handlematrix: bridge outgoing message attachments

pkg/msgconv/from-matrix.go

@@ -17,12 +17,16 @@
 package msgconv
 
 import (
+	"bytes"
 	"context"
 	"fmt"
+	"io"
+	"net/http"
 	"strconv"
 	"time"
 
 	"github.com/bwmarrin/discordgo"
+	"github.com/rs/zerolog"
 	"go.mau.fi/util/variationselector"
 	"maunium.net/go/mautrix/bridgev2"
 	"maunium.net/go/mautrix/event"
@@ -59,14 +63,43 @@ func parseAllowedLinkPreviews(raw map[string]any) []string {
 	return allowedLinkPreviews
 }
 
+func uploadDiscordAttachment(cli *http.Client, url string, data []byte) error {
+	req, err := http.NewRequest(http.MethodPut, url, bytes.NewReader(data))
+	if err != nil {
+		return err
+	}
+
+	for key, value := range discordgo.DroidBaseHeaders {
+		req.Header.Set(key, value)
+	}
+	req.Header.Set("Content-Type", "application/octet-stream")
+	req.Header.Set("Referer", "https://discord.com/")
+	req.Header.Set("Sec-Fetch-Dest", "empty")
+	req.Header.Set("Sec-Fetch-Mode", "cors")
+	req.Header.Set("Sec-Fetch-Site", "cross-site")
+
+	resp, err := cli.Do(req)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode > 300 {
+		respData, _ := io.ReadAll(resp.Body)
+		return fmt.Errorf("unexpected status %d: %s", resp.StatusCode, respData)
+	}
+	return nil
+}
+
 // 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,
+	session *discordgo.Session,
 	msg *bridgev2.MatrixMessage,
-) (discordgo.MessageSend, error) {
+) (*discordgo.MessageSend, error) {
 	var req discordgo.MessageSend
 	req.Nonce = generateMessageNonce()
+	log := zerolog.Ctx(ctx)
 
 	if msg.ReplyTo != nil {
 		req.Reference = &discordgo.MessageReference{
@@ -75,18 +108,73 @@ func (mc *MessageConverter) ToDiscord(
 		}
 	}
 
-	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 {
+	portal := msg.Portal
+	channelID := string(portal.ID)
+	content := msg.Content
+
+	convertMatrix := func() {
+		req.Content, req.AllowedMentions = mc.convertMatrixMessageContent(ctx, msg.Portal, content, parseAllowedLinkPreviews(msg.Event.Content.Raw))
+		if content.MsgType == event.MsgEmote {
 			req.Content = fmt.Sprintf("_%s_", req.Content)
 		}
-		// TODO: Handle attachments.
+	}
+
+	switch content.MsgType {
+	case event.MsgText, event.MsgEmote, event.MsgNotice:
+		convertMatrix()
+	case event.MsgAudio, event.MsgFile, event.MsgVideo:
+		mediaData, err := mc.Bridge.Bot.DownloadMedia(ctx, content.URL, content.File)
+		if err != nil {
+			log.Err(err).Msg("Failed to download Matrix attachment for bridging")
+			return nil, bridgev2.ErrMediaDownloadFailed
+		}
+
+		filename := content.Body
+		if content.FileName != "" && content.FileName != content.Body {
+			filename = content.FileName
+			convertMatrix()
+		}
+		if msg.Event.Content.Raw["page.codeberg.everypizza.msc4193.spoiler"] == true {
+			filename = "SPOILER_" + filename
+		}
+
+		// TODO: Support attachments for relay/webhook. (A branch was removed here.)
+		att := &discordgo.MessageAttachment{
+			ID:       "0",
+			Filename: filename,
+		}
+
+		upload_id := mc.NextDiscordUploadID()
+		log.Debug().Str("upload_id", upload_id).Msg("Preparing attachment")
+		prep, err := session.ChannelAttachmentCreate(channelID, &discordgo.ReqPrepareAttachments{
+			Files: []*discordgo.FilePrepare{{
+				Size: len(mediaData),
+				Name: att.Filename,
+				ID:   mc.NextDiscordUploadID(),
+			}},
+			// TODO: Populate with guild ID. Support threads.
+		}, discordgo.WithChannelReferer("", channelID))
+
+		if err != nil {
+			log.Err(err).Msg("Failed to create attachment in preparation for attachment reupload")
+			return nil, bridgev2.ErrMediaReuploadFailed
+		}
+
+		prepared := prep.Attachments[0]
+		att.UploadedFilename = prepared.UploadFilename
+
+		err = uploadDiscordAttachment(session.Client, prepared.UploadURL, mediaData)
+		if err != nil {
+			log.Err(err).Msg("Failed to reupload Discord attachment after preparing")
+			return nil, bridgev2.ErrMediaReuploadFailed
+		}
+
+		req.Attachments = append(req.Attachments, att)
 	}
 
 	// TODO: Handle (silent) replies and allowed mentions.
 
-	return req, nil
+	return &req, nil
 }
 
 func (mc *MessageConverter) convertMatrixMessageContent(ctx context.Context, portal *bridgev2.Portal, content *event.MessageEventContent, allowedLinkPreviews []string) (string, *discordgo.MessageAllowedMentions) {