Don't start ssh-agent if it's already running

[ojab]

This allows to run the action multiple times to add multiple keys
without removing already added ones.

Test run: https://github.com/ojab/ssh-agent/runs/5110810177, both keys are added.

[ojab]

@mpdude not sure if it's desired, but it would be welcome addition for composite actions. Also not sure about codestyle, line with ssh-add -l check is a bit long.

[mpdude]

You mean that this way, a sub-action (from composite actions) could start or add keys to the running agent without knowing whether the main action started the agent or not?

[ojab]

Yep! And it wouldn't remove keys that are already added, if ssh-agent is already started before the subaction.
So basically we don't care now if ssh-agent it running or not, we just adding the key and starting ssh-agent if needed instead of replacing current keys with new ones.

[ojab]

Run ./
  with:
    ssh-private-key: 
  
  
Error: The ssh-private-key argument is empty. Maybe the secret has not been configured, or you are using a wrong secret name in your workflow file.

in CI, looks unrelated

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[mpdude]

Sorry it took me so long to get back to this.

Two thoughts:

• Do we really need to run ssh -l to check? Or would it suffice to assume that when SSH_AUTH_SOCK is set, an agent has already been started and can be used?
• Do you see legitimate use cases where people intentionally start new agent instances, e. g. for a particular git clone operation, and might kill those agents later on? We might break these workflows.

[ojab]

Ugh, missed you comment and was reminded about this PR by dependabot notification about the new action version, sorry.

1. We want to ssh -l because socket could be provided in core.getInput('ssh-auth-sock') and IMHO separate flow for default case (i. e. ssh-auth-sock is not set) would complicate things.
2. It is a breaking change, but I doubt that it would lead to much breakage, I could imaging three situations:
   1. remote is accepting both ssh-keys and behaves differently depending on the key, e. g. we're using multiple github accounts to fetch multple repos and they have access to single repo each
   2. we could be adding too many keys and get https://superuser.com/questions/268776/how-do-i-configure-ssh-so-it-doesnt-try-all-the-identity-files-automatically
   3. we would send keys that wasn't sent before and in theory rogue ssh server could deanonimize our user, see https://github.com/FiloSottile/whoami.filippo.io

Maybe I'm missing something, but IMHO all of these concerns are theoretical and not practical and could be fixed by setting explicit distinct ssh-auth-sock.

[mpdude]

What about the two env variables SSH_AUTH_SOCK and SSH_AGENT_PID... these would not be set/changed when an agent is already running.

If we say that a correctly started agent requires those to be set, we could also avoid starting the agent in case both are present.

On the other hand, what if SSH_AUTH_SOCK is already present but different from what is configured in this action?

Regarding the shutdown phase: Would it be correct to terminate the agent even if we did not start it? How could we tell if that was the case?

[ojab]

const authSock = core.getInput('ssh-auth-sock');
spawnSync(sshAdd, ['-l'], { env: {  SSH_AUTH_SOCK: authSock || process.env.SSH_AUTH_SOCK } })

const sshAgentArgs = (authSock && authSock.length > 0) ? ['-a', authSock] : [];
child_process.execFileSync(sshAgent, sshAgentArgs)

so

1. if ssh-auth-sock is provided — we're either starting or reusing this agent
2. If ssh-auth-sock is not provided
   1. If env.SSH_AUTH_SOCK is set — we're either starting or reusing this agent
   2. If env.SSH_AUTH_SOCK is not set — we're starting the agent which chooses random socket

And after we're always setting SSH_AUTH_SOCK and SSH_AGENT_PID to the values provided by the agent that was just started or reused.

Regarding the shutdown phase: Would it be correct to terminate the agent even if we did not start it? How could we tell if that was the case?

AFAICS there is no shutdown phase, so all the agents keep running until GHA job is finished?

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