compose: allow writing multipart/alternative messages

Add a new :multipart command that can be executed on the composer review
screen. This command takes a MIME type as argument which needs to match
a setting in the new [multipart-converters] section of aerc.conf. A part
can be removed by using the -d flag.

The [multipart-converters] section has MIME types associated with
commands. These commands are executed with sh -c every time the main
email body is updated to generate each part content. The commands are
expected to output valid UTF-8 text.

If a command fails, an explicit error will be printed next to the part
MIME type to allow users to debug their issue but the email may still be
sent anyway with an empty alternative part.

This is mostly intended for people who *really* need to send html
messages for their boss or for corporate reasons. For now, it is
a manual and explicit action to convert a message in such a way.

Here is an example configuration:

  [multipart-converters]
  text/html = pandoc -f markdown -t html

And the associated binding to append an HTML alternative to a message:

  [compose::review]
  H = :multipart text/html<enter>
  hh = :multipart -d text/html<enter>

Link: https://lists.sr.ht/~rjarry/aerc-discuss/%3CCO5KH4W57XNB.2PZLR1CNFK22H%40mashenka%3E
Co-authored-by: Eric McConville <emcconville@emcconville.com>
Signed-off-by: Robin Jarry <robin@jarry.cc>
Tested-by: Bence Ferdinandy <bence@ferdinandy.com>
Acked-by: Moritz Poldrack <moritz@poldrack.dev>

1 files changed, 65 insertions, 1 deletions

diff --git a/widgets/compose.go b/widgets/compose.go
index 30c5268d..37e09ccb 100644
--- a/widgets/compose.go
+++ b/widgets/compose.go
@@ -464,6 +464,11 @@ func (c *Composer) AppendPart(mimetype string, params map[string]string, body io
 	if !strings.HasPrefix(mimetype, "text") {
 		return fmt.Errorf("can only append text mimetypes")
 	}
+	for _, part := range c.textParts {
+		if part.MimeType == mimetype {
+			return fmt.Errorf("%s part already exists", mimetype)
+		}
+	}
 	newPart, err := lib.NewPart(mimetype, params, body)
 	if err != nil {
 		return err
@@ -473,6 +478,21 @@ func (c *Composer) AppendPart(mimetype string, params map[string]string, body io
 	return nil
 }
 
+func (c *Composer) RemovePart(mimetype string) error {
+	if mimetype == "text/plain" {
+		return fmt.Errorf("cannot remove text/plain parts")
+	}
+	for i, part := range c.textParts {
+		if part.MimeType != mimetype {
+			continue
+		}
+		c.textParts = append(c.textParts[:i], c.textParts[i+1:]...)
+		c.resetReview()
+		return nil
+	}
+	return fmt.Errorf("%s part not found", mimetype)
+}
+
 func (c *Composer) AddTemplate(template string, data interface{}) error {
 	if template == "" {
 		return nil
@@ -1361,7 +1381,15 @@ func newReviewMessage(composer *Composer, err error) *reviewMessage {
 			grid.AddChild(ui.NewText("text/plain", uiConfig.GetStyle(config.STYLE_DEFAULT))).At(i, 0)
 			i += 1
 			for _, p := range composer.textParts {
-				grid.AddChild(ui.NewText(p.MimeType, uiConfig.GetStyle(config.STYLE_DEFAULT))).At(i, 0)
+				err := composer.updateMultipart(p)
+				if err != nil {
+					msg := fmt.Sprintf("%s error: %s", p.MimeType, err)
+					grid.AddChild(ui.NewText(msg,
+						uiConfig.GetStyle(config.STYLE_ERROR))).At(i, 0)
+				} else {
+					grid.AddChild(ui.NewText(p.MimeType,
+						uiConfig.GetStyle(config.STYLE_DEFAULT))).At(i, 0)
+				}
 				i += 1
 			}
 
@@ -1374,6 +1402,42 @@ func newReviewMessage(composer *Composer, err error) *reviewMessage {
 	}
 }
 
+func (c *Composer) updateMultipart(p *lib.Part) error {
+	command, found := c.aerc.Config().Converters[p.MimeType]
+	if !found {
+		// unreachable
+		return fmt.Errorf("no command defined for mime/type")
+	}
+	// reset part body to avoid it leaving outdated if the command fails
+	p.Data = nil
+	err := c.reloadEmail()
+	if err != nil {
+		return errors.Wrap(err, "reloadEmail")
+	}
+	body, err := io.ReadAll(c.email)
+	if err != nil {
+		return errors.Wrap(err, "io.ReadAll")
+	}
+	cmd := exec.Command("sh", "-c", command)
+	cmd.Stdin = bytes.NewReader(body)
+	out, err := cmd.Output()
+	if err != nil {
+		var stderr string
+		var ee *exec.ExitError
+		if errors.As(err, &ee) {
+			// append the first 30 chars of stderr if any
+			stderr = strings.Trim(string(ee.Stderr), " \t\n\r")
+			stderr = strings.ReplaceAll(stderr, "\n", "; ")
+			if stderr != "" {
+				stderr = fmt.Sprintf(": %.30s", stderr)
+			}
+		}
+		return fmt.Errorf("%s: %w%s", command, err, stderr)
+	}
+	p.Data = out
+	return nil
+}
+
 func (rm *reviewMessage) Invalidate() {
 	ui.Invalidate()
 }