http2: improve continuation frame reassembly

by taking into account the flags of the first header frame,
and skip priority and padlength if necessary

Ticket: 8840

rust/src/http2/http2.rs

@@ -1295,14 +1295,20 @@ impl HTTP2State {
                         &mut self.c2s_buf
                     };
                     buf.data.clear();
-                    buf.data.extend(input);
-                    buf.stream_id = head.stream_id;
-                    let hs = parser::HTTP2FrameHeaders {
-                        padlength: None,
-                        priority: None,
-                        blocks: Vec::new(),
-                    };
-                    return (HTTP2FrameTypeData::HEADERS(hs), events);
+                    if let Ok((rem_hpack, hs)) = parser::get_frame_headers_hpack(input, hflags) {
+                        // store only the HPACK fragment: skip Pad Length, Priority, and trailing padding
+                        buf.data.extend(rem_hpack);
+                        buf.stream_id = head.stream_id;
+                        return (HTTP2FrameTypeData::HEADERS(hs), events);
+                    } else {
+                        events.push(HTTP2Event::InvalidFrameData);
+                        return (
+                            HTTP2FrameTypeData::UNHANDLED(HTTP2FrameUnhandled {
+                                reason: HTTP2FrameUnhandledReason::ParsingError,
+                            }),
+                            events,
+                        );
+                    }
                 }
                 let dyn_headers = if dir == Direction::ToClient {
                     &mut self.dynamic_headers_tc

rust/src/http2/parser.rs

@@ -591,6 +591,24 @@ fn http2_parse_headers_blocks<'a>(
     return Ok((i3, blocks));
 }
 
+pub(super) fn get_frame_headers_hpack(
+    input: &[u8], flags: u8,
+) -> IResult<&[u8], HTTP2FrameHeaders> {
+    let (i2, padlength) = cond(flags & HTTP2_FLAG_HEADER_PADDED != 0, be_u8)(input)?;
+    let (i3, priority) = cond(
+        flags & HTTP2_FLAG_HEADER_PRIORITY != 0,
+        http2_parse_headers_priority,
+    )(i2)?;
+    return Ok((
+        i3,
+        HTTP2FrameHeaders {
+            padlength,
+            priority,
+            blocks: Vec::new(),
+        },
+    ));
+}
+
 pub fn http2_parse_frame_headers<'a>(
     input: &'a [u8], flags: u8, dyn_headers: &mut HTTP2DynTable,
 ) -> IResult<&'a [u8], HTTP2FrameHeaders> {