293 lines
7 KiB
Go
293 lines
7 KiB
Go
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package mail
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import (
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"crypto/tls"
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"fmt"
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"io"
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"net"
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"net/smtp"
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"strings"
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"time"
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)
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// A Dialer is a dialer to an SMTP server.
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type Dialer struct {
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// Host represents the host of the SMTP server.
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Host string
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// Port represents the port of the SMTP server.
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Port int
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// Username is the username to use to authenticate to the SMTP server.
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Username string
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// Password is the password to use to authenticate to the SMTP server.
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Password string
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// Auth represents the authentication mechanism used to authenticate to the
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// SMTP server.
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Auth smtp.Auth
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// SSL defines whether an SSL connection is used. It should be false in
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// most cases since the authentication mechanism should use the STARTTLS
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// extension instead.
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SSL bool
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// TLSConfig represents the TLS configuration used for the TLS (when the
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// STARTTLS extension is used) or SSL connection.
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TLSConfig *tls.Config
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// StartTLSPolicy represents the TLS security level required to
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// communicate with the SMTP server.
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//
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// This defaults to OpportunisticStartTLS for backwards compatibility,
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// but we recommend MandatoryStartTLS for all modern SMTP servers.
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//
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// This option has no effect if SSL is set to true.
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StartTLSPolicy StartTLSPolicy
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// LocalName is the hostname sent to the SMTP server with the HELO command.
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// By default, "localhost" is sent.
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LocalName string
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// Timeout to use for read/write operations. Defaults to 10 seconds, can
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// be set to 0 to disable timeouts.
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Timeout time.Duration
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// Whether we should retry mailing if the connection returned an error,
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// defaults to true.
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RetryFailure bool
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}
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// NewDialer returns a new SMTP Dialer. The given parameters are used to connect
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// to the SMTP server.
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func NewDialer(host string, port int, username, password string) *Dialer {
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return &Dialer{
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Host: host,
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Port: port,
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Username: username,
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Password: password,
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SSL: port == 465,
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Timeout: 10 * time.Second,
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RetryFailure: true,
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}
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}
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// NewPlainDialer returns a new SMTP Dialer. The given parameters are used to
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// connect to the SMTP server.
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//
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// Deprecated: Use NewDialer instead.
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func NewPlainDialer(host string, port int, username, password string) *Dialer {
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return NewDialer(host, port, username, password)
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}
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// NetDialTimeout specifies the DialTimeout function to establish a connection
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// to the SMTP server. This can be used to override dialing in the case that a
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// proxy or other special behavior is needed.
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var NetDialTimeout = net.DialTimeout
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// Dial dials and authenticates to an SMTP server. The returned SendCloser
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// should be closed when done using it.
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func (d *Dialer) Dial() (SendCloser, error) {
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conn, err := NetDialTimeout("tcp", addr(d.Host, d.Port), d.Timeout)
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if err != nil {
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return nil, err
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}
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if d.SSL {
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conn = tlsClient(conn, d.tlsConfig())
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}
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c, err := smtpNewClient(conn, d.Host)
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if err != nil {
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return nil, err
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}
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if d.Timeout > 0 {
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conn.SetDeadline(time.Now().Add(d.Timeout))
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}
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if d.LocalName != "" {
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if err := c.Hello(d.LocalName); err != nil {
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return nil, err
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}
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}
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if !d.SSL && d.StartTLSPolicy != NoStartTLS {
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ok, _ := c.Extension("STARTTLS")
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if !ok && d.StartTLSPolicy == MandatoryStartTLS {
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err := StartTLSUnsupportedError{
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Policy: d.StartTLSPolicy}
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return nil, err
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}
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if ok {
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if err := c.StartTLS(d.tlsConfig()); err != nil {
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c.Close()
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return nil, err
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}
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}
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}
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if d.Auth == nil && d.Username != "" {
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if ok, auths := c.Extension("AUTH"); ok {
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if strings.Contains(auths, "CRAM-MD5") {
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d.Auth = smtp.CRAMMD5Auth(d.Username, d.Password)
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} else if strings.Contains(auths, "LOGIN") &&
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!strings.Contains(auths, "PLAIN") {
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d.Auth = &loginAuth{
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username: d.Username,
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password: d.Password,
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host: d.Host,
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}
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} else {
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d.Auth = smtp.PlainAuth("", d.Username, d.Password, d.Host)
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}
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}
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}
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if d.Auth != nil {
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if err = c.Auth(d.Auth); err != nil {
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c.Close()
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return nil, err
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}
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}
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return &smtpSender{c, conn, d}, nil
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}
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func (d *Dialer) tlsConfig() *tls.Config {
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if d.TLSConfig == nil {
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return &tls.Config{ServerName: d.Host}
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}
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return d.TLSConfig
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}
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// StartTLSPolicy constants are valid values for Dialer.StartTLSPolicy.
