imap: monitor the logout channel with an observer

Untangle the observer functionality from the message handling routine.
Observe the imap client's logout channel and trigger a connection error
when necessary to start the reconnect cycle.

Signed-off-by: Koni Marti <koni.marti@gmail.com>
Acked-by: Robin Jarry <robin@jarry.cc>

3 files changed, 186 insertions, 86 deletions

diff --git a/worker/imap/configure.go b/worker/imap/configure.go
index 0bccbae..c25600d 100644
--- a/worker/imap/configure.go
+++ b/worker/imap/configure.go
@@ -50,6 +50,9 @@ func (w *IMAPWorker) handleConfigure(msg *types.Configure) error {
 	w.config.keepalive_period = 0 * time.Second
 	w.config.keepalive_probes = 3
 	w.config.keepalive_interval = 3
+
+	w.config.reconnect_maxwait = 30 * time.Second
+
 	for key, value := range msg.Config.Params {
 		switch key {
 		case "idle-timeout":
@@ -60,6 +63,14 @@ func (w *IMAPWorker) handleConfigure(msg *types.Configure) error {
 					value, err)
 			}
 			w.config.idle_timeout = val
+		case "reconnect-maxwait":
+			val, err := time.ParseDuration(value)
+			if err != nil || val < 0 {
+				return fmt.Errorf(
+					"invalid reconnect-maxwait value %v: %v",
+					value, err)
+			}
+			w.config.reconnect_maxwait = val
 		case "connection-timeout":
 			val, err := time.ParseDuration(value)
 			if err != nil || val < 0 {
@@ -96,6 +107,7 @@ func (w *IMAPWorker) handleConfigure(msg *types.Configure) error {
 	}
 
 	w.idler = newIdler(w.config, w.worker)
+	w.observer = newObserver(w.config, w.worker)
 
 	return nil
 }
diff --git a/worker/imap/observer.go b/worker/imap/observer.go
new file mode 100644
index 0000000..e49744c
--- /dev/null
+++ b/worker/imap/observer.go
@@ -0,0 +1,152 @@
+package imap
+
+import (
+	"fmt"
+	"math"
+	"sync"
+	"time"
+
+	"git.sr.ht/~rjarry/aerc/worker/types"
+	"github.com/emersion/go-imap"
+)
+
+// observer monitors the loggedOut channel of the imap client. If the logout
+// signal is received, the observer will emit a connection error to the ui in
+// order to start the reconnect cycle.
+type observer struct {
+	sync.Mutex
+	config        imapConfig
+	client        *imapClient
+	worker        *types.Worker
+	done          chan struct{}
+	autoReconnect bool
+	retries       int
+	running       bool
+}
+
+func newObserver(cfg imapConfig, w *types.Worker) *observer {
+	return &observer{config: cfg, worker: w, done: make(chan struct{})}
+}
+
+func (o *observer) SetClient(c *imapClient) {
+	o.Stop()
+	o.Lock()
+	o.client = c
+	o.Unlock()
+	o.Start()
+	o.retries = 0
+}
+
+func (o *observer) SetAutoReconnect(auto bool) {
+	o.autoReconnect = auto
+}
+
+func (o *observer) AutoReconnect() bool {
+	return o.autoReconnect
+}
+
+func (o *observer) isClientConnected() bool {
+	o.Lock()
+	defer o.Unlock()
+	return o.client != nil && o.client.State() == imap.SelectedState
+}
+
+func (o *observer) EmitIfNotConnected() bool {
+	if !o.isClientConnected() {
+		o.emit("imap client not connected: attempt reconnect")
+		return true
+	}
+	return false
+}
+
+func (o *observer) IsRunning() bool {
+	return o.running
+}
+
+func (o *observer) Start() {
+	if o.running {
+		o.log("runs already")
+		return
+	}
+	if o.client == nil {
+		return
+	}
+	if o.EmitIfNotConnected() {
+		return
+	}
+	go func() {
+		select {
+		case <-o.client.LoggedOut():
+			o.log("<-logout")
+			if o.autoReconnect {
+				o.emit("logged out")
+			} else {
+				o.log("ignore logout (auto-reconnect off)")
+			}
+		case <-o.done:
+			o.log("<-done")
+		}
+		o.running = false
+		o.log("stopped")
+	}()
+	o.running = true
+	o.log("started")
+}
+
+func (o *observer) Stop() {
+	if o.client == nil {
+		return
+	}
+	if o.done != nil {
+		close(o.done)
+	}
+	o.done = make(chan struct{})
+	o.running = false
+}
+
+func (o *observer) DelayedReconnect() error {
+	if o.client == nil {
+		return nil
+	}
+	var wait time.Duration
+	var reterr error
+
+	if o.retries > 0 {
+		backoff := int(math.Pow(1.8, float64(o.retries)))
+		var err error
+		wait, err = time.ParseDuration(fmt.Sprintf("%ds", backoff))
+		if err != nil {
+			return err
+		}
+		if wait > o.config.reconnect_maxwait {
+			wait = o.config.reconnect_maxwait
+		}
+
+		reterr = fmt.Errorf("reconnect in %v", wait)
+	} else {
+		reterr = fmt.Errorf("reconnect")
+	}
+
+	go func() {
+		<-time.After(wait)
+		o.emit(reterr.Error())
+	}()
+
+	o.retries++
+	return reterr
+}
+
+func (o *observer) emit(errMsg string) {
+	o.log("disconnect done->")
+	o.worker.PostMessage(&types.Done{
+		Message: types.RespondTo(&types.Disconnect{})}, nil)
+	o.log("connection error->")
+	o.worker.PostMessage(&types.ConnError{
+		Error: fmt.Errorf(errMsg),
+	}, nil)
+}
+
+func (o *observer) log(args ...interface{}) {
+	header := fmt.Sprintf("observer (%p) [running:%t]", o, o.running)
+	o.worker.Logger.Println(append([]interface{}{header}, args...)...)
+}
diff --git a/worker/imap/worker.go b/worker/imap/worker.go
index d0f8482..6e47530 100644
--- a/worker/imap/worker.go
+++ b/worker/imap/worker.go
@@ -3,7 +3,6 @@ package imap
 import (
 	"crypto/tls"
 	"fmt"
-	"math"
 	"net"
 	"net/url"
 	"time"
@@ -37,13 +36,14 @@ type imapClient struct {
 }
 
