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Server-side support for enhanced status codes (#37)
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* Basic server-side support for enhanced status codes

* Change argument name, enchCode -> enhCode

* Change RFC for Enhanced Codes in documentation

RFC 3463 is just codes, RFC 2034 defines actual extension.

* Add fallback if backend doesn't return enhanced code

Per RFC 2034 we must include a code, but some backends may not support
it, so provide a generic fallback.

* Fix tests

* Add EnhancedCode type alias

* Fix fallback code for 3xx responses

* Clarify NoEnhancedCode documentation
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@foxcpp @emersion
foxcpp authored and emersion committed Apr 16, 2019
1 parent 93209ab commit 930d6df
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Showing 5 changed files with 108 additions and 66 deletions.
130 changes: 77 additions & 53 deletions conn.go
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Original file line number Diff line number Diff line change
Expand Up @@ -61,52 +61,52 @@ func (c *Conn) init() {
}

func (c *Conn) unrecognizedCommand(cmd string) {
c.WriteResponse(500, fmt.Sprintf("Syntax error, %v command unrecognized", cmd))
c.WriteResponse(500, EnhancedCode{5, 5, 2}, fmt.Sprintf("Syntax error, %v command unrecognized", cmd))

c.nbrErrors++
if c.nbrErrors > 3 {
c.WriteResponse(500, "Too many unrecognized commands")
c.WriteResponse(500, EnhancedCode{5, 5, 2}, "Too many unrecognized commands")
c.Close()
}
}

// Commands are dispatched to the appropriate handler functions.
func (c *Conn) handle(cmd string, arg string) {
if cmd == "" {
c.WriteResponse(500, "Speak up")
c.WriteResponse(500, EnhancedCode{5, 5, 2}, "Speak up")
return
}

cmd = strings.ToUpper(cmd)
switch cmd {
case "SEND", "SOML", "SAML", "EXPN", "HELP", "TURN":
// These commands are not implemented in any state
c.WriteResponse(502, fmt.Sprintf("%v command not implemented", cmd))
c.WriteResponse(502, EnhancedCode{5, 5, 1}, fmt.Sprintf("%v command not implemented", cmd))
case "HELO", "EHLO", "LHLO":
lmtp := cmd == "LHLO"
enhanced := lmtp || cmd == "EHLO"
if c.server.LMTP && !lmtp {
c.WriteResponse(500, "This is a LMTP server, use LHLO")
c.WriteResponse(500, EnhancedCode{5, 5, 1}, "This is a LMTP server, use LHLO")
}
if !c.server.LMTP && lmtp {
c.WriteResponse(500, "This is not a LMTP server")
c.WriteResponse(500, EnhancedCode{5, 5, 1}, "This is not a LMTP server")
}
c.handleGreet(enhanced, arg)
case "MAIL":
c.handleMail(arg)
case "RCPT":
c.handleRcpt(arg)
case "VRFY":
c.WriteResponse(252, "Cannot VRFY user, but will accept message")
c.WriteResponse(252, EnhancedCode{2, 5, 0}, "Cannot VRFY user, but will accept message")
case "NOOP":
c.WriteResponse(250, "I have sucessfully done nothing")
c.WriteResponse(250, EnhancedCode{2, 0, 0}, "I have sucessfully done nothing")
case "RSET": // Reset session
c.reset()
c.WriteResponse(250, "Session reset")
c.WriteResponse(250, EnhancedCode{2, 0, 0}, "Session reset")
case "DATA":
c.handleData(arg)
case "QUIT":
c.WriteResponse(221, "Goodnight and good luck")
c.WriteResponse(221, EnhancedCode{2, 0, 0}, "Goodnight and good luck")
c.Close()
case "AUTH":
if c.server.AuthDisabled {
Expand Down Expand Up @@ -179,16 +179,16 @@ func (c *Conn) handleGreet(enhanced bool, arg string) {
if !enhanced {
domain, err := parseHelloArgument(arg)
if err != nil {
c.WriteResponse(501, "Domain/address argument required for HELO")
c.WriteResponse(501, EnhancedCode{5, 5, 2}, "Domain/address argument required for HELO")
return
}
c.helo = domain

c.WriteResponse(250, fmt.Sprintf("Hello %s", domain))
c.WriteResponse(250, EnhancedCode{2, 0, 0}, fmt.Sprintf("Hello %s", domain))
} else {
domain, err := parseHelloArgument(arg)
if err != nil {
c.WriteResponse(501, "Domain/address argument required for EHLO")
c.WriteResponse(501, EnhancedCode{5, 5, 2}, "Domain/address argument required for EHLO")
return
}

