Allow email relaying to a real MTA

internal/command/relay_email.go

@@ -0,0 +1,164 @@
+package command
+
+import (
+	"context"
+	"crypto/tls"
+	"io"
+	"sync"
+
+	"github.com/emersion/go-sasl"
+
+	"github.com/emersion/go-smtp"
+
+	"forge.cadoles.com/wpetit/fake-smtp/internal/config"
+	"github.com/jhillyerd/enmime"
+	"github.com/pkg/errors"
+	"gitlab.com/wpetit/goweb/cqrs"
+	"gitlab.com/wpetit/goweb/middleware/container"
+)
+
+type RelayEmailRequest struct {
+	Envelope *enmime.Envelope
+}
+
+func HandleRelayEmail(ctx context.Context, cmd cqrs.Command) error {
+	req, ok := cmd.Request().(*RelayEmailRequest)
+	if !ok {
+		return cqrs.ErrUnexpectedRequest
+	}
+
+	ctn, err := container.From(ctx)
+	if err != nil {
+		return errors.Wrap(err, "could not retrieve service container")
+	}
+
+	conf, err := config.From(ctn)
+	if err != nil {
+		return errors.Wrap(err, "could not retrieve config service")
+	}
+
+	relay := conf.Relay
+
+	if err := forwardMail(req.Envelope, relay); err != nil {
+		return errors.Wrap(err, "could not forward mail")
+	}
+
+	return nil
+}
+
+func forwardMail(env *enmime.Envelope, conf config.RelayConfig) error {
+	var tlsConfig *tls.Config
+
+	if conf.InsecureSkipVerify {
+		tlsConfig = &tls.Config{
+			// nolint: gosec
+			InsecureSkipVerify: true,
+		}
+	}
+
+	addr := conf.Address
+
+	var (
+		client *smtp.Client
+		err    error
+	)
+
+	if conf.UseTLS {
+		client, err = smtp.DialTLS(addr, tlsConfig)
+		if err != nil {
+			return errors.WithStack(err)
+		}
+	} else {
+		client, err = smtp.Dial(addr)
+		if err != nil {
+			return errors.WithStack(err)
+		}
+	}
+	defer client.Close()
+
+	if err = client.Hello("localhost"); err != nil {
+		return errors.WithStack(err)
+	}
+
+	if ok, _ := client.Extension("STARTTLS"); ok {
+		if err = client.StartTLS(tlsConfig); err != nil {
+			return errors.WithStack(err)
+		}
+	}
+
+	if conf.Username != "" || conf.Password != "" {
+		if ok, _ := client.Extension("AUTH"); ok {
+			var auth sasl.Client
+			if conf.Anonymous {
+				auth = sasl.NewAnonymousClient("fakesmtp")
+			} else {
+				auth = sasl.NewPlainClient(conf.Identity, conf.Username, conf.Password)
+			}
+
+			if err := client.Auth(auth); err != nil {
+				return errors.WithStack(err)
+			}
+		}
+	}
+
+	var from string
+
+	if conf.FromOverride != "" {
+		from = conf.FromOverride
+	} else {
+		from = env.GetHeader("From")
+	}
+
+	if err = client.Mail(from, nil); err != nil {
+		return errors.WithStack(err)
+	}
+
+	to := env.GetHeaderValues("To")
+
+	for _, addr := range to {
+		if err = client.Rcpt(addr); err != nil {
+			return errors.WithStack(err)
+		}
+	}
+
+	w, err := client.Data()
+	if err != nil {
+		return errors.WithStack(err)
+	}
+
+	pr, pw := io.Pipe()
+
+	var wg sync.WaitGroup
+
+	wg.Add(1)
+
+	go func() {
+		defer wg.Done()
+		defer pw.Close()
+
+		if err = env.Root.Encode(pw); err != nil {
+			err = errors.WithStack(err)
+		}
+	}()
+
+	_, err = io.Copy(w, pr)
+	if err != nil {
+		return err
+	}
+
+	wg.Wait()
+
+	if err != nil {
+		return errors.WithStack(err)
+	}
+
+	if err = w.Close(); err != nil {
+		return err
+	}
+
+	if err := client.Quit(); err != nil {
+		return errors.WithStack(err)
+	}
+
+	return nil
+}

internal/config/config.go

@@ -12,9 +12,10 @@ import (
 )
 
 type Config struct {
-	HTTP HTTPConfig `yaml:"http"`
-	SMTP SMTPConfig `yaml:"smtp"`
-	Data DataConfig `ymal:"data"`
+	HTTP  HTTPConfig  `yaml:"http"`
+	SMTP  SMTPConfig  `yaml:"smtp"`
+	Data  DataConfig  `yaml:"data"`
+	Relay RelayConfig `yaml:"relay"`
 }
 
 type HTTPConfig struct {
@@ -36,6 +37,18 @@ type SMTPConfig struct {
 	Debug             bool          `yaml:"debug" env:"FAKESMTP_SMTP_DEBUG"`
 }
 
+type RelayConfig struct {
+	Enabled            bool   `yaml:"enabled" env:"FAKESMTP_RELAY_ENABLED"`
+	Address            string `yaml:"address" env:"FAKESMTP_RELAY_ADDRESS"`
+	Identity           string `yaml:"identity" env:"FAKESMTP_RELAY_IDENTITY"`
+	Username           string `yaml:"username" env:"FAKESMTP_RELAY_USERNAME"`
+	Password           string `yaml:"password" env:"FAKESMTP_RELAY_PASSWORD"`
+	Anonymous          bool   `yaml:"anonymous" env:"FAKESMTP_RELAY_ANONYMOUS"`
+	UseTLS             bool   `yaml:"useTLS" env:"FAKESMTP_RELAY_USE_TLS"`
+	InsecureSkipVerify bool   `yaml:"insecureSkipVerify" env:"FAKESMTP_RELAY_INSECURE_SKIP_VERIFY"`
+	FromOverride       string `yaml:"fromOverride" env:"FAKESMTP_RELAY_FROM_OVERRIDE"`
+}
+
 type DataConfig struct {
 	Path string `yaml:"path" env:"FAKESMTP_DATA_PATH"`
 }
@@ -91,6 +104,9 @@ func NewDefault() *Config {
 		Data: DataConfig{
 			Path: "fakesmtp.db",
 		},
+		Relay: RelayConfig{
+			Enabled: false,
+		},
 	}
 }