Bridge mentions in both directions

ROADMAP.md

@@ -5,6 +5,7 @@
 | Group and DM text | ✅ | ✅ |
 | Formatting | Plain text | Flattened to plain text |
 | Replies | ✅ | ✅ |
+| Mentions | ✅ | ✅ |
 | Images and GIFs | ✅ | ✅ |
 | Video | ✅ | ⚠️ Uploads, but GroupMe can't play it back |
 | Files | ✅ Groups only | ✅ Groups only |

go.mod

@@ -5,9 +5,10 @@ go 1.26.0
 toolchain go1.27.1
 
 require (
-	github.com/beeper/groupme-lib v0.2.1-0.20261013141939-3f2228f1769b
+	github.com/beeper/groupme-lib v0.2.1-0.20261027164818-a385d1c65167
 	github.com/coder/websocket v1.8.15
 	github.com/google/uuid v1.2.0
+	github.com/mattn/go-sqlite3 v1.14.52
 	github.com/rs/zerolog v1.35.1
 	go.mau.fi/util v0.10.1
 	maunium.net/go/mautrix v0.31.0
@@ -20,7 +21,6 @@ require (
 	github.com/lib/pq v1.12.3 // indirect
 	github.com/mattn/go-colorable v0.1.14 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect
-	github.com/mattn/go-sqlite3 v1.14.52 // indirect
 	github.com/petermattis/goid v0.0.0-20260820044319-269ab09b5261 // indirect
 	github.com/rs/xid v1.6.0 // indirect
 	github.com/skip2/go-qrcode v0.0.0-20200617195104-da1b6568686e // indirect

go.sum

@@ -2,8 +2,8 @@ filippo.io/edwards25519 v1.2.0 h1:crnVqOiS4jqYleHd9vaKZ+HKtHfllngJIiOpNpoJsjo=
 filippo.io/edwards25519 v1.2.0/go.mod h1:xzAOLCNug/yB62zG1bQ8uziwrIqIuxhctzJT18Q77mc=
 github.com/DATA-DOG/go-sqlmock v1.5.2 h1:OcvFkGmslmlZibjAjaHm3L//6LiuBgolP7OputlJIzU=
 github.com/DATA-DOG/go-sqlmock v1.5.2/go.mod h1:88MAG/4G7SMwSE3CeA0ZKzrT5CiOU3OJ+JlNzwDqpNU=
-github.com/beeper/groupme-lib v0.2.1-0.20261013141939-3f2228f1769b h1:l8UARv5mAmOg815nqmQ1tRy7E+qa1X01b6BS19ergxI=
-github.com/beeper/groupme-lib v0.2.1-0.20261013141939-3f2228f1769b/go.mod h1:FYHpsnrrdRvw0kXIiflXpV2NAnlPHPHGgzIf/wSy/mM=
+github.com/beeper/groupme-lib v0.2.1-0.20261027164818-a385d1c65167 h1:OjaO3JFqQp2tuxDLvFzTk6MVNXu/7AaSgCaEMHaVfLU=
+github.com/beeper/groupme-lib v0.2.1-0.20261027164818-a385d1c65167/go.mod h1:FYHpsnrrdRvw0kXIiflXpV2NAnlPHPHGgzIf/wSy/mM=
 github.com/coder/websocket v1.8.15 h1:6B2JPeOGlpff2Uz6vOEH1Vzpi0iUz20A+lPVhPHtNUA=
 github.com/coder/websocket v1.8.15/go.mod h1:NX3SzP+inril6yawo5CQXx8+fk145lPDC6pumgx0mVg=
 github.com/coreos/go-systemd/v22 v22.7.0 h1:LAEzFkke61DFROc7zNLX/WA2i5J8gYqe0rSj9KI28KA=

