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

@@ -6,37 +6,53 @@ import (
 )
 
 var _ = Describe("Stream ID", func() {
-	Context("bidirectional streams", func() {
-		It("doesn't allow any", func() {
-			Expect(MaxBidiStreamID(0, PerspectiveClient)).To(Equal(StreamID(0)))
-			Expect(MaxBidiStreamID(0, PerspectiveServer)).To(Equal(StreamID(0)))
-		})
-
-		It("allows one", func() {
-			Expect(MaxBidiStreamID(1, PerspectiveClient)).To(Equal(StreamID(1)))
-			Expect(MaxBidiStreamID(1, PerspectiveServer)).To(Equal(StreamID(0)))
-		})
-
-		It("allows many", func() {
-			Expect(MaxBidiStreamID(100, PerspectiveClient)).To(Equal(StreamID(397)))
-			Expect(MaxBidiStreamID(100, PerspectiveServer)).To(Equal(StreamID(396)))
-		})
+	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))
 	})
 
-	Context("unidirectional streams", func() {
-		It("doesn't allow any", func() {
-			Expect(MaxUniStreamID(0, PerspectiveClient)).To(Equal(StreamID(0)))
-			Expect(MaxUniStreamID(0, PerspectiveServer)).To(Equal(StreamID(0)))
+	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)))
+				Expect(MaxBidiStreamID(0, PerspectiveServer)).To(Equal(StreamID(0)))
+			})
+
+			It("allows one", func() {
+				Expect(MaxBidiStreamID(1, PerspectiveClient)).To(Equal(StreamID(1)))
+				Expect(MaxBidiStreamID(1, PerspectiveServer)).To(Equal(StreamID(0)))
+			})
+
+			It("allows many", func() {
+				Expect(MaxBidiStreamID(100, PerspectiveClient)).To(Equal(StreamID(397)))
+				Expect(MaxBidiStreamID(100, PerspectiveServer)).To(Equal(StreamID(396)))
+			})
 		})
 
-		It("allows one", func() {
-			Expect(MaxUniStreamID(1, PerspectiveClient)).To(Equal(StreamID(3)))
-			Expect(MaxUniStreamID(1, PerspectiveServer)).To(Equal(StreamID(2)))
-		})
+		Context("unidirectional streams", func() {
+			It("doesn't allow any", func() {
+				Expect(MaxUniStreamID(0, PerspectiveClient)).To(Equal(StreamID(0)))
+				Expect(MaxUniStreamID(0, PerspectiveServer)).To(Equal(StreamID(0)))
+			})
 
-		It("allows many", func() {
-			Expect(MaxUniStreamID(100, PerspectiveClient)).To(Equal(StreamID(399)))
-			Expect(MaxUniStreamID(100, PerspectiveServer)).To(Equal(StreamID(398)))
+			It("allows one", func() {
+				Expect(MaxUniStreamID(1, PerspectiveClient)).To(Equal(StreamID(3)))
+				Expect(MaxUniStreamID(1, PerspectiveServer)).To(Equal(StreamID(2)))
+			})
+
+			It("allows many", func() {
+				Expect(MaxUniStreamID(100, PerspectiveClient)).To(Equal(StreamID(399)))
+				Expect(MaxUniStreamID(100, PerspectiveServer)).To(Equal(StreamID(398)))
+			})
 		})
 	})
 })