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go-mail/smtp/smtp.go
Winni Neessen f823112a4d
Refactor: consolidate ErrNonTLSConnection variable
The variable ErrNonTLSConnection has been simplified from a multi-line declaration to a single-line declaration. This increases code readability and maintains consistency with Go conventions.
2024-10-01 20:32:41 +02:00

603 lines
16 KiB
Go

// SPDX-FileCopyrightText: Copyright 2010 The Go Authors. All rights reserved.
// SPDX-FileCopyrightText: Copyright (c) 2022-2023 The go-mail Authors
//
// Original net/smtp code from the Go stdlib by the Go Authors.
// Use of this source code is governed by a BSD-style
// LICENSE file that can be found in this directory.
//
// go-mail specific modifications by the go-mail Authors.
// Licensed under the MIT License.
// See [PROJECT ROOT]/LICENSES directory for more information.
//
// SPDX-License-Identifier: BSD-3-Clause AND MIT
// Package smtp implements the Simple Mail Transfer Protocol as defined in RFC 5321.
// It also implements the following extensions:
//
// 8BITMIME RFC 1652
// AUTH RFC 2554
// STARTTLS RFC 3207
// DSN RFC 1891
package smtp
import (
"crypto/tls"
"encoding/base64"
"errors"
"fmt"
"io"
"net"
"net/textproto"
"os"
"strings"
"sync"
"time"
"github.com/wneessen/go-mail/log"
)
var ErrNonTLSConnection = errors.New("connection is not using TLS")
// A Client represents a client connection to an SMTP server.
type Client struct {
// Text is the textproto.Conn used by the Client. It is exported to allow for clients to add extensions.
Text *textproto.Conn
// auth supported auth mechanisms
auth []string
// keep a reference to the connection so it can be used to create a TLS connection later
conn net.Conn
// debug logging is enabled
debug bool
// didHello indicates whether we've said HELO/EHLO
didHello bool
// dsnmrtype defines the mail return option in case DSN is enabled
dsnmrtype string
// dsnrntype defines the recipient notify option in case DSN is enabled
dsnrntype string
// ext is a map of supported extensions
ext map[string]string
// helloError is the error from the hello
helloError error
// localName is the name to use in HELO/EHLO
localName string // the name to use in HELO/EHLO
// logger will be used for debug logging
logger log.Logger
// mutex is used to synchronize access to shared resources, ensuring that only one goroutine can access
// the resource at a time.
mutex sync.RWMutex
// tls indicates whether the Client is using TLS
tls bool
// serverName denotes the name of the server to which the application will connect. Used for
// identification and routing.
serverName string
}
// Dial returns a new [Client] connected to an SMTP server at addr.
// The addr must include a port, as in "mail.example.com:smtp".
func Dial(addr string) (*Client, error) {
conn, err := net.Dial("tcp", addr)
if err != nil {
return nil, err
}
host, _, _ := net.SplitHostPort(addr)
return NewClient(conn, host)
}
// NewClient returns a new [Client] using an existing connection and host as a
// server name to be used when authenticating.
func NewClient(conn net.Conn, host string) (*Client, error) {
text := textproto.NewConn(conn)
_, _, err := text.ReadResponse(220)
if err != nil {
if cerr := text.Close(); cerr != nil {
// Since we are being Go <1.20 compatible, we can't combine errorrs and
// duplicate %w vers are not suppored. Therefore let's ignore this linting
// error for now
// nolint:errorlint
return nil, fmt.Errorf("%w, %s", err, cerr)
}
return nil, err
}
c := &Client{Text: text, conn: conn, serverName: host, localName: "localhost"}
_, c.tls = conn.(*tls.Conn)
return c, nil
}
// Close closes the connection.
func (c *Client) Close() error {
c.mutex.Lock()
err := c.Text.Close()
c.mutex.Unlock()
return err
}
// hello runs a hello exchange if needed.
func (c *Client) hello() error {
if !c.didHello {
c.didHello = true
err := c.ehlo()
if err != nil {
c.helloError = c.helo()
}
}
return c.helloError
}
// Hello sends a HELO or EHLO to the server as the given host name.
