Initialize module and dependencies

vendor/github.com/emersion/go-message/writer.go

@@ -0,0 +1,134 @@
+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
+}