app/post_metadata: add a check to type casting (#15821)

app/post_metadata.go

@@ -71,7 +71,11 @@ func (a *App) OverrideIconURLIfEmoji(post *model.Post) {
 	if !ok || prop == nil {
 		return
 	}
-	emojiName := prop.(string)
+
+	emojiName, ok := prop.(string)
+	if !ok {
+		return
+	}
 
 	if !*a.Config().ServiceSettings.EnablePostIconOverride || emojiName == "" {
 		return

app/post_metadata_test.go

@@ -358,6 +358,25 @@ func TestPreparePostForClient(t *testing.T) {
 		})
 	})
 
+	t.Run("post props has invalid fields", func(t *testing.T) {
+		th := setup(t)
+		defer th.TearDown()
+
+		post, err := th.App.CreatePost(&model.Post{
+			UserId:    th.BasicUser.Id,
+			ChannelId: th.BasicChannel.Id,
+			Message:   "some post",
+		}, th.BasicChannel, false, true)
+		require.Nil(t, err)
+
+		// this value expected to be a string
+		post.AddProp(model.POST_PROPS_OVERRIDE_ICON_EMOJI, true)
+
+		require.NotPanics(t, func() {
+			_ = th.App.PreparePostForClient(post, false, false)
+		})
+	})
+
 	t.Run("proxy linked images", func(t *testing.T) {
 		th := setup(t)
 		defer th.TearDown()