compose: add option for LF-only editors

Some editors only support LF line endings. For these, standard compliant
eml files are not an option.

Add an option compose.lf-editor to translate the eml file to lf
lineendings.

Signed-off-by: Moritz Poldrack <git@moritz.sh>
Acked-by: Robin Jarry <robin@jarry.cc>
Tested-by: Matěj Cepl <mcepl@cepl.eu>

4 files changed, 46 insertions, 9 deletions

diff --git a/config/aerc.conf b/config/aerc.conf
index 46b24f1c..00c8501f 100644
--- a/config/aerc.conf
+++ b/config/aerc.conf
@@ -383,6 +383,13 @@
 #editor=
 
 #
+# When set, aerc will create and read .eml files for composing that have
+# non-standard \n linebreaks. This is only relevant if the used editor does not
+# support CRLF linebreaks.
+#
+#lf-editor=false
+
+#
 # Default header fields to display when composing a message. To display
 # multiple headers in the same row, separate them with a pipe, e.g. "To|From".
 #
diff --git a/config/compose.go b/config/compose.go
index 37e46f96..463723cf 100644
--- a/config/compose.go
+++ b/config/compose.go
@@ -17,6 +17,7 @@ type ComposeConfig struct {
 	FilePickerCmd       string         `ini:"file-picker-cmd"`
 	FormatFlowed        bool           `ini:"format-flowed"`
 	EditHeaders         bool           `ini:"edit-headers"`
+	LFEditor            bool           `ini:"lf-editor"`
 }
 
 var Compose = new(ComposeConfig)
diff --git a/doc/aerc-config.5.scd b/doc/aerc-config.5.scd
index b09ce53e..3f0b076a 100644
--- a/doc/aerc-config.5.scd
+++ b/doc/aerc-config.5.scd
@@ -615,6 +615,13 @@ These options are configured in the *[compose]* section of _aerc.conf_.
 
 	Default: _false_
 
+*lf-editor* = _true_|_false_
+	When set, aerc will create and read .eml files for composing that have
+	non-standard \n linebreaks. This is only relevant if the used editor
+	does not support CRLF linebreaks.
+
+	Default: _false_
+
 # MULTIPART CONVERTERS
 
 Converters allow generating _multipart/alternative_ messages by converting the
diff --git a/widgets/compose.go b/widgets/compose.go
index f7bce6d4..1c0aaab5 100644
--- a/widgets/compose.go
+++ b/widgets/compose.go
@@ -462,11 +462,18 @@ func (c *Composer) updateCrypto() error {
 	return nil
 }
 
-func (c *Composer) writeCRLF(reader io.Reader) error {
-	// .eml files must always use '\r\n' line endings
+func (c *Composer) writeEml(reader io.Reader) error {
+	// .eml files must always use '\r\n' line endings, but some editors
+	// don't support these, so if they are using one of those, the
+	// line-endings are transformed
+	lineEnding := "\r\n"
+	if config.Compose.LFEditor {
+		lineEnding = "\n"
+	}
+
 	scanner := bufio.NewScanner(reader)
 	for scanner.Scan() {
-		_, err := c.email.WriteString(scanner.Text() + "\r\n")
+		_, err := c.email.WriteString(scanner.Text() + lineEnding)
 		if err != nil {
 			return err
 		}
@@ -488,6 +495,11 @@ func (c *Composer) setContents(reader io.Reader) error {
 	if err != nil {
 		return err
 	}
+	lineEnding := "\r\n"
+	if config.Compose.LFEditor {
+		lineEnding = "\n"
+	}
+
 	if c.editHeaders {
 		for _, h := range c.headerOrder() {
 			var value string
@@ -506,7 +518,7 @@ func (c *Composer) setContents(reader io.Reader) error {
 					for _, a := range addresses {
 						addr = append(addr, format.AddressForHumans(a))
 					}
-					value = strings.Join(addr, ",\r\n\t")
+					value = strings.Join(addr, ","+lineEnding+"\t")
 				}
 			default:
 				value, err = c.header.Text(h)
@@ -516,17 +528,17 @@ func (c *Composer) setContents(reader io.Reader) error {
 				}
 			}
 			key := textproto.CanonicalMIMEHeaderKey(h)
-			_, err = fmt.Fprintf(c.email, "%s: %s\r\n", key, value)
+			_, err = fmt.Fprintf(c.email, "%s: %s"+lineEnding, key, value)
 			if err != nil {
 				return err
 			}
 		}
-		_, err = c.email.WriteString("\r\n")
+		_, err = c.email.WriteString(lineEnding)
 		if err != nil {
 			return err
 		}
 	}
-	return c.writeCRLF(reader)
+	return c.writeEml(reader)
 }
 
 func (c *Composer) appendContents(reader io.Reader) error {
@@ -534,7 +546,7 @@ func (c *Composer) appendContents(reader io.Reader) error {
 	if err != nil {
 		return err
 	}
-	return c.writeCRLF(reader)
+	return c.writeEml(reader)
 }
 
 func (c *Composer) AppendPart(mimetype string, params map[string]string, body io.Reader) error {
@@ -904,7 +916,17 @@ func (c *Composer) parseEmbeddedHeader() (*mail.Header, error) {
 	if err != nil {
 		return nil, errors.Wrap(err, "Seek")
 	}
-	msg, err := mail.CreateReader(c.email)
+
+	buf := bytes.NewBuffer([]byte{})
+	_, err = io.Copy(buf, c.email)
+	if err != nil {
+		return nil, fmt.Errorf("mail.ReadMessageCopy: %w", err)
+	}
+	if config.Compose.LFEditor {
+		bytes.ReplaceAll(buf.Bytes(), []byte{'\n'}, []byte{'\r', '\n'})
+	}
+
+	msg, err := mail.CreateReader(buf)
 	if errors.Is(err, io.EOF) { // completely empty
 		h := mail.HeaderFromMap(make(map[string][]string))
 		return &h, nil