Add unified search API

[ChristophWurst]

See details and design decisions in the code. I felt like it's the better and more discoverable place than putting it into the PR description.

## Client flow

We decided that the providers should be independent in a way that one slow provider does not slow down the whole search experience, and also that the number of providers register does not influence the total time needed to get all the data.

Therefore the flow for the client (js) code is split into two parts.

1. Get the current list of providers ``
2. Fetch the results for each of the providers concurrently

So we can benefit from the async/concurrent nature of JavaScript in the browser and run multiple search requests in parallel on the server. It's up to the UI code to decide whether the completion of all requests will be awaited or results are shown as they come in.

Get list of providers

GET https://localhost/search/providers

returns

[
  "files",
  "mail"
]

Get individual search results

GET https://localhost/search/providers/files/search?term=cat

returns

{
  "name": "Files",
  "isPaginated": false,
  "entries": [
    {
      "thumbnailUrl": "path/to/icon.png",
      "title": "cute cats.jpg",
      "subline": "/Cats",
      "resourceUrl": "/f/21156"
    },
    {
      "thumbnailUrl": "path/to/icon.png",
      "title": "cat 1.jpg",
      "subline": "/Cats",
      "resourceUrl": "/f/21192"
    },
    {
      "thumbnailUrl": "path/to/icon.png",
      "title": "cat 2.jpg",
      "subline": "/Cats",
      "resourceUrl": "/f/25942"
    }
  ],
  "cursor": null
}

Docs are at nextcloud/documentation#2166

---

[ChristophWurst]

• Blocked by Migrate Files to the new bootstrap mechanism #21524

[nickvergessen]

Can these be OCS so it's easier to use for clients and API consumers?

[nickvergessen]

So we decided to delay OCS, until the frontend is there, so we are more sure it "works" and can do everything we need.

[nickvergessen]

🐘

[ChristophWurst]

@since annotations were missing

[ChristophWurst]

And now a few tests failed 🙄

[skjnldsv]

I found some issues @ChristophWurst

• Files limit is not taken into account
• You're using OCP\Search\Provider & OC\Search\Result\File that are deprecated

  server/lib/private/Search/Provider/File.php

  Line 35 in 27b8637

  * @deprecated 20.0.0

[ChristophWurst]

Files limit is not taken into account

This is about the current files search implementation, right? It's not a paginated one, so there is no limit per page. A limit only makes sense if you break down the result set into chunks as pages. When the provider does not support that, the unification logic is out of luck. You need to factor that in on the UI end.

Summary

• Full results have an arbitrary number of entries
• Paginated results should adhere to the specified limit, thus only return a certain number of entries

You're using OCP\Search\Provider & OC\Search\Result\File that are deprecated

This PR deprecated them 🙈 The files search provider is something that has to be redone. I just used the existing code and plugged it into the new one. This needs storage experts knowledge to transform properly, I lack that.

[skjnldsv]

It's not a paginated one, so there is no limit per page. A limit only makes sense if you break down the result set into chunks as pages

And I can't enforce that?
Part of the spec is being able to paginate every results. I need to be able to show only 5 per types

[ChristophWurst]

As I tried to explain, no, you can't.

The only thing we could do for this is to cap the results at a certain point for those providers that are not paginated. But then the user will never see the full list.

Part of the spec is being able to paginate every results.

But you can still do this. Just because the server gives you more data does not mean you have to show everything? Why not store the results as you get them, show the first x entries and when you would have to get the next page for a paginated provider you just show more of the already known entries.

It's a bit of additional work on the front-end, sure, but that is the best we can do if we want to support paginated and non-paginated providers.

[ChristophWurst]

Docs at nextcloud/documentation#2166