smtp: new package

R=rsc, iant, agl
CC=golang-dev
https://golang.org/cl/2052042

Author: Evan Shaw

src/pkg/Makefile

@@ -109,6 +109,7 @@ DIRS=\
 	runtime\
 	runtime/pprof\
 	scanner\
+	smtp\
 	sort\
 	strconv\
 	strings\

src/pkg/smtp/Makefile

@@ -0,0 +1,12 @@
+# 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.
+
+include ../../Make.inc
+
+TARG=smtp
+GOFILES=\
+	auth.go\
+	smtp.go\
+
+include ../../Make.pkg

src/pkg/smtp/auth.go

@@ -0,0 +1,69 @@
+// 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
+
+import (
+	"os"
+)
+
+// Auth is implemented by an SMTP authentication mechanism.
+type Auth interface {
+	// Start begins an authentication with a server.
+	// It returns the name of the authentication protocol
+	// and optionally data to include in the initial AUTH message
+	// sent to the server. It can return proto == "" to indicate
+	// that the authentication should be skipped.
+	// If it returns a non-nil os.Error, the SMTP client aborts
+	// the authentication attempt and closes the connection.
+	Start(server *ServerInfo) (proto string, toServer []byte, err os.Error)
+
+	// Next continues the authentication. The server has just sent
+	// the fromServer data. If more is true, the server expects a
+	// response, which Next should return as toServer; otherwise
+	// Next should return toServer == nil.
+	// If Next returns a non-nil os.Error, the SMTP client aborts
+	// the authentication attempt and closes the connection.
+	Next(fromServer []byte, more bool) (toServer []byte, err os.Error)
+}
+
+// ServerInfo records information about an SMTP server.
+type ServerInfo struct {
+	Name string   // SMTP server name
+	TLS  bool     // using TLS, with valid certificate for Name
+	Auth []string // advertised authentication mechanisms
+}
+
+type plainAuth struct {
+	identity, username, password string
+	host                         string
+}
+
+// PlainAuth returns an Auth that implements the PLAIN authentication
+// mechanism as defined in RFC 4616.
+// The returned Auth uses the given username and password to authenticate
+// on TLS connections to host and act as identity. Usually identity will be
+// left blank to act as username.
+func PlainAuth(identity, username, password, host string) Auth {
+	return &plainAuth{identity, username, password, host}
+}
+
+func (a *plainAuth) Start(server *ServerInfo) (string, []byte, os.Error) {
+	if !server.TLS {
+		return "", nil, os.NewError("unencrypted connection")
+	}
+	if server.Name != a.host {
+		return "", nil, os.NewError("wrong host name")
+	}
+	resp := []byte(a.identity + "\x00" + a.username + "\x00" + a.password)
+	return "PLAIN", resp, nil
+}
+
+func (a *plainAuth) Next(fromServer []byte, more bool) ([]byte, os.Error) {
+	if more {
+		// We've already sent everything.
+		return nil, os.NewError("unexpected server challenge")
+	}
+	return nil, nil
+}

src/pkg/smtp/smtp.go

@@ -0,0 +1,295 @@
+// 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.Index(msg, "ESMTP") >= 0 {
+		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() os.Error {
+	_, _, err := c.cmd(220, "STARTTLS")
+	if err != nil {
+		return err
+	}
+	c.conn = tls.Client(c.conn, nil)
+	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 = make([]byte, encoding.DecodedLen(len(msg64)))
+			_, err = encoding.Decode(msg, []byte(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(); 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()
+}