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protocol.go
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protocol.go
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package smtp
// http://www.rfc-editor.org/rfc/rfc5321.txt
import (
"encoding/base64"
"errors"
"log"
"regexp"
"strings"
"github.com/mailhog/data"
)
// Command is a struct representing an SMTP command (verb + arguments)
type Command struct {
verb string
args string
orig string
}
// ParseCommand returns a Command from the line string
func ParseCommand(line string) *Command {
words := strings.Split(line, " ")
command := strings.ToUpper(words[0])
args := strings.Join(words[1:len(words)], " ")
return &Command{
verb: command,
args: args,
orig: line,
}
}
// Protocol is a state machine representing an SMTP session
type Protocol struct {
lastCommand *Command
TLSPending bool
TLSUpgraded bool
State State
Message *data.SMTPMessage
Hostname string
Ident string
MaximumLineLength int
MaximumRecipients int
// LogHandler is called for each log message. If nil, log messages will
// be output using log.Printf instead.
LogHandler func(message string, args ...interface{})
// MessageReceivedHandler is called for each message accepted by the
// SMTP protocol. It must return a MessageID or error. If nil, messages
// will be rejected with an error.
MessageReceivedHandler func(*data.SMTPMessage) (string, error)
// ValidateSenderHandler should return true if the sender is valid,
// otherwise false. If nil, all senders will be accepted.
ValidateSenderHandler func(from string) bool
// ValidateRecipientHandler should return true if the recipient is valid,
// otherwise false. If nil, all recipients will be accepted.
ValidateRecipientHandler func(to string) bool
// ValidateAuthenticationhandler should return true if the authentication
// parameters are valid, otherwise false. If nil, all authentication
// attempts will be accepted.
ValidateAuthenticationHandler func(mechanism string, args ...string) (errorReply *Reply, ok bool)
// SMTPVerbFilter is called after each command is parsed, but before
// any code is executed. This provides an opportunity to reject unwanted verbs,
// e.g. to require AUTH before MAIL
SMTPVerbFilter func(verb string, args ...string) (errorReply *Reply)
// TLSHandler is called when a STARTTLS command is received.
//
// It should acknowledge the TLS request and set ok to true.
// It should also return a callback which will be invoked after the reply is
// sent. E.g., a TCP connection can only perform the upgrade after sending the reply
//
// Once the upgrade is complete, invoke the done function (e.g., from the returned callback)
//
// If TLS upgrade isn't possible, return an errorReply and set ok to false.
TLSHandler func(done func(ok bool)) (errorReply *Reply, callback func(), ok bool)
// GetAuthenticationMechanismsHandler should return an array of strings
// listing accepted authentication mechanisms
GetAuthenticationMechanismsHandler func() []string
// RejectBrokenRCPTSyntax controls whether the protocol accepts technically
// invalid syntax for the RCPT command. Set to true, the RCPT syntax requires
// no space between `TO:` and the opening `<`
RejectBrokenRCPTSyntax bool
// RejectBrokenMAILSyntax controls whether the protocol accepts technically
// invalid syntax for the MAIL command. Set to true, the MAIL syntax requires
// no space between `FROM:` and the opening `<`
RejectBrokenMAILSyntax bool
// RequireTLS controls whether TLS is required for a connection before other
// commands can be issued, applied at the protocol layer.
RequireTLS bool
}
// NewProtocol returns a new SMTP state machine in INVALID state
// handler is called when a message is received and should return a message ID
func NewProtocol() *Protocol {
p := &Protocol{
Hostname: "mailhog.example",
Ident: "ESMTP MailHog",
State: INVALID,
MaximumLineLength: -1,
MaximumRecipients: -1,
}
p.resetState()
return p
}
func (proto *Protocol) resetState() {
proto.Message = &data.SMTPMessage{}
}
func (proto *Protocol) logf(message string, args ...interface{}) {
message = strings.Join([]string{"[PROTO: %s]", message}, " ")
args = append([]interface{}{StateMap[proto.State]}, args...)
if proto.LogHandler != nil {
proto.LogHandler(message, args...)
} else {
log.Printf(message, args...)
}
}
// Start begins an SMTP conversation with a 220 reply, placing the state
// machine in ESTABLISH state.
func (proto *Protocol) Start() *Reply {
proto.logf("Started session, switching to ESTABLISH state")
proto.State = ESTABLISH
return ReplyIdent(proto.Hostname + " " + proto.Ident)
}
// Parse parses a line string and returns any remaining line string
// and a reply, if a command was found. Parse does nothing until a
// new line is found.
