feat: Implement Close.

client.go

@@ -646,7 +646,7 @@ func (s *ClientSession) Abort() error {
 
 // Close releases resources associated with the session.
 //
-// If there a milter sequence in progress - it is aborted.
+// If there's a milter sequence in progress - it is aborted.
 func (s *ClientSession) Close() error {
  if s.needAbort {
  _ = s.Abort()

client_test.go

@@ -137,6 +137,10 @@ func (mm *MockMilter) Abort(m *Modifier) error {
  return mm.AbortErr
 }
 
+func (mm *MockMilter) Close(m *Modifier) {
+ return
+}
+
 func TestMilterClient_UsualFlow(t *testing.T) {
  mm := MockMilter{
  ConnResp: RespContinue,

server.go

@@ -54,6 +54,26 @@ type Milter interface {
  // should be reset to prior to the Helo callback. Connection data should be
  // preserved.
  Abort(m *Modifier) error
+
+ // Close is called once at the end of each connection.
+ //
+ // - Close may be called "out-of-order", i.e. before even the
+ // Connect is called. After a connection is established by the
+ // MTA to the filter, if the MTA decides this connection's
+ // traffic will be discarded, no data will be passed to the
+ // filter from the MTA until the client closes down. At that time,
+ // Close is called. It can therefore be the only callback ever
+ // used for a given connection, and developers should anticipate
+ // this possibility when crafting their Close code. In particular,
+ // it is incorrect to assume the private context pointer will be
+ // something other than NULL in this callback.
+ // - Close is called on close even if the previous mail
+ // transaction was aborted.
+ // - Close is responsible for freeing any resources allocated on
+ // a per-connection basis.
+ // - Since the connection is already closing, the return value is
+ // currently ignored.
+ Close(m *Modifier)
 }
 
 // NoOpMilter is a dummy Milter implementation that does nothing.
@@ -97,6 +117,10 @@ func (NoOpMilter) Abort(m *Modifier) error {
  return nil
 }
 
+func (NoOpMilter) Close(m *Modifier) {
+ return
+}
+
 // Server is a milter server.
 type Server struct {
  NewMilter func() Milter

session.go

@@ -210,8 +210,8 @@ func (m *milterSession) Process(msg *Message) (Response, error) {
 
  case CodeQuit:
  // client requested session close
+ m.backend.Close(newModifier(m))
  return nil, errCloseSession
-
  case CodeRcpt:
  // envelope to address
  to := readCString(msg.Data)