Re-use source file / tarball, etc.

[PeterDaveHello]

Can we just download the checksums to verify (if there is) the existing tarball / source file before re-downloading instead of force re-download the files?

The size of nodejs v6.3.1 src tarball is 25MB, the 64-bit binary is 8.7MB, we could save the bandwidth and time.

[ljharb]

The problem there is that not every system nvm supports is able to compute SHA256 checksums - so we'd only be able to do that when the ability to compute checksums exists.

I'd definitely take a PR that added this, though - that would allow travis-ci builds to cache $NVM_DIR and greatly speed up test runs.

[PeterDaveHello]

@ljharb in the meantime, maybe SHA1 first? Or those platforms also don't support SHA1? Since there is https, for the weaker hash, the checksum we can just use to make sure the process or downloading is good, not for the integrity, what do you think?

[ljharb]

SHA1 is no longer used by node as of v4, as you can see here.

In other words, we can definitely make it work with node 0.12 and older, and possibly some iojs versions, with SHA-1, and that would be a great start.

[PeterDaveHello]

@ljharb I'm not sure if it's a bad idea that bad enough to ignore it, what about we maintain a sha1 list by ourselves? If you won't hate it, we can try to do it automatically.

[ljharb]

I definitely don't want to maintain my own list of anything; we already have enough runtime internet dependencies as it is, and the SHAs of old versions might change and would need to be kept up to date.

I'm already working on this; I'm just trying to get some tests passing.

[PeterDaveHello]

Nice, any PR / branch that I can look into? Thanks.

[ljharb]

Nothing quite yet. I'll update here when it's ready.

[tiramgear]

GOOD