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type StartTLSPolicy int
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const (
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// OpportunisticStartTLS means that SMTP transactions are encrypted if
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// STARTTLS is supported by the SMTP server. Otherwise, messages are
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// sent in the clear. This is the default setting.
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OpportunisticStartTLS StartTLSPolicy = iota
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// MandatoryStartTLS means that SMTP transactions must be encrypted.
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// SMTP transactions are aborted unless STARTTLS is supported by the
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// SMTP server.
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MandatoryStartTLS
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// NoStartTLS means encryption is disabled and messages are sent in the
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// clear.
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NoStartTLS = -1
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)
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func (policy *StartTLSPolicy) String() string {
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switch *policy {
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case OpportunisticStartTLS:
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return "OpportunisticStartTLS"
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case MandatoryStartTLS:
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return "MandatoryStartTLS"
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case NoStartTLS:
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return "NoStartTLS"
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default:
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return fmt.Sprintf("StartTLSPolicy:%v", *policy)
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}
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}
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// StartTLSUnsupportedError is returned by Dial when connecting to an SMTP
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// server that does not support STARTTLS.
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type StartTLSUnsupportedError struct {
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Policy StartTLSPolicy
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}
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func (e StartTLSUnsupportedError) Error() string {
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return "gomail: " + e.Policy.String() + " required, but " +
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"SMTP server does not support STARTTLS"
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}
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func addr(host string, port int) string {
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return fmt.Sprintf("%s:%d", host, port)
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}
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// DialAndSend opens a connection to the SMTP server, sends the given emails and
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// closes the connection.
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func (d *Dialer) DialAndSend(m ...*Message) error {
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s, err := d.Dial()
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if err != nil {
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return err
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}
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defer s.Close()
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return Send(s, m...)
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}
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type smtpSender struct {
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smtpClient
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conn net.Conn
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d *Dialer
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}
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func (c *smtpSender) retryError(err error) bool {
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if !c.d.RetryFailure {
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return false
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}
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if nerr, ok := err.(net.Error); ok && nerr.Timeout() {
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return true
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}
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return err == io.EOF
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}
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func (c *smtpSender) Send(from string, to []string, msg io.WriterTo) error {
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if c.d.Timeout > 0 {
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c.conn.SetDeadline(time.Now().Add(c.d.Timeout))
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}
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if err := c.Mail(from); err != nil {
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if c.retryError(err) {
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// This is probably due to a timeout, so reconnect and try again.
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sc, derr := c.d.Dial()
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if derr == nil {
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if s, ok := sc.(*smtpSender); ok {
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*c = *s
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return c.Send(from, to, msg)
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}
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}
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}
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return err
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}
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for _, addr := range to {
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if err := c.Rcpt(addr); err != nil {
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return err
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}
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}
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w, err := c.Data()
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if err != nil {
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return err
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}
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if _, err = msg.WriteTo(w); err != nil {
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w.Close()
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return err
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}
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return w.Close()
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}
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func (c *smtpSender) Close() error {
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return c.Quit()
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}
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// Stubbed out for tests.
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var (
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tlsClient = tls.Client
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smtpNewClient = func(conn net.Conn, host string) (smtpClient, error) {
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return smtp.NewClient(conn, host)
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}
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)
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type smtpClient interface {
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Hello(string) error
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Extension(string) (bool, string)
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StartTLS(*tls.Config) error
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Auth(smtp.Auth) error
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Mail(string) error
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Rcpt(string) error
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Data() (io.WriteCloser, error)
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Quit() error
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Close() error
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}
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