 type imapConfig struct {
-	scheme       string
-	insecure     bool
-	addr         string
-	user         *url.Userinfo
-	folders      []string
-	oauthBearer  lib.OAuthBearer
-	idle_timeout time.Duration
+	scheme            string
+	insecure          bool
+	addr              string
+	user              *url.Userinfo
+	folders           []string
+	oauthBearer       lib.OAuthBearer
+	idle_timeout      time.Duration
+	reconnect_maxwait time.Duration
 	// tcp connection parameters
 	connection_timeout time.Duration
 	keepalive_period   time.Duration
@@ -61,11 +61,8 @@ type IMAPWorker struct {
 	// Map of sequence numbers to UIDs, index 0 is seq number 1
 	seqMap []uint32
 
-	done          chan struct{}
-	autoReconnect bool
-	retries       int
-
-	idler *idler
+	idler    *idler
+	observer *observer
 }
 
 func NewIMAPWorker(worker *types.Worker) (types.Backend, error) {
@@ -74,6 +71,7 @@ func NewIMAPWorker(worker *types.Worker) (types.Backend, error) {
 		worker:   worker,
 		selected: &imap.MailboxStatus{},
 		idler:    newIdler(imapConfig{}, worker),
+		observer: newObserver(imapConfig{}, worker),
 	}, nil
 }
 
@@ -81,6 +79,7 @@ func (w *IMAPWorker) newClient(c *client.Client) {
 	c.Updates = w.updates
 	w.client = &imapClient{c, sortthread.NewThreadClient(c), sortthread.NewSortClient(c)}
 	w.idler.SetClient(w.client)
+	w.observer.SetClient(w.client)
 }
 
 func (w *IMAPWorker) handleMessage(msg types.WorkerMessage) error {
@@ -93,12 +92,6 @@ func (w *IMAPWorker) handleMessage(msg types.WorkerMessage) error {
 
