fake-smtp/internal/command/relay_email.go

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
}