implement sending of MAX_STREAM_ID frames

We can now impose a limit on the number of stream for IETF QUIC, and
advertise that in the transport parameters during the handshake.

internal/protocol/stream_id.go

@@ -0,0 +1,36 @@
+package protocol
+
+// A StreamID in QUIC
+type StreamID uint64
+
+// MaxBidiStreamID is the highest stream ID that the peer is allowed to open,
+// when it is allowed to open numStreams bidirectional streams.
+// It is only valid for IETF QUIC.
+func MaxBidiStreamID(numStreams int, pers Perspective) StreamID {
+	if numStreams == 0 {
+		return 0
+	}
+	var first StreamID
+	if pers == PerspectiveClient {
+		first = 1
+	} else {
+		first = 4
+	}
+	return first + 4*StreamID(numStreams-1)
+}
+
+// MaxUniStreamID is the highest stream ID that the peer is allowed to open,
+// when it is allowed to open numStreams unidirectional streams.
+// It is only valid for IETF QUIC.
+func MaxUniStreamID(numStreams int, pers Perspective) StreamID {
+	if numStreams == 0 {
+		return 0
+	}
+	var first StreamID
+	if pers == PerspectiveClient {
+		first = 3
+	} else {
+		first = 2
+	}
+	return first + 4*StreamID(numStreams-1)
+}