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// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// 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
// Additional extensions may be handled by clients.
package smtp
import (
"crypto/tls"
"encoding/base64"
"io"
"os"
"net"
"net/textproto"
"strings"
)
// 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
// keep a reference to the connection so it can be used to create a TLS
// connection later
conn net.Conn
// whether the Client is using TLS
tls bool
serverName string
// map of supported extensions
ext map[string]string
// supported auth mechanisms
auth []string
}
// Dial returns a new Client connected to an SMTP server at addr.
func Dial(addr string) (*Client, os.Error) {
conn, err := net.Dial("tcp", addr)
if err != nil {
return nil, err
}
host := addr[:strings.Index(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, os.Error) {
text := textproto.NewConn(conn)
_, msg, err := text.ReadResponse(220)
if err != nil {
text.Close()
return nil, err
}
c := &Client{Text: text, conn: conn, serverName: host}
if strings.Contains(msg, "ESMTP") {
err = c.ehlo()
} else {
err = c.helo()
}
return c, err
}
// 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, os.Error) {
id, err := c.Text.Cmd(format, args...)
if err != nil {
return 0, "", err
}
c.Text.StartResponse(id)
defer c.Text.EndResponse(id)
code, msg, err := c.Text.ReadResponse(expectCode)
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() os.Error {
c.ext = nil
_, _, err := c.cmd(250, "HELO localhost")
return err
}
// ehlo sends the EHLO (extended hello) greeting to the server. It
// should be the preferred greeting for servers that support it.
func (c *Client) ehlo() os.Error {
_, msg, err := c.cmd(250, "EHLO localhost")
if err != nil {
return err
}
ext := make(map[string]string)
extList := strings.Split(msg, "\n", -1)
if len(extList) > 1 {
extList = extList[1:]
for _, line := range extList {
args := strings.Split(line, " ", 2)
if len(args) > 1 {
ext[args[0]] = args[1]
} else {
ext[args[0]] = ""
}
}
}
if mechs, ok := ext["AUTH"]; ok {
c.auth = strings.Split(mechs, " ", -1)
}
c.ext = ext
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) os.Error {
_, _, err := c.cmd(220, "STARTTLS")
if err != nil {
return err
}
c.conn = tls.Client(c.conn, config)
c.Text = textproto.NewConn(c.conn)
c.tls = true
return c.ehlo()
}
// 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) os.Error {
_, _, 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) os.Error {
encoding := base64.StdEncoding
mech, resp, err := a.Start(&ServerInfo{c.serverName, c.tls, c.auth})
if err != nil {
c.Quit()
return err
}
resp64 := make([]byte, encoding.EncodedLen(len(resp)))
encoding.Encode(resp64, resp)
code, msg64, err := c.cmd(0, "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, msg64}
}
resp, err = a.Next(msg, code == 334)
if err != nil {
// abort the AUTH
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, string(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.
// This initiates a mail transaction and is followed by one or more Rcpt calls.
func (c *Client) Mail(from string) os.Error {
cmdStr := "MAIL FROM:<%s>"
if c.ext != nil {
if _, ok := c.ext["8BITMIME"]; ok {
cmdStr += " BODY=8BITMIME"
}
}
_, _, 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 Mail and may be followed by
// a Data call or another Rcpt call.
func (c *Client) Rcpt(to string) os.Error {
_, _, err := c.cmd(25, "RCPT TO:<%s>", to)
return err
}
type dataCloser struct {
c *Client
io.WriteCloser
}
func (d *dataCloser) Close() os.Error {
d.WriteCloser.Close()
_, _, err := d.c.Text.ReadResponse(250)
return err
}
// Data issues a DATA command to the server and returns a writer that
// can be used to write the data. 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 Rcpt.
func (c *Client) Data() (io.WriteCloser, os.Error) {
_, _, err := c.cmd(354, "DATA")
if err != nil {
return nil, err
}
return &dataCloser{c, c.Text.DotWriter()}, nil
}
// SendMail connects to the server at addr, switches to TLS if possible,
// authenticates with mechanism a if possible, and then sends an email from
// address from, to addresses to, with message msg.
func SendMail(addr string, a Auth, from string, to []string, msg []byte) os.Error {
c, err := Dial(addr)
if err != nil {
return err
}
if ok, _ := c.Extension("STARTTLS"); ok {
if err = c.StartTLS(nil); err != nil {
return err
}
}
if a != nil && c.ext != nil {
if _, ok := c.ext["AUTH"]; ok {
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 c.ext == nil {
return false, ""
}
ext = strings.ToUpper(ext)
param, ok := c.ext[ext]
return ok, param
}
// Reset sends the RSET command to the server, aborting the current mail
// transaction.
func (c *Client) Reset() os.Error {
_, _, err := c.cmd(250, "RSET")
return err
}
// Quit sends the QUIT command and closes the connection to the server.
func (c *Client) Quit() os.Error {
_, _, err := c.cmd(221, "QUIT")
if err != nil {
return err
}
return c.Text.Close()
}