Avoids crash on invalid comments when the buffer when the buffer was …

…not cleared before

Closes tafia#604

Changelog.md

@@ -18,12 +18,13 @@
 
 ### Bug Fixes
 
-### Misc Changes
+- [#618]: Avoid crashing on wrong comments `<!-->` when the buffer was not cleared before.
 
+### Misc Changes
 
 [#609]: https://github.com/tafia/quick-xml/pull/609
 [#615]: https://github.com/tafia/quick-xml/pull/615
-
+[#618]: https://github.com/tafia/quick-xml/pull/618
 
 ## 0.29.0 -- 2023-06-13
 

src/reader/buffered_reader.rs

@@ -117,7 +117,7 @@ macro_rules! impl_buffered_source {
                     // somewhere sane rather than at the EOF
                     Ok(n) if n.is_empty() => return Err(bang_type.to_err()),
                     Ok(available) => {
-                        if let Some((consumed, used)) = bang_type.parse(buf, available) {
+                        if let Some((consumed, used)) = bang_type.parse(&buf[start..], available) {
                             buf.extend_from_slice(consumed);
 
                             self $(.$reader)? .consume(used);

tests/issues.rs

@@ -4,7 +4,7 @@
 
 use std::sync::mpsc;
 
-use quick_xml::events::{BytesStart, Event};
+use quick_xml::events::{BytesDecl, BytesStart, Event};
 use quick_xml::name::QName;
 use quick_xml::reader::Reader;
 use quick_xml::Error;
@@ -105,3 +105,74 @@ mod issue514 {
         assert_eq!(reader.read_event().unwrap(), Event::Eof);
     }
 }
+
+/// Regression test for https://github.com/tafia/quick-xml/issues/604
+mod issue604 {
+    use super::*;
+    use pretty_assertions::assert_eq;
+    use quick_xml::events::BytesText;
+
+    #[test]
+    fn short() {
+        let data = b"<?xml version=\"1.0\"?><!-->";
+        let mut reader = Reader::from_reader(data.as_slice());
+        let mut buf = Vec::new();
+        assert_eq!(
+            reader.read_event_into(&mut buf).unwrap(),
+            Event::Decl(BytesDecl::new("1.0", None, None))
+        );
+        assert!(matches!(
+            reader.read_event_into(&mut buf),
+            Err(Error::UnexpectedEof(_))
+        ));
+        assert_eq!(reader.read_event_into(&mut buf).unwrap(), Event::Eof);
+    }
+
+    #[test]
+    fn long() {
+        let data = b"<?xml version=\"1.0\"?><!--->";
+        let mut reader = Reader::from_reader(data.as_slice());
+        let mut buf = Vec::new();
+        assert_eq!(
+            reader.read_event_into(&mut buf).unwrap(),
+            Event::Decl(BytesDecl::new("1.0", None, None))
+        );
+        assert!(matches!(
+            reader.read_event_into(&mut buf),
+            Err(Error::UnexpectedEof(_))
+        ));
+        assert_eq!(reader.read_event_into(&mut buf).unwrap(), Event::Eof);
+    }
+
+    #[test]
+    fn small_valid() {
+        let data = b"<?xml version=\"1.0\"?><!-->-->";
+        let mut reader = Reader::from_reader(data.as_slice());
+        let mut buf = Vec::new();
+        assert_eq!(
+            reader.read_event_into(&mut buf).unwrap(),
+            Event::Decl(BytesDecl::new("1.0", None, None))
+        );
+        assert_eq!(
+            reader.read_event_into(&mut buf).unwrap(),
+            Event::Comment(BytesText::from_escaped(">"))
+        );
+        assert_eq!(reader.read_event_into(&mut buf).unwrap(), Event::Eof);
+    }
+
+    #[test]
+    fn long_valid() {
+        let data = b"<?xml version=\"1.0\"?><!--->-->";
+        let mut reader = Reader::from_reader(data.as_slice());
+        let mut buf = Vec::new();
+        assert_eq!(
+            reader.read_event_into(&mut buf).unwrap(),
+            Event::Decl(BytesDecl::new("1.0", None, None))
+        );
+        assert_eq!(
+            reader.read_event_into(&mut buf).unwrap(),
+            Event::Comment(BytesText::from_escaped("->"))
+        );
+        assert_eq!(reader.read_event_into(&mut buf).unwrap(), Event::Eof);
+    }
+}