implement a basic flow controller

needed for #39, #100, #106

flow_controller.go

@@ -0,0 +1,70 @@
+package quic
+
+import (
+	"github.com/lucas-clemente/quic-go/handshake"
+	"github.com/lucas-clemente/quic-go/protocol"
+)
+
+type flowController struct {
+	streamID protocol.StreamID
+
+	bytesSent             protocol.ByteCount
+	sendFlowControlWindow protocol.ByteCount
+
+	bytesRead                         protocol.ByteCount
+	receiveWindowUpdateThreshold      protocol.ByteCount
+	receiveFlowControlWindow          protocol.ByteCount
+	receiveFlowControlWindowIncrement protocol.ByteCount
+}
+
+func newFlowController(connectionParametersManager *handshake.ConnectionParametersManager) *flowController {
+	return &flowController{
+		sendFlowControlWindow:             connectionParametersManager.GetSendStreamFlowControlWindow(),
+		receiveFlowControlWindow:          connectionParametersManager.GetReceiveStreamFlowControlWindow(),
+		receiveWindowUpdateThreshold:      protocol.WindowUpdateThreshold,
+		receiveFlowControlWindowIncrement: protocol.ReceiveStreamFlowControlWindowIncrement,
+	}
+}
+
+func (c *flowController) AddBytesSent(n protocol.ByteCount) {
+	c.bytesSent += n
+}
+
+// UpdateSendWindow should be called after receiving a WindowUpdateFrame
+// it returns true if the window was actually updated
+func (c *flowController) UpdateSendWindow(newOffset protocol.ByteCount) bool {
+	if newOffset > c.sendFlowControlWindow {
+		c.sendFlowControlWindow = newOffset
+		return true
+	}
+	return false
+}
+
+func (c *flowController) SendWindowSize() protocol.ByteCount {
+	if c.bytesSent > c.sendFlowControlWindow { // should never happen, but make sure we don't do an underflow here
+		return 0
+	}
+	return c.sendFlowControlWindow - c.bytesSent
+}
+
+func (c *flowController) AddBytesRead(n protocol.ByteCount) {
+	c.bytesRead += n
+}
+
+// MaybeTriggerWindowUpdate determines if it is necessary to send a WindowUpdate
+// if so, it returns true and the offset of the window
+func (c *flowController) MaybeTriggerWindowUpdate() (bool, protocol.ByteCount) {
+	diff := c.receiveFlowControlWindow - c.bytesRead
+	if diff < c.receiveWindowUpdateThreshold {
+		c.receiveFlowControlWindow += c.receiveFlowControlWindowIncrement
+		return true, c.bytesRead + c.receiveFlowControlWindowIncrement
+	}
+	return false, 0
+}
+
+func (c *flowController) CheckFlowControlViolation(highestByte protocol.ByteCount) bool {
+	if highestByte > c.receiveFlowControlWindow {
+		return true
+	}
+	return false
+}