Check for temp directory write permission before downloading binary

[yankeexe]

Check if the user has permission to write to $TMPDIR before downloading binary. Else the following issue occurs:

$~ arkade get inletsctl
Downloading inletsctl
https://github.com/inlets/inletsctl/releases/download/0.8.2/inletsctl.tgz
Error: check with the vendor whether this tool is available for your system: open /tmp/inletsctl.tgz: permission denied 

Expected Behaviour

If the user running arkade does not have permission to write to $TMPDIR, show error messaging stating such.

Current Behaviour

Shows Binary Download prompt and fails on accessing $TMPDIR to store binary.

Are you a GitHub Sponsor (Yes/No?)

Check at https://github.com/sponsors/alexellis

• Yes
• No

Possible Solution

Check for writable permission to $TMPDIR before downloading the binary

tmp := os.TMPDIR()

info, err := os.Stat(tmp)
if err != nil {
panic(err)
}
     
permission := info.Mode().Perm()

Steps to Reproduce (for bugs)

1. Create any random directory: mkdir test-temp
2. Change directory mod to 100: chmod 100 test-temp
3. Make it the default temp directory: export TMPDIR=<absolute-path-to-'test-temp'-directory>
4. Run arkade get <any-binary>

Your Environment

• Operating System and version (e.g. Linux, Windows, MacOS):

Linux  5.10.56-1  x86_64 GNU/Linux

• What arkade version is this?

0.7.25

[yankeexe]

/add label: proposal

[yankeexe]

@alexellis Can you please take a look at this? 🙂

[alexellis]

Sounds good to me, do you want to try it out in a PR?

[yankeexe]

@alexellis I will create a draft PR

[alexellis]

Thanks @yankeexe, no need to make it a draft however.

[mrichar1]

I can open this as a new bug if needed, but seeing as it's closely related to this issue...

arkade should use a temporary 'tempdir' when downloading, rather than writing to the root $TMPDIR. Otherwise there may be issues if there are equivalent files already present - either being unable to write that file, or accidentally overwriting an existing file.

E.g (when running arkade as non-root user):

sudo touch /tmp/kubectl
arkade get kubectl
Error: open /tmp/kubectl: permission denied

Or in reverse:

$ echo "Some text" >/tmp/kubectl
$ file /tmp/kubectl
/tmp/kubectl: ASCII text

$ sudo arkade get kubectl
$ file /tmp/kubectl
/tmp/kubectl: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), statically linked, stripped

[alexellis]

Hi @mrichar1

I've seen this a few times when I've put my own files into /tmp that conflict on name.

A unique tempdir name would get around that, I don't have a problem with you sending a PR.

What brought you here? Did you run into this issue yourself?

Alex

[mrichar1]

Yes - I hit this when switching from running as root to running non-root, and was looking through existing issues to see if it had already been reported. Happy to have a go at drafting a separate PR for this.

[alexellis]

Thanks a PR would be great @mrichar1