implement some stream ID helper functions

internal/protocol/stream_id.go

@@ -3,6 +3,19 @@ package protocol
 // A StreamID in QUIC
 type StreamID uint64
 
+// InitiatedBy says if the stream was initiated by the client or by the server
+func (s StreamID) InitiatedBy() Perspective {
+	if s%2 == 0 {
+		return PerspectiveClient
+	}
+	return PerspectiveServer
+}
+
+// IsUniDirectional says if this is a unidirectional stream (true) or not (false)
+func (s StreamID) IsUniDirectional() bool {
+	return s%4 >= 2
+}
+
 // MaxBidiStreamID is the highest stream ID that the peer is allowed to open,
 // when it is allowed to open numStreams bidirectional streams.
 func MaxBidiStreamID(numStreams int, pers Perspective) StreamID {

internal/protocol/stream_id_test.go

@@ -6,6 +6,21 @@ import (
 )
 
 var _ = Describe("Stream ID", func() {
+	It("says who initiated a stream", func() {
+		Expect(StreamID(4).InitiatedBy()).To(Equal(PerspectiveClient))
+		Expect(StreamID(5).InitiatedBy()).To(Equal(PerspectiveServer))
+		Expect(StreamID(6).InitiatedBy()).To(Equal(PerspectiveClient))
+		Expect(StreamID(7).InitiatedBy()).To(Equal(PerspectiveServer))
+	})
+
+	It("tells the directionality", func() {
+		Expect(StreamID(4).IsUniDirectional()).To(BeFalse())
+		Expect(StreamID(5).IsUniDirectional()).To(BeFalse())
+		Expect(StreamID(6).IsUniDirectional()).To(BeTrue())
+		Expect(StreamID(7).IsUniDirectional()).To(BeTrue())
+	})
+
+	Context("maximum stream IDs", func() {
 		Context("bidirectional streams", func() {
 			It("doesn't allow any", func() {
 				Expect(MaxBidiStreamID(0, PerspectiveClient)).To(Equal(StreamID(0)))
@@ -40,3 +55,4 @@ var _ = Describe("Stream ID", func() {
 			})
 		})
 	})
+})