Request → Request-Headers *Length-Prefixed-Message EOS Request-Headers are delivered as HTTP2 headers in HEADERS + CONTINUATION frames. Request-Headers → Call-Definition *Custom-Metadata Call-Definition → Method Scheme Path TE [Authority] [Timeout] Content-Type [Message-Type] [Message-Encoding] [Message-Accept-Encoding] [User-Agent] Method → ":method POST" Scheme → ":scheme " ("http" / "https") Pa