Refactor the smtp provider.

- Replace SMTP pool lib with `knadh/smtppool`.
- Replace raw JSON config parsing with a config struct.
- Add support for TLS/STARTTLS and multiple auth modes.

internal/providers/smtp/smtp.go

@@ -1,15 +1,15 @@
-package main
+package smtp
 
 import (
-	"encoding/json"
+	"crypto/tls"
 	"errors"
 	"fmt"
 	"net/smtp"
 	"regexp"
 	"time"
 
-	"github.com/jordan-wright/email"
 	"github.com/knadh/otpgateway/v3/internal/models"
+	"github.com/knadh/smtppool"
 )
 
 const (
@@ -24,129 +24,142 @@ const (
 // http://www.golangprograms.com/regular-expression-to-validate-email-address.html
 var reMail = regexp.MustCompile("^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$")
 
-// cfg represents an SMTP server's credentials.
-type cfg struct {
-	Host         string `json:"Host"`
-	Port         int    `json:"Port"`
-	AuthProtocol string `json:"AuthProtocol"`
-	User         string `json:"User"`
-	Password     string `json:"Password"`
-	FromEmail    string `json:"FromEmail"`
-	SendTimeout  int    `json:"SendTimeout"`
-	MaxConns     int    `json:"MaxConns"`
+// Config represents an SMTP server's credentials.
+type Config struct {
+	Host         string        `json:"host"`
+	Port         int           `json:"port"`
+	AuthProtocol string        `json:"auth_protocol"`
+	Username     string        `json:"username"`
+	Password     string        `json:"password"`
+	FromEmail    string        `json:"from_email"`
+	Timeout      time.Duration `json:"timeout"`
+	MaxConns     int           `json:"max_conns"`
+
+	// STARTTLS or TLS.
+	TLSType       string `json:"tls_type"`
+	TLSSkipVerify bool   `json:"tls_skip_verify"`
 }
 
-type emailer struct {
-	cfg     cfg
-	timeout time.Duration
-	mailer  *email.Pool
+// SMTP is a generic SMTP e-mail provider.
+type SMTP struct {
+	cfg Config
+	p   *smtppool.Pool
 }
 
 // New creates and returns an e-mail Provider backend.
-func New(jsonCfg []byte) (interface{}, error) {
-	var c cfg
-	if err := json.Unmarshal(jsonCfg, &c); err != nil {
-		return nil, fmt.Errorf("error reading config: %v", err)
+func New(cfg Config) (*SMTP, error) {
+	if cfg.FromEmail == "" {
+		cfg.FromEmail = "otp@localhost"
 	}
 
-	if c.Host == "" {
-		c.Host = "127.0.0.1"
-	}
-	if c.Port == 0 {
-		c.Port = 25
-	}
-	if c.MaxConns == 0 {
-		c.MaxConns = 1
+	// Initialize the SMTP mailer.
+	var auth smtp.Auth
+	switch cfg.AuthProtocol {
+	case "login":
+		auth = &smtppool.LoginAuth{Username: cfg.Username, Password: cfg.Password}
+	case "cram":
+		auth = smtp.CRAMMD5Auth(cfg.Username, cfg.Password)
+	case "plain":
+		auth = smtp.PlainAuth("", cfg.Username, cfg.Password, cfg.Host)
+	case "", "none":
+	default:
+		return nil, fmt.Errorf("unknown SMTP auth type '%s'", cfg.AuthProtocol)
 	}
-	if c.FromEmail == "" {
-		c.FromEmail = "otp@localhost"
+
+	opt := smtppool.Opt{
+		Host:            cfg.Host,
+		Port:            cfg.Port,
+		MaxConns:        cfg.MaxConns,
+		IdleTimeout:     time.Second * 10,
+		PoolWaitTimeout: cfg.Timeout,
+		Auth:            auth,
 	}
 
