DAP4: DAP4 Using Multi-part Mime

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Background

As a result of a comment in the OPULS/NOAA telecon, I think we should reconsider using multi-part mime in a limited fashion in our serialization. Basically I propose to resurrect James' original proposal (see DAP 4.0 Design).

Proposal

As with the original proposal, the multipart-mime has two parts. The first is for the DMR and the second is for the whole, chunked serialized data. The general form would look something like this.

Content-Type: multipart/related; \
              type="application/vnd.org.opendap.dap4.dataset-metadata+xml"; \
              start="<<start id>>"; boundary="<<boundary>>"
--<<boundary>>
Content-Type: text/xml; charset=UTF-8
Content-Id: <<start id>>
Content-Length: ddddd
<<blank line>>
<<DMR text>>
--<<boundary>>
Content-Type: application/octet-stream
Content-Encoding: big-endian
Content-Length: -1
<<blank-line>   
<<chunked representation of the serialized data>>
--<<boundary>>

Notes:

1. Every header line should be terminated with CRLF. The <<blankline>> is also terminated with CRLF.
2. The above representation assumes that the DMR is not in chunked format.
3. The Content-Length value for the DMR counts the number of UTF-8 characters from the end of the blank line to the initial "--" of the boundary line.
4. The chunked representation is still in our existing chunked format.
5. I do not know if the start-id is required by the multipart-mime format. If not, then we should remove it.
6. I am not sure about the "type" param of the "Content-Type" line at the beginning.

Dennis Heimbigner Initial draft 3/19/2013