discord: support sending files with just a URL

previously, the code assumed each file had a Data, and crashed if this was not present.
now, we detect this condition, and send the URL instead.

the discord client will display URLs in a message of their own
as inline embeds, without any special behavior needed on our part.

this commit makes the same changes to the webhook and non-webhook code.

bridge/discord/discord.go

@@ -380,26 +380,51 @@ func (b *Bdiscord) handleEventBotUser(msg *config.Message, channelID string) (st
 // handleUploadFile handles native upload of files
 func (b *Bdiscord) handleUploadFile(msg *config.Message, channelID string) (string, error) {
 	for _, f := range msg.Extra["file"] {
+		var err error
 		fi := f.(config.FileInfo)
-		file := discordgo.File{
+
-			Name:        fi.Name,
+		if fi.URL != "" {
-			ContentType: "",
+			err = b.handleUploadFileFromURL(msg, channelID, &fi)
-			Reader:      bytes.NewReader(*fi.Data),
+		} else if fi.Data != nil {
-		}
+			err = b.handleUploadFileFromData(msg, channelID, &fi)
-		m := discordgo.MessageSend{
+		} else {
-			Content:         msg.Username + fi.Comment,
+			b.Log.Errorf("Attachment %#v for message %#v had neither Data nor URL", fi, msg)
-			Files:           []*discordgo.File{&file},
-			AllowedMentions: b.getAllowedMentions(),
-		}
-		res, err := b.c.ChannelMessageSendComplex(channelID, &m)
-		if err != nil {
-			return "", fmt.Errorf("file upload failed: %s", err)
 		}
 
-		// link file_upload_nativeID (file ID from the original bridge) to our upload id
+		if err != nil {
-		// so that we can remove this later when it eg needs to be deleted
+			b.Log.Errorf("Could not send attachment %#v for message %#v: %s", fi, msg, err)
-		b.cache.Add(cFileUpload+fi.NativeID, res.ID)
+			return "", err
+		}
 	}
 
 	return "", nil
 }
+
+func (b *Bdiscord) handleUploadFileFromData(msg *config.Message, channelID string, fi *config.FileInfo) error {
+	file := discordgo.File{
+		Name:        fi.Name,
+		ContentType: "",
+		Reader:      bytes.NewReader(*fi.Data),
+	}
+	m := discordgo.MessageSend{
+		Content:         msg.Username + fi.Comment,
+		Files:           []*discordgo.File{&file},
+		AllowedMentions: b.getAllowedMentions(),
+	}
+	res, err := b.c.ChannelMessageSendComplex(channelID, &m)
+	if err != nil {
+		return fmt.Errorf("file upload failed: %s", err)
+	}
+	// link file_upload_nativeID (file ID from the original bridge) to our upload id
+	// so that we can remove this later when it eg needs to be deleted
+	b.cache.Add(cFileUpload+fi.NativeID, res.ID)
+	return nil
+}
+
+func (b *Bdiscord) handleUploadFileFromURL(msg *config.Message, channelID string, fi *config.FileInfo) error {
+	_, err := b.c.ChannelMessageSendComplex(channelID, &discordgo.MessageSend{
+		Content:         fi.URL,
+		AllowedMentions: b.getAllowedMentions(),
+	})
+	return err
+}

bridge/discord/webhook.go

@@ -69,33 +69,63 @@ func (b *Bdiscord) webhookSendTextOnly(msg *config.Message, channelID string) (s
 func (b *Bdiscord) webhookSendFilesOnly(msg *config.Message, channelID string) error {
 	for _, f := range msg.Extra["file"] {
 		fi := f.(config.FileInfo) //nolint:forcetypeassert
-		file := discordgo.File{
+		var err error
-			Name:        fi.Name,
+
-			ContentType: "",
+		if fi.URL != "" {
-			Reader:      bytes.NewReader(*fi.Data),
+			err = b.webhookSendFileFromURL(msg, channelID, &fi)
-		}
+		} else if fi.Data != nil {
-		content := fi.Comment
+			err = b.webhookSendFileFromData(msg, channelID, &fi)
+		} else {
+			b.Log.Errorf("Attachment %#v for message %#v had neither Data nor URL", fi, msg)
+		}
 
-		// Cannot use the resulting ID for any edits anyway, so throw it away.
-		// This has to be re-enabled when we implement message deletion.
-		_, err := b.transmitter.Send(
-			channelID,
-			&discordgo.WebhookParams{
-				Username:        msg.Username,
-				AvatarURL:       msg.Avatar,
-				Files:           []*discordgo.File{&file},
-				Content:         content,
-				AllowedMentions: b.getAllowedMentions(),
-			},
-		)
 		if err != nil {
-			b.Log.Errorf("Could not send file %#v for message %#v: %s", file, msg, err)
+			b.Log.Errorf("Could not send attachment %#v for message %#v: %s", fi, msg, err)
 			return err
 		}
 	}
+
 	return nil
 }
 
+func (b *Bdiscord) webhookSendFileFromData(msg *config.Message, channelID string, fi *config.FileInfo) error {
+	file := discordgo.File{
+		Name:        fi.Name,
+		ContentType: "",
+		Reader:      bytes.NewReader(*fi.Data),
+	}
+	content := fi.Comment
+
+	// Cannot use the resulting ID for any edits anyway, so throw it away.
+	// This has to be re-enabled when we implement message deletion.
+	_, err := b.transmitter.Send(
+		channelID,
+		&discordgo.WebhookParams{
+			Username:        msg.Username,
+			AvatarURL:       msg.Avatar,
+			Files:           []*discordgo.File{&file},
+			Content:         content,
+			AllowedMentions: b.getAllowedMentions(),
+		},
+	)
+	return err
+}
+
+func (b *Bdiscord) webhookSendFileFromURL(msg *config.Message, channelID string, fi *config.FileInfo) error {
+	// discord client will display any file url as an inline embed,
+	// without us having to do anything special.
+	_, err := b.transmitter.Send(
+		channelID,
+		&discordgo.WebhookParams{
+			Content:             fi.URL,
+			Username:            msg.Username,
+			AvatarURL:           msg.Avatar,
+			AllowedMentions:     b.getAllowedMentions(),
+		},
+	)
+	return err
+}
+
 // webhookSend send one or more message via webhook, taking care of file
 // uploads (from slack, telegram or mattermost).
 // Returns messageID and error.