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

CHANGELOG.md

 ## 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 {
@@ -416,9 +416,9 @@ func (m *MuxConn) loop() {
 					stream.mu.Unlock()
 				}
 			}
-}
+		}
 
-func (m *MuxConn) write(from muxPacketFrom, id uint32, dataType muxPacketType, p []byte) (int, error) {
+		func (m *MuxConn) write(from muxPacketFrom, id uint32, dataType muxPacketType, p []byte) (int, error) {
 			m.wlock.Lock()
 			defer m.wlock.Unlock()
 
@@ -438,11 +438,11 @@ func (m *MuxConn) write(from muxPacketFrom, id uint32, dataType muxPacketType, p
 				return 0, nil
 			}
 			return m.rwc.Write(p)
-}
+		}
 
-// Stream is a single stream of data and implements io.ReadWriteCloser.
-// A Stream is full-duplex so you can write data as well as read data.
-type Stream struct {
+		// Stream is a single stream of data and implements io.ReadWriteCloser.
+		// A Stream is full-duplex so you can write data as well as read data.
+		type Stream struct {
 			from         muxPacketFrom
 			id           uint32
 			mux          *MuxConn
@@ -452,11 +452,11 @@ type Stream struct {
 			stateUpdated time.Time
 			mu           sync.Mutex
 			writeCh      chan<- []byte
-}
+		}
 
-type streamState byte
+		type streamState byte
 
-const (
+		const (
 			streamStateClosed streamState = iota
 			streamStateListen
 			streamStateSynRecv
@@ -467,9 +467,9 @@ const (
 			streamStateCloseWait
 			streamStateClosing
 			streamStateLastAck
-)
+		)
 
-func newStream(from muxPacketFrom, id uint32, m *MuxConn) *Stream {
+		func newStream(from muxPacketFrom, id uint32, m *MuxConn) *Stream {
 			// Create the stream object and channel where data will be sent to
 			dataR, dataW := io.Pipe()
 			writeCh := make(chan []byte, 4096)
@@ -505,9 +505,9 @@ func newStream(from muxPacketFrom, id uint32, m *MuxConn) *Stream {
 			}()
 
 			return stream
-}
+		}
 
-func (s *Stream) Close() error {
+		func (s *Stream) Close() error {
 			s.mu.Lock()
 			defer s.mu.Unlock()
 
@@ -523,13 +523,13 @@ func (s *Stream) Close() error {
 
 			s.write(muxPacketFin, nil)
 			return nil
-}
+		}
 
-func (s *Stream) Read(p []byte) (int, error) {
+		func (s *Stream) Read(p []byte) (int, error) {
 			return s.reader.Read(p)
-}
+		}
 
-func (s *Stream) Write(p []byte) (int, error) {
+		func (s *Stream) Write(p []byte) (int, error) {
 			s.mu.Lock()
 			state := s.state
 			s.mu.Unlock()
@@ -539,13 +539,13 @@ func (s *Stream) Write(p []byte) (int, error) {
 			}
 
 			return s.write(muxPacketData, p)
-}
+		}
 
-func (s *Stream) closeWriter() {
+		func (s *Stream) closeWriter() {
 			s.writeCh <- nil
-}
+		}
 
-func (s *Stream) setState(state streamState) {
+		func (s *Stream) setState(state streamState) {
 			//log.Printf("[TRACE] %p: Stream %d (%s) went to state %d", s.mux, s.id, s.from, state)
 			s.state = state
 			s.stateUpdated = time.Now().UTC()
@@ -555,9 +555,9 @@ func (s *Stream) setState(state streamState) {
 				default:
 				}
 			}
-}
+		}
 
-func (s *Stream) waitState(target streamState) error {
+		func (s *Stream) waitState(target streamState) error {
 			// Register a state change listener to wait for changes
 			stateCh := make(chan streamState, 10)
 			s.stateChange[stateCh] = struct{}{}
@@ -574,8 +574,8 @@ func (s *Stream) waitState(target streamState) error {
 			} else {
 				return fmt.Errorf("Stream %d went to bad state: %d", s.id, state)
 			}
-}
+		}
 
-func (s *Stream) write(dataType muxPacketType, p []byte) (int, error) {
+		func (s *Stream) write(dataType muxPacketType, p []byte) (int, error) {
 			return s.mux.write(s.from, s.id, dataType, p)
-}
+		}