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package gomail
import (
"bytes"
"errors"
"fmt"
"net/smtp"
)
// plainAuth is an smtp.Auth that implements the PLAIN authentication mechanism.
// It fallbacks to the LOGIN mechanism if it is the only mechanism advertised
// by the server.
type plainAuth struct {
username string
password string
host string
login bool
}
func (a *plainAuth) Start(server *smtp.ServerInfo) (string, []byte, error) {
if server.Name != a.host {
return "", nil, errors.New("gomail: wrong host name")
}
var plain, login bool
for _, a := range server.Auth {
switch a {
case "PLAIN":
plain = true
case "LOGIN":
login = true
}
}
if !server.TLS && !plain && !login {
return "", nil, errors.New("gomail: unencrypted connection")
}
if !plain && login {
a.login = true
return "LOGIN", nil, nil
}
return "PLAIN", []byte("\x00" + a.username + "\x00" + a.password), nil
}
func (a *plainAuth) Next(fromServer []byte, more bool) ([]byte, error) {
if !a.login {
if more {
return nil, errors.New("gomail: unexpected server challenge")
}
return nil, nil
}
if !more {
return nil, nil
}
switch {
case bytes.Equal(fromServer, []byte("Username:")):
return []byte(a.username), nil
case bytes.Equal(fromServer, []byte("Password:")):
return []byte(a.password), nil
default:
return nil, fmt.Errorf("gomail: unexpected server challenge: %s", fromServer)
}
}
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