional streams on the connection, although a new connection can be established for new streams.

Implementation

def ignore_frame?(frame)
	if self.closed?
		# puts "ignore_frame? #{frame.stream_id} -> #{valid_remote_stream_id?(frame.stream_id)} > #{@remote_stream_id}"
		if valid_remote_stream_id?(frame.stream_id)
			return frame.stream_id > @remote_stream_id
		end
	end
end

def synchronize

Execute a block within a synchronized context. This method provides a synchronization primitive for thread safety.

Implementation

def synchronize
	yield
end

def read_frame

Reads one frame from the network and processes. Processing the frame updates the state of the connection and related streams. If the frame triggers an error, e.g. a protocol error, the connection will typically emit a goaway frame and re-raise the exception. You should continue processing frames until the underlying connection is closed.

Implementation

def read_frame
	frame = @framer.read_frame(@local_settings.maximum_frame_size)
	
	# puts "#{self.class} #{@state} read_frame: class=#{frame.class} stream_id=#{frame.stream_id} flags=#{frame.flags} length=#{frame.length} (remote_stream_id=#{@remote_stream_id})"
	# puts "Windows: local_window=#{@local_window.inspect}; remote_window=#{@remote_window.inspect}"
	
	return if ignore_frame?(frame)
	
	yield frame if block_given?
	frame.apply(self)
	
	return frame
rescue GoawayError => error
	# Go directly to jail. Do not pass go, do not collect $200.
	raise
rescue ProtocolError => error
	send_goaway(error.code || PROTOCOL_ERROR, error.message)
	
	raise
rescue HPACK::Error => error
	send_goaway(COMPRESSION_ERROR, error.message)
	
	raise
end

def send_settings(changes)

Send updated settings to the remote peer.

Signature

parameter changes Hash

The settings changes to send.

Implementation

def send_settings(changes)
	@local_settings.append(changes)
	
	frame = SettingsFrame.new
	frame.pack(changes)
	
	write_frame(frame)
end

def close!

Transition the connection into the closed state.

Implementation

def close!
	@state = :closed
	
	return self
end

def send_goaway(error_code = 0, message = "")

Tell the remote end that the connection is being shut down. If the error_code is 0, this is a graceful shutdown. The other end of the connection should not make any new streams, but existing streams may be completed.

Implementation

def send_goaway(error_code = 0, message = "")
	frame = GoawayFrame.new
	frame.pack @remote_stream_id, error_code, message
	
	write_frame(frame)
ensure
	self.close!
end

def receive_goaway(frame)

Process a GOAWAY frame from the remote peer.

Signature

parameter frame GoawayFrame

The GOAWAY frame to process.

raises GoawayError

If the frame indicates a connection error.

Implementation

def receive_goaway(frame)
	# We capture the last stream that was processed.
	@remote_stream_id, error_code, message = frame.unpack
	
	self.close!
	
	if error_code != 0
		# Shut down immediately.
		raise GoawayError.new(message, error_code)
	end
end

def write_frame(frame)

Write a single frame to the connection.

Signature

parameter frame Frame

The frame to write.

Implementation

def write_frame(frame)
	synchronize do
		@framer.write_frame(frame)
	end
	
	@framer.flush
end

def write_frames

Write multiple frames within a synchronized block.

Signature

yields {|framer| ...}

The framer for writing multiple frames.

parameter framer Framer

The framer instance.

raises EOFError

If the connection is closed.

Implementation

def write_frames
	if @framer
		synchronize do
			yield @framer
		end
		
		@framer.flush
	else
		raise EOFError, "Connection closed!"
	end
end

def update_local_settings(changes)

Update local settings and adjust stream window capacities.

Signature

parameter changes Hash

The settings changes to apply locally.

Implementation

def update_local_settings(changes)
	capacity = @local_settings.initial_window_size
	
	@streams.each_value do |stream|
		stream.local_window.capacity = capacity
	end
	
	@local_window.desired = capacity
end

def update_remote_settings(changes)

Update remote settings and adjust stream window capacities.

Signature

parameter changes Hash

The settings changes to apply to remote peer.

Implementation

def update_remote_settings(changes)
	capacity = @remote_settings.initial_window_size
	
	@streams.each_value do |stream|
		stream.remote_window.capacity = capacity
	end
end

def process_settings(frame)

In addition to changing the flow-control window for streams that are not yet active, a SETTINGS frame can alter the initial flow-control window size for streams with active flow-control windows (that is, streams in the "open" or "half-closed (remote)" state). When the value of SETTINGS_INITIAL_WINDOW_SIZE changes, a receiver MUST adjust the size of all stream flow-control windows that it maintains by the difference between the new value and the old value.