// - TODO decide whether to move this to a buffer inside Protocol
// sort of like it this way, since it gives control back to the caller
func (proto *Protocol) Parse(line string) (string, *Reply) {
var reply *Reply
if !strings.Contains(line, "\r\n") {
return line, reply
}
parts := strings.SplitN(line, "\r\n", 2)
line = parts[1]
if proto.MaximumLineLength > -1 {
if len(parts[0]) > proto.MaximumLineLength {
return line, ReplyLineTooLong()
}
}
// TODO collapse AUTH states into separate processing
if proto.State == DATA {
reply = proto.ProcessData(parts[0])
} else {
reply = proto.ProcessCommand(parts[0])
}
return line, reply
}
// ProcessData handles content received (with newlines stripped) while
// in the SMTP DATA state
func (proto *Protocol) ProcessData(line string) (reply *Reply) {
proto.Message.Data += line + "\r\n"
if strings.HasSuffix(proto.Message.Data, "\r\n.\r\n") {
proto.Message.Data = strings.Replace(proto.Message.Data, "\r\n..", "\r\n.", -1)
proto.logf("Got EOF, storing message and switching to MAIL state")
proto.Message.Data = strings.TrimSuffix(proto.Message.Data, "\r\n.\r\n")
proto.State = MAIL
defer proto.resetState()
if proto.MessageReceivedHandler == nil {
return ReplyStorageFailed("No storage backend")
}
id, err := proto.MessageReceivedHandler(proto.Message)
if err != nil {
proto.logf("Error storing message: %s", err)
return ReplyStorageFailed("Unable to store message")
}
return ReplyOk("Ok: queued as " + id)
}
return
}
// ProcessCommand processes a line of text as a command
// It expects the line string to be a properly formed SMTP verb and arguments
func (proto *Protocol) ProcessCommand(line string) (reply *Reply) {
line = strings.Trim(line, "\r\n")
proto.logf("Processing line: %s", line)
words := strings.Split(line, " ")
command := strings.ToUpper(words[0])
args := strings.Join(words[1:len(words)], " ")
proto.logf("In state %d, got command '%s', args '%s'", proto.State, command, args)
cmd := ParseCommand(strings.TrimSuffix(line, "\r\n"))
return proto.Command(cmd)
}
// Command applies an SMTP verb and arguments to the state machine
func (proto *Protocol) Command(command *Command) (reply *Reply) {
defer func() {
proto.lastCommand = command
}()
if proto.SMTPVerbFilter != nil {
proto.logf("sending to SMTP verb filter")
r := proto.SMTPVerbFilter(command.verb)
if r != nil {
proto.logf("response returned by SMTP verb filter")
return r
}
}
switch {
case proto.TLSPending && !proto.TLSUpgraded:
proto.logf("Got command before TLS upgrade complete")
// FIXME what to do?
return ReplyBye()
case "RSET" == command.verb:
proto.logf("Got RSET command, switching to MAIL state")
proto.State = MAIL
proto.Message = &data.SMTPMessage{}
return ReplyOk()
case "NOOP" == command.verb:
proto.logf("Got NOOP verb, staying in %s state", StateMap[proto.State])
return ReplyOk()
case "QUIT" == command.verb:
proto.logf("Got QUIT verb, staying in %s state", StateMap[proto.State])
proto.State = DONE
return ReplyBye()
case ESTABLISH == proto.State:
proto.logf("In ESTABLISH state")
switch command.verb {
case "HELO":
return proto.HELO(command.args)
case "EHLO":
return proto.EHLO(command.args)
case "STARTTLS":
return proto.STARTTLS(command.args)
default:
proto.logf("Got unknown command for ESTABLISH state: '%s'", command.verb)
return ReplyUnrecognisedCommand()
}
case "STARTTLS" == command.verb:
proto.logf("Got STARTTLS command outside ESTABLISH state")
return proto.STARTTLS(command.args)
case proto.RequireTLS && !proto.TLSUpgraded:
proto.logf("RequireTLS set and not TLS not upgraded")
return ReplyMustIssueSTARTTLSFirst()
