From 9fafd50368557e26de82637ab00e52c11c140366 Mon Sep 17 00:00:00 2001
From: Yoonchae Lee <bluegreenmagick@gmail.com>
Date: Thu, 19 Sep 2024 12:41:52 +0900
Subject: [PATCH] Fix DOCTYPE closing tag recognition in bufread

---
 src/reader/mod.rs |  7 +++++--
 tests/issues.rs   | 16 ++++++++++++++++
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/src/reader/mod.rs b/src/reader/mod.rs
index 9a81e90e..53647b22 100644
--- a/src/reader/mod.rs
+++ b/src/reader/mod.rs
@@ -1088,10 +1088,13 @@ impl BangType {
             Self::DocType => {
                 for i in memchr::memchr_iter(b'>', chunk) {
                     let content = &chunk[..i];
-                    let balance = memchr::memchr2_iter(b'<', b'>', content)
+                    let balance_buf = memchr::memchr2_iter(b'<', b'>', buf)
+                        .map(|p| if buf[p] == b'<' { 1i32 } else { -1 })
+                        .sum::<i32>();
+                    let balance_content = memchr::memchr2_iter(b'<', b'>', content)
                         .map(|p| if content[p] == b'<' { 1i32 } else { -1 })
                         .sum::<i32>();
-                    if balance == 0 {
+                    if balance_buf + balance_content == 0 {
                         return Some((content, i + 1)); // +1 for `>`
                     }
                 }
diff --git a/tests/issues.rs b/tests/issues.rs
index 95dd64ff..17fea178 100644
--- a/tests/issues.rs
+++ b/tests/issues.rs
@@ -477,3 +477,19 @@ fn issue776() {
         Event::End(BytesEnd::new(r#"tag attr=">""#))
     );
 }
+
+/// Regression test for https://github.com/tafia/quick-xml/issues/801
+#[test]
+fn issue801() {
+    let xml = BufReader::with_capacity(4, b"<!DOCTYPE X [<!-- --><!ENTITY a \"a\">]>" as &[u8]);
+    let mut reader = Reader::from_reader(xml);
+    let mut buf = Vec::new();
+    loop {
+        buf.clear();
+        match reader.read_event_into(&mut buf) {
+            Err(e) => panic!("Error at position {}: {:?}", reader.error_position(), e),
+            Ok(Event::Eof) => {break}
+            Ok(_) => {}
+        }
+    }
+}
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