Implementation

def process_settings(frame)
	if frame.acknowledgement?
		# The remote end has confirmed the settings have been received:
		changes = @local_settings.acknowledge
		
		update_local_settings(changes)
		
		return true
	else
		# The remote end is updating the settings, we reply with acknowledgement:
		reply = frame.acknowledge
		
		write_frame(reply)
		
		changes = frame.unpack
		@remote_settings.update(changes)
		
		update_remote_settings(changes)
		
		return false
	end
end

def open!

Transition the connection to the open state.

Signature

returns Connection

Self for method chaining.

Implementation

def open!
	@state = :open
	
	return self
end

def receive_settings(frame)

Receive and process a SETTINGS frame from the remote peer.

Signature

parameter frame SettingsFrame

The settings frame to process.

raises ProtocolError

If the connection is in an invalid state.

Implementation

def receive_settings(frame)
	if @state == :new
		# We transition to :open when we receive acknowledgement of first settings frame:
		open! if process_settings(frame)
	elsif @state != :closed
		process_settings(frame)
	else
		raise ProtocolError, "Cannot receive settings in state #{@state}"
	end
end

def send_ping(data)

Send a PING frame to the remote peer.

Signature

parameter data String

The 8-byte ping payload data.

Implementation

def send_ping(data)
	if @state != :closed
		frame = PingFrame.new
		frame.pack data
		
		write_frame(frame)
	else
		raise ProtocolError, "Cannot send ping in state #{@state}"
	end
end

def receive_ping(frame)

Process a PING frame from the remote peer.

Signature

parameter frame PingFrame

The ping frame to process.

raises ProtocolError

If ping is received in invalid state.

Implementation

def receive_ping(frame)
	if @state != :closed
		# This is handled in `read_payload`:
		# if frame.stream_id != 0
		# 	raise ProtocolError, "Ping received for non-zero stream!"
		# end
		
		unless frame.acknowledgement?
			reply = frame.acknowledge
			
			write_frame(reply)
		end
	else
		raise ProtocolError, "Cannot receive ping in state #{@state}"
	end
end

def receive_data(frame)

Process a DATA frame from the remote peer.

Signature

parameter frame DataFrame

The data frame to process.

raises ProtocolError

If data is received for invalid stream.

Implementation

def receive_data(frame)
	update_local_window(frame)
	
	if stream = @streams[frame.stream_id]
		stream.receive_data(frame)
	elsif closed_stream_id?(frame.stream_id)
		# This can occur if one end sent a stream reset, while the other end was sending a data frame. It's mostly harmless.
	else
		raise ProtocolError, "Cannot receive data for stream id #{frame.stream_id}"
	end
end

def valid_remote_stream_id?(stream_id)

Check if the given stream ID is valid for remote initiation. This method should be overridden by client/server implementations.

Signature

parameter stream_id Integer

The stream ID to validate.

returns Boolean

True if the stream ID is valid for remote initiation.

Implementation

def valid_remote_stream_id?(stream_id)
	false
end

def accept_stream(stream_id, &block)

Accept an incoming stream from the other side of the connnection. On the server side, we accept requests.

Implementation

def accept_stream(stream_id, &block)
	unless valid_remote_stream_id?(stream_id)
		raise ProtocolError, "Invalid stream id: #{stream_id}"
	end
	
	create_stream(stream_id, &block)
end

def accept_push_promise_stream(stream_id, &block)

Accept an incoming push promise from the other side of the connection. On the client side, we accept push promise streams. On the server side, existing streams create push promise streams.

Implementation

def accept_push_promise_stream(stream_id, &block)
	accept_stream(stream_id, &block)
end

def create_stream(id = next_stream_id, &block)

Create a stream, defaults to an outgoing stream. On the client side, we create requests.

Implementation

def create_stream(id = next_stream_id, &block)
	if @streams.key?(id)
		raise ProtocolError, "Cannot create stream with id #{id}, already exists!"
	end
	
	if block_given?
		return yield(self, id)
	else
		return Stream.create(self, id)
	end
end

def create_push_promise_stream(&block)

Create a push promise stream. This method should be overridden by client/server implementations.

Signature

yields {|stream| ...}

Optional block to configure the created stream.

returns Stream

The created push promise stream.

Implementation

def create_push_promise_stream(&block)
	create_stream(&block)
end

def receive_headers(frame)

On the server side, starts a new request.

