From 4b0748ecf9eca4a412ece7efb149bf6653804302 Mon Sep 17 00:00:00 2001
From: Zixuan James Li <zixuan@zulip.com>
Date: Thu, 29 Aug 2024 21:22:55 -0400
Subject: [PATCH 1/2] content [nfc]: Use single and last instead to access
 child.

This improves readability, especially in the .last case.

Signed-off-by: Zixuan James Li <zixuan@zulip.com>
---
 lib/model/content.dart | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/model/content.dart b/lib/model/content.dart
index e9ee7875ef..3228fe9406 100644
--- a/lib/model/content.dart
+++ b/lib/model/content.dart
@@ -986,7 +986,7 @@ class _ZulipContentParser {
           && divElement.className == "codehilite");
 
       if (divElement.nodes.length != 1) return null;
-      final child = divElement.nodes[0];
+      final child = divElement.nodes.single;
       if (child is! dom.Element) return null;
       if (child.localName != 'pre') return null;
 
@@ -997,7 +997,7 @@ class _ZulipContentParser {
             || first.localName != 'span'
             || first.nodes.isNotEmpty) return null;
       }
-      final grandchild = child.nodes[child.nodes.length - 1];
+      final grandchild = child.nodes.last;
       if (grandchild is! dom.Element) return null;
       if (grandchild.localName != 'code') return null;
 

From 5d369770eb7506f6e6f87a2bd15c55ae28e67915 Mon Sep 17 00:00:00 2001
From: Zixuan James Li <zixuan@zulip.com>
Date: Wed, 28 Aug 2024 02:58:43 -0400
Subject: [PATCH 2/2] content: Handle code block elements without
 grandchildren.

A code block containing no grandchildren (i.e. a
<div class="codehilite"> element containing an empty <pre> block)
appears in some very old messages.  The parser was crashing on them.

The affect messages in public https://chat.zulip.org history ranged
from message ID 5020 to 29855, all in 2016.

Signed-off-by: Zixuan James Li <zixuan@zulip.com>
---
 lib/model/content.dart       |  2 +-
 test/model/content_test.dart | 12 ++++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/lib/model/content.dart b/lib/model/content.dart
index 3228fe9406..e99d4d391a 100644
--- a/lib/model/content.dart
+++ b/lib/model/content.dart
@@ -990,7 +990,7 @@ class _ZulipContentParser {
       if (child is! dom.Element) return null;
       if (child.localName != 'pre') return null;
 
-      if (child.nodes.length > 2) return null;
+      if (child.nodes.length > 2 || child.nodes.isEmpty) return null;
       if (child.nodes.length == 2) {
         final first = child.nodes[0];
         if (first is! dom.Element
diff --git a/test/model/content_test.dart b/test/model/content_test.dart
index 0846273795..4aef38d5cc 100644
--- a/test/model/content_test.dart
+++ b/test/model/content_test.dart
@@ -344,6 +344,17 @@ class ContentExample {
       ]),
     ]);
 
+  // Current servers no longer produce this, but it can be found in ancient
+  // messages.  For example:
+  //   https://chat.zulip.org/#narrow/stream/2-general/topic/Error.20in.20dev.20server/near/18765
+  static final codeBlockWithEmptyBody = ContentExample(
+      'code block, with an empty body',
+      '```',
+      '<div class="codehilite"><pre></pre></div>', [
+      blockUnimplemented(
+          '<div class="codehilite"><pre></pre></div>'),
+  ]);
+
   static final codeBlockWithHighlightedLines = ContentExample(
     'code block, with syntax highlighting and highlighted lines',
     '```\n::markdown hl_lines="2 4"\n# he\n## llo\n### world\n```',
@@ -1149,6 +1160,7 @@ void main() {
   testParseExample(ContentExample.codeBlockPlain);
   testParseExample(ContentExample.codeBlockHighlightedShort);
   testParseExample(ContentExample.codeBlockHighlightedMultiline);
+  testParseExample(ContentExample.codeBlockWithEmptyBody);
   testParseExample(ContentExample.codeBlockWithHighlightedLines);
   testParseExample(ContentExample.codeBlockWithUnknownSpanType);
   testParseExample(ContentExample.codeBlockFollowedByMultipleLineBreaks);