Provide a diff endpoint for comparing two arbitrary versions of a Pact

[jubobs]

Similar to the existing previous-distinct endpoint, but allowing arbitrary versions of a Pact to be diff'ed.

This would come in particularly handy for us, where we want to send—as part of our CI/CD pipeline—Slack notifications to the provider team if a consumer team pushes a new version of the pact that is different from latest/prod.

The endpoint URI to get the diff between <version_a> and <version_b> could be something like

pacts/provider/<provider>/consumer/<consumer>/version/<version_a>/diff/<version_b>

Ideally,

pacts/provider/<provider>/consumer/<consumer>/latest/<tag>/diff/<some_version>

would also be available.

[bethesque]

I've always had this in the back of my mind to do, but you're the first person to actually ask for it. It should be quite easy. I can't get on to it right now because I've sworn not to do any more broker code until pact message is done, but I'll get on to it as soon as I can. Happy to accept PRs if you're interested.

[mefellows]

Love this idea!

[jubobs]

@bethesque Great to hear! 😃

Happy to accept PRs if you're interested.

I've never used Ruby in anger; I can't promise anything, but I can give it a shot.

[bethesque]

I've thrown together some developer docs that should help https://github.com/pact-foundation/pact_broker/blob/master/CONTRIBUTING.md

[bethesque]

This is done. See the pb:diff relation in the latest version of the pact broker, and its HAL related documentation.