Using file.managed for downloading a file in Salt

Question

salt.states.file.managed takes source_hash as an argument to verify a downloaded file. This blocks me from using file.managed for a file on an online server I don't have control over. The file also changes regularly. My configuration looks like this.

download_stuff:
  file.managed:
    - name: localfile.tar.gz
    - source: http://someserver.net/onlinefile.tar.gz
    - source_hash: ???

I don't want to use cmd.run with Curl or wget because this would always download the file, even when it's already on the local machine.

I would like the know if one of the options below is possible/exists:

• online md5 calculation service. Is there any way of getting an md5 hash of the file, using a free web service? I'm thinking of something like http://md5service.net?url={url-to-file}.
• salt-internal conversion or workaround. Is it possible to handle this in Salt? Maybe by leaving out source_hash somehow?
• alternative state. Is there another state in Salt for doing something like this, without losing the benefit of only downloading the file when needed?

Solution

If you can't control the other server, please make sure that you can trust it to download its content. Not using a hash will prevent you from detecting partial or corrupted downloads. There's also no way to work with a file that has changed on the remote server.

Nevertheless you could use a state like this to circumvent the hashcode. The creates part will prevent a second download once the file has been downloaded:

bootstrap:
  cmd.run:
    - name: curl -L https://bootstrap.saltstack.com -o /etc/salt/cloud.deploy.d/bootstrap-salt.sh
    - creates: /etc/salt/cloud.deploy.d/bootstrap-salt.sh

Comments

[cdMinix]

I don't want to use curl or wget, as stated in the question, because this would always download and install/extract the file, even when it hasn't changed.

[ahus1]

@cdMinix - this state will download the file exactly once. The creates prevents the second download. See docs.saltstack.com/en/latest/ref/states/all/… for details.