textproto: add multipart implementation

entity.go

@@ -3,7 +3,6 @@ package message
 import (
 	"bufio"
 	"io"
-	"mime/multipart"
 	"strings"
 
 	"github.com/emersion/go-message/textproto"
@@ -93,7 +92,7 @@ func (e *Entity) MultipartReader() MultipartReader {
 	if mb, ok := e.Body.(*multipartBody); ok {
 		return mb
 	}
-	return &multipartReader{multipart.NewReader(e.Body, e.mediaParams["boundary"])}
+	return &multipartReader{textproto.NewMultipartReader(e.Body, e.mediaParams["boundary"])}
 }
 
 // writeBodyTo writes this entity's body to w (without the header).

header.go

@@ -2,7 +2,6 @@ package message
 
 import (
 	"mime"
-	stdtextproto "net/textproto"
 
 	"github.com/emersion/go-message/textproto"
 )
@@ -26,26 +25,6 @@ func formatHeaderWithParams(f string, params map[string]string) string {
 	return mime.FormatMediaType(f, encParams)
 }
 
-func mapToHeader(m stdtextproto.MIMEHeader) textproto.Header {
-	var h textproto.Header
-	for k, vs := range m {
-		for i := len(vs) - 1; i >= 0; i-- {
-			h.Add(k, vs[i])
-		}
-	}
-	return h
-}
-
-// headerToMap converts a textproto.Header to a map. It looses information.
-func headerToMap(h textproto.Header) stdtextproto.MIMEHeader {
-	m := make(stdtextproto.MIMEHeader)
-	fields := h.Fields()
-	for fields.Next() {
-		m.Add(fields.Key(), fields.Value())
-	}
-	return m
-}
-
 // A Header represents the key-value pairs in a message header.
 type Header struct {
 	textproto.Header

multipart.go

@@ -2,7 +2,8 @@ package message
 
 import (
 	"io"
-	"mime/multipart"
+
+	"github.com/emersion/go-message/textproto"
 )
 
 // MultipartReader is an iterator over parts in a MIME multipart body.
@@ -18,7 +19,7 @@ type MultipartReader interface {
 }
 
 type multipartReader struct {
-	r *multipart.Reader
+	r *textproto.MultipartReader
 }
 
 // NextPart implements MultipartReader.
@@ -27,7 +28,7 @@ func (r *multipartReader) NextPart() (*Entity, error) {
 	if err != nil {
 		return nil, err
 	}
-	return New(Header{mapToHeader(p.Header)}, p)
+	return New(Header{p.Header}, p)
 }
 
 // Close implements io.Closer.