Add 'Message.OriginalUsername' and use it for Discord name spoofing.

Discord does not allow replies to be created via webhook
- discord/discord-api-docs#2251
- discord/discord-api-docs#3282
in that case, discord.go falls back to using the REST API, which is fine
except it doesn't allow masquerading the displayed username/avatar.
Trying to set a single RemoteNickFormat that covers both cases nicely is
impossible. Instead, force the webhook case to use the plain username,
as if `RemoteNickFormat="{NICK}"` in that case, but respect it in the
reply case, which has to inline the username in the message text.

Author: kousu

bridge/config/config.go

@@ -35,19 +35,20 @@ const (
 const ParentIDNotFound = "msg-parent-not-found"
 
 type Message struct {
-	Text      string    `json:"text"`
-	Channel   string    `json:"channel"`
-	Username  string    `json:"username"`
-	UserID    string    `json:"userid"` // userid on the bridge
-	Avatar    string    `json:"avatar"`
-	Account   string    `json:"account"`
-	Event     string    `json:"event"`
-	Protocol  string    `json:"protocol"`
-	Gateway   string    `json:"gateway"`
-	ParentID  string    `json:"parent_id"`
-	Timestamp time.Time `json:"timestamp"`
-	ID        string    `json:"id"`
-	Extra     map[string][]interface{}
+	Text             string    `json:"text"`
+	Channel          string    `json:"channel"`
+	Username         string    `json:"username"`
+	OriginalUsername string    `json:"original_username"` // Username before RemoteNickFormat gets applied
+	UserID           string    `json:"userid"`            // userid on the bridge
+	Avatar           string    `json:"avatar"`
+	Account          string    `json:"account"`
+	Event            string    `json:"event"`
+	Protocol         string    `json:"protocol"`
+	Gateway          string    `json:"gateway"`
+	ParentID         string    `json:"parent_id"`
+	Timestamp        time.Time `json:"timestamp"`
+	ID               string    `json:"id"`
+	Extra            map[string][]interface{}
 }
 
 func (m Message) ParentNotFound() bool {

bridge/discord/discord.go

@@ -287,22 +287,6 @@ func (b *Bdiscord) Send(msg config.Message) (string, error) {
 		return b.handleEventWebhook(&msg, channelID)
 	}
 
-	if msg.ParentID != "" && b.GetString("RemoteNickFormat") == "{NICK}" {
-		// Discord does not allow replies to be created via webhook
-		// - https://github.com/discord/discord-api-docs/issues/2251
-		// - https://github.com/discord/discord-api-docs/discussions/3282
-		// discord.go falls back to using the REST API, which is fine except it
-		// doesn't allow masquerading the displayed username/avatar, so instead
-		// the nickname is placed inline in the message body, as other bridges.
-		// Usually with webhooks you would want RemoteNickFormat="{NICK}",
-		// but this looks bad when inlined, so as a janky workaround,
-		// hardcode the outgoing Discord message as if a _separate_ format string like RemoteNickFormatInline="<{NICK}> ".
-		//
-		// Note that at this point in the code, gateway.go has already applied RemoteNickFormat,
-		// so msg.Username has already been modified once. The only way
-		msg.Username = fmt.Sprintf("<%s> ", msg.Username)
-	}
-
 	return b.handleEventBotUser(&msg, channelID)
 }
 

bridge/discord/webhook.go

@@ -33,7 +33,7 @@ func (b *Bdiscord) maybeGetLocalAvatar(msg *config.Message) string {
 			continue
 		}
 
-		member, err := b.getGuildMemberByNick(msg.Username)
+		member, err := b.getGuildMemberByNick(msg.OriginalUsername)
 		if err != nil {
 			return ""
 		}
@@ -51,7 +51,7 @@ func (b *Bdiscord) webhookSendTextOnly(msg *config.Message, channelID string) (s
 			channelID,
 			&discordgo.WebhookParams{
 				Content:         msgPart,
-				Username:        msg.Username,
+				Username:        msg.OriginalUsername,
 				AvatarURL:       msg.Avatar,
 				AllowedMentions: b.getAllowedMentions(),
 			},
@@ -81,7 +81,7 @@ func (b *Bdiscord) webhookSendFilesOnly(msg *config.Message, channelID string) e
 		_, err := b.transmitter.Send(
 			channelID,
 			&discordgo.WebhookParams{
-				Username:        msg.Username,
+				Username:        msg.OriginalUsername,
 				AvatarURL:       msg.Avatar,
 				Files:           []*discordgo.File{&file},
 				Content:         content,
@@ -137,8 +137,8 @@ func (b *Bdiscord) handleEventWebhook(msg *config.Message, channelID string) (st
 	}
 
 	// discord username must be [0..32] max
-	if len(msg.Username) > 32 {
-		msg.Username = msg.Username[0:32]
+	if len(msg.OriginalUsername) > 32 {
+		msg.OriginalUsername = msg.OriginalUsername[0:32]
 	}
 
 	if msg.ID != "" {
@@ -155,7 +155,7 @@ func (b *Bdiscord) handleEventWebhook(msg *config.Message, channelID string) (st
 			// TODO: Optimize away noop-updates of un-edited messages
 			editErr = b.transmitter.Edit(channelID, msgIds[i], &discordgo.WebhookParams{
 				Content:         msgParts[i],
-				Username:        msg.Username,
+				Username:        msg.OriginalUsername,
 				AllowedMentions: b.getAllowedMentions(),
 			})
 			if editErr != nil {

gateway/gateway.go

@@ -476,6 +476,7 @@ func (gw *Gateway) SendMessage(
 
 	msg.Channel = channel.Name
 	msg.Avatar = gw.modifyAvatar(rmsg, dest)
+	msg.OriginalUsername = msg.Username
 	msg.Username = gw.modifyUsername(rmsg, dest)
 
 	// exclude file delete event as the msg ID here is the native file ID that needs to be deleted