http2: avoid quadratic complexity in headers

When adding an element to the dynamic headers table, the oldest
ones may get evicted. When multiple elements get evicted, they
should get evicted all at once with drain, instead of one by one
as there will be a massive move each time.

Ticket: #6103

diff --git a/rust/src/http2/parser.rs b/rust/src/http2/parser.rs
index 88486f03b03933e6dcbf6e6c0a867644e8b1f89a..adabeb28c6e4592cf3de7d2190844bb209f209ad 100644 (file)
--- a/rust/src/http2/parser.rs
+++ b/rust/src/http2/parser.rs
@@ -456,13 +456,15 @@ fn http2_parse_headers_block_literal_incindex<'a>(
                 } else {
                     dyn_headers.table.push(headcopy);
                 }
+                let mut toremove = 0;
                 while dyn_headers.current_size > dyn_headers.max_size
-                    && !dyn_headers.table.is_empty()
+                    && toremove < dyn_headers.table.len()
                 {
                     dyn_headers.current_size -=
-                        32 + dyn_headers.table[0].name.len() + dyn_headers.table[0].value.len();
-                    dyn_headers.table.remove(0);
+                        32 + dyn_headers.table[toremove].name.len() + dyn_headers.table[toremove].value.len();
+                    toremove += 1;
                 }
+                dyn_headers.table.drain(0..toremove);
             }
             return Ok((r, head));
         }