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This commit is contained in:
Mechiel Lukkien
2023-01-30 14:27:06 +01:00
commit cb229cb6cf
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// Package dsn parses and composes Delivery Status Notification messages, see
// RFC 3464 and RFC 6533.
package dsn
import (
"bufio"
"bytes"
"context"
"encoding/base64"
"errors"
"fmt"
"io"
"mime/multipart"
"net/textproto"
"strconv"
"strings"
"time"
"github.com/mjl-/mox/dkim"
"github.com/mjl-/mox/message"
"github.com/mjl-/mox/mlog"
"github.com/mjl-/mox/mox-"
"github.com/mjl-/mox/smtp"
)
// Message represents a DSN message, with basic message headers, human-readable text,
// machine-parsable data, and optional original message/headers.
//
// A DSN represents a delayed, failed or successful delivery. Failing incoming
// deliveries over SMTP, and failing outgoing deliveries from the message queue,
// can result in a DSN being sent.
type Message struct {
SMTPUTF8 bool // Whether the original was received with smtputf8.
// DSN message From header. E.g. postmaster@ourdomain.example. NOTE:
// DSNs should be sent with a null reverse path to prevent mail loops.
// ../rfc/3464:421
From smtp.Path
// "To" header, and also SMTP RCP TO to deliver DSN to. Should be taken
// from original SMTP transaction MAIL FROM.
// ../rfc/3464:415
To smtp.Path
// Message subject header, e.g. describing mail delivery failure.
Subject string
// Human-readable text explaining the failure. Line endings should be
// bare newlines, not \r\n. They are converted to \r\n when composing.
TextBody string
// Per-message fields.
OriginalEnvelopeID string
ReportingMTA string // Required.
DSNGateway string
ReceivedFromMTA smtp.Ehlo // Host from which message was received.
ArrivalDate time.Time
// All per-message fields, including extensions. Only used for parsing,
// not composing.
MessageHeader textproto.MIMEHeader
// One or more per-recipient fields.
// ../rfc/3464:436
Recipients []Recipient
// Original message or headers to include in DSN as third MIME part.
// Optional. Only used for generating DSNs, not set for parsed DNSs.
Original []byte
}
// Action is a field in a DSN.
type Action string
// ../rfc/3464:890
const (
Failed Action = "failed"
Delayed Action = "delayed"
Delivered Action = "delivered"
Relayed Action = "relayed"
Expanded Action = "expanded"
)
// ../rfc/3464:1530 ../rfc/6533:370
// Recipient holds the per-recipient delivery-status lines in a DSN.
type Recipient struct {
// Required fields.
FinalRecipient smtp.Path // Final recipient of message.
Action Action
// Enhanced status code. First digit indicates permanent or temporary
// error. If the string contains more than just a status, that
// additional text is added as comment when composing a DSN.
Status string
// Optional fields.
// Original intended recipient of message. Used with the DSN extensions ORCPT
// parameter.
// ../rfc/3464:1197
OriginalRecipient smtp.Path
// Remote host that returned an error code. Can also be empty for
// deliveries.
RemoteMTA NameIP
// If RemoteMTA is present, DiagnosticCode is from remote. When
// creating a DSN, additional text in the string will be added to the
// DSN as comment.
DiagnosticCode string
LastAttemptDate time.Time
FinalLogID string
// For delayed deliveries, deliveries may be retried until this time.
WillRetryUntil *time.Time
// All fields, including extensions. Only used for parsing, not
// composing.
Header textproto.MIMEHeader
}
// Compose returns a DSN message.
//
// smtputf8 indicates whether the remote MTA that is receiving the DSN
// supports smtputf8. This influences the message media (sub)types used for the
// DSN.
//
// DKIM signatures are added if DKIM signing is configured for the "from" domain.
func (m *Message) Compose(log *mlog.Log, smtputf8 bool) ([]byte, error) {
// ../rfc/3462:119
// ../rfc/3464:377
// We'll make a multipart/report with 2 or 3 parts:
// - 1. human-readable explanation;
// - 2. message/delivery-status;
// - 3. (optional) original message (either in full, or only headers).
// todo future: add option to send full message. but only do so if the message is <100kb.
// todo future: possibly write to a file directly, instead of building up message in memory.
