From 0840425ed2063dbd3899ee97843bb6eaf8cdf251 Mon Sep 17 00:00:00 2001
From: aler9 <46489434+aler9@users.noreply.github.com>
Date: Wed, 25 Aug 2021 09:47:12 +0200
Subject: [PATCH] server: return specific error message in case interleaved IDs
 are in use

---
 pkg/liberrors/server.go | 8 ++++++++
 serversession.go        | 6 +++---
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/pkg/liberrors/server.go b/pkg/liberrors/server.go
index 0996c9a7..24e0481e 100644
--- a/pkg/liberrors/server.go
+++ b/pkg/liberrors/server.go
@@ -175,6 +175,14 @@ func (e ErrServerTransportHeaderInvalidInterleavedIDs) Error() string {
 	return "invalid interleaved IDs"
 }
 
+// ErrServerTransportHeaderInterleavedIDsAlreadyUsed is an error that can be returned by a server.
+type ErrServerTransportHeaderInterleavedIDsAlreadyUsed struct{}
+
+// Error implements the error interface.
+func (e ErrServerTransportHeaderInterleavedIDsAlreadyUsed) Error() string {
+	return "interleaved IDs already used"
+}
+
 // ErrServerTracksDifferentProtocols is an error that can be returned by a server.
 type ErrServerTracksDifferentProtocols struct{}
 
diff --git a/serversession.go b/serversession.go
index a1e60d8a..f599545b 100644
--- a/serversession.go
+++ b/serversession.go
@@ -605,8 +605,8 @@ func (ss *ServerSession) handleRequest(sc *ServerConn, req *base.Request) (*base
 				}, liberrors.ErrServerTransportHeaderNoInterleavedIDs{}
 			}
 
-			if (inTH.InterleavedIDs[0]+1) != inTH.InterleavedIDs[1] ||
-				(inTH.InterleavedIDs[0]%2) != 0 {
+			if (inTH.InterleavedIDs[0]%2) != 0 ||
+				(inTH.InterleavedIDs[0]+1) != inTH.InterleavedIDs[1] {
 				return &base.Response{
 					StatusCode: base.StatusBadRequest,
 				}, liberrors.ErrServerTransportHeaderInvalidInterleavedIDs{}
@@ -615,7 +615,7 @@ func (ss *ServerSession) handleRequest(sc *ServerConn, req *base.Request) (*base
 			if _, ok := ss.setuppedTracksByChannel[inTH.InterleavedIDs[0]]; ok {
 				return &base.Response{
 					StatusCode: base.StatusBadRequest,
-				}, liberrors.ErrServerTransportHeaderInvalidInterleavedIDs{}
+				}, liberrors.ErrServerTransportHeaderInterleavedIDsAlreadyUsed{}
 			}
 		}