feat: handle foreign encodings

pkg/message/parser/part.go

@@ -2,8 +2,12 @@ package parser
 
 import (
 	"errors"
+	"unicode/utf8"
 
+	pmmime "github.com/ProtonMail/proton-bridge/pkg/mime"
 	"github.com/emersion/go-message"
+	"golang.org/x/net/html/charset"
+	"golang.org/x/text/encoding"
 )
 
 type Parts []*Part
@@ -30,35 +34,32 @@ func (p *Part) AddChild(child *Part) {
 	p.children = append(p.children, child)
 }
 
-func (p *Part) write(writer *message.Writer, w *Writer) (err error) {
-	if len(p.children) > 0 {
-		for _, child := range p.children {
-			if err = child.writeAsChild(writer, w); err != nil {
-				return
-			}
-		}
-	}
-
-	if _, err = writer.Write(p.Body); err != nil {
-		return
-	}
-
-	return
+func (p *Part) isUTF8() bool {
+	return utf8.Valid(p.Body)
 }
 
-func (p *Part) writeAsChild(writer *message.Writer, w *Writer) (err error) {
-	if !w.shouldWrite(p) {
-		return
-	}
-
-	childWriter, err := writer.CreatePart(p.Header)
+// TODO: Do we then need to set charset to utf-8? What if it's embedded in html?
+func (p *Part) convertToUTF8() error {
+	t, params, err := p.Header.ContentType()
 	if err != nil {
-		return
+		return err
 	}
 
-	if err = p.write(childWriter, w); err != nil {
-		return
+	var decoder *encoding.Decoder
+
+	if knownCharset, ok := params["charset"]; !ok {
+		encoding, _, _ := charset.DetermineEncoding(p.Body, t)
+		decoder = encoding.NewDecoder()
+	} else if decoder, err = pmmime.SelectDecoder(knownCharset); err != nil {
+		return err
 	}
 
-	return childWriter.Close()
+	if p.Body, err = decoder.Bytes(p.Body); err != nil {
+		return err
+	}
+
+	params["charset"] = "utf-8"
+	p.Header.SetContentType(t, params)
+
+	return nil
 }