// If message does not require smtputf8, we are never generating a utf-8 DSN.
if !m.SMTPUTF8 {
smtputf8 = false
}
// We check for errors once after all the writes.
msgw := &errWriter{w: &bytes.Buffer{}}
header := func(k, v string) {
fmt.Fprintf(msgw, "%s: %s\r\n", k, v)
}
line := func(w io.Writer) {
w.Write([]byte("\r\n"))
}
// Outer message headers.
header("From", fmt.Sprintf("<%s>", m.From.XString(smtputf8))) // todo: would be good to have a local ascii-only name for this address.
header("To", fmt.Sprintf("<%s>", m.To.XString(smtputf8))) // todo: we could just leave this out if it has utf-8 and remote does not support utf-8.
header("Subject", m.Subject)
header("Message-Id", fmt.Sprintf("<%s>", mox.MessageIDGen(smtputf8)))
header("Date", time.Now().Format(message.RFC5322Z))
header("MIME-Version", "1.0")
mp := multipart.NewWriter(msgw)
header("Content-Type", fmt.Sprintf(`multipart/report; report-type="delivery-status"; boundary="%s"`, mp.Boundary()))
line(msgw)
// First part, human-readable message.
msgHdr := textproto.MIMEHeader{}
if smtputf8 {
msgHdr.Set("Content-Type", "text/plain; charset=utf-8")
msgHdr.Set("Content-Transfer-Encoding", "8BIT")
} else {
msgHdr.Set("Content-Type", "text/plain")
msgHdr.Set("Content-Transfer-Encoding", "7BIT")
}
msgp, err := mp.CreatePart(msgHdr)
if err != nil {
return nil, err
}
msgp.Write([]byte(strings.ReplaceAll(m.TextBody, "\n", "\r\n")))
// Machine-parsable message. ../rfc/3464:455
statusHdr := textproto.MIMEHeader{}
if smtputf8 {
// ../rfc/6533:325
statusHdr.Set("Content-Type", "message/global-delivery-status")
statusHdr.Set("Content-Transfer-Encoding", "8BIT")
} else {
statusHdr.Set("Content-Type", "message/delivery-status")
statusHdr.Set("Content-Transfer-Encoding", "7BIT")
}
statusp, err := mp.CreatePart(statusHdr)
if err != nil {
return nil, err
}
// ../rfc/3464:470
// examples: ../rfc/3464:1855
// type fields: ../rfc/3464:536 https://www.iana.org/assignments/dsn-types/dsn-types.xhtml
status := func(k, v string) {
fmt.Fprintf(statusp, "%s: %s\r\n", k, v)
}
// Per-message fields first. ../rfc/3464:575
// todo future: once we support the smtp dsn extension, the envid should be saved/set as OriginalEnvelopeID. ../rfc/3464:583 ../rfc/3461:1139
if m.OriginalEnvelopeID != "" {
status("Original-Envelope-ID", m.OriginalEnvelopeID)
}
status("Reporting-MTA", "dns; "+m.ReportingMTA) // ../rfc/3464:628
if m.DSNGateway != "" {
// ../rfc/3464:714
status("DSN-Gateway", "dns; "+m.DSNGateway)
}
if !m.ReceivedFromMTA.IsZero() {
// ../rfc/3464:735
status("Received-From-MTA", fmt.Sprintf("dns;%s (%s)", m.ReceivedFromMTA.Name, smtp.AddressLiteral(m.ReceivedFromMTA.ConnIP)))
}
status("Arrival-Date", m.ArrivalDate.Format(message.RFC5322Z)) // ../rfc/3464:758
// Then per-recipient fields. ../rfc/3464:769
// todo: should also handle other address types. at least recognize "unknown". Probably just store this field. ../rfc/3464:819
addrType := "rfc822;" // ../rfc/3464:514
if smtputf8 {
addrType = "utf-8;" // ../rfc/6533:250
}
if len(m.Recipients) == 0 {
return nil, fmt.Errorf("missing per-recipient fields")
}
for _, r := range m.Recipients {
line(statusp)
if !r.OriginalRecipient.IsZero() {
// ../rfc/3464:807
status("Original-Recipient", addrType+r.OriginalRecipient.DSNString(smtputf8))
}
status("Final-Recipient", addrType+r.FinalRecipient.DSNString(smtputf8)) // ../rfc/3464:829
status("Action", string(r.Action)) // ../rfc/3464:879
st := r.Status
if st == "" {
// ../rfc/3464:944
// Making up a status code is not great, but the field is required. We could simply
// require the caller to make one up...
