packer/rpc: muxconn can't use stream ID 0 ever

CHANGELOG.md

@@ -1,6 +1,8 @@
 ## 0.5.1 (unreleased)
 
+BUG FIXES:
 
+* core: If a stream ID loops around, don't let it use stream ID 0 [GH-767]
 
 ## 0.5.0 (12/30/2013)
 

packer/rpc/muxconn.go

@@ -191,13 +191,13 @@ func (m *MuxConn) NextId() uint32 {
 	m.muAccept.Lock()
 	defer m.muAccept.Unlock()
 
+	for {
 		// We never use stream ID 0 because 0 is the zero value of a uint32
 		// and we want to reserve that for "not in use"
 		if m.curId == 0 {
 			m.curId = 1
 		}
 
-	for {
 		result := m.curId
 		m.curId += 1
 		if _, ok := m.streamsAccept[result]; !ok {