-	// Initialize the SMTP mailer.
-	var auth smtp.Auth
-	if c.AuthProtocol == "cram" {
-		auth = smtp.CRAMMD5Auth(c.User, c.Password)
-	} else {
-		auth = smtp.PlainAuth("", c.User, c.Password, c.Host)
+	// TLS config.
+	if cfg.TLSType != "none" {
+		opt.TLSConfig = &tls.Config{}
+		if cfg.TLSSkipVerify {
+			opt.TLSConfig.InsecureSkipVerify = cfg.TLSSkipVerify
+		} else {
+			opt.TLSConfig.ServerName = cfg.Host
+		}
+
+		// SSL/TLS, not cfg.
+		if cfg.TLSType == "TLS" {
+			opt.SSL = true
+		}
 	}
 
-	pool, err := email.NewPool(fmt.Sprintf("%s:%d", c.Host, c.Port), c.MaxConns, auth)
+	pool, err := smtppool.New(opt)
 	if err != nil {
 		return nil, err
 	}
 
-	// Push timeout.
-	t := 5
-	if c.SendTimeout == 0 {
-		t = c.SendTimeout
-	}
-
-	return &emailer{
-		mailer:  pool,
-		cfg:     c,
-		timeout: time.Second * time.Duration(t),
+	return &SMTP{
+		p:   pool,
+		cfg: cfg,
 	}, nil
 }
 
 // ID returns the Provider's ID.
-func (e *emailer) ID() string {
+func (s *SMTP) ID() string {
 	return providerID
 }
 
 // ChannelName returns the e-mail Provider's name.
-func (e *emailer) ChannelName() string {
+func (s *SMTP) ChannelName() string {
 	return channelName
 }
 
 // ChannelDesc returns help text for the e-mail verification Provider.
-func (e *emailer) ChannelDesc() string {
+func (s *SMTP) ChannelDesc() string {
 	return fmt.Sprintf(`
-	We've e-mailed you a %d digit code.
+	A %d digit code has been e-mailed to you.
 	Please check your e-mail and enter the code here
 	to complete the verification.`, maxOTPlen)
 }
 
 // AddressName returns the e-mail Provider's address name.
-func (e *emailer) AddressName() string {
+func (s *SMTP) AddressName() string {
 	return addressName
 }
 
 // AddressDesc returns the help text that is shown to the end users when
 // they're asked to enter their addresses (eg: e-mail or phone), if the OTP
 // registered without an address.
-func (e *emailer) AddressDesc() string {
+func (s *SMTP) AddressDesc() string {
 	return `Please enter the e-mail ID you want to verify`
 }
 
 // ValidateAddress "validates" an e-mail address.
-func (e *emailer) ValidateAddress(to string) error {
+func (s *SMTP) ValidateAddress(to string) error {
 	if !reMail.MatchString(to) {
 		return errors.New("invalid e-mail address")
 	}
 	return nil
 }
 
 // Push pushes an e-mail to the SMTP server.
-func (e *emailer) Push(otp models.OTP, subject string, m []byte) error {
-	return e.mailer.Send(&email.Email{
-		From:    e.cfg.FromEmail,
+func (s *SMTP) Push(otp models.OTP, subject string, m []byte) error {
+	return s.p.Send(smtppool.Email{
+		From:    s.cfg.FromEmail,
 		To:      []string{otp.To},
 		Subject: subject,
 		HTML:    m,
-	}, e.timeout)
+	})
 }
 
 // MaxAddressLen returns the maximum allowed length of the e-mail address.
-func (e *emailer) MaxAddressLen() int {
+func (s *SMTP) MaxAddressLen() int {
 	return maxAddressLen
 }
 
 // MaxOTPLen returns the maximum allowed length of the OTP value.
-func (e *emailer) MaxOTPLen() int {
+func (s *SMTP) MaxOTPLen() int {
 	return maxOTPlen
 }
 
 // MaxBodyLen returns the max permitted body size.
-func (e *emailer) MaxBodyLen() int {
+func (s *SMTP) MaxBodyLen() int {
 	return maxBodyLen
 }