From 0e1d6151b9612de23d750dd7dddc11d9a9c5351b Mon Sep 17 00:00:00 2001
From: Kyle Zhao <kzhao.sw@gmail.com>
Date: Thu, 25 Jul 2019 09:21:01 -0400
Subject: [PATCH] FIX: Frozen string error in `TopicEmbed.import` (#7938)

When `SiteSetting.embed_truncate` is enabled (by default), the truncated
string is mutatable and does not raise an error.

However, when the setting is disabled, the `contents` string is frozen
and immutable, and will raise a `FrozenError`.
---
 app/models/topic_embed.rb       |  4 ++--
 spec/models/topic_embed_spec.rb | 20 ++++++++++++++++++++
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/app/models/topic_embed.rb b/app/models/topic_embed.rb
index f7b46b711f1..c1948d89af8 100644
--- a/app/models/topic_embed.rb
+++ b/app/models/topic_embed.rb
@@ -36,8 +36,8 @@ class TopicEmbed < ActiveRecord::Base
     if SiteSetting.embed_truncate
       contents = first_paragraph_from(contents)
     end
-    contents ||= +''
-    contents << imported_from_html(url)
+    contents ||= ''
+    contents = +contents << imported_from_html(url)
 
     url = normalize_url(url)
 
diff --git a/spec/models/topic_embed_spec.rb b/spec/models/topic_embed_spec.rb
index 71c60afb3ab..18d4dd97648 100644
--- a/spec/models/topic_embed_spec.rb
+++ b/spec/models/topic_embed_spec.rb
@@ -86,6 +86,26 @@ describe TopicEmbed do
         expect(post.cook_method).to eq(Post.cook_methods[:regular])
       end
     end
+
+    describe 'embedded content truncation' do
+      MAX_LENGTH_BEFORE_TRUNCATION = 100
+
+      let(:long_content) { "<p>#{'a' * MAX_LENGTH_BEFORE_TRUNCATION}</p>\n<p>more</p>" }
+
+      it 'truncates the imported post when truncation is enabled' do
+        SiteSetting.embed_truncate = true
+        post = TopicEmbed.import(user, url, title, long_content)
+
+        expect(post.raw).not_to include(long_content)
+      end
+
+      it 'keeps everything in the imported post when truncation is disabled' do
+        SiteSetting.embed_truncate = false
+        post = TopicEmbed.import(user, url, title, long_content)
+
+        expect(post.raw).to include(long_content)
+      end
+    end
   end
 
   context '.topic_id_for_embed' do