 	var reterr error // will be returned at the end, needed to support idle
 
-	checkConn := func(wait time.Duration) {
-		time.Sleep(wait)
-		w.stopConnectionObserver()
-		w.startConnectionObserver()
-	}
-
 	// set connection timeout for calls to imap server
 	if w.client != nil {
 		w.client.Timeout = w.config.connection_timeout
@@ -111,53 +104,43 @@ func (w *IMAPWorker) handleMessage(msg types.WorkerMessage) error {
 		reterr = w.handleConfigure(msg)
 	case *types.Connect:
 		if w.client != nil && w.client.State() == imap.SelectedState {
-			if !w.autoReconnect {
-				w.autoReconnect = true
-				checkConn(0)
+			if !w.observer.AutoReconnect() {
+				w.observer.SetAutoReconnect(true)
+				w.observer.EmitIfNotConnected()
 			}
 			reterr = errAlreadyConnected
 			break
 		}
 
-		w.autoReconnect = true
+		w.observer.SetAutoReconnect(true)
 		c, err := w.connect()
 		if err != nil {
-			checkConn(0)
+			w.observer.EmitIfNotConnected()
 			reterr = err
 			break
 		}
 
-		w.stopConnectionObserver()
-
 		w.newClient(c)
 
-		w.startConnectionObserver()
-
 		w.worker.PostMessage(&types.Done{Message: types.RespondTo(msg)}, nil)
 	case *types.Reconnect:
-		if !w.autoReconnect {
+		if !w.observer.AutoReconnect() {
 			reterr = fmt.Errorf("auto-reconnect is disabled; run connect to enable it")
 			break
 		}
 		c, err := w.connect()
 		if err != nil {
-			wait, msg := w.exponentialBackoff()
-			go checkConn(wait)
-			w.retries++
-			reterr = errors.Wrap(err, msg)
+			errReconnect := w.observer.DelayedReconnect()
+			reterr = errors.Wrap(errReconnect, err.Error())
 			break
 		}
 
-		w.stopConnectionObserver()
-
 		w.newClient(c)
 
-		w.startConnectionObserver()
-
 		w.worker.PostMessage(&types.Done{Message: types.RespondTo(msg)}, nil)
 	case *types.Disconnect:
-		w.autoReconnect = false
-		w.stopConnectionObserver()
+		w.observer.SetAutoReconnect(false)
+		w.observer.Stop()
 		if w.client == nil || w.client.State() != imap.SelectedState {
 			reterr = errNotConnected
 			break
@@ -267,51 +250,6 @@ func (w *IMAPWorker) handleImapUpdate(update client.Update) {
 	}
 }
 
-func (w *IMAPWorker) exponentialBackoff() (time.Duration, string) {
-	maxWait := 16
-	if w.retries > 0 {
-		backoff := int(math.Pow(2.0, float64(w.retries)))
-		if backoff > maxWait {
-			backoff = maxWait
-		}
-		waitStr := fmt.Sprintf("%ds", backoff)
-		wait, err := time.ParseDuration(waitStr)
-		if err == nil {
-			return wait, fmt.Sprintf("wait %s before reconnect", waitStr)
-		}
-	}
-	return 0 * time.Second, ""
-}
-
-func (w *IMAPWorker) startConnectionObserver() {
-	emitConnErr := func(errMsg string) {
-		w.worker.PostMessage(&types.ConnError{
-			Error: fmt.Errorf(errMsg),
-		}, nil)
-	}
-	if w.client == nil {
-		emitConnErr("imap client not connected")
-		return
-	}
-	go func() {
-		select {
-		case <-w.client.LoggedOut():
-			if w.autoReconnect {
-				emitConnErr("imap: logged out")
-			}
-		case <-w.done:
-			return
-		}
-	}()
-}
-
-func (w *IMAPWorker) stopConnectionObserver() {
-	if w.done != nil {
-		close(w.done)
-	}
-	w.done = make(chan struct{})
-}
-
 func (w *IMAPWorker) connect() (*client.Client, error) {
 	var (
 		conn *net.TCPConn
@@ -391,8 +329,6 @@ func (w *IMAPWorker) connect() (*client.Client, error) {
 		return nil, err
 	}
 
-	w.retries = 0
-
 	return c, nil
 }