client: expose handler replies to third-parties

Client.replies was previously unexported, making it impossible to implement
AUTHENTICATE-like responses (e.g. IDLE) outside of the client package.

This commit adds responses.Replier and makes the replies channel per-command.

client/client.go

@@ -62,7 +62,6 @@ type Client struct {
 	conn  *imap.Conn
 	isTLS bool
 
-	replies   chan []byte
 	loggedOut chan struct{}
 	upgrading bool
 
@@ -184,6 +183,11 @@ func (c *Client) execute(cmdr imap.Commander, h responses.Handler) (*imap.Status
 	cmd := cmdr.Command()
 	cmd.Tag = generateTag()
 
+	var replies <-chan []byte
+	if replier, ok := h.(responses.Replier); ok {
+		replies = replier.Replies()
+	}
+
 	if c.Timeout > 0 {
 		err := c.conn.SetDeadline(time.Now().Add(c.Timeout))
 		if err != nil {
@@ -255,7 +259,7 @@ func (c *Client) execute(cmdr imap.Commander, h responses.Handler) (*imap.Status
 
 	for {
 		select {
-		case reply := <-c.replies:
+		case reply := <-replies:
 			// Response handler needs to send a reply (Used for AUTHENTICATE)
 			if err := c.writeReply(reply); err != nil {
 				close(unregister)
@@ -562,7 +566,6 @@ func New(conn net.Conn) (*Client, error) {
 
 	c := &Client{
 		conn:      imap.NewConn(conn, r, w),
-		replies:   make(chan []byte),
 		loggedOut: make(chan struct{}),
 		state:     imap.ConnectingState,
 		ErrorLog:  log.New(os.Stderr, "imap/client: ", log.LstdFlags),

client/cmd_noauth.go

@@ -93,10 +93,7 @@ func (c *Client) Authenticate(auth sasl.Client) error {
 	res := &responses.Authenticate{
 		Mechanism:       auth,
 		InitialResponse: ir,
-		AuthReply: func(reply []byte) error {
-			c.replies <- reply
-			return nil
-		},
+		RepliesCh:       make(chan []byte, 10),
 	}
 
 	status, err := c.execute(cmd, res)

responses/authenticate.go

@@ -7,17 +7,21 @@ import (
 	"github.com/emersion/go-sasl"
 )
 
-type AuthReplyFunc func(reply []byte) error
-
 // An AUTHENTICATE response.
 type Authenticate struct {
 	Mechanism       sasl.Client
 	InitialResponse []byte
-	AuthReply       AuthReplyFunc
+	RepliesCh       chan []byte
+}
+
+// Implements
+func (r *Authenticate) Replies() <-chan []byte {
+	return r.RepliesCh
 }
 
 func (r *Authenticate) writeLine(l string) error {
-	return r.AuthReply([]byte(l + "\r\n"))
+	r.RepliesCh <- []byte(l + "\r\n")
+	return nil
 }
 
 func (r *Authenticate) cancel() error {

responses/responses.go

@@ -26,3 +26,10 @@ type HandlerFunc func(resp imap.Resp) error
 func (f HandlerFunc) Handle(resp imap.Resp) error {
 	return f(resp)
 }
+
+// Replier is a Handler that needs to send raw data (for instance
+// AUTHENTICATE).
+type Replier interface {
+	Handler
+	Replies() <-chan []byte
+}