1 files changed, 40 insertions, 22 deletions

diff --git a/pkg/flipcall/flipcall.go b/pkg/flipcall/flipcall.go
index 5c9212c33..991018684 100644
--- a/pkg/flipcall/flipcall.go
+++ b/pkg/flipcall/flipcall.go
@@ -42,11 +42,6 @@ type Endpoint struct {
 	// dataCap is immutable.
 	dataCap uint32
 
-	// shutdown is non-zero if Endpoint.Shutdown() has been called, or if the
-	// Endpoint has acknowledged shutdown initiated by the peer. shutdown is
-	// accessed using atomic memory operations.
-	shutdown uint32
-
 	// activeState is csClientActive if this is a client Endpoint and
 	// csServerActive if this is a server Endpoint.
 	activeState uint32
@@ -55,9 +50,27 @@ type Endpoint struct {
 	// csClientActive if this is a server Endpoint.
 	inactiveState uint32
 
+	// shutdown is non-zero if Endpoint.Shutdown() has been called, or if the
+	// Endpoint has acknowledged shutdown initiated by the peer. shutdown is
+	// accessed using atomic memory operations.
+	shutdown uint32
+
 	ctrl endpointControlImpl
 }
 
+// EndpointSide indicates which side of a connection an Endpoint belongs to.
+type EndpointSide int
+
+const (
+	// ClientSide indicates that an Endpoint is a client (initially-active;
+	// first method call should be Connect).
+	ClientSide EndpointSide = iota
+
+	// ServerSide indicates that an Endpoint is a server (initially-inactive;
+	// first method call should be RecvFirst.)
+	ServerSide
+)
+
 // Init must be called on zero-value Endpoints before first use. If it
 // succeeds, ep.Destroy() must be called once the Endpoint is no longer in use.
 //
@@ -65,7 +78,17 @@ type Endpoint struct {
 // Endpoint. FD may differ between Endpoints if they are in different
 // processes, but must represent the same file. The packet window must
 // initially be filled with zero bytes.
-func (ep *Endpoint) Init(pwd PacketWindowDescriptor, opts ...EndpointOption) error {
+func (ep *Endpoint) Init(side EndpointSide, pwd PacketWindowDescriptor, opts ...EndpointOption) error {
+	switch side {
+	case ClientSide:
+		ep.activeState = csClientActive
+		ep.inactiveState = csServerActive
+	case ServerSide:
+		ep.activeState = csServerActive
+		ep.inactiveState = csClientActive
+	default:
+		return fmt.Errorf("invalid EndpointSide: %v", side)
+	}
 	if pwd.Length < pageSize {
 		return fmt.Errorf("packet window size (%d) less than minimum (%d)", pwd.Length, pageSize)
 	}
@@ -78,9 +101,6 @@ func (ep *Endpoint) Init(pwd PacketWindowDescriptor, opts ...EndpointOption) err
 	}
 	ep.packet = m
 	ep.dataCap = uint32(pwd.Length) - uint32(PacketHeaderBytes)
-	// These will be overwritten by ep.Connect() for client Endpoints.
-	ep.activeState = csServerActive
-	ep.inactiveState = csClientActive
 	if err := ep.ctrlInit(opts...); err != nil {
 		ep.unmapPacket()
 		return err
@@ -90,9 +110,9 @@ func (ep *Endpoint) Init(pwd PacketWindowDescriptor, opts ...EndpointOption) err
 
 // NewEndpoint is a convenience function that returns an initialized Endpoint
 // allocated on the heap.
-func NewEndpoint(pwd PacketWindowDescriptor, opts ...EndpointOption) (*Endpoint, error) {
+func NewEndpoint(side EndpointSide, pwd PacketWindowDescriptor, opts ...EndpointOption) (*Endpoint, error) {
 	var ep Endpoint
-	if err := ep.Init(pwd, opts...); err != nil {
+	if err := ep.Init(side, pwd, opts...); err != nil {
 		return nil, err
 	}
 	return &ep, nil
@@ -115,9 +135,9 @@ func (ep *Endpoint) unmapPacket() {
 }
 
 // Shutdown causes concurrent and future calls to ep.Connect(), ep.SendRecv(),
-// ep.RecvFirst(), and ep.SendLast() to unblock and return errors. It does not
-// wait for concurrent calls to return. The effect of Shutdown on the peer
-// Endpoint is unspecified. Successive calls to Shutdown have no effect.
+// ep.RecvFirst(), and ep.SendLast(), as well as the same calls in the peer
+// Endpoint, to unblock and return errors. It does not wait for concurrent
+// calls to return. Successive calls to Shutdown have no effect.
 //
 // Shutdown is the only Endpoint method that may be called concurrently with
 // other methods on the same Endpoint.
@@ -152,24 +172,22 @@ const (
 	// The client is, by definition, initially active, so this must be 0.
 	csClientActive = 0
 	csServerActive = 1
+	csShutdown     = 2
 )
 
-// Connect designates ep as a client Endpoint and blocks until the peer
-// Endpoint has called Endpoint.RecvFirst().
+// Connect blocks until the peer Endpoint has called Endpoint.RecvFirst().
 //
-// Preconditions: ep.Connect(), ep.RecvFirst(), ep.SendRecv(), and
-// ep.SendLast() have never been called.
+// Preconditions: ep is a client Endpoint. ep.Connect(), ep.RecvFirst(),
+// ep.SendRecv(), and ep.SendLast() have never been called.
 func (ep *Endpoint) Connect() error {
-	ep.activeState = csClientActive
-	ep.inactiveState = csServerActive
 	return ep.ctrlConnect()
 }
 
 // RecvFirst blocks until the peer Endpoint calls Endpoint.SendRecv(), then
 // returns the datagram length specified by that call.
 //
-// Preconditions: ep.SendRecv(), ep.RecvFirst(), and ep.SendLast() have never
-// been called.
+// Preconditions: ep is a server Endpoint. ep.SendRecv(), ep.RecvFirst(), and
+// ep.SendLast() have never been called.
 func (ep *Endpoint) RecvFirst() (uint32, error) {
 	if err := ep.ctrlWaitFirst(); err != nil {
 		return 0, err