Expand All @@ -213,42 +213,46 @@ func (c *Conn) handleGreet(enhanced bool, arg string) {

args := []string{"Hello " + domain}
args = append(args, caps...)
c.WriteResponse(250, args...)
c.WriteResponse(250, NoEnhancedCode, args...)
}
}

// READY state -> waiting for MAIL
func (c *Conn) handleMail(arg string) {
if c.helo == "" {
c.WriteResponse(502, "Please introduce yourself first.")
c.WriteResponse(502, EnhancedCode{2, 5, 1}, "Please introduce yourself first.")
return
}

if c.Session() == nil {
state := c.State()
session, err := c.server.Backend.AnonymousLogin(&state)
if err != nil {
c.WriteResponse(502, err.Error())
if smtpErr, ok := err.(*SMTPError); ok {
c.WriteResponse(smtpErr.Code, smtpErr.EnhancedCode, smtpErr.Message)
} else {
c.WriteResponse(502, EnhancedCode{5, 7, 0}, err.Error())
}
return
}

c.SetSession(session)
}

if len(arg) < 6 || strings.ToUpper(arg[0:5]) != "FROM:" {
c.WriteResponse(501, "Was expecting MAIL arg syntax of FROM:<address>")
c.WriteResponse(501, EnhancedCode{5, 5, 2}, "Was expecting MAIL arg syntax of FROM:<address>")
return
}
fromArgs := strings.Split(strings.Trim(arg[5:], " "), " ")
if c.server.Strict {
if !strings.HasPrefix(fromArgs[0], "<") || !strings.HasSuffix(fromArgs[0], ">") {
c.WriteResponse(501, "Was expecting MAIL arg syntax of FROM:<address>")
c.WriteResponse(501, EnhancedCode{5, 5, 2}, "Was expecting MAIL arg syntax of FROM:<address>")
return
}
}
from := strings.Trim(fromArgs[0], "<> ")
if from == "" {
c.WriteResponse(501, "Was expecting MAIL arg syntax of FROM:<address>")
c.WriteResponse(501, EnhancedCode{5, 5, 2}, "Was expecting MAIL arg syntax of FROM:<address>")
return
}

Expand All @@ -257,77 +261,77 @@ func (c *Conn) handleMail(arg string) {
if len(fromArgs) > 1 {
args, err := parseArgs(fromArgs[1:])
if err != nil {
c.WriteResponse(501, "Unable to parse MAIL ESMTP parameters")
c.WriteResponse(501, EnhancedCode{5, 5, 4}, "Unable to parse MAIL ESMTP parameters")
return
}

if args["SIZE"] != "" {
size, err := strconv.ParseInt(args["SIZE"], 10, 32)
if err != nil {
c.WriteResponse(501, "Unable to parse SIZE as an integer")
c.WriteResponse(501, EnhancedCode{5, 5, 4}, "Unable to parse SIZE as an integer")
return
}

if c.server.MaxMessageBytes > 0 && int(size) > c.server.MaxMessageBytes {
c.WriteResponse(552, "Max message size exceeded")
c.WriteResponse(552, EnhancedCode{5, 3, 4}, "Max message size exceeded")
return
}
}
}

if err := c.Session().Mail(from); err != nil {
if smtpErr, ok := err.(*SMTPError); ok {
c.WriteResponse(smtpErr.Code, smtpErr.Message)
c.WriteResponse(smtpErr.Code, smtpErr.EnhancedCode, smtpErr.Message)
return
}
c.WriteResponse(451, err.Error())
c.WriteResponse(451, EnhancedCode{4, 0, 0}, err.Error())
return
}

c.WriteResponse(250, fmt.Sprintf("Roger, accepting mail from <%v>", from))
c.WriteResponse(250, EnhancedCode{2, 0, 0}, fmt.Sprintf("Roger, accepting mail from <%v>", from))
c.fromReceived = true
}

