Handle local archives without requiring network tooling

[lexmag]

No description provided.

[josevalim]

Given we don't support reading from any other host either, I would remove this version.

[josevalim]

I don't think we should support this version. I can't see it on the spec.

[josevalim]

Ah, it seems to be used by KDE. I am 👎.

[lexmag]

RFC 3986 mentions that:

the "file" URI scheme is defined so that no authority, an empty host, and "localhost" all mean the end-user's machine

[josevalim]

This doesn't support "file:///c:/foo/bar" on Windows.

[lexmag]

Unable to test on Windows; we have to rewrite that to use backslashes, right?

[josevalim]

No, that's not necessary, but you don't need to add a prefixing "/". Using a separate env var will be simpler.

[lexmag]

don't need to add a prefixing "/"

Indeed. 🙈

[josevalim]

I am not a big fan of this approach. The current implementation is too complex by trying to support three different formats and it does not work on Windows. Perhaps it would make more sense to introduce another environment variable, instead of overloading this one?

[jonatanklosko]

@josevalim I just thought the same, we can have XLA_ARCHIVE_PATH. And we don't have to copy it to the cache dir, since the file is already accessible locally!

[lexmag]

I'm personally also not that positive about supporting file: all the way.
That's said, I think if we decide to go just with a single format (for example, empty host), it is justifiable and does not seem worse than adding an extra environment variable (which, in turn, brings a question of priority).

[jonatanklosko]

@lexmag there's still the advantage of not creating a copy of the file at all. And having an env var for path makes it much more intuitive/discoverable. I don't think prioritisation is an issue, we can check the path before url, similarly to how we respect XLA_BUILD=true first. So the path env var check would go between these:

xla/lib/xla.ex

Lines 22 to 29 in 137ca69

	build?() ->
	# The archive should have already been built by this point
	archive_path_for_build()
	url = xla_archive_url() ->
	path = archive_path_for_external_download(url)
	unless File.exists?(path), do: download_external!(url, path)
	path

[jonatanklosko]

We now use httpc for requests and I've just added support for XLA_ARCHIVE_PATH in #99 :)