// Calling this method is only necessary if the client needs control
// over the host name used. The client will introduce itself as "localhost"
// automatically otherwise. If Hello is called, it must be called before
// any of the other methods.
func (c *Client) Hello(localName string) error {
if err := validateLine(localName); err != nil {
return err
}
if c.didHello {
return errors.New("smtp: Hello called after other methods")
}
c.mutex.Lock()
c.localName = localName
c.mutex.Unlock()
return c.hello()
}
// cmd is a convenience function that sends a command and returns the response
func (c *Client) cmd(expectCode int, format string, args ...interface{}) (int, string, error) {
c.mutex.Lock()
c.debugLog(log.DirClientToServer, format, args...)
id, err := c.Text.Cmd(format, args...)
if err != nil {
c.mutex.Unlock()
return 0, "", err
}
c.Text.StartResponse(id)
code, msg, err := c.Text.ReadResponse(expectCode)
c.debugLog(log.DirServerToClient, "%d %s", code, msg)
c.Text.EndResponse(id)
c.mutex.Unlock()
return code, msg, err
}
// helo sends the HELO greeting to the server. It should be used only when the
// server does not support ehlo.
func (c *Client) helo() error {
c.mutex.Lock()
c.ext = nil
c.mutex.Unlock()
_, _, err := c.cmd(250, "HELO %s", c.localName)
return err
}
// StartTLS sends the STARTTLS command and encrypts all further communication.
// Only servers that advertise the STARTTLS extension support this function.
func (c *Client) StartTLS(config *tls.Config) error {
if err := c.hello(); err != nil {
return err
}
_, _, err := c.cmd(220, "STARTTLS")
if err != nil {
return err
}
c.mutex.Lock()
c.conn = tls.Client(c.conn, config)
c.Text = textproto.NewConn(c.conn)
c.tls = true
c.mutex.Unlock()
return c.ehlo()
}
// TLSConnectionState returns the client's TLS connection state.
// The return values are their zero values if [Client.StartTLS] did
// not succeed.
func (c *Client) TLSConnectionState() (state tls.ConnectionState, ok bool) {
c.mutex.RLock()
defer c.mutex.RUnlock()
tc, ok := c.conn.(*tls.Conn)
if !ok {
return
}
state, ok = tc.ConnectionState(), true
return
}
// Verify checks the validity of an email address on the server.
// If Verify returns nil, the address is valid. A non-nil return
// does not necessarily indicate an invalid address. Many servers
// will not verify addresses for security reasons.
func (c *Client) Verify(addr string) error {
if err := validateLine(addr); err != nil {
return err
}
if err := c.hello(); err != nil {
return err
}
_, _, err := c.cmd(250, "VRFY %s", addr)
return err
}
// Auth authenticates a client using the provided authentication mechanism.
// A failed authentication closes the connection.
// Only servers that advertise the AUTH extension support this function.
func (c *Client) Auth(a Auth) error {
if err := c.hello(); err != nil {
return err
}
encoding := base64.StdEncoding
mech, resp, err := a.Start(&ServerInfo{c.serverName, c.tls, c.auth})
if err != nil {
if qerr := c.Quit(); qerr != nil {
// Since we are being Go <1.20 compatible, we can't combine errorrs and
// duplicate %w vers are not suppored. Therefore let's ignore this linting
// error for now
// nolint:errorlint
return fmt.Errorf("%w, %s", err, qerr)
}
return err
}
resp64 := make([]byte, encoding.EncodedLen(len(resp)))
encoding.Encode(resp64, resp)
code, msg64, err := c.cmd(0, "%s", strings.TrimSpace(fmt.Sprintf("AUTH %s %s", mech,
resp64)))
for err == nil {
var msg []byte
switch code {
case 334:
msg, err = encoding.DecodeString(msg64)
case 235:
// the last message isn't base64 because it isn't a challenge
msg = []byte(msg64)
default:
err = &textproto.Error{Code: code, Msg: msg64}
}
if err == nil {
resp, err = a.Next(msg, code == 334)
}
if err != nil {
if mech != "XOAUTH2" {
// abort the AUTH. Not required for XOAUTH2
_, _, _ = c.cmd(501, "*")
}
_ = c.Quit()
break
}
if resp == nil {
break
}
resp64 = make([]byte, encoding.EncodedLen(len(resp)))
encoding.Encode(resp64, resp)
code, msg64, err = c.cmd(0, "%s", resp64)
}
return err
}
// Mail issues a MAIL command to the server using the provided email address.
