sender.go

// Copyright (C) 2019 Storj Labs, Inc.
// See LICENSE for copying information

package post

import (
	"context"
	"crypto/tls"
	"io"
	"net"
	"net/mail"
	"net/smtp"

	"github.com/spacemonkeygo/monkit/v3"
	"github.com/zeebo/errs"
)

// Address is alias of net/mail.Address.
type Address = mail.Address

var mon = monkit.Package()

// SMTPSender is smtp sender.
type SMTPSender struct {
	ServerAddress string

	From Address
	Auth smtp.Auth
}

// FromAddress implements satellite/mail.SMTPSender.
func (sender *SMTPSender) FromAddress() Address {
	return sender.From
}

// SendEmail sends email message to the given recipient.
func (sender *SMTPSender) SendEmail(ctx context.Context, msg *Message) (err error) {
	defer mon.Task()(&ctx)(&err)

	client, err := smtp.Dial(sender.ServerAddress)
	if err != nil {
		return err
	}

	if err = sender.communicate(ctx, client, msg); err != nil {
		return errs.Combine(err, client.Close())
	}

	return nil
}

// communicate sends mail via SMTP using provided client and message.
func (sender *SMTPSender) communicate(ctx context.Context, client *smtp.Client, msg *Message) error {
	// suppress error because address should be validated
	// before creating SMTPSender
	host, _, _ := net.SplitHostPort(sender.ServerAddress)

	// send smtp hello or ehlo msg and establish connection over tls
	err := client.StartTLS(&tls.Config{ServerName: host})
	if err != nil {
		return err
	}

	err = client.Auth(sender.Auth)
	if err != nil {
		return err
	}

	err = client.Mail(sender.From.Address)
	if err != nil {
		return err
	}

	// add recipients
	for _, to := range msg.To {
		err = client.Rcpt(to.Address)
		if err != nil {
			return err
		}
	}

	mess, err := msg.Bytes()
	if err != nil {
		return err
	}

	data, err := client.Data()
	if err != nil {
		return err
	}

	err = writeData(data, mess)
	if err != nil {
		return err
	}

	// send quit msg to stop gracefully
	return client.Quit()
}

// writeData ensures that writer will be closed after data is written.
func writeData(writer io.WriteCloser, data []byte) (err error) {
	defer func() {
		err = errs.Combine(err, writer.Close())
	}()

	_, err = writer.Write(data)
	return
}