Don't request a window update for a closed HTTP/2 stream

lib/async/http/protocol/http2/stream.rb

@@ -111,6 +111,11 @@ def update_local_window(frame)
 						# request_window_update
 					end
 
+					# A closed stream receives no more data, so there is no window to extend. This happens when the application reads a body which was fully buffered before the connection closed, e.g. after a graceful GOAWAY.
+					def request_window_update
+						super unless closed?
+					end
+
 					# Process an incoming DATA frame and write it to the input body.
 					# @parameter frame [Protocol::HTTP2::DataFrame] The data frame to process.
 					# @returns [String] The unpacked data.

test/async/http/protocol/http2/graceful_goaway.rb

@@ -11,6 +11,7 @@
 require "sus/fixtures/async/scheduler_context"
 
 require "async/queue"
+require "protocol/http/body/writable"
 require "io/stream"
 require "socket"
 
@@ -117,6 +118,46 @@ def handle_connection(socket, index, processed)
 		end
 	end
 
+	with "a response body which is still buffered when the GOAWAY closes the connection" do
+		let(:sockets) {::Socket.pair(::Socket::AF_UNIX, ::Socket::SOCK_STREAM)}
+
+		def after(error = nil)
+			sockets.each{|socket| socket.close unless socket.closed?}
+
+			super
+		end
+
+		it "can read the whole body" do
+			chunk = "x" * 100_000
+
+			server_task = Async do
+				server = subject.server(sockets.last)
+
+				server.each do
+					body = ::Protocol::HTTP::Body::Writable.new
+
+					Async do
+						60.times{body.write(chunk)}
+						server.write_frame(goaway_frame(1))
+						body.close_write
+					end
+
+					::Protocol::HTTP::Response[200, {}, body]
+				end
+			end
+
+			client = subject.client(sockets.first)
+			response = client.call(::Protocol::HTTP::Request["GET", "/", authority: "localhost", scheme: "http"])
+
+			# The stream completes, so the connection closes, before the body has been read:
+			Async::Task.current.sleep(0.01) until client.closed?
+
+			expect(response.read.bytesize).to be == 6_000_000
+		ensure
+			server_task&.stop
+		end
+	end
+
 	with "a connection which received a GOAWAY" do
 		let(:sockets) {::Socket.pair(::Socket::AF_UNIX, ::Socket::SOCK_STREAM)}
 		let(:connection) {Async::HTTP::Protocol::HTTP2::Client.new(IO::Stream(sockets.first))}