pkg/connector/capabilities.go

@@ -63,7 +63,10 @@ var fileMimes = map[string]event.CapabilitySupportLevel{
 }
 
 var roomCaps = &event.RoomFeatures{
-	ID: "fi.mau.groupme.capabilities.2026_10_26.2",
+	ID: "fi.mau.groupme.capabilities.2026_10_26.4",
+	Formatting: event.FormattingFeatureMap{
+		event.FmtUserLink: event.CapLevelFullySupported,
+	},
 	File: event.FileFeatureMap{
 		event.MsgImage: {
 			MimeTypes: imageMimes,

pkg/connector/edits.go

@@ -98,13 +98,14 @@ func (gc *GMClient) HandleMatrixEdit(ctx context.Context, msg *bridgev2.MatrixEd
 	default:
 		return bridgev2.ErrUnsupportedMessageType
 	}
+	fmtCtx := format.NewContext(ctx)
 	if msg.Content.Format == event.FormatHTML && msg.Content.FormattedBody != "" {
-		text = groupmeHTMLParser.Parse(msg.Content.FormattedBody, format.NewContext(ctx))
+		text = gc.htmlParser().Parse(msg.Content.FormattedBody, fmtCtx)
 	}
 	if msg.Content.MsgType == event.MsgEmote {
 		text = "/me " + text
 	}
-	text = strings.TrimSpace(text)
+	text, mentions := takeMentions(strings.TrimSpace(text), fmtCtx)
 	if utf8.RuneCountInString(text) > 1000 {
 		return permanentFailure(event.MessageStatusUnsupported, "GroupMe messages are limited to 1000 characters")
 	}
@@ -119,6 +120,9 @@ func (gc *GMClient) HandleMatrixEdit(ctx context.Context, msg *bridgev2.MatrixEd
 			content.Attachments = append(content.Attachments, attachment)
 		}
 	}
+	if mentions != nil {
+		content.Attachments = append(content.Attachments, mentions)
+	}
 	updated, err := groupmeext.EditMessage(ctx, gc.Meta.Token, kind == PortalTypeDM, chatID, ParseMessageID(target.ID), content)
 	if err != nil {
 		return wrapGroupMeError(err, "failed to edit message")

pkg/connector/handlegroupme.go

@@ -241,13 +241,15 @@ func (gc *GMClient) convertGroupMeMessage(ctx context.Context, portal *bridgev2.
 	}
 
 	if text := visibleText(msg); len(text) > 0 || len(cm.Parts) == 0 {
+		content := &event.MessageEventContent{
+			MsgType: event.MsgText,
+			Body:    text,
+		}
+		gc.applyMentions(content, msg.Attachments)
 		cm.Parts = append(cm.Parts, &bridgev2.ConvertedMessagePart{
-			ID:   "",
-			Type: event.EventMessage,
-			Content: &event.MessageEventContent{
-				MsgType: event.MsgText,
-				Body:    text,
-			},
+			ID:      "",
+			Type:    event.EventMessage,
+			Content: content,
 		})
 	}
 

