[PLT-7362] Option to add user to channel if mentioned user is not currently in the channel (#7619)

* Option to add user to channel if mentioned user is not currently in the channel

* instead of link from server, just add component on client side to add channel member

* change implementation using post.props

* do clean up and add test

* sanitize post.props['add_channel_member'] on post creation

* move sanitize to app.CreatePost and also apply to app.UpdatePost

model/post.go

@@ -33,6 +33,7 @@ const (
 	POST_MESSAGE_MAX_RUNES     = 4000
 	POST_PROPS_MAX_RUNES       = 8000
 	POST_CUSTOM_TYPE_PREFIX    = "custom_"
+	PROPS_ADD_CHANNEL_MEMBER   = "add_channel_member"
 )
 
 type Post struct {
@@ -188,6 +189,18 @@ func (o *Post) IsValid() *AppError {
 	return nil
 }
 
+func (o *Post) SanitizeProps() {
+	membersToSanitize := []string{
+		PROPS_ADD_CHANNEL_MEMBER,
+	}
+
+	for _, member := range membersToSanitize {
+		if _, ok := o.Props[member]; ok {
+			delete(o.Props, member)
+		}
+	}
+}
+
 func (o *Post) PreSave() {
 	if o.Id == "" {
 		o.Id = NewId()

model/post_test.go

@@ -123,3 +123,46 @@ func TestPostIsSystemMessage(t *testing.T) {
 		t.Fatalf("TestPostIsSystemMessage failed, expected post2.IsSystemMessage() to be true")
 	}
 }
+
+func TestPostSanitizeProps(t *testing.T) {
+	post1 := &Post{
+		Message: "test",
+	}
+
+	post1.SanitizeProps()
+
+	if post1.Props[PROPS_ADD_CHANNEL_MEMBER] != nil {
+		t.Fatal("should be nil")
+	}
+
+	post2 := &Post{
+		Message: "test",
+		Props: StringInterface{
+			PROPS_ADD_CHANNEL_MEMBER: "test",
+		},
+	}
+
+	post2.SanitizeProps()
+
+	if post2.Props[PROPS_ADD_CHANNEL_MEMBER] != nil {
+		t.Fatal("should be nil")
+	}
+
+	post3 := &Post{
+		Message: "test",
+		Props: StringInterface{
+			PROPS_ADD_CHANNEL_MEMBER: "no good",
+			"attachments":            "good",
+		},
+	}
+
+	post3.SanitizeProps()
+
+	if post3.Props[PROPS_ADD_CHANNEL_MEMBER] != nil {
+		t.Fatal("should be nil")
+	}
+
+	if post3.Props["attachments"] == nil {
+		t.Fatal("should not be nil")
+	}
+}