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Date: Mon, 30 Mar 2015 16:49:16 -0500
From: Brendan Long <self@brendanlong.com>
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To: Martin Thomson <martin.thomson@gmail.com>
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Subject: Re: "Timeout" request header to tell server to wait for resource to
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    On 03/30/2015 10:20 AM, Martin Thomson wrote:<br>
    <blockquote
cite="mid:CABkgnnV2AKxCXEmmjPhGwYTfRwQprO+zxCoqudmPG61TWtz-yg@mail.gmail.com"
      type="cite">If-None-Match in combination with Prefer: wait does
      exactly what you want here.
    </blockquote>
    <br>
    I've read RFC 7240 a few times now, and I'm not convinced that it's
    specific enough, but I guess it will work.<br>
    <blockquote type="cite">
      <pre class="newpage">   1.  Return a 202 (Accepted) response for asynchronous processing if
   the request cannot be processed within 10 seconds.  An undefined
   "priority" preference is also specified:

     POST /some-resource HTTP/1.1
     Host: example.org
     Content-Type: text/plain
     Prefer: respond-async, wait=10
     Prefer: priority=5</pre>
    </blockquote>
    <blockquote type="cite">
      <pre class="newpage"><span class="h3"><h3><a class="selflink" name="section-4.3" href="http://tools.ietf.org/html/rfc7240#section-4.3">4.3</a>.  The "wait" Preference</h3></span>

   The "wait" preference can be used to establish an upper bound on the
   length of time, in seconds, the client expects it will take the
   server to process the request once it has been received.  In the case
   that generating a response will take longer than the time specified,
   the server, or proxy, can choose to utilize an asynchronous
   processing model by returning -- for example -- a 202 (Accepted)
   response.</pre>
    </blockquote>
    <br>
    Waiting for a file to appear or change doesn't really fit "the
    request cannot be processed". It's just that we *don't want the
    request to be processed*.<br>
    <br>
    I'll make my server implement it with this header though, and I
    guess if it takes off it'll become de-facto correct behavior.<br>
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