Merge pull request #38 from wneessen/37-attachment-length

Fixes bug with attachment encoding

base64_writer.go

@@ -0,0 +1,60 @@
+// SPDX-FileCopyrightText: 2022 Winni Neessen <winni@neessen.dev>
+//
+// SPDX-License-Identifier: MIT
+
+package mail
+
+import "io"
+
+// Base64LineBreaker is a io.WriteCloser that writes Base64 encoded data streams
+// with line breaks at a given line length
+type Base64LineBreaker struct {
+	line [MaxBodyLength]byte
+	used int
+	out  io.Writer
+}
+
+var nl = []byte(SingleNewLine)
+
+// Write writes the data stream and inserts a SingleNewLine when the maximum
+// line length is reached
+func (l *Base64LineBreaker) Write(b []byte) (n int, err error) {
+	if l.used+len(b) < MaxBodyLength {
+		copy(l.line[l.used:], b)
+		l.used += len(b)
+		return len(b), nil
+	}
+
+	n, err = l.out.Write(l.line[0:l.used])
+	if err != nil {
+		return
+	}
+	excess := MaxBodyLength - l.used
+	l.used = 0
+
+	n, err = l.out.Write(b[0:excess])
+	if err != nil {
+		return
+	}
+
+	n, err = l.out.Write(nl)
+	if err != nil {
+		return
+	}
+
+	return l.Write(b[excess:])
+}
+
+// Close closes the Base64LineBreaker and writes any access data that is still
+// unwritten in memory
+func (l *Base64LineBreaker) Close() (err error) {
+	if l.used > 0 {
+		_, err = l.out.Write(l.line[0:l.used])
+		if err != nil {
+			return
+		}
+		_, err = l.out.Write(nl)
+	}
+
+	return
+}

msgwriter.go

@@ -22,6 +22,10 @@ import (
 // RFC 2047 suggests 76 characters
 const MaxHeaderLength = 76
 
+// MaxBodyLength defines the maximum line length for the mail body
+// RFC 2047 suggests 76 characters
+const MaxBodyLength = 76
+
 // SingleNewLine represents a new line that can be used by the msgWriter to issue a carriage return
 const SingleNewLine = "\r\n"
 
@@ -277,12 +281,14 @@ func (mw *msgWriter) writeBody(f func(io.Writer) (int64, error), e Encoding) {
 		w = mw.pw
 	}
 	wbuf := bytes.Buffer{}
+	lb := Base64LineBreaker{}
+	lb.out = &wbuf
 
 	switch e {
 	case EncodingQP:
 		ew = quotedprintable.NewWriter(&wbuf)
 	case EncodingB64:
-		ew = base64.NewEncoder(base64.StdEncoding, &wbuf)
+		ew = base64.NewEncoder(base64.StdEncoding, &lb)
 	case NoEncoding:
 		_, mw.err = f(&wbuf)
 		n, mw.err = io.Copy(w, &wbuf)
@@ -296,6 +302,7 @@ func (mw *msgWriter) writeBody(f func(io.Writer) (int64, error), e Encoding) {
 
 	_, mw.err = f(ew)
 	mw.err = ew.Close()
+	mw.err = lb.Close()
 	n, mw.err = io.Copy(w, &wbuf)
 
 	// Since the part writer uses the WriteTo() method, we don't need to add the