Draft proposal for Prefer header to suggest how a server should store and provide access to

prefer-header-resolution.txt

   o  Preference: content-resolution

   o  Value: copy, proxy, redirect

   o  Optional Parameters: "content-type", it allows a client to indicate a preferred mimetype for the server to
         provide in responses for this resource.  To be used when the client is unable to provide type information for
         the message content in the "Content-Type" header.  Values defined as in 
         https://tools.ietf.org/html/rfc7231#section-3.1.1.5

   o  Description:  Indicates the client's preference for how the server will store and provide access to the content
         of a message for a PUT or POST request.  When the value is "copy", it indicates that the client prefers that
         the server store a copy of the content and serve requests for that resource using the copy.  When the value is
         "proxy", it indicates that the client prefers that requests for the content of the resource be proxied by the
         server from the original location.  When the value is "redirect", it indicates that the client prefers that
         requests for the content of the resource result in a 307 redirect response, directing the client to
         the original location of the content.

   o  Reference: https://gist.github.com/bbpennel/e10355fa93993849868a60559edac6a0

   o  Notes: This preference was designed to supplement the functionality of the "Content-Type: message/external-body; 
         access-type=url, url=<url>" header, but could potentially apply to the Content-Location header and other
         situations.  It allows a client to specify a preference for how a server would provide access to content
         submitted to the server, in this case from an external body at a URL.
             
Proxy Example:
  Request:
    PUT /rest/object
    Content-Type: message/external-body; access-type=URL, URL="http://example.com/image.png"
    Prefer: message-resolution="proxy"

  Response:
    Status: 204
    Content-Location: /rest/object
    Preference-Applied: message-resolution="proxy"

  Request:
    GET /rest/object

  Response:
    Status: 200
    Content-Type: application/octet-stream
    Content-Location: http://example.com/image.png
    Body: 
    <binary content from image.png>

Copy Example:
  Request:
    PUT /rest/object2
    Content-Type: message/external-body; access-type=URL, URL="file:/path/to/image"
    Prefer: message-resolution="copy"; content-type="image/png"

  Response:
    Status: 204
    Content-Location: /rest/object2
    Preference-Applied: message-resolution="copy"; content-type="image/png"

  Request:
    GET /rest/object2

  Response:
    Status: 200
    Content-Type: image/png
    Content-Location: file:/path/to/image.png
    Body: 
    <binary content from image>

Redirect Example:
  Request:
    PUT /rest/object3
    Content-Type: message/external-body; access-type=URL, URL="http://example.com/image.png"
    Prefer: message-resolution="redirect"

  Response:
    Status: 204
    Content-Location: /rest/object3
    Preference-Applied: message-resolution="redirect"

  Request:
    GET /rest/object

  Response:
    Status: 307
    Location: http://example.com/image.png