Add support for deleting files from slack to discord. Fixes #1705 (#1709)

We create a new event EventFileDelete which will be used to delete
specific uploaded files using the Extra["file"] in the config.Message.

We also add a new NativeID key to the FileInfo struct which will contain
the native file ID of the sending bridge.

When a new file is added to the config.Message.Extra["file"] map, now
the bridge native file ID should be added here.

When the receiving bridge receives such a message, it should keep an
internal mapping of NativeID <> bridge fileid/message id. In the case of
discord we map it to the resulted discord message ID after uploading it.

Now when a bridge deletes a file, it should send a EventFileDelete and
setting the ID to the native file ID of the bridge.

When the receiving bridge will get this event it'll look into the
NativeID <> bridge id mapping to find their internal ID and use it to
delete the specific file on their side.

For now this is implemented for slack to discord but this will be add to
other bridges where useful.

5 files changed, 108 insertions, 36 deletions

diff --git a/bridge/config/config.go b/bridge/config/config.go
index 7b7c2f2e..16b397f3 100644
--- a/bridge/config/config.go
+++ b/bridge/config/config.go
@@ -23,6 +23,7 @@ const (
 	EventRejoinChannels    = "rejoin_channels"
 	EventUserAction        = "user_action"
 	EventMsgDelete         = "msg_delete"
+	EventFileDelete        = "file_delete"
 	EventAPIConnected      = "api_connected"
 	EventUserTyping        = "user_typing"
 	EventGetChannelMembers = "get_channel_members"
@@ -56,13 +57,14 @@ func (m Message) ParentValid() bool {
 }
 
 type FileInfo struct {
-	Name    string
-	Data    *[]byte
-	Comment string
-	URL     string
-	Size    int64
-	Avatar  bool
-	SHA     string
+	Name     string
+	Data     *[]byte
+	Comment  string
+	URL      string
+	Size     int64
+	Avatar   bool
+	SHA      string
+	NativeID string
 }
 
 type ChannelInfo struct {
diff --git a/bridge/discord/discord.go b/bridge/discord/discord.go
index 0ac2b50c..9b9065f8 100644
--- a/bridge/discord/discord.go
+++ b/bridge/discord/discord.go
@@ -10,10 +10,14 @@ import (
 	"github.com/42wim/matterbridge/bridge/config"
 	"github.com/42wim/matterbridge/bridge/discord/transmitter"
 	"github.com/42wim/matterbridge/bridge/helper"
+	lru "github.com/hashicorp/golang-lru"
 	"github.com/matterbridge/discordgo"
 )
 
-const MessageLength = 1950
+const (
+	MessageLength = 1950
+	cFileUpload   = "file_upload"
+)
 
 type Bdiscord struct {
 	*bridge.Config
@@ -35,10 +39,20 @@ type Bdiscord struct {
 	// Webhook specific logic
 	useAutoWebhooks bool
 	transmitter     *transmitter.Transmitter
+	cache           *lru.Cache
 }
 
 func New(cfg *bridge.Config) bridge.Bridger {
-	b := &Bdiscord{Config: cfg}
+	newCache, err := lru.New(5000)
+	if err != nil {
+		cfg.Log.Fatalf("Could not create LRU cache: %v", err)
+	}
+
+	b := &Bdiscord{
+		Config: cfg,
+		cache:  newCache,
+	}
+
 	b.userMemberMap = make(map[string]*discordgo.Member)
 	b.nickMemberMap = make(map[string]*discordgo.Member)
 	b.channelInfoMap = make(map[string]*config.ChannelInfo)
@@ -280,6 +294,21 @@ func (b *Bdiscord) handleEventBotUser(msg *config.Message, channelID string) (st
 		return "", err
 	}
 
+	// Delete a file
+	if msg.Event == config.EventFileDelete {
+		if msg.ID == "" {
+			return "", nil
+		}
+
+		if fi, ok := b.cache.Get(cFileUpload + msg.ID); ok {
+			err := b.c.ChannelMessageDelete(channelID, fi.(string)) // nolint:forcetypeassert
+			b.cache.Remove(cFileUpload + msg.ID)
+			return "", err
+		}
+
+		return "", fmt.Errorf("file %s not found", msg.ID)
+	}
+
 	// Upload a file if it exists
 	if msg.Extra != nil {
 		for _, rmsg := range helper.HandleExtra(msg, b.General) {
@@ -327,7 +356,6 @@ func (b *Bdiscord) handleEventBotUser(msg *config.Message, channelID string) (st
 
