handlematrix: handle basic matrix rich text messages

Added the necessary room capabilities, too. Support for replies,
editing, deletion, and attachments are forthcoming.

pkg/msgconv/from-matrix.go

@@ -0,0 +1,104 @@
+// mautrix-discord - A Matrix-Discord puppeting bridge.
+// Copyright (C) 2024 Tulir Asokan
+//
+// 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 msgconv
+
+import (
+	"context"
+	"fmt"
+	"strconv"
+	"time"
+
+	"github.com/bwmarrin/discordgo"
+	"go.mau.fi/util/variationselector"
+	"maunium.net/go/mautrix/bridgev2"
+	"maunium.net/go/mautrix/event"
+	"maunium.net/go/mautrix/format"
+)
+
+const discordEpochMillis = 1420070400000
+
+func generateMessageNonce() string {
+	snowflake := (time.Now().UnixMilli() - discordEpochMillis) << 22
+	// Nonce snowflakes don't have internal IDs or increments
+	return strconv.FormatInt(snowflake, 10)
+}
+
+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
+}
+
+// ToDiscord converts a Matrix message into a discordgo.MessageSend that is appropriate
+// for bridging the message to Discord.
+func (mc *MessageConverter) ToDiscord(
+	ctx context.Context,
+	msg *bridgev2.MatrixMessage,
+) (discordgo.MessageSend, error) {
+	var req discordgo.MessageSend
+	req.Nonce = generateMessageNonce()
+
+	switch msg.Content.MsgType {
+	case event.MsgText, event.MsgEmote, event.MsgNotice:
+		req.Content, req.AllowedMentions = mc.convertMatrixMessageContent(ctx, msg.Portal, msg.Content, parseAllowedLinkPreviews(msg.Event.Content.Raw))
+		if msg.Content.MsgType == event.MsgEmote {
+			req.Content = fmt.Sprintf("_%s_", req.Content)
+		}
+		// TODO: Handle attachments.
+	}
+
+	// TODO: Handle (silent) replies and allowed mentions.
+
+	return req, nil
+}
+
+func (mc *MessageConverter) convertMatrixMessageContent(ctx context.Context, portal *bridgev2.Portal, content *event.MessageEventContent, allowedLinkPreviews []string) (string, *discordgo.MessageAllowedMentions) {
+	allowedMentions := &discordgo.MessageAllowedMentions{
+		Parse:       []discordgo.AllowedMentionType{},
+		Users:       []string{},
+		RepliedUser: true,
+	}
+
+	if content.Format == event.FormatHTML && len(content.FormattedBody) > 0 {
+		ctx := format.NewContext(ctx)
+		ctx.ReturnData[formatterContextInputAllowedLinkPreviewsKey] = allowedLinkPreviews
+		ctx.ReturnData[formatterContextPortalKey] = portal
+		ctx.ReturnData[formatterContextAllowedMentionsKey] = allowedMentions
+		if content.Mentions != nil {
+			ctx.ReturnData[formatterContextInputAllowedMentionsKey] = content.Mentions.UserIDs
+		}
+		return variationselector.FullyQualify(matrixHTMLParser.Parse(content.FormattedBody, ctx)), allowedMentions
+	} else {
+		return variationselector.FullyQualify(escapeDiscordMarkdown(content.Body)), allowedMentions
+	}
+}