// MAIL state -> waiting for RCPTs followed by DATA
func (c *Conn) handleRcpt(arg string) {
if !c.fromReceived {
c.WriteResponse(502, "Missing MAIL FROM command.")
c.WriteResponse(502, EnhancedCode{5, 5, 1}, "Missing MAIL FROM command.")
return
}

if (len(arg) < 4) || (strings.ToUpper(arg[0:3]) != "TO:") {
c.WriteResponse(501, "Was expecting RCPT arg syntax of TO:<address>")
c.WriteResponse(501, EnhancedCode{5, 5, 2}, "Was expecting RCPT arg syntax of TO:<address>")
return
}

// TODO: This trim is probably too forgiving
recipient := strings.Trim(arg[3:], "<> ")

if c.server.MaxRecipients > 0 && len(c.recipients) >= c.server.MaxRecipients {
c.WriteResponse(552, fmt.Sprintf("Maximum limit of %v recipients reached", c.server.MaxRecipients))
c.WriteResponse(552, EnhancedCode{5, 5, 3}, fmt.Sprintf("Maximum limit of %v recipients reached", c.server.MaxRecipients))
return
}

if err := c.Session().Rcpt(recipient); err != nil {
if smtpErr, ok := err.(*SMTPError); ok {
c.WriteResponse(smtpErr.Code, smtpErr.Message)
c.WriteResponse(smtpErr.Code, smtpErr.EnhancedCode, smtpErr.Message)
return
}
c.WriteResponse(451, err.Error())
c.WriteResponse(451, EnhancedCode{4, 0, 0}, err.Error())
return
}
c.recipients = append(c.recipients, recipient)
c.WriteResponse(250, fmt.Sprintf("I'll make sure <%v> gets this", recipient))
c.WriteResponse(250, EnhancedCode{2, 0, 0}, fmt.Sprintf("I'll make sure <%v> gets this", recipient))
}

func (c *Conn) handleAuth(arg string) {
if c.helo == "" {
c.WriteResponse(502, "Please introduce yourself first.")
c.WriteResponse(502, EnhancedCode{5, 5, 1}, "Please introduce yourself first.")
return
}

if arg == "" {
c.WriteResponse(502, "Missing parameter")
c.WriteResponse(502, EnhancedCode{5, 5, 4}, "Missing parameter")
return
}

Expand All @@ -346,7 +350,7 @@ func (c *Conn) handleAuth(arg string) {

newSasl, ok := c.server.auths[mechanism]
if !ok {
c.WriteResponse(504, "Unsupported authentication mechanism")
c.WriteResponse(504, EnhancedCode{5, 7, 4}, "Unsupported authentication mechanism")
return
}

Expand All @@ -356,7 +360,7 @@ func (c *Conn) handleAuth(arg string) {
for {
challenge, done, err := sasl.Next(response)
if err != nil {
c.WriteResponse(454, err.Error())
c.WriteResponse(454, EnhancedCode{4, 7, 0}, err.Error())
return
}

Expand All @@ -368,7 +372,7 @@ func (c *Conn) handleAuth(arg string) {
if len(challenge) > 0 {
encoded = base64.StdEncoding.EncodeToString(challenge)
}
c.WriteResponse(334, encoded)
c.WriteResponse(334, NoEnhancedCode, encoded)

encoded, err = c.ReadLine()
if err != nil {
Expand All @@ -377,35 +381,35 @@ func (c *Conn) handleAuth(arg string) {

response, err = base64.StdEncoding.DecodeString(encoded)
if err != nil {
c.WriteResponse(454, "Invalid base64 data")
c.WriteResponse(454, EnhancedCode{4, 7, 0}, "Invalid base64 data")
return
}
}

if c.Session() != nil {
c.WriteResponse(235, "Authentication succeeded")
c.WriteResponse(235, EnhancedCode{2, 0, 0}, "Authentication succeeded")
}
}

func (c *Conn) handleStartTLS() {
if _, isTLS := c.TLSConnectionState(); isTLS {
c.WriteResponse(502, "Already running in TLS")
c.WriteResponse(502, EnhancedCode{5, 5, 1}, "Already running in TLS")
return
}

if c.server.TLSConfig == nil {
c.WriteResponse(502, "TLS not supported")
c.WriteResponse(502, EnhancedCode{5, 5, 1}, "TLS not supported")
return
}

c.WriteResponse(220, "Ready to start TLS")
c.WriteResponse(220, EnhancedCode{2, 0, 0}, "Ready to start TLS")

