http://http2.github.io/http2-spec/#FrameHeader section on Flags being unset

William Chan (陈智昌) <willchan@google.com> Wed, 08 May 2013 18:29 UTC

Return-Path: <ietf-http-wg-request@listhub.w3.org>
X-Original-To: ietfarch-httpbisa-archive-bis2Juki@ietfa.amsl.com
Delivered-To: ietfarch-httpbisa-archive-bis2Juki@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 43CC021F854D for <ietfarch-httpbisa-archive-bis2Juki@ietfa.amsl.com>; Wed, 8 May 2013 11:29:10 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -9.676
X-Spam-Level:
X-Spam-Status: No, score=-9.676 tagged_above=-999 required=5 tests=[BAYES_00=-2.599, FM_FORGED_GMAIL=0.622, HTML_MESSAGE=0.001, MIME_8BIT_HEADER=0.3, RCVD_IN_DNSWL_HI=-8]
Received: from mail.ietf.org ([12.22.58.30]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 1DlLtwVoZ1NX for <ietfarch-httpbisa-archive-bis2Juki@ietfa.amsl.com>; Wed, 8 May 2013 11:29:05 -0700 (PDT)
Received: from frink.w3.org (frink.w3.org [128.30.52.56]) by ietfa.amsl.com (Postfix) with ESMTP id C3C4D21F8B54 for <httpbisa-archive-bis2Juki@lists.ietf.org>; Wed, 8 May 2013 11:29:04 -0700 (PDT)
Received: from lists by frink.w3.org with local (Exim 4.72) (envelope-from <ietf-http-wg-request@listhub.w3.org>) id 1Ua95K-0003en-98 for ietf-http-wg-dist@listhub.w3.org; Wed, 08 May 2013 18:27:26 +0000
Resent-Date: Wed, 08 May 2013 18:27:26 +0000
Resent-Message-Id: <E1Ua95K-0003en-98@frink.w3.org>
Received: from maggie.w3.org ([128.30.52.39]) by frink.w3.org with esmtp (Exim 4.72) (envelope-from <willchan@google.com>) id 1Ua959-0003e3-0V for ietf-http-wg@listhub.w3.org; Wed, 08 May 2013 18:27:15 +0000
Received: from mail-qc0-f180.google.com ([209.85.216.180]) by maggie.w3.org with esmtps (TLS1.0:RSA_ARCFOUR_SHA1:16) (Exim 4.72) (envelope-from <willchan@google.com>) id 1Ua957-0007FO-CG for ietf-http-wg@w3.org; Wed, 08 May 2013 18:27:14 +0000
Received: by mail-qc0-f180.google.com with SMTP id a10so1186310qcx.25 for <ietf-http-wg@w3.org>; Wed, 08 May 2013 11:26:47 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20120113; h=mime-version:x-received:reply-to:date:message-id:subject:from:to :content-type; bh=8MdUeKKQQ63sKLVQKf7gL/tzjL1UTjQpwxl0Q2JBd6k=; b=QyeX9JIINv5t9tGHFUvcEvd2S9feHUamtIv5zf8p7rnxVgjoOJIyiFso6aUtTfZvwD rPHyA0hkZX5tZEGWhfbGyZeKUt+X40iUfuAcLJrT5imAqQp2P7RyTsnKL/my0EJ+mWCC ciIAGLSL6M9sIBmjmAUHPxcD6kW5AAGXNtDjrbcm2ifOx6EwavVYT89E/PkkU3R99687 O0nI6GPSDtlZFV+Nulc7kMnjmt3HBkyPDpwfPsx4NOo21TerVWFHddc9d8uOH1Gik7t4 Ag8feLQJAimMNcjw5hxWjY6Qs8TEUjT7SYzV2aqmkUkUN7+neBnQoT6lM3dA9zYw2YPg qTWw==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20120113; h=mime-version:x-received:reply-to:date:message-id:subject:from:to :content-type:x-gm-message-state; bh=8MdUeKKQQ63sKLVQKf7gL/tzjL1UTjQpwxl0Q2JBd6k=; b=ABWJmKEljg2gRo0XDXjaYlL/Vut9Zv7rN+3r90BX8AFDCYaUR1qznOUu1zeZb/epml ZFe5UcrP5wUshLZIskZX1ZU7lDwOOPC3Uh3Gh5QqYEJ501kuXJ7M6Z+wIfGPt/AsiIQF iS+M3bAstZzS11wsUJIob88MPqG8efUDpeFdbq9B8m2ihYmb4LwdNptHMSCZ27f8FEmw oKCpnLl05CWNGeQs3p9Wa1/ch8H6LGJ1TjAcBb47EVqz8XGjm/7GQ9y596LjqvzzNUJD NxI+heurtqq6m6jBCIHAoRwhDe/dEJnw4ji/0SQ6NRz9AlWvgTK/SxwNmuqS0+8QmkcU vO3Q==
MIME-Version: 1.0
X-Received: by 10.49.82.45 with SMTP id f13mr6611105qey.53.1368037607562; Wed, 08 May 2013 11:26:47 -0700 (PDT)
Received: by 10.229.180.4 with HTTP; Wed, 8 May 2013 11:26:47 -0700 (PDT)
Reply-To: willchan@google.com
Date: Wed, 8 May 2013 15:26:47 -0300
Message-ID: <CAA4WUYgewyw-N2vjTinaQkarL0brveCam2XKKBSrMzz4HMiT8A@mail.gmail.com>
From: =?UTF-8?B?V2lsbGlhbSBDaGFuICjpmYjmmbrmmIwp?= <willchan@google.com>
To: HTTP Working Group <ietf-http-wg@w3.org>
Content-Type: multipart/alternative; boundary=047d7b5dbf32a4425304dc39134a
X-Gm-Message-State: ALoCoQm7ujUI/PMHEjbtRNPn8DYz5Q6nZYc1IoWt43O0+4UTMoJ/odEr8qSxXg+CGvpOlh0qnbNl/6FmOvAXtLk8MXfrGvnXRA8TaGulVyN/AvaZVF+NtXXwD7S9zeCkIGexoaXSquIppRTvBock+vj6adMy3icaY0gKGS1LOR/FeTgWEgta4pLeix/vr8sMpb88ysFvesff
Received-SPF: pass client-ip=209.85.216.180; envelope-from=willchan@google.com; helo=mail-qc0-f180.google.com
X-W3C-Hub-Spam-Status: No, score=-2.2
X-W3C-Hub-Spam-Report: DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_LOW=-0.7, RP_MATCHES_RCVD=-1.353, SPF_PASS=-0.001
X-W3C-Scan-Sig: maggie.w3.org 1Ua957-0007FO-CG 5f77fbabe7bdb2638aa24024a49ad3c1
X-Original-To: ietf-http-wg@w3.org
Subject: http://http2.github.io/http2-spec/#FrameHeader section on Flags being unset
Archived-At: <http://www.w3.org/mid/CAA4WUYgewyw-N2vjTinaQkarL0brveCam2XKKBSrMzz4HMiT8A@mail.gmail.com>
Resent-From: ietf-http-wg@w3.org
X-Mailing-List: <ietf-http-wg@w3.org> archive/latest/17893
X-Loop: ietf-http-wg@w3.org
Resent-Sender: ietf-http-wg-request@w3.org
Precedence: list
List-Id: <ietf-http-wg.w3.org>
List-Help: <http://www.w3.org/Mail/>
List-Post: <mailto:ietf-http-wg@w3.org>
List-Unsubscribe: <mailto:ietf-http-wg-request@w3.org?subject=unsubscribe>

"""
The remaining flags can be assigned semantics specific to the indicated
frame type. Flags that have no defined semantics for a particular frame
type MUST be ignored, and MUST be left unset (0) when sending.
"""

Is there a reason that it MUST be left unset? Why not allow extensibility
like we do for unknown frames? I actually don't think there's much value to
specifying behavior for unused bits.