simplify stream ID handling in the incoming streams map (#5207)

* simplify stream ID handling in the incoming streams map

No functional change expected.

* protocol: move stream ID constant definition

internal/protocol/stream.go

@@ -1,5 +1,7 @@
 package protocol
 
+import "github.com/quic-go/quic-go/quicvarint"
+
 // StreamType encodes if this is a unidirectional or bidirectional stream
 type StreamType uint8
 
@@ -23,6 +25,30 @@ const (
 	// MaxStreamCount is the maximum stream count value that can be sent in MAX_STREAMS frames
 	// and as the stream count in the transport parameters
 	MaxStreamCount StreamNum = 1 << 60
+	// MaxStreamID is the maximum stream ID
+	MaxStreamID StreamID = quicvarint.Max
+)
+
+const (
+	// FirstOutgoingBidiStreamClient is the first bidirectional stream opened by the client
+	FirstOutgoingBidiStreamClient StreamID = 0
+	// FirstOutgoingUniStreamClient is the first unidirectional stream opened by the client
+	FirstOutgoingUniStreamClient StreamID = 2
+	// FirstOutgoingBidiStreamServer is the first bidirectional stream opened by the server
+	FirstOutgoingBidiStreamServer StreamID = 1
+	// FirstOutgoingUniStreamServer is the first unidirectional stream opened by the server
+	FirstOutgoingUniStreamServer StreamID = 3
+)
+
+const (
+	// FirstIncomingBidiStreamServer is the first bidirectional stream accepted by the server
+	FirstIncomingBidiStreamServer = FirstOutgoingBidiStreamClient
+	// FirstIncomingUniStreamServer is the first unidirectional stream accepted by the server
+	FirstIncomingUniStreamServer = FirstOutgoingUniStreamClient
+	// FirstIncomingBidiStreamClient is the first bidirectional stream accepted by the client
+	FirstIncomingBidiStreamClient = FirstOutgoingBidiStreamServer
+	// FirstIncomingUniStreamClient is the first unidirectional stream accepted by the client
+	FirstIncomingUniStreamClient = FirstOutgoingUniStreamServer
 )
 
 // StreamID calculates the stream ID.