How to compare files with if-diff

if-diff is a command line tool that allows you to compare two if-run output files. They either match according to if-diff's matching rules, or they don't. If they match, then if-diff returns a simple success response. If the differ, then if-diff returns a report of the differences it finds.

Why is this useful?

if-diff can be used to verify that a given output file was correctly executed and that it was not tampered with after it was computed. Imagine you received an output file from someone, reporting their carbon expenditure. It is better to verify than trust this person's report, so you simply delete the outputs block from the file (creating a manifest), run it through if-run and compare the output to the original file you received. All being well, the two files are identical. if not, you can see exactly where the differences are.

if-diff can also be used for debugging your own files. Maybe you have some large manifest files in development and have accidentally introduced some changes that you are now struggling to identify, but are leading to different if-run outcomes. if-diff can quickly scan your two files and tell you where the differences are so you can get back in sync.

Example: output verification

Let's say someone provides you with this output file, given-output-file.yml:

name: sum
description: successful path
tags:
initialize:
  plugins:
    sum:
      method: Sum
      path: 'builtin'
      config:
        input-parameters: ['cpu/energy', 'network/energy']
        output-parameter: 'energy'
tree:
  children:
    child:
      pipeline:
        observe:
        regroup:
        compute:
          - sum
      inputs:
        - timestamp: 2023-08-06T00:00
          duration: 3600
          cpu/energy: 0.001
          network/energy: 0.001
      outputs:
        - timestamp: 2023-08-06T00:00
          duration: 3600
          cpu/energy: 0.001
          network/energy: 0.001
          energy: 0.0005

This manifest simply sums two components, cpu/energy and network/energy and assigns the result to energy in the outputs array. You receive this file and feel like something's not quite right. So you delete the outputs block to create test-manifest.yml:

name: sum
description: successful path
tags:
initialize:
  plugins:
    sum:
      method: Sum
      path: 'builtin'
      config:
        input-parameters: ['cpu/energy', 'network/energy']
        output-parameter: 'energy'
tree:
  children:
    child:
      pipeline:
        observe:
        regroup:
        compute:
          - sum
      inputs:
        - timestamp: 2023-08-06T00:00
          duration: 3600
          cpu/energy: 0.001
          network/energy: 0.001

Now you want to run the manifest through if-run and compare the result to the given output file. You can do this by piping the result of if-run directly into if-diff as follows:

if-run -m test-manifest.yml | if-diff --target given-output-file.yml

The result is:

Files do not match!
tree.children.child[0].energy
source: 0.002
target:  0.0005

Uh oh. It seems there has been some mistake or tampering with the outputs in given-output-file.yml. The right result of summing cpu/energy and network/energy is 0.002, but they reported 0.0005. You can now query that result with the sender and ask them to fix it.

Obviously, this is an arbitrary, simplified example, but if-diff enables you to do this kind of output verification on very complex manifests where errors are harder to spot by eye and to do it programmatically over large numbers of files.

Example: debugging

Imagine you developed a manifest that was giving you a consistent result, but now when you run it your result is different and you are not sure why. Maybe one of your colleagues changed something and forgot to tell you, maybe you accidentally inserted or removed something while you were working.

You could revert to an archived version, but you moved all the components around into a structure you prefer! if-diff has you covered. It will step through the files identifying all the functional differences between the files to help you identify the problematic one(s).

You have original-manifest.yml and new-manifest.yml. Pass them to if-diff as follows:

if-diff --source original-manifest.yml --target new-manifest.yml

if-diff will report each difference it finds. You can fix the difference and run if-diff again until you get a success response - since if-diff ignores positional differences and only considers differences in context and tree keys and values, your two manifests will run identically even though you persist your tree reorganization.