1package message

2

3import (

4 "errors"

5 "fmt"

6 "io"

7 "log/slog"

8 "net/textproto"

9

10 "github.com/mjl-/mox/dns"

11 "github.com/mjl-/mox/mlog"

12 "github.com/mjl-/mox/smtp"

13)

14

15var (

16 errFromHeaders = errors.New("missing or duplicate from header")

17 errFromAddresses = errors.New("from header does not have exactly one address")

18)

19

20// From extracts the address in the From-header.

21//

22// An RFC5322 message must have a From header.

23// In theory, multiple addresses may be present. In practice zero or multiple

24// From headers may be present. From returns an error if there is not exactly

25// one From header with exactly one address. This address can be used for

26// evaluating a DMARC policy against SPF and DKIM results.

27func From(elog *slog.Logger, strict bool, r io.ReaderAt, p *Part) (raddr smtp.Address, envelope *Envelope, header textproto.MIMEHeader, rerr error) {

28 log := mlog.New("message", elog)

29

30 // ../rfc/7489:1243

31

32 // todo: only allow utf8 if enabled in session/message?

33

34 var err error

35 if p == nil {

36 var pp Part

37 pp, err = Parse(log.Logger, strict, r)

38 if err != nil {

39 // todo: should we continue with p, perhaps headers can be parsed?

40 return raddr, nil, nil, fmt.Errorf("parsing message: %v", err)

41 }

42 p = &pp

43 }

44 header, err = p.Header()

45 if err != nil {

46 return raddr, nil, nil, fmt.Errorf("parsing message header: %v", err)

47 }

48 // A message must have exactly one From header. ../rfc/5322:1145

49 // Multiple From headers are only allowed by the obsolete syntax, which leaves

50 // their interpretation unspecified. ../rfc/5322:1993

51 // We would use the first, while DKIM signs the physically last instance

52 // (../rfc/6376:2320), so the header we evaluate DMARC against and the header

53 // covered by the signature need not be the same. Reject instead of picking.

54 if l := header.Values("From"); len(l) != 1 {

55 return raddr, nil, nil, fmt.Errorf("%w: %d headers", errFromHeaders, len(l))

56 }

57 from := p.Envelope.From

58 if len(from) != 1 {

59 return raddr, nil, nil, fmt.Errorf("%w: %d addresses", errFromAddresses, len(from))

60 }

61 d, err := dns.ParseDomain(from[0].Host)

62 if err != nil {

63 return raddr, nil, nil, fmt.Errorf("bad domain in from address: %v", err)

64 }

65 lp, err := smtp.ParseLocalpart(from[0].User)

66 if err != nil {

67 return raddr, nil, nil, fmt.Errorf("parsing localpart in from address: %v", err)

68 }

69 addr := smtp.NewAddress(lp, d)

70 return addr, p.Envelope, textproto.MIMEHeader(header), nil

71}

72