smtp.go

Documentation: net/smtp

		 1  // Copyright 2010 The Go Authors. All rights reserved.
		 2  // Use of this source code is governed by a BSD-style
		 3  // license that can be found in the LICENSE file.
		 4  
		 5  // Package smtp implements the Simple Mail Transfer Protocol as defined in RFC 5321.
		 6  // It also implements the following extensions:
		 7  //	8BITMIME	RFC 1652
		 8  //	AUTH			RFC 2554
		 9  //	STARTTLS	RFC 3207
		10  // Additional extensions may be handled by clients.
		11  //
		12  // The smtp package is frozen and is not accepting new features.
		13  // Some external packages provide more functionality. See:
		14  //
		15  //	 https://godoc.org/?q=smtp
		16  package smtp
		17  
		18  import (
		19  	"crypto/tls"
		20  	"encoding/base64"
		21  	"errors"
		22  	"fmt"
		23  	"io"
		24  	"net"
		25  	"net/textproto"
		26  	"strings"
		27  )
		28  
		29  // A Client represents a client connection to an SMTP server.
		30  type Client struct {
		31  	// Text is the textproto.Conn used by the Client. It is exported to allow for
		32  	// clients to add extensions.
		33  	Text *textproto.Conn
		34  	// keep a reference to the connection so it can be used to create a TLS
		35  	// connection later
		36  	conn net.Conn
		37  	// whether the Client is using TLS
		38  	tls				bool
		39  	serverName string
		40  	// map of supported extensions
		41  	ext map[string]string
		42  	// supported auth mechanisms
		43  	auth			 []string
		44  	localName	string // the name to use in HELO/EHLO
		45  	didHello	 bool	 // whether we've said HELO/EHLO
		46  	helloError error	// the error from the hello
		47  }
		48  
		49  // Dial returns a new Client connected to an SMTP server at addr.
		50  // The addr must include a port, as in "mail.example.com:smtp".
		51  func Dial(addr string) (*Client, error) {
		52  	conn, err := net.Dial("tcp", addr)
		53  	if err != nil {
		54  		return nil, err
		55  	}
		56  	host, _, _ := net.SplitHostPort(addr)
		57  	return NewClient(conn, host)
		58  }
		59  
		60  // NewClient returns a new Client using an existing connection and host as a
		61  // server name to be used when authenticating.
		62  func NewClient(conn net.Conn, host string) (*Client, error) {
		63  	text := textproto.NewConn(conn)
		64  	_, _, err := text.ReadResponse(220)
		65  	if err != nil {
		66  		text.Close()
		67  		return nil, err
		68  	}
		69  	c := &Client{Text: text, conn: conn, serverName: host, localName: "localhost"}
		70  	_, c.tls = conn.(*tls.Conn)
		71  	return c, nil
		72  }
		73  
		74  // Close closes the connection.
		75  func (c *Client) Close() error {
		76  	return c.Text.Close()
		77  }
		78  
		79  // hello runs a hello exchange if needed.
		80  func (c *Client) hello() error {
		81  	if !c.didHello {
		82  		c.didHello = true
		83  		err := c.ehlo()
		84  		if err != nil {
		85  			c.helloError = c.helo()
		86  		}
		87  	}
		88  	return c.helloError
		89  }
		90  
		91  // Hello sends a HELO or EHLO to the server as the given host name.
		92  // Calling this method is only necessary if the client needs control
		93  // over the host name used. The client will introduce itself as "localhost"
		94  // automatically otherwise. If Hello is called, it must be called before
		95  // any of the other methods.
		96  func (c *Client) Hello(localName string) error {
		97  	if err := validateLine(localName); err != nil {
		98  		return err
		99  	}
	 100  	if c.didHello {
	 101  		return errors.New("smtp: Hello called after other methods")
	 102  	}
	 103  	c.localName = localName
	 104  	return c.hello()
	 105  }
	 106  
	 107  // cmd is a convenience function that sends a command and returns the response
	 108  func (c *Client) cmd(expectCode int, format string, args ...interface{}) (int, string, error) {
	 109  	id, err := c.Text.Cmd(format, args...)
