Exclude sending file metadata to plugin hooks (#18454)

* Exclude sending file metadata to plugin hooks

A FileInfo object contained a MiniPreview which is
a slice of bytes. This can be particularly costly
while marshalling to plugin hooks.

We avoid this by refactoring the Embeds and Images
population to a separate method and calling that
to prevent posts from getting updated.

https://community-daily.mattermost.com/boards/workspace/zyoahc9uapdn3xdptac6jb69ic/285b80a3-257d-41f6-8cf4-ed80ca9d92e5/495cdb4d-c13a-4992-8eb9-80cfee2819a4?c=9c0b5413-5401-4ef2-83d5-b9f756585bbc

```release-note
NONE
```

* refactor to separate method

```release-note
NONE
```

api4/post.go

@@ -128,7 +128,7 @@ func createEphemeralPost(c *Context, w http.ResponseWriter, r *http.Request) {
 
 	w.WriteHeader(http.StatusCreated)
 	rp = model.AddPostActionCookies(rp, c.App.PostActionCookieSecret())
-	rp = c.App.PreparePostForClient(rp, true, false)
+	rp = c.App.PreparePostForClientWithEmbedsAndImages(rp, true, false)
 	rp, err := c.App.SanitizePostMetadataForUser(rp, c.AppContext.Session().UserId)
 	if err != nil {
 		c.Err = err
@@ -376,7 +376,7 @@ func getPost(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	post = c.App.PreparePostForClient(post, false, false)
+	post = c.App.PreparePostForClientWithEmbedsAndImages(post, false, false)
 	post, err = c.App.SanitizePostMetadataForUser(post, c.AppContext.Session().UserId)
 	if err != nil {
 		c.Err = err

app/app_iface.go

@@ -880,7 +880,8 @@ type AppIface interface {
 	PostUpdateChannelPurposeMessage(c *request.Context, userID string, channel *model.Channel, oldChannelPurpose string, newChannelPurpose string) *model.AppError
 	PostWithProxyAddedToImageURLs(post *model.Post) *model.Post
 	PostWithProxyRemovedFromImageURLs(post *model.Post) *model.Post
-	PreparePostForClient(originalPost *model.Post, isNewPost bool, isEditPost bool) *model.Post
+	PreparePostForClient(originalPost *model.Post, isNewPost, isEditPost bool) *model.Post
+	PreparePostForClientWithEmbedsAndImages(originalPost *model.Post, isNewPost, isEditPost bool) *model.Post
 	PreparePostListForClient(originalList *model.PostList) *model.PostList
 	ProcessSlackText(text string) string
 	Publish(message *model.WebSocketEvent)

app/opentracing/opentracing_layer.go

@@ -12220,6 +12220,23 @@ func (a *OpenTracingAppLayer) PreparePostForClient(originalPost *model.Post, isN
 	return resultVar0
 }
 
+func (a *OpenTracingAppLayer) PreparePostForClientWithEmbedsAndImages(originalPost *model.Post, isNewPost bool, isEditPost bool) *model.Post {
+	origCtx := a.ctx
+	span, newCtx := tracing.StartSpanWithParentByContext(a.ctx, "app.PreparePostForClientWithEmbedsAndImages")
+
+	a.ctx = newCtx
+	a.app.Srv().Store.SetContext(newCtx)
+	defer func() {
+		a.app.Srv().Store.SetContext(origCtx)
+		a.ctx = origCtx
+	}()
+
+	defer span.Finish()
+	resultVar0 := a.app.PreparePostForClientWithEmbedsAndImages(originalPost, isNewPost, isEditPost)
+
+	return resultVar0
+}
+
 func (a *OpenTracingAppLayer) PreparePostListForClient(originalList *model.PostList) *model.PostList {
 	origCtx := a.ctx
 	span, newCtx := tracing.StartSpanWithParentByContext(a.ctx, "app.PreparePostListForClient")

app/post.go

@@ -297,7 +297,7 @@ func (a *App) CreatePost(c *request.Context, post *model.Post, channel *model.Ch
 		}
 	}
 