switch r.Action {
case Delayed:
st = "4.0.0"
case Failed:
st = "5.0.0"
default:
st = "2.0.0"
}
}
var rest string
st, rest = codeLine(st)
statusLine := st
if rest != "" {
statusLine += " (" + rest + ")"
}
status("Status", statusLine) // ../rfc/3464:975
if !r.RemoteMTA.IsZero() {
// ../rfc/3464:1015
status("Remote-MTA", fmt.Sprintf("dns;%s (%s)", r.RemoteMTA.Name, smtp.AddressLiteral(r.RemoteMTA.IP)))
}
// Presence of Diagnostic-Code indicates the code is from Remote-MTA. ../rfc/3464:1053
if r.DiagnosticCode != "" {
diagCode, rest := codeLine(r.DiagnosticCode)
diagLine := diagCode
if rest != "" {
diagLine += " (" + rest + ")"
}
// ../rfc/6533:589
status("Diagnostic-Code", "smtp; "+diagLine)
}
if !r.LastAttemptDate.IsZero() {
status("Last-Attempt-Date", r.LastAttemptDate.Format(message.RFC5322Z)) // ../rfc/3464:1076
}
if r.FinalLogID != "" {
// todo future: think about adding cid as "Final-Log-Id"?
status("Final-Log-ID", r.FinalLogID) // ../rfc/3464:1098
}
if r.WillRetryUntil != nil {
status("Will-Retry-Until", r.WillRetryUntil.Format(message.RFC5322Z)) // ../rfc/3464:1108
}
}
// We include only the header of the original message.
// todo: add the textual version of the original message, if it exists and isn't too large.
if m.Original != nil {
headers, err := message.ReadHeaders(bufio.NewReader(bytes.NewReader(m.Original)))
if err != nil && errors.Is(err, message.ErrHeaderSeparator) {
// Whole data is a header.
headers = m.Original
} else if err != nil {
return nil, err
} else {
// This is a whole message. We still only include the headers.
// todo: include the whole body.
}
origHdr := textproto.MIMEHeader{}
if smtputf8 {
// ../rfc/6533:431
// ../rfc/6533:605
origHdr.Set("Content-Type", "message/global-headers") // ../rfc/6533:625
origHdr.Set("Content-Transfer-Encoding", "8BIT")
} else {
// ../rfc/3462:175
if m.SMTPUTF8 {
// ../rfc/6533:480
origHdr.Set("Content-Type", "text/rfc822-headers; charset=utf-8")
origHdr.Set("Content-Transfer-Encoding", "BASE64")
} else {
origHdr.Set("Content-Type", "text/rfc822-headers")
origHdr.Set("Content-Transfer-Encoding", "7BIT")
}
}
origp, err := mp.CreatePart(origHdr)
if err != nil {
return nil, err
}
if !smtputf8 && m.SMTPUTF8 {
data := base64.StdEncoding.EncodeToString(headers)
for len(data) > 0 {
line := data
n := len(line)
if n > 78 {
n = 78
}
line, data = data[:n], data[n:]
origp.Write([]byte(line + "\r\n"))
}
} else {
origp.Write(headers)
}
}
if err := mp.Close(); err != nil {
return nil, err
}
if msgw.err != nil {
return nil, err
}
data := msgw.w.Bytes()
fd := m.From.IPDomain.Domain
confDom, _ := mox.Conf.Domain(fd)
if len(confDom.DKIM.Sign) > 0 {
if dkimHeaders, err := dkim.Sign(context.Background(), m.From.Localpart, fd, confDom.DKIM, smtputf8, bytes.NewReader(data)); err != nil {
log.Errorx("dsn: dkim sign for domain, returning unsigned dsn", err, mlog.Field("domain", fd))
} else {
data = append([]byte(dkimHeaders), data...)
}
}
return data, nil
}
type errWriter struct {
w *bytes.Buffer
err error
}
func (w *errWriter) Write(buf []byte) (int, error) {
if w.err != nil {
return -1, w.err
}
n, err := w.w.Write(buf)
w.err = err
return n, err
}
// split a line into enhanced status code and rest.
func codeLine(s string) (string, string) {
t := strings.SplitN(s, " ", 2)
l := strings.Split(t[0], ".")
if len(l) != 3 {
return "", s
}
for i, e := range l {
_, err := strconv.ParseInt(e, 10, 32)
if err != nil {
return "", s
}
if i == 0 && len(e) != 1 {
return "", s
}
}
var rest string
if len(t) == 2 {
rest = t[1]
}
return t[0], rest
}
// HasCode returns whether line starts with an enhanced SMTP status code.
func HasCode(line string) bool {
// ../rfc/3464:986
ecode, _ := codeLine(line)
return ecode != ""
}