case AUTHPLAIN == proto.State:
proto.logf("Got PLAIN authentication response: '%s', switching to MAIL state", command.args)
proto.State = MAIL
if proto.ValidateAuthenticationHandler != nil {
// TODO error handling
val, _ := base64.StdEncoding.DecodeString(command.orig)
bits := strings.Split(string(val), string(rune(0)))
if len(bits) < 3 {
return ReplyError(errors.New("Badly formed parameter"))
}
user, pass := bits[1], bits[2]
if reply, ok := proto.ValidateAuthenticationHandler("PLAIN", user, pass); !ok {
return reply
}
}
return ReplyAuthOk()
case AUTHLOGIN == proto.State:
proto.logf("Got LOGIN authentication response: '%s', switching to AUTHLOGIN2 state", command.args)
proto.State = AUTHLOGIN2
return ReplyAuthResponse("UGFzc3dvcmQ6")
case AUTHLOGIN2 == proto.State:
proto.logf("Got LOGIN authentication response: '%s', switching to MAIL state", command.args)
proto.State = MAIL
if proto.ValidateAuthenticationHandler != nil {
if reply, ok := proto.ValidateAuthenticationHandler("LOGIN", proto.lastCommand.orig, command.orig); !ok {
return reply
}
}
return ReplyAuthOk()
case AUTHCRAMMD5 == proto.State:
proto.logf("Got CRAM-MD5 authentication response: '%s', switching to MAIL state", command.args)
proto.State = MAIL
if proto.ValidateAuthenticationHandler != nil {
if reply, ok := proto.ValidateAuthenticationHandler("CRAM-MD5", command.orig); !ok {
return reply
}
}
return ReplyAuthOk()
case MAIL == proto.State:
proto.logf("In MAIL state")
switch command.verb {
case "AUTH":
proto.logf("Got AUTH command, staying in MAIL state")
switch {
case strings.HasPrefix(command.args, "PLAIN "):
proto.logf("Got PLAIN authentication: %s", strings.TrimPrefix(command.args, "PLAIN "))
if proto.ValidateAuthenticationHandler != nil {
val, _ := base64.StdEncoding.DecodeString(strings.TrimPrefix(command.args, "PLAIN "))
bits := strings.Split(string(val), string(rune(0)))
if len(bits) < 3 {
return ReplyError(errors.New("Badly formed parameter"))
}
user, pass := bits[1], bits[2]
if reply, ok := proto.ValidateAuthenticationHandler("PLAIN", user, pass); !ok {
return reply
}
}
return ReplyAuthOk()
case "LOGIN" == command.args:
proto.logf("Got LOGIN authentication, switching to AUTH state")
proto.State = AUTHLOGIN
return ReplyAuthResponse("VXNlcm5hbWU6")
case "PLAIN" == command.args:
proto.logf("Got PLAIN authentication (no args), switching to AUTH2 state")
proto.State = AUTHPLAIN
return ReplyAuthResponse("")
case "CRAM-MD5" == command.args:
proto.logf("Got CRAM-MD5 authentication, switching to AUTH state")
proto.State = AUTHCRAMMD5
return ReplyAuthResponse("PDQxOTI5NDIzNDEuMTI4Mjg0NzJAc291cmNlZm91ci5hbmRyZXcuY211LmVkdT4=")
case strings.HasPrefix(command.args, "EXTERNAL "):
proto.logf("Got EXTERNAL authentication: %s", strings.TrimPrefix(command.args, "EXTERNAL "))
if proto.ValidateAuthenticationHandler != nil {
if reply, ok := proto.ValidateAuthenticationHandler("EXTERNAL", strings.TrimPrefix(command.args, "EXTERNAL ")); !ok {
return reply
}
}
return ReplyAuthOk()
default:
return ReplyUnsupportedAuth()
}
case "MAIL":
proto.logf("Got MAIL command, switching to RCPT state")
from, err := proto.ParseMAIL(command.args)
if err != nil {
return ReplyError(err)
}
if proto.ValidateSenderHandler != nil {
if !proto.ValidateSenderHandler(from) {
// TODO correct sender error response
return ReplyError(errors.New("Invalid sender " + from))
}
}
proto.Message.From = from
proto.State = RCPT
return ReplySenderOk(from)
case "HELO":
return proto.HELO(command.args)
case "EHLO":
return proto.EHLO(command.args)
default:
proto.logf("Got unknown command for MAIL state: '%s'", command)
