Feature request: Point in Time as a virtual dependency #511

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1. mblumtritt commented on Aug 28, 2023

   

   mblumtritt

   on Aug 28, 2023

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   Just use #file_create:

   file_create 'dir/my_file.txt' => 'dir' do |f|
     File.write(f.name, 'It is soo easy!')
   end
2. hadmut commented on Aug 30, 2023

   

   hadmut

   on Aug 30, 2023

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   I haven't found any documentation about what file_create does in context of Rake, https://apidock.com/ruby/v2_2_9/Rake/DSL/file_create doesn't even know it. https://ruby.github.io/rake/ neither.

   However, the source code in lib/rake/file_creation_task.rb says that this is definitely not the solution to the problem, since it says

   # A FileCreationTask is a file task that when used as a dependency will be
   # needed if and only if the file has not been created.  Once created, it is
   # not re-triggered if any of its dependencies are newer, nor does trigger
   # any rebuilds of tasks that depend on it whenever it is updated.
   
   
   

   Which clearly says that this is not what's needed here, because this is about recreation of an existing file.

   Furthermore, I do not see how a point in time is involved in your example.

   Would it be possible by any means, that you simply did not understand at all what I proposed?
3. mblumtritt commented on Aug 30, 2023

   

   mblumtritt

   on Aug 30, 2023

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   The proposed syntax will not work because the DSL requires to have the prerequisites after the => :/

   But you can create a task which checks for the time:

   def (task(:outdated)).timestamp
     ts = File.mtime('test.txt')
     Time.now - 60 > ts ? Rake::LATE : ts
   end
   
   des 'creates test.txt when older than a minute'
   file 'test.txt' => :outdated do |f|
     File.write(f.name, 'FRESH!')
   end
4. fatkodima commented on Nov 9, 2023

   

   fatkodima

   on Nov 9, 2023

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   But quite often I have requirements to not have a file get too old, which is not exactly straightforward in Rake.

   Can you provide a real-world use case?
5. hadmut commented on Nov 9, 2023

   

   hadmut

   on Nov 9, 2023

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   There's plenty of.

   The use case, where I developed the wish to have this feature was creating virtual machines for kvm using the ubuntu cloud image ubuntu-22.04-server-cloudimg-amd64-disk-kvm.img

   from http://cloud-images.ubuntu.com/releases/jammy/release/
   (or other versions, 22.04 and jammy are variables).

   I defined all steps, i.e. download the cloud image, create the cloud-init-script, create the disk image, create keys, if missing, with a Rakefile, using file tasks and dependencies.

   Worked great except for a nasty detail:

   These cloud images are updated by ubuntu every few weeks to incorporate latest updates, security fixes etc.

   The problem is, that Rake can easily have a file task to download the cloud image if it does not exist, but it requires a completely different task structure if that cloud-image becomes too old. I need to have the Rakefile to download a fresh image from ubuntu in both cases: If the file does not yet exist locally, or if it is too old. It does not make sense to use a cloud image file older than e.g. 3 months and to update every single virtual machine built with this image.

   There's lots of other cases where things

   • must not get too old
   • must not get older than something which's age is not a file mod date

   e.g. updating package dependencies for Ruby Gems, go, or rust programs, where the dependency versions should be updated every now and then.

   Another good example is a docker/podman image. These things need to be rebuilt even if they do exist and all dependencies are fulfilled, just because these things cannot be updated, and need to be recreated every now and then.

   I do have applications and do create their docker images with geo data such as openstreetmap excerpts and country border files. These files are rather huge, so you don't want to download them with every run or build. But at the same time, you don't want them to become too old, because data like street maps are getting worse when not properly updated.

   So it would be really nice and useful to have something like

   cloudimage = "ubuntu-22.04-server-cloudimg-amd64-disk-kvm.img"

   file cloudimage => (Time.now - 86400*30) do
   sh "wget ..."
   end

   to download the file if it does not exist or becomes older than 30 days. Just use the given time instead of the mtime of a file dependency. Should not be too difficult.

   👍React with 👍1Reacted by fatkodima
6. hadmut commented on Jul 2, 2024

   

   hadmut

   on Jul 2, 2024

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   Simpler:

   def (task(:outdated)).timestamp
   Time.now - 60
   end

   file 'test.txt' => :outdated do |f|
   File.write(f.name, 'FRESH!')
   end