	 110  	if err != nil {
	 111  		return 0, "", err
	 112  	}
	 113  	c.Text.StartResponse(id)
	 114  	defer c.Text.EndResponse(id)
	 115  	code, msg, err := c.Text.ReadResponse(expectCode)
	 116  	return code, msg, err
	 117  }
	 118  
	 119  // helo sends the HELO greeting to the server. It should be used only when the
	 120  // server does not support ehlo.
	 121  func (c *Client) helo() error {
	 122  	c.ext = nil
	 123  	_, _, err := c.cmd(250, "HELO %s", c.localName)
	 124  	return err
	 125  }
	 126  
	 127  // ehlo sends the EHLO (extended hello) greeting to the server. It
	 128  // should be the preferred greeting for servers that support it.
	 129  func (c *Client) ehlo() error {
	 130  	_, msg, err := c.cmd(250, "EHLO %s", c.localName)
	 131  	if err != nil {
	 132  		return err
	 133  	}
	 134  	ext := make(map[string]string)
	 135  	extList := strings.Split(msg, "\n")
	 136  	if len(extList) > 1 {
	 137  		extList = extList[1:]
	 138  		for _, line := range extList {
	 139  			args := strings.SplitN(line, " ", 2)
	 140  			if len(args) > 1 {
	 141  				ext[args[0]] = args[1]
	 142  			} else {
	 143  				ext[args[0]] = ""
	 144  			}
	 145  		}
	 146  	}
	 147  	if mechs, ok := ext["AUTH"]; ok {
	 148  		c.auth = strings.Split(mechs, " ")
	 149  	}
	 150  	c.ext = ext
	 151  	return err
	 152  }
	 153  
	 154  // StartTLS sends the STARTTLS command and encrypts all further communication.
	 155  // Only servers that advertise the STARTTLS extension support this function.
	 156  func (c *Client) StartTLS(config *tls.Config) error {
	 157  	if err := c.hello(); err != nil {
	 158  		return err
	 159  	}
	 160  	_, _, err := c.cmd(220, "STARTTLS")
	 161  	if err != nil {
	 162  		return err
	 163  	}
	 164  	c.conn = tls.Client(c.conn, config)
	 165  	c.Text = textproto.NewConn(c.conn)
	 166  	c.tls = true
	 167  	return c.ehlo()
	 168  }
	 169  
	 170  // TLSConnectionState returns the client's TLS connection state.
	 171  // The return values are their zero values if StartTLS did
	 172  // not succeed.
	 173  func (c *Client) TLSConnectionState() (state tls.ConnectionState, ok bool) {
	 174  	tc, ok := c.conn.(*tls.Conn)
	 175  	if !ok {
	 176  		return
	 177  	}
	 178  	return tc.ConnectionState(), true
	 179  }
	 180  
	 181  // Verify checks the validity of an email address on the server.
	 182  // If Verify returns nil, the address is valid. A non-nil return
	 183  // does not necessarily indicate an invalid address. Many servers
	 184  // will not verify addresses for security reasons.
	 185  func (c *Client) Verify(addr string) error {
	 186  	if err := validateLine(addr); err != nil {
	 187  		return err
	 188  	}
	 189  	if err := c.hello(); err != nil {
	 190  		return err
	 191  	}
	 192  	_, _, err := c.cmd(250, "VRFY %s", addr)
	 193  	return err
	 194  }
	 195  
	 196  // Auth authenticates a client using the provided authentication mechanism.
	 197  // A failed authentication closes the connection.
	 198  // Only servers that advertise the AUTH extension support this function.
