feat(imapx): connect, endpoint test, login test with folder listing

internal/imapx/dial.go

@@ -0,0 +1,50 @@
+package imapx
+
+import (
+	"context"
+	"crypto/tls"
+	"fmt"
+
+	"github.com/emersion/go-imap/v2/imapclient"
+)
+
+type Endpoint struct {
+	Host    string
+	Port    int
+	TLSMode string // ssl | starttls | plain
+}
+
+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
+	)
+	switch ep.TLSMode {
+	case "ssl":
+		c, err = imapclient.DialTLS(ep.addr(), &imapclient.Options{
+			TLSConfig: &tls.Config{ServerName: ep.Host},
+		})
+	case "starttls":
+		c, err = imapclient.DialStartTLS(ep.addr(), &imapclient.Options{
+			TLSConfig: &tls.Config{ServerName: ep.Host},
+		})
+	case "plain":
+		c, err = imapclient.DialInsecure(ep.addr(), nil)
+	default:
+		return nil, fmt.Errorf("unknown tls_mode %q", ep.TLSMode)
+	}
+	if err != nil {
+		return nil, err
+	}
+	return c, nil
+}
+
+func TestEndpoint(ctx context.Context, ep Endpoint) error {
+	c, err := Connect(ctx, ep)
+	if err != nil {
+		return err
+	}
+	return c.Logout().Wait()
+}