add Content-Disposition and Filename to the payload of incoming webhooks

for each message part. The ContentDisposition value is the base value without
header key/value parameters. the Filename field is the likely filename of the
part. the different email clients encode filenames differently. there is a
standard mime mechanism from rfc 2231. and there is the q/b-word-encoding from
rfc 2047. instead of letting users of the webhook api deal with those
differences, we provide just the parsed filename.

for issue #258 by morki, thanks for reporting!

queue/hook.go

@@ -796,13 +796,18 @@ func Incoming(ctx context.Context, log mlog.Log, acc *store.Account, messageID s
 
 		log.Debug("composing webhook for incoming message")
 
+		structure, err := webhook.PartStructure(log, &part)
+		if err != nil {
+			return fmt.Errorf("parsing part structure: %v", err)
+		}
+
 		isIncoming = true
 		var rcptTo string
 		if m.RcptToDomain != "" {
 			rcptTo = m.RcptToLocalpart.String() + "@" + m.RcptToDomain
 		}
 		in := webhook.Incoming{
-			Structure: webhook.PartStructure(&part),
+			Structure: structure,
 			Meta: webhook.IncomingMeta{
 				MsgID:               m.ID,
 				MailFrom:            m.MailFrom,

queue/hook_test.go

@@ -82,6 +82,9 @@ func TestHookIncoming(t *testing.T) {
 		tcheck(t, err, "decode incoming webhook")
 		in.Meta.Received = in.Meta.Received.Local() // For TZ UTC.
 
+		structure, err := webhook.PartStructure(pkglog, &part)
+		tcheck(t, err, "part structure")
+
 		expIncoming := webhook.Incoming{
 			From:       []webhook.NameAddress{{Address: "mjl@mox.example"}},
 			To:         []webhook.NameAddress{{Address: "mjl@mox.example"}},
@@ -92,7 +95,7 @@ func TestHookIncoming(t *testing.T) {
 			Subject:    "test",
 			Text:       "test email\n",
 
-			Structure: webhook.PartStructure(&part),
+			Structure: structure,
 			Meta: webhook.IncomingMeta{
 				MsgID:               m.ID,
 				MailFrom:            m.MailFrom,