Re: [core] draft-ietf-core-block-08 - size request

[Likepeng <[e-mail]>]

Hi,



>How does the server need to behave upon the reception of a size request?
>-(1) does it send back an empty response with a size option that gives the size estimate of the response? In this case, what is the response when the server does not support this option?
>or
>-(2) does it send back a response with a size option giving the size estimate of the response, but with a payload already containing the first block?



We can differentiate these two cases by giving the Size a zero value or not. Here is the text from Block draft:



   o  in a request, to ask the server to provide a size estimate in the
      response ("size request").  For this usage, the value MUST be set
      to 0.

So, if Size=0, that means case 1. If Size option is empty, that means case 2.



>It would be good to add the desired behavior to the description of the size request to avoid confusion.

Agree, we should add some texts to clarify the situation. I propose to take some texts (or change it a little bit) from the Size draft to Block draft.



Here is the text from draft-li-core-coap-size-option-02.txt:



   The GET request including Size=0 is treated as a request to get the
   size of the resource representation (but not the resource payload).

   The GET request including an empty Size option is treated as a
   request to get the size of the resource representation with the
   resource payload.

   The Size option SHOULD be included for resources larger than a single
   PDU, if the Size information is available.  And it MAY be included
   for resources smaller than a single MTU.



   The Size option SHOULD be used in a POST/PUT request in the first
   Block1 Option message.  If the recipient is not capable to receive the
   data with the indicated size, the recipient MUST return a 4.13
   (Request Entity Too Large) response code to the requester, and the
   data transmission is avoided, so that the cost of the actual data
   transmission is saved.

   For a GET request with Block2, if it includes an empty Size option, the Size
   option MUST be included in the response.  If the GET request includes
   a Block2 option, the Size option SHOULD be included in the first Block2
   response.  In other cases the GET response MAY contain a Size option.

Kind Regards

Kepeng



________________________________
发件人: [e-mail] [[e-mail]] 代表 Jeroen Hoebeke [[e-mail]]
发送时间: 2012年3月29日 4:13
到: core WG
主题: [core] draft-ietf-core-block-08 - size request

Dear WG,

After giving the block draft a final reading, I discovered one minor issue that is not clear to me:

How does the server need to behave upon the reception of a size request?
- does it send back an empty response with a size option that gives the size estimate of the response? In this case, what is the response when the server does not support this option?
or
- does it send back a response with a size option giving the size estimate of the response, but with a payload already containing the first block?

It would be good to add the desired behavior to the description of the size request to avoid confusion.

Kind regards,
Jeroen