// Upgrade to TLS
var tlsConn *tls.Conn
tlsConn = tls.Server(c.conn, c.server.TLSConfig)

if err := tlsConn.Handshake(); err != nil {
c.WriteResponse(550, "Handshake error")
c.WriteResponse(550, EnhancedCode{5, 0, 0}, "Handshake error")
}

c.conn = tlsConn
Expand All @@ -418,69 +422,89 @@ func (c *Conn) handleStartTLS() {
// DATA
func (c *Conn) handleData(arg string) {
if arg != "" {
c.WriteResponse(501, "DATA command should not have any arguments")
c.WriteResponse(501, EnhancedCode{5, 5, 4}, "DATA command should not have any arguments")
return
}

if !c.fromReceived || len(c.recipients) == 0 {
c.WriteResponse(502, "Missing RCPT TO command.")
c.WriteResponse(502, EnhancedCode{5, 5, 1}, "Missing RCPT TO command.")
return
}

// We have recipients, go to accept data
c.WriteResponse(354, "Go ahead. End your data with <CR><LF>.<CR><LF>")
c.WriteResponse(354, EnhancedCode{2, 0, 0}, "Go ahead. End your data with <CR><LF>.<CR><LF>")

var (
code int
msg string
code int
enhancedCode EnhancedCode
msg string
)
r := newDataReader(c)
err := c.Session().Data(r)
io.Copy(ioutil.Discard, r) // Make sure all the data has been consumed
if err != nil {
if smtperr, ok := err.(*SMTPError); ok {
code = smtperr.Code
enhancedCode = smtperr.EnhancedCode
msg = smtperr.Message
} else {
code = 554
enhancedCode = EnhancedCode{5, 0, 0}
msg = "Error: transaction failed, blame it on the weather: " + err.Error()
}
} else {
code = 250
enhancedCode = EnhancedCode{2, 0, 0}
msg = "OK: queued"
}

if c.server.LMTP {
// TODO: support per-recipient responses
for _, rcpt := range c.recipients {
c.WriteResponse(code, "<"+rcpt+"> "+msg)
c.WriteResponse(code, enhancedCode, "<"+rcpt+"> "+msg)
}
} else {
c.WriteResponse(code, msg)
c.WriteResponse(code, enhancedCode, msg)
}

c.resetMessage()
}

func (c *Conn) Reject() {
c.WriteResponse(421, "Too busy. Try again later.")
c.WriteResponse(421, EnhancedCode{4, 4, 5}, "Too busy. Try again later.")
c.Close()
}

func (c *Conn) greet() {
c.WriteResponse(220, fmt.Sprintf("%v ESMTP Service Ready", c.server.Domain))
c.WriteResponse(220, NoEnhancedCode, fmt.Sprintf("%v ESMTP Service Ready", c.server.Domain))
}

func (c *Conn) WriteResponse(code int, text ...string) {
func (c *Conn) WriteResponse(code int, enhCode EnhancedCode, text ...string) {
// TODO: error handling
if c.server.WriteTimeout != 0 {
c.conn.SetWriteDeadline(time.Now().Add(c.server.WriteTimeout))
}

// All responses must include an enhanced code, if it is missing - use
// a generic code X.0.0.
if enhCode == EnhancedCodeNotSet {
cat := code / 100
switch cat {
case 2, 4, 5:
enhCode = EnhancedCode{cat, 0, 0}
default:
enhCode = NoEnhancedCode
}
}

for i := 0; i < len(text)-1; i++ {
c.text.PrintfLine("%v-%v", code, text[i])
}
c.text.PrintfLine("%v %v", code, text[len(text)-1])
if enhCode == NoEnhancedCode {
c.text.PrintfLine("%v %v", code, text[len(text)-1])
} else {
c.text.PrintfLine("%v %v.%v.%v %v", code, enhCode[0], enhCode[1], enhCode[2], text[len(text)-1])
}
}

// Reads a line of input
Expand Down
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