pub const CLIENT_PREFACE: &[u8] = b"PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n";Expand description
The connection preface a client sends before anything else (RFC 7540
section 3.5). Exact bytes, including the deliberately odd PRI method — its
purpose is to make an HTTP/1.1 server fail immediately rather than
misinterpret what follows.