53 lines
2.1 KiB
Markdown
53 lines
2.1 KiB
Markdown
The problem: WHEREIS must come after PREPARE, and external remotes are
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encouraged to establish network connections in PREPARE to simplify their
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implementations. So `git annex whereis` with such an external remote
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enabled and content on that remote is slowed down by an unnecessary network
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connection.
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Note that this even happens when the external remote does not implement
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support for WHEREIS.
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So, we want to deprecate WHEREIS needing to come after PREPARE.
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GETINFO has the same problem. (GETCOST and GETAVAILABILITY also, but
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those are cached to avoid needing to be run more than once per remote.)
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The transition:
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* Add an extension to the protocol that lets WHEREIS come before/without
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PREPARE. The external remote can indicate it supports this by negotiating
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EXTENSIONS WHEREIS.
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And similarly for GETINFO, with EXTENSIONS GETINFO.
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* For a while, git-annex can continue to send WHEREIS after PREPARE when
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the external remote doesn't support the protocol extension. If the
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external remote replies with WHEREIS-SUCCESS, then git-annex can warn
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that it needs to be updated for the transition. (If it replies with
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WHEREIS-FAILURE, it may be that it only has stub whereis support that
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doesn't do anything, so probably git-annex should avoid warning in that
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case).
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And similarly for GETINFO, warning when it is sent after PREPARE and
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there are any INFOFIELD replies, but not warning if there's only an
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INFOEND.
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* Eventually, git-annex can stop sending WHEREIS unless the protocol
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extension was negotiated. So WHEREIS stops being part of the
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base protocol and becomes an extension.
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Ditto for GETINFO.
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Possible complications:
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An external remote may need to do some kind of expensive setup to prepare
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to reply to WHEREIS, such as querying with GETCONFIG or looking at its own
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internal state or whatever. With WHEREIS run before PREPARE, such a remote
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will need to defer that setup until the first WHEREIS and cache it for
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subsequent WHEREIS, which may complicate its code slightly.
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Note that the protocol does allow querying with GETCONFIG etc before
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responding to a WHEREIS request.
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[[!tag confirmed]]
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[[!tag projects/datalad/potential]]
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