return ReplyUnrecognisedCommand()
}
case RCPT == proto.State:
proto.logf("In RCPT state")
switch command.verb {
case "RCPT":
proto.logf("Got RCPT command")
if proto.MaximumRecipients > -1 && len(proto.Message.To) >= proto.MaximumRecipients {
return ReplyTooManyRecipients()
}
to, err := proto.ParseRCPT(command.args)
if err != nil {
return ReplyError(err)
}
if proto.ValidateRecipientHandler != nil {
if !proto.ValidateRecipientHandler(to) {
// TODO correct send error response
return ReplyError(errors.New("Invalid recipient " + to))
}
}
proto.Message.To = append(proto.Message.To, to)
proto.State = RCPT
return ReplyRecipientOk(to)
case "HELO":
return proto.HELO(command.args)
case "EHLO":
return proto.EHLO(command.args)
case "DATA":
proto.logf("Got DATA command, switching to DATA state")
proto.State = DATA
return ReplyDataResponse()
default:
proto.logf("Got unknown command for RCPT state: '%s'", command)
return ReplyUnrecognisedCommand()
}
default:
proto.logf("Command not recognised")
return ReplyUnrecognisedCommand()
}
}
// HELO creates a reply to a HELO command
func (proto *Protocol) HELO(args string) (reply *Reply) {
proto.logf("Got HELO command, switching to MAIL state")
proto.State = MAIL
proto.Message.Helo = args
return ReplyOk("Hello " + args)
}
// EHLO creates a reply to a EHLO command
func (proto *Protocol) EHLO(args string) (reply *Reply) {
proto.logf("Got EHLO command, switching to MAIL state")
proto.State = MAIL
proto.Message.Helo = args
replyArgs := []string{"Hello " + args, "PIPELINING"}
if proto.TLSHandler != nil && !proto.TLSPending && !proto.TLSUpgraded {
replyArgs = append(replyArgs, "STARTTLS")
}
if !proto.RequireTLS || proto.TLSUpgraded {
if proto.GetAuthenticationMechanismsHandler != nil {
mechanisms := proto.GetAuthenticationMechanismsHandler()
if len(mechanisms) > 0 {
replyArgs = append(replyArgs, "AUTH "+strings.Join(mechanisms, " "))
}
}
}
return ReplyOk(replyArgs...)
}
// STARTTLS creates a reply to a STARTTLS command
func (proto *Protocol) STARTTLS(args string) (reply *Reply) {
if proto.TLSUpgraded {
return ReplyUnrecognisedCommand()
}
if proto.TLSHandler == nil {
proto.logf("tls handler not found")
return ReplyUnrecognisedCommand()
}
if len(args) > 0 {
return ReplySyntaxError("no parameters allowed")
}
r, callback, ok := proto.TLSHandler(func(ok bool) {
proto.TLSUpgraded = ok
proto.TLSPending = ok
if ok {
proto.resetState()
proto.State = ESTABLISH
}
})
if !ok {
return r
}
proto.TLSPending = true
return ReplyReadyToStartTLS(callback)
}
var parseMailBrokenRegexp = regexp.MustCompile("(?i:From):\\s*<([^>]+)>")
var parseMailRFCRegexp = regexp.MustCompile("(?i:From):<([^>]+)>")
// ParseMAIL returns the forward-path from a MAIL command argument
func (proto *Protocol) ParseMAIL(mail string) (string, error) {
var match []string
if proto.RejectBrokenMAILSyntax {
match = parseMailRFCRegexp.FindStringSubmatch(mail)
} else {
match = parseMailBrokenRegexp.FindStringSubmatch(mail)
}
if len(match) != 2 {
return "", errors.New("Invalid syntax in MAIL command")
}
return match[1], nil
}
var parseRcptBrokenRegexp = regexp.MustCompile("(?i:To):\\s*<([^>]+)>")
var parseRcptRFCRegexp = regexp.MustCompile("(?i:To):<([^>]+)>")
// ParseRCPT returns the return-path from a RCPT command argument
func (proto *Protocol) ParseRCPT(rcpt string) (string, error) {
var match []string
if proto.RejectBrokenRCPTSyntax {
match = parseRcptRFCRegexp.FindStringSubmatch(rcpt)
} else {
match = parseRcptBrokenRegexp.FindStringSubmatch(rcpt)
}
if len(match) != 2 {
return "", errors.New("Invalid syntax in RCPT command")
}
return match[1], nil
}