pkg/connector/handlematrix.go

@@ -117,24 +117,22 @@ func (gc *GMClient) HandleMatrixMessage(ctx context.Context, msg *bridgev2.Matri
 		return nil, permanentFailure(event.MessageStatusUnsupported, "GroupMe replies cannot target poll votes").WithSendNotice(true)
 	}
 	content := msg.Content
-	text := content.Body
-	if content.Format == event.FormatHTML && content.FormattedBody != "" {
-		text = groupmeHTMLParser.Parse(content.FormattedBody, format.NewContext(ctx))
-	}
-	if content.MsgType == event.MsgEmote {
-		text = "/me " + text
-	}
-
 	portalType, gmid := ParsePortalID(msg.Portal.ID)
 	if gmid == "" || (portalType != PortalTypeGroup && portalType != PortalTypeDM) {
 		return nil, fmt.Errorf("invalid GroupMe portal")
 	}
+	text := content.Body
 	if content.MsgType == event.MsgImage || content.MsgType == event.MsgVideo || content.MsgType == event.MsgFile {
 		text = content.GetCaption()
-		if text != "" && content.Format == event.FormatHTML && content.FormattedBody != "" {
-			text = groupmeHTMLParser.Parse(content.FormattedBody, format.NewContext(ctx))
-		}
 	}
+	fmtCtx := format.NewContext(ctx)
+	if text != "" && content.Format == event.FormatHTML && content.FormattedBody != "" {
+		text = gc.htmlParser().Parse(content.FormattedBody, fmtCtx)
+	}
+	if content.MsgType == event.MsgEmote {
+		text = "/me " + text
+	}
+	text, mentions := takeMentions(text, fmtCtx)
 	if utf8.RuneCountInString(text) > 1000 {
 		return nil, permanentFailure(event.MessageStatusUnsupported, "GroupMe messages are limited to 1000 characters").WithSendNotice(true)
 	}
@@ -168,6 +166,9 @@ func (gc *GMClient) HandleMatrixMessage(ctx context.Context, msg *bridgev2.Matri
 		return nil, bridgev2.ErrUnsupportedMessageType
 	}
 
+	if mentions != nil && out.Text != "" {
+		out.Attachments = append(out.Attachments, mentions)
+	}
 	if msg.ReplyTo != nil {
 		out.Attachments = append(out.Attachments, &groupme.Attachment{
 			Type:        groupme.Reply,

pkg/connector/mediainfo.go

@@ -24,6 +24,7 @@ import (
 	"slices"
 	"strconv"
 	"strings"
+	"unicode"
 
 	"maunium.net/go/mautrix/event"
 
@@ -65,14 +66,14 @@ func sameMediaURL(a, b string) bool {
 func visibleText(msg *groupme.Message) string {
 	text := msg.Text
 	for {
-		trimmed := strings.TrimSpace(text)
+		trimmed := strings.TrimRightFunc(text, unicode.IsSpace)
 		cut := strings.LastIndexAny(trimmed, " \t\n") + 1
 		if !slices.ContainsFunc(msg.Attachments, func(att *groupme.Attachment) bool {
 			return att != nil && (att.Type == groupme.Image || att.Type == groupme.Video) && sameMediaURL(trimmed[cut:], att.URL)
 		}) {
 			break
 		}
-		text = strings.TrimSpace(trimmed[:cut])
+		text = strings.TrimRightFunc(trimmed[:cut], unicode.IsSpace)
 	}
 	// File attachments are only bridged in groups.
 	if msg.GroupID != "" && strings.HasPrefix(text, "Shared a document:") && slices.ContainsFunc(msg.Attachments, func(att *groupme.Attachment) bool {