-	post = a.PreparePostForClient(post, true, false)
+	post = a.getEmbedsAndImages(post, true)
 	previewPost := post.GetPreviewPost()
 	if previewPost != nil {
 		post.AddProp(model.PostPropsPreviewedPost, previewPost.PostID)
@@ -521,7 +521,7 @@ func (a *App) SendEphemeralPost(userID string, post *model.Post) *model.Post {
 
 	post.GenerateActionIds()
 	message := model.NewWebSocketEvent(model.WebsocketEventEphemeralMessage, "", post.ChannelId, userID, nil)
-	post = a.PreparePostForClient(post, true, false)
+	post = a.PreparePostForClientWithEmbedsAndImages(post, true, false)
 	post = model.AddPostActionCookies(post, a.PostActionCookieSecret())
 
 	postJSON, jsonErr := post.ToJSON()
@@ -544,7 +544,7 @@ func (a *App) UpdateEphemeralPost(userID string, post *model.Post) *model.Post {
 
 	post.GenerateActionIds()
 	message := model.NewWebSocketEvent(model.WebsocketEventPostEdited, "", post.ChannelId, userID, nil)
-	post = a.PreparePostForClient(post, true, false)
+	post = a.PreparePostForClientWithEmbedsAndImages(post, true, false)
 	post = model.AddPostActionCookies(post, a.PostActionCookieSecret())
 	postJSON, jsonErr := post.ToJSON()
 	if jsonErr != nil {
@@ -685,7 +685,7 @@ func (a *App) UpdatePost(c *request.Context, post *model.Post, safeUpdate bool)
 		})
 	}
 
-	rpost = a.PreparePostForClient(rpost, false, true)
+	rpost = a.PreparePostForClientWithEmbedsAndImages(rpost, false, true)
 
 	// Ensure IsFollowing is nil since this updated post will be broadcast to all users
 	// and we don't want to have to populate it for every single user and broadcast to each

app/post_metadata.go

@@ -60,7 +60,7 @@ func (a *App) PreparePostListForClient(originalList *model.PostList) *model.Post
 	}
 
 	for id, originalPost := range originalList.Posts {
-		post := a.PreparePostForClient(originalPost, false, false)
+		post := a.PreparePostForClientWithEmbedsAndImages(originalPost, false, false)
 
 		list.Posts[id] = post
 	}
@@ -94,15 +94,16 @@ func (a *App) OverrideIconURLIfEmoji(post *model.Post) {
 	}
 }
 
-func (a *App) PreparePostForClient(originalPost *model.Post, isNewPost bool, isEditPost bool) *model.Post {
+func (a *App) PreparePostForClient(originalPost *model.Post, isNewPost, isEditPost bool) *model.Post {
 	post := originalPost.Clone()
 
 	// Proxy image links before constructing metadata so that requests go through the proxy
 	post = a.PostWithProxyAddedToImageURLs(post)
 
 	a.OverrideIconURLIfEmoji(post)
-
+	if post.Metadata == nil {
-	post.Metadata = &model.PostMetadata{}
+		post.Metadata = &model.PostMetadata{}
+	}
 
 	if post.DeleteAt > 0 {
 		// For deleted posts we don't fill out metadata nor do we return the post content
@@ -125,9 +126,22 @@ func (a *App) PreparePostForClient(originalPost *model.Post, isNewPost bool, isE
 		post.Metadata.Files = fileInfos
 	}
 
+	return post
+}
+
+func (a *App) PreparePostForClientWithEmbedsAndImages(originalPost *model.Post, isNewPost, isEditPost bool) *model.Post {
+	post := a.PreparePostForClient(originalPost, isNewPost, isEditPost)
+	post = a.getEmbedsAndImages(post, true)
+	return post
+}
+
+func (a *App) getEmbedsAndImages(post *model.Post, isNewPost bool) *model.Post {
+	if post.Metadata == nil {
+		post.Metadata = &model.PostMetadata{}
+	}
+
 	// Embeds and image dimensions
 	firstLink, images := a.getFirstLinkAndImages(post.Message)
-
 	if embed, err := a.getEmbedForPost(post, firstLink, isNewPost); err != nil {
 		appErr, ok := err.(*model.AppError)
 		isNotFound := ok && appErr.StatusCode == http.StatusNotFound
@@ -142,7 +156,6 @@ func (a *App) PreparePostForClient(originalPost *model.Post, isNewPost bool, isE
 	}
 
 	post.Metadata.Images = a.getImagesForPost(post, images, isNewPost)
-
 	return post
 }
 

app/post_metadata_test.go

@@ -122,7 +122,7 @@ func TestPreparePostForClient(t *testing.T) {
 			Message: message,
 		}
 
-		clientPost := th.App.PreparePostForClient(post, false, false)
+		clientPost := th.App.PreparePostForClient(post, false, true)
 
 		t.Run("doesn't mutate provided post", func(t *testing.T) {
 			assert.NotEqual(t, clientPost, post, "should've returned a new post")