Implement discord webhooks message splitting

bridge/discord/webhook.go

@@ -2,6 +2,7 @@ package bdiscord
 
 import (
 	"bytes"
+	"strings"
 
 	"github.com/42wim/matterbridge/bridge/config"
 	"github.com/42wim/matterbridge/bridge/helper"
@@ -45,11 +46,12 @@ func (b *Bdiscord) maybeGetLocalAvatar(msg *config.Message) string {
 // webhookSend send one or more message via webhook, taking care of file
 // uploads (from slack, telegram or mattermost).
 // Returns messageID and error.
-func (b *Bdiscord) webhookSend(msg *config.Message, channelID string) (*discordgo.Message, error) {
+func (b *Bdiscord) webhookSend(msg *config.Message, channelID string, clippingMessage string, splitMax int) (string, error) {
 	var (
-		res  *discordgo.Message
+		res  string = ""
 		res2 *discordgo.Message
 		err  error
+		err2 error
 	)
 
 	// If avatar is unset, mutate the message to include the local avatar (but only if settings say we should do this)
@@ -61,17 +63,28 @@ func (b *Bdiscord) webhookSend(msg *config.Message, channelID string) (*discordg
 
 	// We can't send empty messages.
 	if msg.Text != "" {
-		res, err = b.transmitter.Send(
-			channelID,
-			&discordgo.WebhookParams{
-				Content:         msg.Text,
-				Username:        msg.Username,
-				AvatarURL:       msg.Avatar,
-				AllowedMentions: b.getAllowedMentions(),
-			},
-		)
-		if err != nil {
-			b.Log.Errorf("Could not send text (%s) for message %#v: %s", msg.Text, msg, err)
+		msgParts := helper.ClipOrSplitMessage(msg.Text, MessageLength, clippingMessage, splitMax)
+		var msgIds = []string{}
+		for _, msgPart := range msgParts {
+			partialRes, partialErr := b.transmitter.Send(
+				channelID,
+				&discordgo.WebhookParams{
+					Content:         msgPart,
+					Username:        msg.Username,
+					AvatarURL:       msg.Avatar,
+					AllowedMentions: b.getAllowedMentions(),
+				},
+			)
+			if partialErr != nil {
+				err = partialErr
+				break
+			} else {
+				msgIds = append(msgIds, partialRes.ID)
+			}
+		}
+		// Exploit that a discord message ID is actually just a large number, so we encode a list of IDs by separating them with ";".
+		if err == nil {
+			res = strings.Join(msgIds, ";")
 		}
 	}
 
@@ -85,7 +98,7 @@ func (b *Bdiscord) webhookSend(msg *config.Message, channelID string) (*discordg
 			}
 			content := fi.Comment
 
-			res2, err = b.transmitter.Send(
+			res2, err2 = b.transmitter.Send(
 				channelID,
 				&discordgo.WebhookParams{
 					Username:        msg.Username,
@@ -95,14 +108,15 @@ func (b *Bdiscord) webhookSend(msg *config.Message, channelID string) (*discordg
 					AllowedMentions: b.getAllowedMentions(),
 				},
 			)
-			if err != nil {
+			if err2 != nil {
+				err = err2
 				b.Log.Errorf("Could not send file %#v for message %#v: %s", file, msg, err)
 			}
 		}
 	}
 
 	if msg.Text == "" {
-		res = res2
+		res = res2.ID
 	}
 
 	return res, err
@@ -120,35 +134,44 @@ func (b *Bdiscord) handleEventWebhook(msg *config.Message, channelID string) (st
 		return "", nil
 	}
 
-	msg.Text = helper.ClipMessage(msg.Text, MessageLength, b.GetString("MessageClipped"))
-	msg.Text = b.replaceUserMentions(msg.Text)
 	// discord username must be [0..32] max
 	if len(msg.Username) > 32 {
 		msg.Username = msg.Username[0:32]
 	}
 
 	if msg.ID != "" {
+		// Exploit that a discord message ID is actually just a large number, and we encode a list of IDs by separating them with ";".
+		var msgIds = strings.Split(msg.ID, ";")
+		msgParts := helper.ClipOrSplitMessage(b.replaceUserMentions(msg.Text), MessageLength, b.GetString("MessageClipped"), len(msgIds))
+		for len(msgParts) < len(msgIds) {
+			msgParts = append(msgParts, "((obsoleted by edit))")
+		}
 		b.Log.Debugf("Editing webhook message")
-		err := b.transmitter.Edit(channelID, msg.ID, &discordgo.WebhookParams{
-			Content:         msg.Text,
-			Username:        msg.Username,
-			AllowedMentions: b.getAllowedMentions(),
-		})
-		if err == nil {
+		var edit_err error = nil
+		for i := range msgParts {
+			// In case of split-messages where some parts remain the same (i.e. only a typo-fix in a huge message), this causes some noop-updates.
+			// TODO: Optimize away noop-updates of un-edited messages
+			edit_err = b.transmitter.Edit(channelID, msgIds[i], &discordgo.WebhookParams{
+				Content:         msgParts[i],
+				Username:        msg.Username,
+				AllowedMentions: b.getAllowedMentions(),
+			})
+			if edit_err != nil {
+				break
+			}
+		}
+		if edit_err == nil {
 			return msg.ID, nil
 		}
-		b.Log.Errorf("Could not edit webhook message: %s", err)
+		b.Log.Errorf("Could not edit webhook message(s): %s; sending as new message(s) instead", edit_err)
 	}
 
 	b.Log.Debugf("Processing webhook sending for message %#v", msg)
-	discordMsg, err := b.webhookSend(msg, channelID)
+	msg.Text = b.replaceUserMentions(msg.Text)
+	msgId, err := b.webhookSend(msg, channelID, b.GetString("MessageClipped"), b.GetInt("MessageSplitMaxCount"))
 	if err != nil {
-		b.Log.Errorf("Could not broadcast via webhook for message %#v: %s", msg, err)
+		b.Log.Errorf("Could not broadcast via webhook for message %#v: %s", msgId, err)
 		return "", err
 	}
-	if discordMsg == nil {
-		return "", nil
-	}
-
-	return discordMsg.ID, nil
+	return msgId, nil
 }