pkg/connector/mentions.go

@@ -0,0 +1,151 @@
+// mautrix-groupme - A Matrix-GroupMe puppeting bridge.
+// Copyright (C) 2026 The mautrix-groupme contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package connector
+
+import (
+	"html"
+	"slices"
+	"strings"
+	"unicode/utf16"
+
+	"maunium.net/go/mautrix/event"
+	"maunium.net/go/mautrix/format"
+	"maunium.net/go/mautrix/id"
+
+	"github.com/beeper/groupme-lib"
+)
+
+// GroupMe mention loci are UTF-16 offsets into the plain text.
+
+const (
+	mentionStart       = '\uE000'
+	mentionEnd         = '\uE001'
+	mentionsContextKey = "fi.mau.groupme.mentions"
+)
+
+func (gc *GMClient) htmlParser() *format.HTMLParser {
+	parser := *groupmeHTMLParser
+	parser.PillConverter = gc.convertPill
+	return &parser
+}
+
+func (gc *GMClient) convertPill(displayname, mxid, eventID string, ctx format.Context) string {
+	if eventID == "" && strings.HasPrefix(mxid, "@") {
+		if userID := gc.mentionedUser(id.UserID(mxid)); userID != "" {
+			ids, _ := ctx.ReturnData[mentionsContextKey].([]groupme.ID)
+			ctx.ReturnData[mentionsContextKey] = append(ids, userID)
+			return string(mentionStart) + "@" + strings.TrimPrefix(displayname, "@") + string(mentionEnd)
+		}
+	}
+	return format.DefaultPillConverter(displayname, mxid, eventID, ctx)
+}
+
+func (gc *GMClient) mentionedUser(mxid id.UserID) groupme.ID {
+	if mxid == gc.UserLogin.UserMXID {
+		return groupme.ID(gc.Meta.GMID)
+	}
+	if userID, ok := gc.Main.br.Matrix.ParseGhostMXID(mxid); ok {
+		return ParseUserID(userID)
+	}
+	return ""
+}
+
+func takeMentions(text string, ctx format.Context) (string, *groupme.Attachment) {
+	ids, _ := ctx.ReturnData[mentionsContextKey].([]groupme.ID)
+	if len(ids) == 0 {
+		return text, nil
+	}
+	var out strings.Builder
+	mentions := &groupme.Attachment{Type: groupme.Mentions}
+	offset, start := 0, -1
+	for _, r := range text {
+		switch {
+		case r == mentionStart:
+			start = offset
+		case r == mentionEnd:
+			if start >= 0 && len(mentions.UserIDs) < len(ids) {
+				mentions.UserIDs = append(mentions.UserIDs, ids[len(mentions.UserIDs)])
+				mentions.Loci = append(mentions.Loci, []int{start, offset - start})
+			}
+			start = -1
+		default:
+			out.WriteRune(r)
+			offset += utf16.RuneLen(r)
+		}
+	}
+	if len(mentions.UserIDs) == 0 {
+		return out.String(), nil
+	}
+	return out.String(), mentions
+}
+
+func (gc *GMClient) applyMentions(content *event.MessageEventContent, attachments []*groupme.Attachment) {
+	var mentions *groupme.Attachment
+	for _, att := range attachments {
+		if att != nil && att.Type == groupme.Mentions {
+			mentions = att
+			break
+		}
+	}
+	if mentions == nil || len(mentions.UserIDs) == 0 {
+		return
+	}
+	type span struct {
+		start, end int
+		user       groupme.ID
+	}
+	text := utf16.Encode([]rune(content.Body))
+	spans := make([]span, 0, len(mentions.UserIDs))
+	for i, user := range mentions.UserIDs {
+		if i >= len(mentions.Loci) || len(mentions.Loci[i]) != 2 || user == "" {
+			continue
+		}
+		start, length := mentions.Loci[i][0], mentions.Loci[i][1]
+		if start >= 0 && length > 0 && start+length <= len(text) {
+			spans = append(spans, span{start, start + length, user})
+		}
+	}
+	slices.SortFunc(spans, func(a, b span) int { return a.start - b.start })
+	escape := func(units []uint16) string {
+		return strings.ReplaceAll(html.EscapeString(string(utf16.Decode(units))), "\n", "<br>")
+	}
+	var out strings.Builder
+	content.Mentions = &event.Mentions{}
+	prev := 0
+	for _, s := range spans {
+		if s.start < prev {
+			continue
+		}
+		mxid := gc.UserLogin.UserMXID
+		if string(s.user) != gc.Meta.GMID {
+			mxid = gc.Main.br.Matrix.FormatGhostMXID(MakeUserID(s.user))
+		}
+		out.WriteString(escape(text[prev:s.start]))
+		out.WriteString(`<a href="` + html.EscapeString(mxid.URI().MatrixToURL()) + `">`)
+		out.WriteString(escape(text[s.start:s.end]))
+		out.WriteString("</a>")
+		content.Mentions.Add(mxid)
+		prev = s.end
+	}
+	if prev == 0 {
+		content.Mentions = nil
+		return
+	}
+	out.WriteString(escape(text[prev:]))
+	content.Format = event.FormatHTML
+	content.FormattedBody = out.String()
+}