Implementation

def receive_headers(frame)
	stream_id = frame.stream_id
	
	if stream_id.zero?
		raise ProtocolError, "Cannot receive headers for stream 0!"
	end
	
	if stream = @streams[stream_id]
		stream.receive_headers(frame)
	else
		if stream_id <= @remote_stream_id
			raise ProtocolError, "Invalid stream id: #{stream_id} <= #{@remote_stream_id}!"
		end
		
		# We need to validate that we have less streams than the specified maximum:
		if @streams.size < @local_settings.maximum_concurrent_streams
			stream = accept_stream(stream_id)
			@remote_stream_id = stream_id
			
			stream.receive_headers(frame)
		else
			raise ProtocolError, "Exceeded maximum concurrent streams"
		end
	end
end

def receive_push_promise(frame)

Receive and process a PUSH_PROMISE frame.

Signature

parameter frame PushPromiseFrame

The push promise frame.

raises ProtocolError

Always raises as push promises are not supported.

Implementation

def receive_push_promise(frame)
	raise ProtocolError, "Unable to receive push promise!"
end

def receive_priority_update(frame)

Receive and process a PRIORITY_UPDATE frame.

Signature

parameter frame PriorityUpdateFrame

The priority update frame.

raises ProtocolError

If the stream ID is invalid.

Implementation

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)

Check if the given stream ID represents a client-initiated stream. Client streams always have odd numbered IDs.

Signature

parameter id Integer

The stream ID to check.

returns Boolean

True if the stream ID is client-initiated.

Implementation

def client_stream_id?(id)
	id.odd?
end

def server_stream_id?(id)

Check if the given stream ID represents a server-initiated stream. Server streams always have even numbered IDs.

Signature

parameter id Integer

The stream ID to check.

returns Boolean

True if the stream ID is server-initiated.

Implementation

def server_stream_id?(id)
	id.even?
end

def idle_stream_id?(id)

Check if the given stream ID represents an idle stream.

Signature

parameter id Integer

The stream ID to check.

returns Boolean

True if the stream ID is idle (not yet used).

Implementation

def idle_stream_id?(id)
	if id.even?
		# Server-initiated streams are even.
		if @local_stream_id.even?
			id >= @local_stream_id
		else
			id > @remote_stream_id
		end
	elsif id.odd?
		# Client-initiated streams are odd.
		if @local_stream_id.odd?
			id >= @local_stream_id
		else
			id > @remote_stream_id
		end
	end
end

def closed_stream_id?(id)

This is only valid if the stream doesn't exist in @streams.

Implementation

def closed_stream_id?(id)
	if id.zero?
		# The connection "stream id" can never be closed:
		false
	else
		!idle_stream_id?(id)
	end
end

def receive_reset_stream(frame)

Receive and process a RST_STREAM frame.

Signature

parameter frame ResetStreamFrame

The reset stream frame.

raises ProtocolError

If the frame is invalid for connection context.

Implementation

def receive_reset_stream(frame)
	if frame.connection?
		raise ProtocolError, "Cannot reset connection!"
	elsif stream = @streams[frame.stream_id]
		stream.receive_reset_stream(frame)
	elsif closed_stream_id?(frame.stream_id)
		# Ignore.
	else
		raise StreamClosed, "Cannot reset stream #{frame.stream_id}"
	end
end

def consume_window(size = self.available_size)

Traverse active streams and allow them to consume the available flow-control window.

Signature

parameter amount Integer

the amount of data to write. Defaults to the current window capacity.

Implementation

def consume_window(size = self.available_size)
	# Return if there is no window to consume:
	return unless size > 0
	
	@streams.each_value do |stream|
		if stream.active?
			stream.window_updated(size)
		end
	end
end

def receive_window_update(frame)

Receive and process a WINDOW_UPDATE frame.

Signature

parameter frame WindowUpdateFrame

The window update frame.

Implementation

def receive_window_update(frame)
	if frame.connection?
		super
		
		self.consume_window
	elsif stream = @streams[frame.stream_id]
		begin
			stream.receive_window_update(frame)
		rescue ProtocolError => error
			stream.send_reset_stream(error.code)
		end
	elsif closed_stream_id?(frame.stream_id)
		# Ignore.
	else
		# Receiving any frame other than HEADERS or PRIORITY on a stream in this state (idle) MUST be treated as a connection error of type PROTOCOL_ERROR.
		raise ProtocolError, "Cannot update window of idle stream #{frame.stream_id}"
	end
end

def receive_continuation(frame)

Receive and process a CONTINUATION frame.

Signature

parameter frame ContinuationFrame

The continuation frame.

raises ProtocolError

Always raises as unexpected continuation frames are not supported.

Implementation

def receive_continuation(frame)
	raise ProtocolError, "Received unexpected continuation: #{frame.class}"
end

def receive_frame(frame)

Receive and process a generic frame (default handler).

Signature

parameter frame Frame

The frame to receive.

Implementation

def receive_frame(frame)
	# ignore.
end