Implement discord botuser message splitting

bridge/config/config.go

@@ -121,6 +121,7 @@ type Protocol struct {
 	MessageLength          int        // IRC, max length of a message allowed
 	MessageQueue           int        // IRC, size of message queue for flood control
 	MessageSplit           bool       // IRC, split long messages with newlines on MessageLength instead of clipping
+	MessageSplitMaxCount   int        // discord, split long messages into at most this many messages instead of clipping (MessageLength=1950 cannot be configured)
 	Muc                    string     // xmpp
 	MxID                   string     // matrix
 	Name                   string     // all protocols

bridge/discord/discord.go

@@ -316,6 +316,7 @@ func (b *Bdiscord) handleEventBotUser(msg *config.Message, channelID string) (st
 	// Upload a file if it exists
 	if msg.Extra != nil {
 		for _, rmsg := range helper.HandleExtra(msg, b.General) {
+			// TODO: Use ClipOrSplitMessage
 			rmsg.Text = helper.ClipMessage(rmsg.Text, MessageLength, b.GetString("MessageClipped"))
 			if _, err := b.c.ChannelMessageSend(channelID, rmsg.Username+rmsg.Text); err != nil {
 				b.Log.Errorf("Could not send message %#v: %s", rmsg, err)
@@ -327,35 +328,53 @@ func (b *Bdiscord) handleEventBotUser(msg *config.Message, channelID string) (st
 		}
 	}
 
-	msg.Text = helper.ClipMessage(msg.Text, MessageLength, b.GetString("MessageClipped"))
-	msg.Text = b.replaceUserMentions(msg.Text)
-
 	// Edit message
 	if msg.ID != "" {
-		_, err := b.c.ChannelMessageEdit(channelID, msg.ID, msg.Username+msg.Text)
-		return msg.ID, err
-	}
-
-	m := discordgo.MessageSend{
-		Content:         msg.Username + msg.Text,
-		AllowedMentions: b.getAllowedMentions(),
-	}
-
-	if msg.ParentValid() {
-		m.Reference = &discordgo.MessageReference{
-			MessageID: msg.ParentID,
-			ChannelID: channelID,
-			GuildID:   b.guildID,
+		// 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))")
 		}
+		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
+			// TODO: Use RemoteNickFormat instead of this broken concatenation
+			_, err := b.c.ChannelMessageEdit(channelID, msgIds[i], msg.Username+msgParts[i])
+			if err != nil {
+				return "", err
+			}
+		}
+		return msg.ID, nil
 	}
 
-	// Post normal message
-	res, err := b.c.ChannelMessageSendComplex(channelID, &m)
-	if err != nil {
-		return "", err
+	msgParts := helper.ClipOrSplitMessage(b.replaceUserMentions(msg.Text), MessageLength, b.GetString("MessageClipped"), b.GetInt("MessageSplitMaxCount"))
+	var msgIds = []string{}
+
+	for _, msgPart := range msgParts {
+		m := discordgo.MessageSend{
+			Content:         msg.Username + msgPart,
+			AllowedMentions: b.getAllowedMentions(),
+		}
+
+		if msg.ParentValid() {
+			m.Reference = &discordgo.MessageReference{
+				MessageID: msg.ParentID,
+				ChannelID: channelID,
+				GuildID:   b.guildID,
+			}
+		}
+
+		// Post normal message
+		res, err := b.c.ChannelMessageSendComplex(channelID, &m)
+		if err != nil {
+			return "", err
+		}
+		msgIds = append(msgIds, res.ID)
 	}
 
-	return res.ID, nil
+	// Exploit that a discord message ID is actually just a large number, so we encode a list of IDs by separating them with ";".
+	return strings.Join(msgIds, ";"), nil
 }
 
 // handleUploadFile handles native upload of files

matterbridge.toml.sample

@@ -925,10 +925,17 @@ ShowTopicChange=false
 # Supported from the following bridges: slack
 SyncTopic=false
 
-#Message to show when a message is too big
-#Default "<clipped message>"
+# Message to show when a message is too big
+# Default "<clipped message>"
 MessageClipped="<clipped message>"
 
+# Before clipping, try to split messages into at most this many parts. 0 is treated like 1.
+# Be careful with large numbers, as this might cause flooding.
+# Example: A maximum telegram message of 4096 bytes is received. This requires 3 Discord
+# messages (each capped at a hardcoded 1950 bytes).
+# Default 1
+MessageSplitMaxCount=3
+
 ###################################################################
 #telegram section
 ###################################################################