Fix incorrect reading of CDATA and comments when end sequence crosses the boundary of chunks in buffered reader

The bug was introduced in f2b99f0

Author: Mingun

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(available, read) {
+                        if let Some((consumed, used)) = bang_type.parse(buf, available) {
                             buf.extend_from_slice(consumed);
 
                             self $(.$reader)? .consume(used);

src/reader/mod.rs

@@ -742,25 +742,50 @@ impl BangType {
 
     /// If element is finished, returns its content up to `>` symbol and
     /// an index of this symbol, otherwise returns `None`
+    ///
+    /// # Parameters
+    /// - `buf`: buffer with data consumed on previous iterations
+    /// - `chunk`: data read on current iteration and not yet consumed from reader
     #[inline(always)]
-    fn parse<'b>(&self, chunk: &'b [u8], offset: usize) -> Option<(&'b [u8], usize)> {
+    fn parse<'b>(&self, buf: &[u8], chunk: &'b [u8]) -> Option<(&'b [u8], usize)> {
         for i in memchr::memchr_iter(b'>', chunk) {
             match self {
                 // Need to read at least 6 symbols (`!---->`) for properly finished comment
                 // <!----> - XML comment
                 //  012345 - i
-                Self::Comment => {
-                    if offset + i > 4 && chunk[..i].ends_with(b"--") {
+                Self::Comment if buf.len() + i > 4 => {
+                    if chunk[..i].ends_with(b"--") {
                         // We cannot strip last `--` from the buffer because we need it in case of
                         // check_comments enabled option. XML standard requires that comment
                         // will not end with `--->` sequence because this is a special case of
                         // `--` in the comment (https://www.w3.org/TR/xml11/#sec-comments)
                         return Some((&chunk[..i], i + 1)); // +1 for `>`
                     }
+                    // End sequence `-|->` was splitted at |
+                    //        buf --/   \-- chunk
+                    if i == 1 && buf.ends_with(b"-") && chunk[0] == b'-' {
+                        return Some((&chunk[..i], i + 1)); // +1 for `>`
+                    }
+                    // End sequence `--|>` was splitted at |
+                    //         buf --/   \-- chunk
+                    if i == 0 && buf.ends_with(b"--") {
+                        return Some((&[], i + 1)); // +1 for `>`
+                    }
                 }
+                Self::Comment => {}
                 Self::CData => {
                     if chunk[..i].ends_with(b"]]") {
-                        return Some((&chunk[..i - 2], i + 1)); // +1 for `>`
+                        return Some((&chunk[..i], i + 1)); // +1 for `>`
+                    }
+                    // End sequence `]|]>` was splitted at |
+                    //        buf --/   \-- chunk
+                    if i == 1 && buf.ends_with(b"]") && chunk[0] == b']' {
+                        return Some((&chunk[..i], i + 1)); // +1 for `>`
+                    }
+                    // End sequence `]]|>` was splitted at |
+                    //         buf --/   \-- chunk
+                    if i == 0 && buf.ends_with(b"]]") {
+                        return Some((&[], i + 1)); // +1 for `>`
                     }
                 }
                 Self::DocType => {
@@ -1021,7 +1046,7 @@ mod test {
                                 $(.$await)?
                                 .unwrap()
                                 .map(|(ty, data)| (ty, Bytes(data))),
-                            Some((BangType::CData, Bytes(b"![CDATA[")))
+                            Some((BangType::CData, Bytes(b"![CDATA[]]")))
                         );
                         assert_eq!(position, 11);
                     }
@@ -1042,7 +1067,7 @@ mod test {
                                 $(.$await)?
                                 .unwrap()
                                 .map(|(ty, data)| (ty, Bytes(data))),
-                            Some((BangType::CData, Bytes(b"![CDATA[cdata]] ]>content")))
+                            Some((BangType::CData, Bytes(b"![CDATA[cdata]] ]>content]]")))
                         );
                         assert_eq!(position, 28);
                     }

src/reader/parser.rs

@@ -90,6 +90,7 @@ impl Parser {
         let len = buf.len();
         match bang_type {
             BangType::Comment if buf.starts_with(b"!--") => {
+                debug_assert!(buf.ends_with(b"--"));
                 if self.check_comments {
                     // search if '--' not in comments
                     if let Some(p) = memchr::memchr_iter(b'-', &buf[3..len - 2])
@@ -105,7 +106,11 @@ impl Parser {
                 )))
             }
             BangType::CData if uncased_starts_with(buf, b"![CDATA[") => {
-                Ok(Event::CData(BytesCData::wrap(&buf[8..], self.decoder())))
+                debug_assert!(buf.ends_with(b"]]"));
+                Ok(Event::CData(BytesCData::wrap(
+                    &buf[8..len - 2],
+                    self.decoder(),
+                )))
             }
             BangType::DocType if uncased_starts_with(buf, b"!DOCTYPE") => {
                 let start = buf[8..]

src/reader/slice_reader.rs

@@ -289,7 +289,7 @@ impl<'a> XmlSource<'a, ()> for &'a [u8] {
 
         let bang_type = BangType::new(self[1..].first().copied())?;
 
-        if let Some((bytes, i)) = bang_type.parse(self, 0) {
+        if let Some((bytes, i)) = bang_type.parse(&[], self) {
             *position += i;
             *self = &self[i..];
             return Ok(Some((bang_type, bytes)));