 // handleUploadFile handles native upload of files
 func (b *Bdiscord) handleUploadFile(msg *config.Message, channelID string) (string, error) {
-	var err error
 	for _, f := range msg.Extra["file"] {
 		fi := f.(config.FileInfo)
 		file := discordgo.File{
@@ -340,10 +368,15 @@ func (b *Bdiscord) handleUploadFile(msg *config.Message, channelID string) (stri
 			Files:           []*discordgo.File{&file},
 			AllowedMentions: b.getAllowedMentions(),
 		}
-		_, err = b.c.ChannelMessageSendComplex(channelID, &m)
+		res, err := b.c.ChannelMessageSendComplex(channelID, &m)
 		if err != nil {
 			return "", fmt.Errorf("file upload failed: %s", err)
 		}
+
+		// link file_upload_nativeID (file ID from the original bridge) to our upload id
+		// so that we can remove this later when it eg needs to be deleted
+		b.cache.Add(cFileUpload+fi.NativeID, res.ID)
 	}
+
 	return "", nil
 }
diff --git a/bridge/helper/helper.go b/bridge/helper/helper.go
index 581a2c43..fb65d8d9 100644
--- a/bridge/helper/helper.go
+++ b/bridge/helper/helper.go
@@ -168,17 +168,23 @@ func HandleDownloadSize(logger *logrus.Entry, msg *config.Message, name string,
 
 // HandleDownloadData adds the data for a remote file into a Matterbridge gateway message.
 func HandleDownloadData(logger *logrus.Entry, msg *config.Message, name, comment, url string, data *[]byte, general *config.Protocol) {
+	HandleDownloadData2(logger, msg, name, "", comment, url, data, general)
+}
+
+// HandleDownloadData adds the data for a remote file into a Matterbridge gateway message.
+func HandleDownloadData2(logger *logrus.Entry, msg *config.Message, name, id, comment, url string, data *[]byte, general *config.Protocol) {
 	var avatar bool
 	logger.Debugf("Download OK %#v %#v", name, len(*data))
 	if msg.Event == config.EventAvatarDownload {
 		avatar = true
 	}
 	msg.Extra["file"] = append(msg.Extra["file"], config.FileInfo{
-		Name:    name,
-		Data:    data,
-		URL:     url,
-		Comment: comment,
-		Avatar:  avatar,
+		Name:     name,
+		Data:     data,
+		URL:      url,
+		Comment:  comment,
+		Avatar:   avatar,
+		NativeID: id,
 	})
 }
 
diff --git a/bridge/slack/handlers.go b/bridge/slack/handlers.go
index 4dc57d0d..c469b9a5 100644
--- a/bridge/slack/handlers.go
+++ b/bridge/slack/handlers.go
@@ -27,7 +27,8 @@ func (b *Bslack) handleSlack() {
 	b.Log.Debug("Start listening for Slack messages")
 	for message := range messages {
 		// don't do any action on deleted/typing messages
-		if message.Event != config.EventUserTyping && message.Event != config.EventMsgDelete {
+		if message.Event != config.EventUserTyping && message.Event != config.EventMsgDelete &&
+			message.Event != config.EventFileDelete {
 			b.Log.Debugf("<= Sending message from %s on %s to gateway", message.Username, b.Account)
 			// cleanup the message
 			message.Text = b.replaceMention(message.Text)
@@ -76,6 +77,13 @@ func (b *Bslack) handleSlackClient(messages chan *config.Message) {
 				continue
 			}
 			messages <- rmsg
+		case *slack.FileDeletedEvent:
+			rmsg, err := b.handleFileDeletedEvent(ev)
+			if err != nil {
+				b.Log.Errorf("%#v", err)
+				continue
+			}
+			messages <- rmsg
 		case *slack.OutgoingErrorEvent:
 			b.Log.Debugf("%#v", ev.Error())
 		case *slack.ChannelJoinedEvent:
@@ -222,6 +230,26 @@ func (b *Bslack) handleMessageEvent(ev *slack.MessageEvent) (*config.Message, er
 	return rmsg, nil
 }
 
