fix(imapx): honor context in Connect with bounded dial retry

internal/imapx/dial.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"crypto/tls"
 	"fmt"
+	"time"
 
 	"github.com/emersion/go-imap/v2/imapclient"
 )
@@ -16,30 +17,46 @@ type Endpoint struct {
 
 func (e Endpoint) addr() string { return fmt.Sprintf("%s:%d", e.Host, e.Port) }
 
-func Connect(ctx context.Context, ep Endpoint) (*imapclient.Client, error) {
-	var (
-		c   *imapclient.Client
-		err error
-	)
+func dialOnce(ep Endpoint) (*imapclient.Client, error) {
 	switch ep.TLSMode {
 	case "ssl":
-		c, err = imapclient.DialTLS(ep.addr(), &imapclient.Options{
+		return imapclient.DialTLS(ep.addr(), &imapclient.Options{
 			TLSConfig: &tls.Config{ServerName: ep.Host},
 		})
 	case "starttls":
-		c, err = imapclient.DialStartTLS(ep.addr(), &imapclient.Options{
+		return imapclient.DialStartTLS(ep.addr(), &imapclient.Options{
 			TLSConfig: &tls.Config{ServerName: ep.Host},
 		})
 	case "plain":
-		c, err = imapclient.DialInsecure(ep.addr(), nil)
+		return imapclient.DialInsecure(ep.addr(), nil)
 	default:
 		return nil, fmt.Errorf("unknown tls_mode %q", ep.TLSMode)
 	}
-	if err != nil {
+}
+
+func Connect(ctx context.Context, ep Endpoint) (*imapclient.Client, error) {
+	const attempts = 3
+	var lastErr error
+	for i := 0; i < attempts; i++ {
+		if err := ctx.Err(); err != nil {
 			return nil, err
 		}
+		c, err := dialOnce(ep)
+		if err == nil {
 			return c, nil
 		}
+		lastErr = err
+		if i < attempts-1 {
+			backoff := time.Duration(200*(i+1)) * time.Millisecond
+			select {
+			case <-ctx.Done():
+				return nil, ctx.Err()
+			case <-time.After(backoff):
+			}
+		}
+	}
+	return nil, lastErr
+}
 
 func TestEndpoint(ctx context.Context, ep Endpoint) error {
 	c, err := Connect(ctx, ep)

internal/imapx/dial_test.go

@@ -40,3 +40,12 @@ func TestTestLoginListsFolders(t *testing.T) {
 		t.Fatalf("INBOX not in folders: %v", folders)
 	}
 }
+
+func TestConnectHonorsCancelledContext(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+	_, err := Connect(ctx, Endpoint{Host: "10.255.255.1", Port: 993, TLSMode: "ssl"})
+	if err == nil {
+		t.Fatal("expected error for cancelled context")
+	}
+}