Re: [Ace] ace-coap-est-08: using /skg with Accept Option set to TBD287

"Panos Kampanakis (pkampana)" <> Tue, 12 February 2019 21:11 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id 30A2C12DF71 for <>; Tue, 12 Feb 2019 13:11:18 -0800 (PST)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -14.502
X-Spam-Status: No, score=-14.502 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, RCVD_IN_DNSWL_HI=-5, SPF_PASS=-0.001, USER_IN_DEF_DKIM_WL=-7.5] autolearn=ham autolearn_force=no
Authentication-Results: (amavisd-new); dkim=pass (1024-bit key)
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id pCXToxwkDplc for <>; Tue, 12 Feb 2019 13:11:16 -0800 (PST)
Received: from ( []) (using TLSv1.2 with cipher DHE-RSA-SEED-SHA (128/128 bits)) (No client certificate requested) by (Postfix) with ESMTPS id 0E139128B36 for <>; Tue, 12 Feb 2019 13:11:15 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple;;; l=2704; q=dns/txt; s=iport; t=1550005876; x=1551215476; h=from:to:cc:subject:date:message-id:references: in-reply-to:content-transfer-encoding:mime-version; bh=VCPRr36yavjKbmn2bk6drGYax4OWBmWCvyMjBvFBq3A=; b=WuQmEA0NsDQhgeQ3x8ADrOBVsRCcFSrY+sSIgY9uVCxc80VWNmkD+PuM pfxiPZdOktgvLM2eiK/aD5MzqvUmGldr/Dmoy4IMg1tl5zPgSAKZDTQWy 6pCsv+nIBRtzD7dzhLr8hGxrv/+/JVljVR+Csjw4Yt0BzhTbMt16oltb0 g=;
X-IronPort-Anti-Spam-Filtered: true
X-IronPort-AV: E=Sophos;i="5.58,362,1544486400"; d="scan'208";a="237502434"
Received: from ([]) by with ESMTP; 12 Feb 2019 21:11:13 +0000
Received: from ( []) by (8.15.2/8.15.2) with ESMTPS id x1CL4f64003053 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=FAIL); Tue, 12 Feb 2019 21:04:41 GMT
Received: from ( by ( with Microsoft SMTP Server (TLS) id 15.0.1395.4; Tue, 12 Feb 2019 15:02:50 -0600
Received: from ([]) by ([]) with mapi id 15.00.1395.000; Tue, 12 Feb 2019 15:02:50 -0600
From: "Panos Kampanakis (pkampana)" <>
To: Klaus Hartke <>, Esko Dijk <>
CC: "" <>
Thread-Topic: [Ace] ace-coap-est-08: using /skg with Accept Option set to TBD287
Thread-Index: AdTC4NsGsEh+3phhQKaxfGxN5m15WwAN7hcAAAELuzA=
Date: Tue, 12 Feb 2019 21:02:49 +0000
Message-ID: <>
References: <DB6P190MB0054313C1BA6E125FA07813BFD650@DB6P190MB0054.EURP190.PROD.OUTLOOK.COM> <>
In-Reply-To: <>
Accept-Language: en-US
Content-Language: en-US
x-ms-exchange-transport-fromentityheader: Hosted
x-originating-ip: []
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
Archived-At: <>
Subject: Re: [Ace] ace-coap-est-08: using /skg with Accept Option set to TBD287
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: "Authentication and Authorization for Constrained Environments \(ace\)" <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Tue, 12 Feb 2019 21:11:18 -0000

Thanks Klaus and Esko. 

>    If the preferred Content-Format cannot be returned, then a 4.06 "Not Acceptable" MUST be sent as a response, unless another error code takes precedence for this response.

Well, RFC7252 refers to a singular content format. In our case we are talking about a dual content format (286 or 281 and 280 or 284) returned in a 62 multipart-content. Would it be a violation of RFC7252, since RFC7252's text had single content format responses in mind only? 

>  Maybe the draft-ietf-core-multipart-ct should extend the semantics of "Accept" to cover this case?

I think that is good idea. The simplest way to do that would be encode the 3 content formats (for example 62, 286 and 280) into a single CF included in the Accept option which tells the server what combination of content formats to send back. Would that violate RFC7252 because the Content-Formats needs to be actual CFs defined in the IANA registry and not a combination of them?


>From a previous thread with Jim S., I was under the impression that In the virtual CoAP WG meeting a month back we went through in some explicit detail that both Content-Format and Max-Age have no meaning when appearing on a request and therefore should not be there.

-----Original Message-----
From: Ace <> On Behalf Of Klaus Hartke
Sent: Tuesday, February 12, 2019 10:19 AM
To: Esko Dijk <>
Subject: Re: [Ace] ace-coap-est-08: using /skg with Accept Option set to TBD287

Esko Dijk wrote:
> So the client asks for 286, but gets 62 (which has 286 embedded in it 
> as one of the parts). At first sight this appears incompatible with 
> CoAP RFC7252 logic.
> A strict server implementation might return 4.06 Not Acceptable since 
> the server code has registered the response type to be 62; and the 
> client asks something different.

 RFC 7252 is quite strict about this:

   If the preferred Content-
   Format cannot be returned, then a 4.06 "Not Acceptable" MUST be sent
   as a response, unless another error code takes precedence for this

That's a MUST, not a SHOULD.

Since a client might actually support multiple formats, it might make sense to indicate all supported formats in order of preference e.g. as query parameters:

  POST /.well-known/est/skg?ct=TBD287&ct=281
    Accept: 62

  Content-Format: 62
  Payload: (multipart containing TBD287)


Ace mailing list