// If the server supports the 8BITMIME extension, Mail adds the BODY=8BITMIME
// parameter. If the server supports the SMTPUTF8 extension, Mail adds the
// SMTPUTF8 parameter.
// This initiates a mail transaction and is followed by one or more [Client.Rcpt] calls.
func (c *Client) Mail(from string) error {
if err := validateLine(from); err != nil {
return err
}
if err := c.hello(); err != nil {
return err
}
cmdStr := "MAIL FROM:<%s>"
c.mutex.RLock()
if c.ext != nil {
if _, ok := c.ext["8BITMIME"]; ok {
cmdStr += " BODY=8BITMIME"
}
if _, ok := c.ext["SMTPUTF8"]; ok {
cmdStr += " SMTPUTF8"
}
_, ok := c.ext["DSN"]
if ok && c.dsnmrtype != "" {
cmdStr += fmt.Sprintf(" RET=%s", c.dsnmrtype)
}
}
c.mutex.RUnlock()
_, _, err := c.cmd(250, cmdStr, from)
return err
}
// Rcpt issues a RCPT command to the server using the provided email address.
// A call to Rcpt must be preceded by a call to [Client.Mail] and may be followed by
// a [Client.Data] call or another Rcpt call.
func (c *Client) Rcpt(to string) error {
if err := validateLine(to); err != nil {
return err
}
c.mutex.RLock()
_, ok := c.ext["DSN"]
c.mutex.RUnlock()
if ok && c.dsnrntype != "" {
_, _, err := c.cmd(25, "RCPT TO:<%s> NOTIFY=%s", to, c.dsnrntype)
return err
}
_, _, err := c.cmd(25, "RCPT TO:<%s>", to)
return err
}
type dataCloser struct {
c *Client
io.WriteCloser
}
// Close releases the lock, closes the WriteCloser, waits for a response, and then returns any error encountered.
func (d *dataCloser) Close() error {
d.c.mutex.Lock()
_ = d.WriteCloser.Close()
_, _, err := d.c.Text.ReadResponse(250)
d.c.mutex.Unlock()
return err
}
// Write writes data to the underlying WriteCloser while ensuring thread-safety by locking and unlocking a mutex.
func (d *dataCloser) Write(p []byte) (n int, err error) {
d.c.mutex.Lock()
n, err = d.WriteCloser.Write(p)
d.c.mutex.Unlock()
return
}
// Data issues a DATA command to the server and returns a writer that
// can be used to write the mail headers and body. The caller should
// close the writer before calling any more methods on c. A call to
// Data must be preceded by one or more calls to [Client.Rcpt].
func (c *Client) Data() (io.WriteCloser, error) {
_, _, err := c.cmd(354, "DATA")
if err != nil {
return nil, err
}
datacloser := &dataCloser{}
c.mutex.Lock()
datacloser.c = c
datacloser.WriteCloser = c.Text.DotWriter()
c.mutex.Unlock()
return datacloser, nil
}
var testHookStartTLS func(*tls.Config) // nil, except for tests
// 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, a Auth, from string, to []string, msg []byte) error {
if err := validateLine(from); err != nil {
return err
}
for _, recp := range to {
if err := validateLine(recp); err != nil {
return err
}
}
c, err := Dial(addr)
if err != nil {
return err
}
defer func() {
_ = c.Close()
}()
if err = c.hello(); err != nil {
return err
}
if ok, _ := c.Extension("STARTTLS"); ok {
config := &tls.Config{ServerName: c.serverName}
if testHookStartTLS != nil {
testHookStartTLS(config)
}
if err = c.StartTLS(config); err != nil {
return err
}
}
if a != nil && c.ext != nil {
if _, ok := c.ext["AUTH"]; !ok {
return errors.New("smtp: server doesn't support AUTH")
}
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()
}
// Extension reports whether an extension is support by the server.
