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checker.go
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checker.go
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// Package emailcheryp
package emailcheryp
import (
"errors"
"fmt"
"net"
"net/smtp"
"regexp"
"strings"
"time"
)
type SmtpError struct {
Err error
}
func (e SmtpError) Error() string {
return e.Err.Error()
}
func (e SmtpError) Code() string {
return e.Err.Error()[0:3]
}
func NewSmtpError(err error) SmtpError {
return SmtpError{
Err: err,
}
}
const forceDisconnectAfter = time.Second * 5
var (
ErrBadFormat = errors.New("invalid format")
ErrUnresolvableDomain = errors.New("unresolvable domain")
emailRegexp = regexp.MustCompile(`(?m)^(((((((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?([A-Za-z0-9!#-'*+\/=?^_\x60{|}~-])+((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?)|(((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?"((\s? +)?(([!#-[\]-~])|(\\([ -~]|\s))))*(\s? +)?"))?)?(((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?<(((((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?(([A-Za-z0-9!#-'*+\/=?^_\x60{|}~-])+(\.([A-Za-z0-9!#-'*+\/=?^_\x60{|}~-])+)*)((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?)|(((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?"((\s? +)?(([!#-[\]-~])|(\\([ -~]|\s))))*(\s? +)?"))@((((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?(([A-Za-z0-9!#-'*+\/=?^_\x60{|}~-])+(\.([A-Za-z0-9!#-'*+\/=?^_\x60{|}~-])+)*)((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?)|(((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?\[((\s? +)?([!-Z^-~]))*(\s? +)?\]((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?)))>((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?))|(((((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?(([A-Za-z0-9!#-'*+\/=?^_\x60{|}~-])+(\.([A-Za-z0-9!#-'*+\/=?^_\x60{|}~-])+)*)((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?)|(((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?"((\s? +)?(([!#-[\]-~])|(\\([ -~]|\s))))*(\s? +)?"))@((((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?(([A-Za-z0-9!#-'*+\/=?^_\x60{|}~-])+(\.([A-Za-z0-9!#-'*+\/=?^_\x60{|}~-])+)*)((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?)|(((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?\[((\s? +)?([!-Z^-~]))*(\s? +)?\]((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?))))$`)
)
func ValidateFormat(email string) error {
if !emailRegexp.MatchString(strings.ToLower(email)) {
return ErrBadFormat
}
return nil
}
// ValidateMX validate if MX record exists for a domain.
func ValidateMX(email string) error {
_, domain := split(email)
if _, err := net.LookupMX(domain); err != nil {
return ErrUnresolvableDomain
}
return nil
}
// ValidateDomain validate mail host.
func ValidateDomain(email string) error {
var err error
var mx []*net.MX
var client *smtp.Client
_, domain := split(email)
mx, err = net.LookupMX(domain)
if err != nil {
return ErrUnresolvableDomain
}
client, err = DialTimeout(fmt.Sprintf("%s:%d", mx[0].Host, 25), forceDisconnectAfter)
if err != nil {
return NewSmtpError(err)
}
err = client.Close()
if err != nil {
return NewSmtpError(err)
}
return nil
}
// ValidateLocalAndDomain validate mail host and user.
// If host is valid, requires valid SMTP [1] serverHostName and serverMailAddress to reverse validation
// for prevent SPAN and BOTS.
// [1] https://mxtoolbox.com/SuperTool.aspx
func ValidateLocalAndDomain(serverHostName, serverMailAddress, email string) error {
var err error
var mx []*net.MX
var client *smtp.Client
_, domain := split(email)
mx, err = net.LookupMX(domain)
if err != nil {
return ErrUnresolvableDomain
}
client, err = DialTimeout(fmt.Sprintf("%s:%d", mx[0].Host, 25), forceDisconnectAfter)
if err != nil {
return NewSmtpError(err)
}
defer client.Close()
err = client.Hello(serverHostName)
if err != nil {
return NewSmtpError(err)
}
err = client.Mail(serverMailAddress)
if err != nil {
return NewSmtpError(err)
}
err = client.Rcpt(email)
if err != nil {
return NewSmtpError(err)
}
return nil
}
// DialTimeout returns a new Client connected to an SMTP server at addr.
// The addr must include a port, as in "mail.example.com:smtp".
func DialTimeout(addr string, timeout time.Duration) (*smtp.Client, error) {
conn, err := net.DialTimeout("tcp", addr, timeout)
if err != nil {
return nil, err
}
t := time.AfterFunc(timeout, func() { conn.Close() })
defer t.Stop()
host, _, _ := net.SplitHostPort(addr)
return smtp.NewClient(conn, host)
}
func split(email string) (local, domain string) {
// remove leading and trailing whitespaces
e := strings.TrimSpace(email)
at := strings.LastIndexByte(e, '@')
// no @ present
// or should we just return "", ""?
if at == -1 {
return e, ""
}
return e[:at], e[at+1:]
}