Constant MAX_HEADER_BUF_SIZE 

const MAX_HEADER_BUF_SIZE: usize = _; // 65_536usize

The most a connection buffers of the head of its request, the request line and the headers, see MAX_CONNECTIONS. A longer one gets a 431 response. hyper takes about 400 KiB otherwise, which lets local processes make the server hold about 100 MiB without a token. The kubelet sends the headers of the client and its own, a few KiB, Go servers take up to 1 MiB by default, nginx 32 KiB.