// The extension name is case-insensitive. If the extension is supported,
// Extension also returns a string that contains any parameters the
// server specifies for the extension.
func (c *Client) Extension(ext string) (bool, string) {
if err := c.hello(); err != nil {
return false, ""
}
if c.ext == nil {
return false, ""
}
ext = strings.ToUpper(ext)
c.mutex.RLock()
param, ok := c.ext[ext]
c.mutex.RUnlock()
return ok, param
}
// Reset sends the RSET command to the server, aborting the current mail
// transaction.
func (c *Client) Reset() error {
if err := c.hello(); err != nil {
return err
}
_, _, err := c.cmd(250, "RSET")
return err
}
// Noop sends the NOOP command to the server. It does nothing but check
// that the connection to the server is okay.
func (c *Client) Noop() error {
if err := c.hello(); err != nil {
return err
}
_, _, err := c.cmd(250, "NOOP")
return err
}
// Quit sends the QUIT command and closes the connection to the server.
func (c *Client) Quit() error {
if err := c.hello(); err != nil {
return err
}
_, _, err := c.cmd(221, "QUIT")
if err != nil {
return err
}
c.mutex.Lock()
err = c.Text.Close()
c.mutex.Unlock()
return err
}
// SetDebugLog enables the debug logging for incoming and outgoing SMTP messages
func (c *Client) SetDebugLog(v bool) {
c.debug = v
if v {
if c.logger == nil {
c.logger = log.New(os.Stderr, log.LevelDebug)
}
return
}
c.logger = nil
}
// SetLogger overrides the default log.Stdlog for the debug logging with a logger that
// satisfies the log.Logger interface
func (c *Client) SetLogger(l log.Logger) {
if l == nil {
return
}
c.logger = l
}
// SetDSNMailReturnOption sets the DSN mail return option for the Mail method
func (c *Client) SetDSNMailReturnOption(d string) {
c.dsnmrtype = d
}
// SetDSNRcptNotifyOption sets the DSN recipient notify option for the Mail method
func (c *Client) SetDSNRcptNotifyOption(d string) {
c.dsnrntype = d
}
// HasConnection checks if the client has an active connection.
// Returns true if the `conn` field is not nil, indicating an active connection.
func (c *Client) HasConnection() bool {
return c.conn != nil
}
func (c *Client) UpdateDeadline(timeout time.Duration) error {
c.mutex.Lock()
if err := c.conn.SetDeadline(time.Now().Add(timeout)); err != nil {
return fmt.Errorf("smtp: failed to update deadline: %w", err)
}
c.mutex.Unlock()
return nil
}
// GetTLSConnectionState retrieves the TLS connection state of the client's current connection.
// Returns an error if the connection is not using TLS or if the connection is not established.
func (c *Client) GetTLSConnectionState() (*tls.ConnectionState, error) {
c.mutex.RLock()
defer c.mutex.RUnlock()
if !c.tls {
return nil, ErrNonTLSConnection
}
if c.conn == nil {
return nil, errors.New("smtp: connection is not established")
}
if conn, ok := c.conn.(*tls.Conn); ok {
cstate := conn.ConnectionState()
return &cstate, nil
}
return nil, errors.New("smtp: connection is not a TLS connection")
}
// debugLog checks if the debug flag is set and if so logs the provided message to
// the log.Logger interface
func (c *Client) debugLog(d log.Direction, f string, a ...interface{}) {
if c.debug {
c.logger.Debugf(log.Log{Direction: d, Format: f, Messages: a})
}
}
// validateLine checks to see if a line has CR or LF as per RFC 5321.
func validateLine(line string) error {
if strings.ContainsAny(line, "\n\r") {
return errors.New("smtp: A line must not contain CR or LF")
}
return nil
}