1package message

2

3import (

4 "io"

5)

6

7// Writer is a write-through helper, collecting properties about the written

8// message.

9type Writer struct {

10 writer io.Writer

11

12 HaveBody bool // Body is optional. ../rfc/5322:343

13 Has8bit bool // Whether a byte with the high/8bit has been read. So whether this is 8BITMIME instead of 7BIT.

14 Size int64

15

16 tail [3]byte // For detecting header/body-separating crlf.

17 // todo: should be parsing headers here, as we go

18}

19

20func NewWriter(w io.Writer) *Writer {

21 // Pretend we already saw \r\n, for handling empty header.

22 return &Writer{writer: w, tail: [3]byte{0, '\r', '\n'}}

23}

24

25// Write implements io.Writer.

26func (w *Writer) Write(buf []byte) (int, error) {

27 if !w.HaveBody && len(buf) > 0 {

28 get := func(i int) byte {

29 if i < 0 {

30 return w.tail[3+i]

31 }

32 return buf[i]

33 }

34

35 for i, b := range buf {

36 if b == '\n' && get(i-3) == '\r' && get(i-2) == '\n' && get(i-1) == '\r' {

37 w.HaveBody = true

38 break

39 }

40 }

41

42 n := len(buf)

43 if n > 3 {

44 n = 3

45 }

46 copy(w.tail[:], w.tail[n:])

47 copy(w.tail[3-n:], buf[len(buf)-n:])

48 }

49 if !w.Has8bit {

50 for _, b := range buf {

51 if b&0x80 != 0 {

52 w.Has8bit = true

53 break

54 }

55 }

56 }

57 n, err := w.writer.Write(buf)

58 if n > 0 {

59 w.Size += int64(n)

60 }

61 return n, err

62}

63