Removed PostPreview from MessageHasBeenPosted payload. (#18613)

Automatic Merge

app/post.go

@@ -292,6 +292,14 @@ func (a *App) CreatePost(c *request.Context, post *model.Post, channel *model.Ch
 
 	// We make a copy of the post for the plugin hook to avoid a race condition.
 	rPostCopy := rpost.Clone()
+
+	// FIXME: Removes PreviewPost from the post payload sent to the MessageHasBeenPosted hook so that plugins compiled with older versions of
+	// Mattermost—without the gob registeration of the PreviewPost struct—won't crash.
+	if rPostCopy.Metadata != nil {
+		rPostCopy.Metadata = rPostCopy.Metadata.Copy()
+	}
+	rPostCopy.RemovePreviewPost()
+
 	if pluginsEnvironment := a.GetPluginsEnvironment(); pluginsEnvironment != nil {
 		a.Srv().Go(func() {
 			pluginContext := pluginContext(c)

model/post.go

@@ -686,6 +686,20 @@ func (o *Post) ToNilIfInvalid() *Post {
 	return o
 }
 
+func (o *Post) RemovePreviewPost() {
+	if o.Metadata == nil || o.Metadata.Embeds == nil {
+		return
+	}
+	n := 0
+	for _, embed := range o.Metadata.Embeds {
+		if embed.Type != PostEmbedPermalink {
+			o.Metadata.Embeds[n] = embed
+			n++
+		}
+	}
+	o.Metadata.Embeds = o.Metadata.Embeds[:n]
+}
+
 func (o *Post) GetPreviewPost() *PreviewPost {
 	for _, embed := range o.Metadata.Embeds {
 		if embed.Type == PostEmbedPermalink {

model/post_metadata.go

@@ -34,3 +34,31 @@ type PostImage struct {
 	// FrameCount stores the number of frames in this image, if it is an animated gif. It will be 0 for other formats.
 	FrameCount int `json:"frame_count"`
 }
+
+// Copy does a deep copy
+func (p *PostMetadata) Copy() *PostMetadata {
+	embedsCopy := make([]*PostEmbed, len(p.Embeds))
+	copy(embedsCopy, p.Embeds)
+
+	emojisCopy := make([]*Emoji, len(p.Emojis))
+	copy(emojisCopy, p.Emojis)
+
+	filesCopy := make([]*FileInfo, len(p.Files))
+	copy(filesCopy, p.Files)
+
+	imagesCopy := map[string]*PostImage{}
+	for k, v := range p.Images {
+		imagesCopy[k] = v
+	}
+
+	reactionsCopy := make([]*Reaction, len(p.Reactions))
+	copy(reactionsCopy, p.Reactions)
+
+	return &PostMetadata{
+		Embeds:    embedsCopy,
+		Emojis:    emojisCopy,
+		Files:     filesCopy,
+		Images:    imagesCopy,
+		Reactions: reactionsCopy,
+	}
+}