	 199  func (c *Client) Auth(a Auth) error {
	 200  	if err := c.hello(); err != nil {
	 201  		return err
	 202  	}
	 203  	encoding := base64.StdEncoding
	 204  	mech, resp, err := a.Start(&ServerInfo{c.serverName, c.tls, c.auth})
	 205  	if err != nil {
	 206  		c.Quit()
	 207  		return err
	 208  	}
	 209  	resp64 := make([]byte, encoding.EncodedLen(len(resp)))
	 210  	encoding.Encode(resp64, resp)
	 211  	code, msg64, err := c.cmd(0, strings.TrimSpace(fmt.Sprintf("AUTH %s %s", mech, resp64)))
	 212  	for err == nil {
	 213  		var msg []byte
	 214  		switch code {
	 215  		case 334:
	 216  			msg, err = encoding.DecodeString(msg64)
	 217  		case 235:
	 218  			// the last message isn't base64 because it isn't a challenge
	 219  			msg = []byte(msg64)
	 220  		default:
	 221  			err = &textproto.Error{Code: code, Msg: msg64}
	 222  		}
	 223  		if err == nil {
	 224  			resp, err = a.Next(msg, code == 334)
	 225  		}
	 226  		if err != nil {
	 227  			// abort the AUTH
	 228  			c.cmd(501, "*")
	 229  			c.Quit()
	 230  			break
	 231  		}
	 232  		if resp == nil {
	 233  			break
	 234  		}
	 235  		resp64 = make([]byte, encoding.EncodedLen(len(resp)))
	 236  		encoding.Encode(resp64, resp)
	 237  		code, msg64, err = c.cmd(0, string(resp64))
	 238  	}
	 239  	return err
	 240  }
	 241  
	 242  // Mail issues a MAIL command to the server using the provided email address.
	 243  // If the server supports the 8BITMIME extension, Mail adds the BODY=8BITMIME
	 244  // parameter. If the server supports the SMTPUTF8 extension, Mail adds the
	 245  // SMTPUTF8 parameter.
	 246  // This initiates a mail transaction and is followed by one or more Rcpt calls.
	 247  func (c *Client) Mail(from string) error {
	 248  	if err := validateLine(from); err != nil {
	 249  		return err
	 250  	}
	 251  	if err := c.hello(); err != nil {
	 252  		return err
	 253  	}
	 254  	cmdStr := "MAIL FROM:<%s>"
	 255  	if c.ext != nil {
	 256  		if _, ok := c.ext["8BITMIME"]; ok {
	 257  			cmdStr += " BODY=8BITMIME"
	 258  		}
	 259  		if _, ok := c.ext["SMTPUTF8"]; ok {
	 260  			cmdStr += " SMTPUTF8"
	 261  		}
	 262  	}
	 263  	_, _, err := c.cmd(250, cmdStr, from)
	 264  	return err
	 265  }
	 266  
	 267  // Rcpt issues a RCPT command to the server using the provided email address.
	 268  // A call to Rcpt must be preceded by a call to Mail and may be followed by
	 269  // a Data call or another Rcpt call.
	 270  func (c *Client) Rcpt(to string) error {
	 271  	if err := validateLine(to); err != nil {
	 272  		return err
	 273  	}
	 274  	_, _, err := c.cmd(25, "RCPT TO:<%s>", to)
	 275  	return err
	 276  }
	 277  
	 278  type dataCloser struct {
	 279  	c *Client
	 280  	io.WriteCloser
	 281  }
	 282  
	 283  func (d *dataCloser) Close() error {
	 284  	d.WriteCloser.Close()
	 285  	_, _, err := d.c.Text.ReadResponse(250)
	 286  	return err
	 287  }
	 288  
	 289  // Data issues a DATA command to the server and returns a writer that
	 290  // can be used to write the mail headers and body. The caller should
	 291  // close the writer before calling any more methods on c. A call to
	 292  // Data must be preceded by one or more calls to Rcpt.
	 293  func (c *Client) Data() (io.WriteCloser, error) {
	 294  	_, _, err := c.cmd(354, "DATA")
	 295  	if err != nil {
	 296  		return nil, err
	 297  	}
	 298  	return &dataCloser{c, c.Text.DotWriter()}, nil
	 299  }
	 300  
	 301  var testHookStartTLS func(*tls.Config) // nil, except for tests
	 302  
	 303  // SendMail connects to the server at addr, switches to TLS if
	 304  // possible, authenticates with the optional mechanism a if possible,
	 305  // and then sends an email from address from, to addresses to, with
	 306  // message msg.
	 307  // The addr must include a port, as in "mail.example.com:smtp".
	 308  //
	 309  // The addresses in the to parameter are the SMTP RCPT addresses.
	 310  //
	 311  // The msg parameter should be an RFC 822-style email with headers
	 312  // first, a blank line, and then the message body. The lines of msg
	 313  // should be CRLF terminated. The msg headers should usually include
	 314  // fields such as "From", "To", "Subject", and "Cc".	Sending "Bcc"
	 315  // messages is accomplished by including an email address in the to
	 316  // parameter but not including it in the msg headers.
