From b0644c3a17dfd1a55f4ed5f4f91fcc84e74359ed Mon Sep 17 00:00:00 2001
From: Alex Auvolat <alex@adnab.me>
Date: Fri, 21 Feb 2020 19:28:00 +0100
Subject: Basic backlogging

---
 appservice/account.go              | 12 +++++++++++-
 connector/connector.go             | 11 +++++++++++
 connector/mattermost/mattermost.go | 31 +++++++++++++++++++++++++++----
 main.go                            |  1 +
 mxlib/registration.go              |  1 +
 5 files changed, 51 insertions(+), 5 deletions(-)

diff --git a/appservice/account.go b/appservice/account.go
index 3791ee3..e2f2ee9 100644
--- a/appservice/account.go
+++ b/appservice/account.go
@@ -230,7 +230,7 @@ func (a *Account) eventInternal(event *Event) error {
 		err = mx.RoomInvite(mx_room_id, mx_user_id)
 		if err != nil {
 			if strings.Contains(err.Error(), "already in the room") {
-				err = nil
+				return nil
 			}
 			return err
 		}
@@ -260,6 +260,16 @@ func (a *Account) eventInternal(event *Event) error {
 			}
 		}
 
+		if event.Id != "" {
+			cache_key := fmt.Sprintf("%s/event_seen/%s/%s",
+				a.Protocol, mx_room_id, event.Id)
+			if !dbCacheTestAndSet(cache_key, "yes") {
+				// false: cache key was not modified, meaning we
+				// already saw the event
+				return nil
+			}
+		}
+
 		typ := "m.text"
 		if event.Type == EVENT_ACTION {
 			typ = "m.emote"
diff --git a/connector/connector.go b/connector/connector.go
index 2235318..30dfea4 100644
--- a/connector/connector.go
+++ b/connector/connector.go
@@ -98,6 +98,11 @@ const (
 type Event struct {
 	Type EventType
 
+	// If non-empty, the event Id is used to deduplicate events in a channel
+	// This is usefull for backends that provide a backlog of channel messages
+	// when (re-)joining a room
+	Id string
+
 	// UserID of the user that sent the event
 	// If this is a direct message event, this event can only have been authored
 	// by the user we are talking to (and not by ourself)
@@ -120,12 +125,18 @@ type Event struct {
 
 type UserInfo struct {
 	DisplayName string
+
+	// If non-empty, the Filename of the avatar object will be used by Easybridge
+	// to deduplicate the update events and prevent needless reuploads.
+	// Example strategy that works for the mattermost backend: use the update timestamp as fictious file name
 	Avatar      MediaObject
 }
 
 type RoomInfo struct {
 	Name    string
 	Topic   string
+
+	// Same deduplication comment as for UserInfo.Avatar
 	Picture MediaObject
 }
 
diff --git a/connector/mattermost/mattermost.go b/connector/mattermost/mattermost.go
index 6282831..117286b 100644
--- a/connector/mattermost/mattermost.go
+++ b/connector/mattermost/mattermost.go
@@ -354,6 +354,22 @@ func (mm *Mattermost) handleConnected() {
 		} else {
 			log.Warnf("Could not get channel members: %s", resp.Error)
 		}
+
+		// Read backlog
+		// TODO: remember what was the last seen post in this channel
+		backlog, resp := mm.conn.Client.GetPostsForChannel(ch.Id, 0, 1000, "")
+		if resp.Error == nil {
+			for i := 0; i < len(backlog.Order); i++ {
+				post_id := backlog.Order[len(backlog.Order)-i-1]
+				post := backlog.Posts[post_id]
+				post_time := time.Unix(post.CreateAt/1000, 0)
+				post.Message = fmt.Sprintf("[%s] %s",
+					post_time.Format("2006-01-02 15:04:05 MST"), post.Message)
+				mm.handlePost(ch.Name, post, true)
+			}
+		} else {
+			log.Warnf("Could not get channel backlog: %s", resp.Error)
+		}
 	}
 }
 
@@ -425,6 +441,10 @@ func (mm *Mattermost) handlePosted(msg *model.WebSocketEvent) error {
 		return err
 	}
 
+	return mm.handlePost(channel_name, &post, false)
+}
+
+func (mm *Mattermost) handlePost(channel_name string, post *model.Post, only_messages bool) error {
 	// Skip self messages
 	if post.UserId == mm.conn.User.Id {
 		return nil
@@ -440,6 +460,7 @@ func (mm *Mattermost) handlePosted(msg *model.WebSocketEvent) error {
 
 	// Build message event
 	msg_ev := &Event{
+		Id: post.Id,
 		Author: userId,
 		Text: post.Message,
 		Type: EVENT_MESSAGE,
@@ -489,10 +510,12 @@ func (mm *Mattermost) handlePosted(msg *model.WebSocketEvent) error {
 		mm.ensureJoined(user, roomId)
 
 		if post.Type == "system_header_change" {
-			new_header := post.Props["new_header"].(string)
-			mm.handler.RoomInfoUpdated(roomId, userId, &RoomInfo{
-				Topic: new_header,
-			})
+			if !only_messages {
+				new_header := post.Props["new_header"].(string)
+				mm.handler.RoomInfoUpdated(roomId, userId, &RoomInfo{
+					Topic: new_header,
+				})
+			}
 		} else if post.Type == "" || post.Type == "me" {
 			msg_ev.Room = roomId
 			mm.handler.Event(msg_ev)
diff --git a/main.go b/main.go
index 60272a7..0155892 100644
--- a/main.go
+++ b/main.go
@@ -102,6 +102,7 @@ func readRegistration(file string) mxlib.Registration {
 		AsToken:         hex.EncodeToString(rnd[:32]),
 		HsToken:         hex.EncodeToString(rnd[32:]),
 		SenderLocalpart: "_ezbr_",
+		RateLimited: false,
 		Namespaces: mxlib.RegistrationNamespaceSet{
 			Users: []mxlib.RegistrationNamespace{
 				mxlib.RegistrationNamespace{
diff --git a/mxlib/registration.go b/mxlib/registration.go
index cae3f29..5aabdd6 100644
--- a/mxlib/registration.go
+++ b/mxlib/registration.go
@@ -10,6 +10,7 @@ type Registration struct {
 	AsToken         string                   `yaml:"as_token"`
 	HsToken         string                   `yaml:"hs_token"`
 	SenderLocalpart string                   `yaml:"sender_localpart"`
+	RateLimited bool `yaml:"rate_limited"`
 	Namespaces      RegistrationNamespaceSet `yaml:"namespaces"`
 }
 
-- 
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