From 820951cb6e7a3261703c83f4ef8dea1d12e742a6 Mon Sep 17 00:00:00 2001
From: Tulir Asokan <tulir@maunium.net>
Date: Sun, 10 Aug 2025 23:47:39 +0300
Subject: [PATCH] Add support for disabling link previews via MSC4095

---
 formatter.go | 14 ++++++++++++--
 portal.go    | 29 ++++++++++++++++++++++++++---
 2 files changed, 38 insertions(+), 5 deletions(-)

diff --git a/formatter.go b/formatter.go
index 6452532..2112b04 100644
--- a/formatter.go
+++ b/formatter.go
@@ -98,6 +98,7 @@ func (portal *Portal) renderDiscordMarkdownOnlyHTML(text string, allowInlineLink
 const formatterContextPortalKey = "fi.mau.discord.portal"
 const formatterContextAllowedMentionsKey = "fi.mau.discord.allowed_mentions"
 const formatterContextInputAllowedMentionsKey = "fi.mau.discord.input_allowed_mentions"
+const formatterContextInputAllowedLinkPreviewsKey = "fi.mau.discord.input_allowed_link_previews"
 
 func appendIfNotContains(arr []string, newItem string) []string {
 	for _, item := range arr {
@@ -221,16 +222,24 @@ var matrixHTMLParser = &format.HTMLParser{
 		return fmt.Sprintf("||%s||", text)
 	},
 	LinkConverter: func(text, href string, ctx format.Context) string {
+		linkPreviews := ctx.ReturnData[formatterContextInputAllowedLinkPreviewsKey].([]string)
+		allowPreview := linkPreviews == nil || slices.Contains(linkPreviews, href)
 		if text == href {
+			if !allowPreview {
+				return fmt.Sprintf("<%s>", text)
+			}
 			return text
 		} else if !discordLinkRegexFull.MatchString(href) {
 			return fmt.Sprintf("%s (%s)", escapeDiscordMarkdown(text), escapeDiscordMarkdown(href))
+		} else if !allowPreview {
+			return fmt.Sprintf("[%s](<%s>)", escapeDiscordMarkdown(text), href)
+		} else {
+			return fmt.Sprintf("[%s](%s)", escapeDiscordMarkdown(text), href)
 		}
-		return fmt.Sprintf("[%s](%s)", escapeDiscordMarkdown(text), href)
 	},
 }
 
-func (portal *Portal) parseMatrixHTML(content *event.MessageEventContent) (string, *discordgo.MessageAllowedMentions) {
+func (portal *Portal) parseMatrixHTML(content *event.MessageEventContent, allowedLinkPreviews []string) (string, *discordgo.MessageAllowedMentions) {
 	allowedMentions := &discordgo.MessageAllowedMentions{
 		Parse:       []discordgo.AllowedMentionType{},
 		Users:       []string{},
@@ -238,6 +247,7 @@ func (portal *Portal) parseMatrixHTML(content *event.MessageEventContent) (strin
 	}
 	if content.Format == event.FormatHTML && len(content.FormattedBody) > 0 {
 		ctx := format.NewContext()
+		ctx.ReturnData[formatterContextInputAllowedLinkPreviewsKey] = allowedLinkPreviews
 		ctx.ReturnData[formatterContextPortalKey] = portal
 		ctx.ReturnData[formatterContextAllowedMentionsKey] = allowedMentions
 		if content.Mentions != nil {
diff --git a/portal.go b/portal.go
index d5dc879..439cdfd 100644
--- a/portal.go
+++ b/portal.go
@@ -1544,7 +1544,8 @@ func (portal *Portal) handleMatrixMessage(sender *User, evt *event.Event) {
 	if editMXID := content.GetRelatesTo().GetReplaceID(); editMXID != "" && content.NewContent != nil {
 		edits := portal.bridge.DB.Message.GetByMXID(portal.Key, editMXID)
 		if edits != nil {
-			discordContent, allowedMentions := portal.parseMatrixHTML(content.NewContent)
+			newContentRaw, _ := evt.Content.Raw["m.new_content"].(map[string]any)
+			discordContent, allowedMentions := portal.parseMatrixHTML(content.NewContent, parseAllowedLinkPreviews(newContentRaw))
 			var err error
 			var msg *discordgo.Message
 			if !isWebhookSend {
@@ -1623,7 +1624,7 @@ func (portal *Portal) handleMatrixMessage(sender *User, evt *event.Event) {
 	}
 	switch content.MsgType {
 	case event.MsgText, event.MsgEmote, event.MsgNotice:
-		sendReq.Content, sendReq.AllowedMentions = portal.parseMatrixHTML(content)
+		sendReq.Content, sendReq.AllowedMentions = portal.parseMatrixHTML(content, parseAllowedLinkPreviews(evt.Content.Raw))
 		if content.MsgType == event.MsgEmote {
 			sendReq.Content = fmt.Sprintf("_%s_", sendReq.Content)
 		}
@@ -1636,7 +1637,7 @@ func (portal *Portal) handleMatrixMessage(sender *User, evt *event.Event) {
 		filename := content.Body
 		if content.FileName != "" && content.FileName != content.Body {
 			filename = content.FileName
-			sendReq.Content, sendReq.AllowedMentions = portal.parseMatrixHTML(content)
+			sendReq.Content, sendReq.AllowedMentions = portal.parseMatrixHTML(content, parseAllowedLinkPreviews(evt.Content.Raw))
 		}
 
 		if evt.Content.Raw["page.codeberg.everypizza.msc4193.spoiler"] == true {
@@ -1744,6 +1745,28 @@ func (portal *Portal) handleMatrixMessage(sender *User, evt *event.Event) {
 	}
 }
 
+func parseAllowedLinkPreviews(raw map[string]any) []string {
+	if raw == nil {
+		return nil
+	}
+	linkPreviews, ok := raw["com.beeper.linkpreviews"].([]any)
+	if !ok {
+		return nil
+	}
+	allowedLinkPreviews := make([]string, 0, len(linkPreviews))
+	for _, preview := range linkPreviews {
+		previewMap, ok := preview.(map[string]any)
+		if !ok {
+			continue
+		}
+		matchedURL, _ := previewMap["matched_url"].(string)
+		if matchedURL != "" {
+			allowedLinkPreviews = append(allowedLinkPreviews, matchedURL)
+		}
+	}
+	return allowedLinkPreviews
+}
+
 func (portal *Portal) sendDeliveryReceipt(eventID id.EventID) {
 	if portal.bridge.Config.Bridge.DeliveryReceipts {
 		err := portal.bridge.Bot.MarkRead(portal.MXID, eventID)