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package message
import (
"errors"
"fmt"
"io"
"strings"
"github.com/emersion/go-message/textproto"
)
// Writer writes message entities.
//
// If the message is not multipart, it should be used as a WriteCloser. Don't
// forget to call Close.
//
// If the message is multipart, users can either use CreatePart to write child
// parts or Write to directly pipe a multipart message. In any case, Close must
// be called at the end.
type Writer struct {
w io.Writer
c io.Closer
mw *textproto.MultipartWriter
}
// createWriter creates a new Writer writing to w with the provided header.
// Nothing is written to w when it is called. header is modified in-place.
func createWriter(w io.Writer, header *Header) (*Writer, error) {
ww := &Writer{w: w}
mediaType, mediaParams, _ := header.ContentType()
if strings.HasPrefix(mediaType, "multipart/") {
ww.mw = textproto.NewMultipartWriter(ww.w)
// Do not set ww's io.Closer for now: if this is a multipart entity but
// CreatePart is not used (only Write is used), then the final boundary
// is expected to be written by the user too. In this case, ww.Close
// shouldn't write the final boundary.
if mediaParams["boundary"] != "" {
ww.mw.SetBoundary(mediaParams["boundary"])
} else {
mediaParams["boundary"] = ww.mw.Boundary()
header.SetContentType(mediaType, mediaParams)
}
header.Del("Content-Transfer-Encoding")
} else {
wc, err := encodingWriter(header.Get("Content-Transfer-Encoding"), ww.w)
if err != nil {
return nil, err
}
ww.w = wc
ww.c = wc
}
switch strings.ToLower(mediaParams["charset"]) {
case "", "us-ascii", "utf-8":
// This is OK
default:
// Anything else is invalid
return nil, fmt.Errorf("unhandled charset %q", mediaParams["charset"])
}
return ww, nil
}
// CreateWriter creates a new message writer to w. If header contains an
// encoding, data written to the Writer will automatically be encoded with it.
// The charset needs to be utf-8 or us-ascii.
func CreateWriter(w io.Writer, header Header) (*Writer, error) {
// ensure that modifications are invisible to the caller
header = header.Copy()
// If the message uses MIME, it has to include MIME-Version
if !header.Has("Mime-Version") {
header.Set("MIME-Version", "1.0")
}
ww, err := createWriter(w, &header)
if err != nil {
return nil, err
}
if err := textproto.WriteHeader(w, header.Header); err != nil {
return nil, err
}
return ww, nil
}
// Write implements io.Writer.
func (w *Writer) Write(b []byte) (int, error) {
return w.w.Write(b)
}
// Close implements io.Closer.
func (w *Writer) Close() error {
if w.c != nil {
return w.c.Close()
}
return nil
}
// CreatePart returns a Writer to a new part in this multipart entity. If this
// entity is not multipart, it fails. The body of the part should be written to
// the returned io.WriteCloser.
func (w *Writer) CreatePart(header Header) (*Writer, error) {
if w.mw == nil {
return nil, errors.New("cannot create a part in a non-multipart message")
}
if w.c == nil {
// We know that the user calls CreatePart so Close should write the final
// boundary
w.c = w.mw
}
// cw -> ww -> pw -> w.mw -> w.w
ww := &struct{ io.Writer }{nil}
// ensure that modifications are invisible to the caller
header = header.Copy()
cw, err := createWriter(ww, &header)
if err != nil {
return nil, err
}
pw, err := w.mw.CreatePart(header.Header)
if err != nil {
return nil, err
}
ww.Writer = pw
return cw, nil
}
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