	 317  //
	 318  // The SendMail function and the net/smtp package are low-level
	 319  // mechanisms and provide no support for DKIM signing, MIME
	 320  // attachments (see the mime/multipart package), or other mail
	 321  // functionality. Higher-level packages exist outside of the standard
	 322  // library.
	 323  func SendMail(addr string, a Auth, from string, to []string, msg []byte) error {
	 324  	if err := validateLine(from); err != nil {
	 325  		return err
	 326  	}
	 327  	for _, recp := range to {
	 328  		if err := validateLine(recp); err != nil {
	 329  			return err
	 330  		}
	 331  	}
	 332  	c, err := Dial(addr)
	 333  	if err != nil {
	 334  		return err
	 335  	}
	 336  	defer c.Close()
	 337  	if err = c.hello(); err != nil {
	 338  		return err
	 339  	}
	 340  	if ok, _ := c.Extension("STARTTLS"); ok {
	 341  		config := &tls.Config{ServerName: c.serverName}
	 342  		if testHookStartTLS != nil {
	 343  			testHookStartTLS(config)
	 344  		}
	 345  		if err = c.StartTLS(config); err != nil {
	 346  			return err
	 347  		}
	 348  	}
	 349  	if a != nil && c.ext != nil {
	 350  		if _, ok := c.ext["AUTH"]; !ok {
	 351  			return errors.New("smtp: server doesn't support AUTH")
	 352  		}
	 353  		if err = c.Auth(a); err != nil {
	 354  			return err
	 355  		}
	 356  	}
	 357  	if err = c.Mail(from); err != nil {
	 358  		return err
	 359  	}
	 360  	for _, addr := range to {
	 361  		if err = c.Rcpt(addr); err != nil {
	 362  			return err
	 363  		}
	 364  	}
	 365  	w, err := c.Data()
	 366  	if err != nil {
	 367  		return err
	 368  	}
	 369  	_, err = w.Write(msg)
	 370  	if err != nil {
	 371  		return err
	 372  	}
	 373  	err = w.Close()
	 374  	if err != nil {
	 375  		return err
	 376  	}
	 377  	return c.Quit()
	 378  }
	 379  
	 380  // Extension reports whether an extension is support by the server.
	 381  // The extension name is case-insensitive. If the extension is supported,
	 382  // Extension also returns a string that contains any parameters the
	 383  // server specifies for the extension.
	 384  func (c *Client) Extension(ext string) (bool, string) {
	 385  	if err := c.hello(); err != nil {
	 386  		return false, ""
	 387  	}
	 388  	if c.ext == nil {
	 389  		return false, ""
	 390  	}
	 391  	ext = strings.ToUpper(ext)
	 392  	param, ok := c.ext[ext]
	 393  	return ok, param
	 394  }
	 395  
	 396  // Reset sends the RSET command to the server, aborting the current mail
	 397  // transaction.
	 398  func (c *Client) Reset() error {
	 399  	if err := c.hello(); err != nil {
	 400  		return err
	 401  	}
	 402  	_, _, err := c.cmd(250, "RSET")
	 403  	return err
	 404  }
	 405  
	 406  // Noop sends the NOOP command to the server. It does nothing but check
	 407  // that the connection to the server is okay.
	 408  func (c *Client) Noop() error {
	 409  	if err := c.hello(); err != nil {
	 410  		return err
	 411  	}
	 412  	_, _, err := c.cmd(250, "NOOP")
	 413  	return err
	 414  }
	 415  
	 416  // Quit sends the QUIT command and closes the connection to the server.
	 417  func (c *Client) Quit() error {
	 418  	if err := c.hello(); err != nil {
	 419  		return err
	 420  	}
	 421  	_, _, err := c.cmd(221, "QUIT")
	 422  	if err != nil {
	 423  		return err
	 424  	}
	 425  	return c.Text.Close()
	 426  }
	 427  
	 428  // validateLine checks to see if a line has CR or LF as per RFC 5321
	 429  func validateLine(line string) error {
	 430  	if strings.ContainsAny(line, "\n\r") {
	 431  		return errors.New("smtp: A line must not contain CR or LF")
	 432  	}
	 433  	return nil
	 434  }
	 435
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