+func (b *Bslack) handleFileDeletedEvent(ev *slack.FileDeletedEvent) (*config.Message, error) {
+	if rawChannel, ok := b.cache.Get(cfileDownloadChannel + ev.FileID); ok {
+		channel, err := b.channels.getChannelByID(rawChannel.(string))
+		if err != nil {
+			return nil, err
+		}
+
+		return &config.Message{
+			Event:    config.EventFileDelete,
+			Text:     config.EventFileDelete,
+			Channel:  channel.Name,
+			Account:  b.Account,
+			ID:       ev.FileID,
+			Protocol: b.Protocol,
+		}, nil
+	}
+
+	return nil, fmt.Errorf("channel ID for file ID %s not found", ev.FileID)
+}
+
 func (b *Bslack) handleStatusEvent(ev *slack.MessageEvent, rmsg *config.Message) bool {
 	switch ev.SubType {
 	case sChannelJoined, sMemberJoined:
@@ -281,6 +309,8 @@ func (b *Bslack) handleAttachments(ev *slack.MessageEvent, rmsg *config.Message)
 
 	// If we have files attached, download them (in memory) and put a pointer to it in msg.Extra.
 	for i := range ev.Files {
+		// keep reference in cache on which channel we added this file
+		b.cache.Add(cfileDownloadChannel+ev.Files[i].ID, ev.Channel)
 		if err := b.handleDownloadFile(rmsg, &ev.Files[i], false); err != nil {
 			b.Log.Errorf("Could not download incoming file: %#v", err)
 		}
@@ -330,7 +360,7 @@ func (b *Bslack) handleDownloadFile(rmsg *config.Message, file *slack.File, retr
 	// that the comment is not duplicated.
 	comment := rmsg.Text
 	rmsg.Text = ""
-	helper.HandleDownloadData(b.Log, rmsg, file.Name, comment, file.URLPrivateDownload, data, b.General)
+	helper.HandleDownloadData2(b.Log, rmsg, file.Name, file.ID, comment, file.URLPrivateDownload, data, b.General)
 	return nil
 }
 
diff --git a/bridge/slack/slack.go b/bridge/slack/slack.go
index 5db0c33e..55231c38 100644
--- a/bridge/slack/slack.go
+++ b/bridge/slack/slack.go
@@ -36,24 +36,25 @@ type Bslack struct {
 }
 
 const (
-	sHello           = "hello"
-	sChannelJoin     = "channel_join"
-	sChannelLeave    = "channel_leave"
-	sChannelJoined   = "channel_joined"
-	sMemberJoined    = "member_joined_channel"
-	sMessageChanged  = "message_changed"
-	sMessageDeleted  = "message_deleted"
-	sSlackAttachment = "slack_attachment"
-	sPinnedItem      = "pinned_item"
-	sUnpinnedItem    = "unpinned_item"
-	sChannelTopic    = "channel_topic"
-	sChannelPurpose  = "channel_purpose"
-	sFileComment     = "file_comment"
-	sMeMessage       = "me_message"
-	sUserTyping      = "user_typing"
-	sLatencyReport   = "latency_report"
-	sSystemUser      = "system"
-	sSlackBotUser    = "slackbot"
+	sHello               = "hello"
+	sChannelJoin         = "channel_join"
+	sChannelLeave        = "channel_leave"
+	sChannelJoined       = "channel_joined"
+	sMemberJoined        = "member_joined_channel"
+	sMessageChanged      = "message_changed"
+	sMessageDeleted      = "message_deleted"
+	sSlackAttachment     = "slack_attachment"
+	sPinnedItem          = "pinned_item"
+	sUnpinnedItem        = "unpinned_item"
+	sChannelTopic        = "channel_topic"
+	sChannelPurpose      = "channel_purpose"
+	sFileComment         = "file_comment"
+	sMeMessage           = "me_message"
+	sUserTyping          = "user_typing"
+	sLatencyReport       = "latency_report"
+	sSystemUser          = "system"
+	sSlackBotUser        = "slackbot"
+	cfileDownloadChannel = "file_download_channel"
 
 	tokenConfig           = "Token"
 	incomingWebhookConfig = "WebhookBindAddress"