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// writer.go largerly mimics github.com/emersion/go-pgpmail, with changes made
// to interface with the gpg package in aerc
package gpg
import (
"bytes"
"fmt"
"io"
"mime"
"git.sr.ht/~rjarry/aerc/lib/crypto/gpg/gpgbin"
"github.com/emersion/go-message"
"github.com/emersion/go-message/textproto"
)
type EncrypterSigner struct {
msgBuf bytes.Buffer
encryptedWriter io.Writer
to []string
from string
}
func (es *EncrypterSigner) Write(p []byte) (int, error) {
return es.msgBuf.Write(p)
}
func (es *EncrypterSigner) Close() (err error) {
r := bytes.NewReader(es.msgBuf.Bytes())
enc, err := gpgbin.Encrypt(r, es.to, es.from)
if err != nil {
return err
}
_, err = es.encryptedWriter.Write(enc)
if err != nil {
return fmt.Errorf("gpg: failed to write encrypted writer: %w", err)
}
return nil
}
type Signer struct {
mw *textproto.MultipartWriter
signedMsg bytes.Buffer
w io.Writer
from string
header textproto.Header
}
func (s *Signer) Write(p []byte) (int, error) {
return s.signedMsg.Write(p)
}
func (s *Signer) Close() (err error) {
msg, err := message.Read(&s.signedMsg)
if err != nil {
return err
}
// Make sure that MIME-Version is *not* set on the signed part header.
// It must be set *only* on the top level header.
//
// Some MTAs actually normalize the case of all headers (including
// signed text parts). MIME-Version can be normalized to different
// casing depending on the implementation (MIME- vs Mime-).
//
// Since the signature is computed on the whole part, including its
// header, changing the case can cause the signature to become invalid.
msg.Header.Del("Mime-Version")
var buf bytes.Buffer
_ = textproto.WriteHeader(&buf, msg.Header.Header)
_, _ = io.Copy(&buf, msg.Body)
sig, micalg, err := gpgbin.Sign(bytes.NewReader(buf.Bytes()), s.from)
if err != nil {
return err
}
params := map[string]string{
"boundary": s.mw.Boundary(),
"protocol": "application/pgp-signature",
"micalg": micalg,
}
s.header.Set("Content-Type", mime.FormatMediaType("multipart/signed", params))
// Ensure Mime-Version header is set on the top level to be compliant
// with RFC 2045
s.header.Set("Mime-Version", "1.0")
if err = textproto.WriteHeader(s.w, s.header); err != nil {
return err
}
boundary := s.mw.Boundary()
fmt.Fprintf(s.w, "--%s\r\n", boundary)
_, _ = s.w.Write(buf.Bytes())
_, _ = s.w.Write([]byte("\r\n"))
var signedHeader textproto.Header
signedHeader.Set("Content-Type", "application/pgp-signature; name=\"signature.asc\"")
signatureWriter, err := s.mw.CreatePart(signedHeader)
if err != nil {
return err
}
_, err = signatureWriter.Write(sig)
if err != nil {
return err
}
return nil
}
// for tests
var forceBoundary = ""
type multiCloser []io.Closer
func (mc multiCloser) Close() error {
for _, c := range mc {
if err := c.Close(); err != nil {
return err
}
}
return nil
}
func Encrypt(w io.Writer, h textproto.Header, rcpts []string, from string) (io.WriteCloser, error) {
mw := textproto.NewMultipartWriter(w)
if forceBoundary != "" {
err := mw.SetBoundary(forceBoundary)
if err != nil {
return nil, fmt.Errorf("gpg: failed to set boundary: %w", err)
}
}
params := map[string]string{
"boundary": mw.Boundary(),
"protocol": "application/pgp-encrypted",
}
h.Set("Content-Type", mime.FormatMediaType("multipart/encrypted", params))
// Ensure Mime-Version header is set on the top level to be compliant
// with RFC 2045
h.Set("Mime-Version", "1.0")
if err := textproto.WriteHeader(w, h); err != nil {
return nil, err
}
var controlHeader textproto.Header
controlHeader.Set("Content-Type", "application/pgp-encrypted")
controlWriter, err := mw.CreatePart(controlHeader)
if err != nil {
return nil, err
}
if _, err = controlWriter.Write([]byte("Version: 1\r\n")); err != nil {
return nil, err
}
var encryptedHeader textproto.Header
encryptedHeader.Set("Content-Type", "application/octet-stream")
encryptedWriter, err := mw.CreatePart(encryptedHeader)
if err != nil {
return nil, err
}
var buf bytes.Buffer
plaintext := &EncrypterSigner{
msgBuf: buf,
encryptedWriter: encryptedWriter,
to: rcpts,
from: from,
}
return struct {
io.Writer
io.Closer
}{
plaintext,
multiCloser{
plaintext,
mw,
},
}, nil
}
func Sign(w io.Writer, h textproto.Header, from string) (io.WriteCloser, error) {
mw := textproto.NewMultipartWriter(w)
if forceBoundary != "" {
err := mw.SetBoundary(forceBoundary)
if err != nil {
return nil, fmt.Errorf("gpg: failed to set boundary: %w", err)
}
}
var msg bytes.Buffer
plaintext := &Signer{
mw: mw,
signedMsg: msg,
w: w,
from: from,
header: h,
}
return struct {
io.Writer
io.Closer
}{
plaintext,
multiCloser{
plaintext,
mw,
},
}, nil
}
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