http/h2_stream: fixed stream dependency errors

http/h2_stream.lua

@@ -362,12 +362,15 @@ frame_handlers[0x1] = function(stream, flags, payload)
 		pos = pos + 5
 
 		local new_parent = stream.connection.streams[stream_dep]
-		if new_parent == nil then
-			error("parent doesn't exist " .. stream_dep) -- FIXME
+
+		-- 5.3.1. Stream Dependencies
+		-- A dependency on a stream that is not currently in the tree
+		-- results in that stream being given a default priority
+		if new_parent then
+			local ok, err = new_parent:reprioritise(stream, exclusive)
+			if not ok then return nil, err end
+			stream.weight = weight
 		end
-		local ok, err = new_parent:reprioritise(stream, exclusive)
-		if not ok then return nil, err end
-		stream.weight = weight
 	end
 
 	if #payload - pos + 1 > MAX_HEADER_BUFFER_SIZE then

spec/h2_connection_spec.lua

@@ -157,6 +157,37 @@ describe("http2 connection", function()
 			assert.truthy(cq:empty())
 		end)
 	end)
+	describe("priority on missing stream", function()
+		it("sets default priority for streams with missing parent", function()
+			local cq = cqueues.new()
+			local c, s = cs.pair()
+			cq:wrap(function()
+				c = h2_connection.new(c, "client")
+				local client_stream = c:new_stream()
+				local req_headers = new_headers()
+				req_headers:append(":method", "GET")
+				req_headers:append(":scheme", "http")
+				req_headers:append(":path", "/")
+				-- Encode HEADER payload and send with dependency on missing stream
+				c.encoding_context:encode_headers(req_headers)
+				local payload = c.encoding_context:render_data()
+				c.encoding_context:clear_data()
+				assert(client_stream:write_headers_frame(payload, true, true, nil, nil, 99, 99))
+				client_stream:shutdown()
+				assert(c:close())
+			end)
+			cq:wrap(function()
+				s = h2_connection.new(s, "server")
+				local stream = assert(s:get_next_incoming_stream())
+				-- Check if set to default priority instead of missing parent
+				assert.is_not.same(stream.weight, 99)
+				stream:shutdown()
+				assert(s:close())
+			end)
+			assert_loop(cq, TEST_TIMEOUT)
+			assert.truthy(cq:empty())
+		end)
+	end)
 	describe("settings", function()
 		it("correctly handles odd frame sizes", function()
 			local c = cs.pair()