rustup: Add option to skip download

[mkpankov]

When combined with '--save' and '--date', it uses previously saved
tarball, making possible to re-install in offline mode.
r?

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @pcwalton (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. The way Github handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see CONTRIBUTING.md for more information.

[flaper87]

could you change this to:

if [ -z "${CFG_SKIP_DOWNLOAD}" ]

[mkpankov]

Will do

[flaper87]

@mkpankov thanks a lot for your patch. is rustup actually re-downloading things even when the tarball is present?

The download_package function already checks if the tarball exists before downloading it. https://github.com/mkpankov/rust/blob/master/src/etc/rustup.sh#L506

[mkpankov]

@flaper87 the actual problem is verify_hash.
Call: https://github.com/mkpankov/rust/blob/master/src/etc/rustup.sh#L519
Definition: https://github.com/mkpankov/rust/blob/master/src/etc/rustup.sh#L457
Here it unconditionally downloads the remote SHA256, making it impossible to run the installation w/o Internet.

Should I check if rust-nightly-x86_64-unknown-linux-gnu.tar.gz.sha256 is present and treat it as a remote SHA256? Then I'd save a local one to something like rust-nightly-x86_64-unknown-linux-gnu.tar.gz.sha256.local and compare that.

[mkpankov]

Should be fine now.

I now check if --save is specified and previously saved SHA is available. I then use it if possible for verification of whatever archive there happens to be.

I tested it in offline mode, specifying both --save and --date or just --date. Installer attempts to download stuff when it should.

[flaper87]

Since download_hash already checks on "${CFG_SAVE}" I believe this could become:

if [ -f "${local_sha_file}" ]; then
    ....
else
    download_hash
fi

[mkpankov]

Not sure, currently download_hash can be called when ${CFG_SAVE} is both specified or not specified.
In case of specified, if file exists, we use that. If file doesn't exist, we download it to compare with, and save for future use.
In case ${CFG_SAVE} is specified, we download the file anyway and don't save it since it's not requested.
Simplifying to suggested variant would mean we check existence of saved file when ${CFG_SAVE} wasn't specified at all. I believe we shouldn't look at local files when saving wasn't requested.

[flaper87]

@mkpankov thanks for updating the patch. Would you mind squashing these commits into 1?

[mkpankov]

@flaper87 I squashed everything, fixing stuff you pointed out but leaving the two calls to download_hash. I explained it in line comment above :)

[brson]

@bors: r+ 785176b

[flaper87]

@mkpankov awesome, thanks for contributing!

[alexcrichton]

@bors: rollup