filters: add matching against attachment filename

The mimetype of attachments are set by the sender, which can results in
attachments getting not so useful mimetypes (e.g.
application/octet-stream for a csv). Allow matching filter against
filenames directly, by adding the `.filename,` and `.filename,~` syntax,
similarly to headers.

Changelog-added: Match filters on filename via `.filename,~<regexp> =`.
Signed-off-by: Bence Ferdinandy <bence@ferdinandy.com>
Acked-by: Robin Jarry <robin@jarry.cc>

3 files changed, 31 insertions, 1 deletions

diff --git a/app/msgviewer.go b/app/msgviewer.go
index 7b24e756..a78daa3a 100644
--- a/app/msgviewer.go
+++ b/app/msgviewer.go
@@ -480,6 +480,11 @@ func NewPartViewer(
 			if f.Regex.Match([]byte(header)) {
 				filter = exec.Command("sh", "-c", f.Command)
 			}
+		case config.FILTER_FILENAME:
+			if f.Regex.Match([]byte(part.DispositionParams["filename"])) {
+				filter = exec.Command("sh", "-c", f.Command)
+				log.Tracef("command %v", f.Command)
+			}
 		}
 		if filter != nil {
 			break
diff --git a/config/filters.go b/config/filters.go
index 1bbeaa30..e843c5fa 100644
--- a/config/filters.go
+++ b/config/filters.go
@@ -14,6 +14,7 @@ const (
 	FILTER_MIMETYPE FilterType = iota
 	FILTER_HEADER
 	FILTER_HEADERS
+	FILTER_FILENAME
 )
 
 type FilterConfig struct {
@@ -37,7 +38,22 @@ func parseFilters(file *ini.File) error {
 			Command: key.Value(),
 			Filter:  key.Name(),
 		}
+
 		switch {
+		case strings.HasPrefix(filter.Filter, ".filename,~"):
+			filter.Type = FILTER_FILENAME
+			regex := filter.Filter[strings.Index(filter.Filter, "~")+1:]
+			filter.Regex, err = regexp.Compile(regex)
+			if err != nil {
+				return err
+			}
+		case strings.HasPrefix(filter.Filter, ".filename,"):
+			filter.Type = FILTER_FILENAME
+			value := filter.Filter[strings.Index(filter.Filter, ",")+1:]
+			filter.Regex, err = regexp.Compile(regexp.QuoteMeta(value))
+			if err != nil {
+				return err
+			}
 		case strings.Contains(filter.Filter, ",~"):
 			filter.Type = FILTER_HEADER
 			//nolint:gocritic // guarded by strings.Contains
diff --git a/doc/aerc-config.5.scd b/doc/aerc-config.5.scd
index b26d7695..60fc5b7f 100644
--- a/doc/aerc-config.5.scd
+++ b/doc/aerc-config.5.scd
@@ -906,7 +906,8 @@ filter which matches the part's MIME type will be used, so order them from most
 to least specific. You can also match on non-MIME types, by prefixing with the
 header to match against (non-case-sensitive) and a comma, e.g. _subject,text_
 will match a subject which contains _text_. Use _header,~regex_ to match
-against a _regex_.
+against a _regex_. Using _.filename_ instead of a header will match against the
+filename of an attachment.
 
 Note that aerc will pipe the content into the configured filter program, so
 filters need to be able to read from standard input. Many programs support
@@ -1080,6 +1081,14 @@ _image/\*_
 	image/\*=catimg -w$(tput cols) -
 	```
 
+_.filename,~<regexp>_
+	Match <regexp> against the filename of an attachment, e.g. to split
+	csv-s into columns:
+
+	```
+	.filename,~.*\.csv=column -t --separator=","
+	```
+
 See the wiki at https://man.sr.ht/~rjarry/aerc/ for more examples and possible
 customizations of the built-in filters.