watchtower/pkg/notifications/smtp.go

// Package notifications ...
// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license.
package notifications

import (
	"crypto/tls"
	"net"
	"net/smtp"
)

// SendMail connects to the server at addr, switches to TLS if
// possible, authenticates with the optional mechanism a if possible,
// and then sends an email from address from, to addresses to, with
// message msg.
// The addr must include a port, as in "mail.example.com:smtp".
//
// The addresses in the to parameter are the SMTP RCPT addresses.
//
// The msg parameter should be an RFC 822-style email with headers
// first, a blank line, and then the message body. The lines of msg
// should be CRLF terminated. The msg headers should usually include
// fields such as "From", "To", "Subject", and "Cc".  Sending "Bcc"
// messages is accomplished by including an email address in the to
// parameter but not including it in the msg headers.
//
// The SendMail function and the net/smtp package are low-level
// mechanisms and provide no support for DKIM signing, MIME
// attachments (see the mime/multipart package), or other mail
// functionality. Higher-level packages exist outside of the standard
// library.
func SendMail(addr string, insecureSkipVerify bool, a smtp.Auth, from string, to []string, msg []byte) error {
	c, err := smtp.Dial(addr)
	if err != nil {
		return err
	}
	defer c.Close()
	if err = c.Hello("localHost"); err != nil {
		return err
	}
	if ok, _ := c.Extension("STARTTLS"); ok {
		serverName, _, _ := net.SplitHostPort(addr)
		config := &tls.Config{ServerName: serverName, InsecureSkipVerify: insecureSkipVerify}
		if err = c.StartTLS(config); err != nil {
			return err
		}
	}
	if a != nil {
		if ok, _ := c.Extension("AUTH"); ok {
			if err = c.Auth(a); err != nil {
				return err
			}
		}
	}
	if err = c.Mail(from); err != nil {
		return err
	}
	for _, addr := range to {
		if err = c.Rcpt(addr); err != nil {
			return err
		}
	}
	w, err := c.Data()
	if err != nil {
		return err
	}
	_, err = w.Write(msg)
	if err != nil {
		return err
	}
	err = w.Close()
	if err != nil {
		return err
	}
	return c.Quit()
}