1package message
2
3import (
4 "io"
5)
6
7// Writer is a write-through helper, collecting properties about the written
8// message and replacing bare \n line endings with \r\n.
9type Writer struct {
10 writer io.Writer
11
12 HaveBody bool // Body is optional in a message. ../rfc/5322:343
13 Has8bit bool // Whether a byte with the high/8bit has been read. So whether this needs SMTP 8BITMIME instead of 7BIT.
14 Size int64 // Number of bytes written, may be different from bytes read due to LF to CRLF conversion.
15
16 // For detecting header/body-separating crlf and fixing up bare lf. These are the
17 // incoming bytes, not the fixed up bytes. So CRs may be missing from tail.
18 tail [3]byte
19 // todo: should be parsing headers here, as we go
20}
21
22func NewWriter(w io.Writer) *Writer {
23 // Pretend we already saw \r\n, for handling empty header.
24 return &Writer{writer: w, tail: [3]byte{0, '\r', '\n'}}
25}
26
27// Write implements io.Writer, and writes buf as message to the Writer's underlying
28// io.Writer. It converts bare new lines (LF) to carriage returns with new lines
29// (CRLF).
30func (w *Writer) Write(buf []byte) (int, error) {
31 if !w.Has8bit {
32 for _, b := range buf {
33 if b >= 0x80 {
34 w.Has8bit = true
35 break
36 }
37 }
38 }
39
40 if !w.HaveBody {
41 get := func(i int) byte {
42 if i < 0 {
43 return w.tail[3+i]
44 }
45 return buf[i]
46 }
47
48 for i, b := range buf {
49 if b == '\n' && (get(i-1) == '\n' || get(i-1) == '\r' && get(i-2) == '\n') {
50 w.HaveBody = true
51 break
52 }
53 }
54 }
55
56 // Update w.tail after having written. Regardless of error, writers can't expect
57 // subsequent writes to work again properly anyway.
58 defer func() {
59 n := min(len(buf), 3)
60 copy(w.tail[:], w.tail[n:])
61 copy(w.tail[3-n:], buf[len(buf)-n:])
62 }()
63
64 wrote := 0
65 o := 0
66Top:
67 for o < len(buf) {
68 // Look for bare newline. If present, write up to that position while adding the
69 // missing carriage return. Then start the loop again.
70 for i := o; i < len(buf); i++ {
71 if buf[i] == '\n' && (i > 0 && buf[i-1] != '\r' || i == 0 && w.tail[2] != '\r') {
72 // Write buffer leading up to missing \r.
73 if i > o {
74 n, err := w.writer.Write(buf[o:i])
75 if n > 0 {
76 wrote += n
77 w.Size += int64(n)
78 }
79 if err != nil {
80 return wrote, err
81 }
82 }
83 n, err := w.writer.Write([]byte{'\r', '\n'})
84 if n == 2 {
85 wrote += 1 // For only the newline.
86 w.Size += int64(2)
87 }
88 if err != nil {
89 return wrote, err
90 }
91 o = i + 1
92 continue Top
93 }
94 }
95 n, err := w.writer.Write(buf[o:])
96 if n > 0 {
97 wrote += n
98 w.Size += int64(n)
99 }
100 if err != nil {
101 return wrote, err
102 }
103 break
104 }
105 return wrote, nil
106}
107