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.

1 files changed, 37 insertions, 4 deletions

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
 }