Summary:
This gives a mechanism for controlling access control within a document that is distinct from (though implemented with the same machinery as) granular access rules.
It was hard to find a good way to insert this that didn't dissolve in a soup of complications, so here's what I went with:
* When reading rules, if there are shares, extra rules are added.
* If there are shares, all rules are made conditional on a "ShareRef" user property.
* "ShareRef" is null when a doc is accessed in normal way, and the row id of a share when accessed via a share.
There's no UI for controlling shares (George is working on it for forms), but you can do it by editing a `_grist_Shares` table in a document. Suppose you make a fresh document with a single page/table/widget, then to create an empty share you can do:
```
gristDocPageModel.gristDoc.get().docData.sendAction(['AddRecord', '_grist_Shares', null, {linkId: 'xyz', options: '{"publish": true}'}])
```
If you look at the home db now there should be something in the `shares` table:
```
$ sqlite3 -table landing.db "select * from shares"
+----+------------------------+------------------------+--------------+---------+
| id | key | doc_id | link_id | options |
+----+------------------------+------------------------+--------------+---------+
| 1 | gSL4g38PsyautLHnjmXh2K | 4qYuace1xP2CTcPunFdtan | xyz | ... |
+----+------------------------+------------------------+--------------+---------+
```
If you take the key from that (gSL4g38PsyautLHnjmXh2K in this case) and replace the document's urlId in its URL with `s.<key>` (in this case `s.gSL4g38PsyautLHnjmXh2K` then you can use the regular document landing page (it will be quite blank initially) or API endpoint via the share.
E.g. for me `http://localhost:8080/o/docs/s0gSL4g38PsyautLHnjmXh2K/share-inter-3` accesses the doc.
To actually share some material - useful commands:
```
gristDocPageModel.gristDoc.get().docData.getMetaTable('_grist_Views_section').getRecords()
gristDocPageModel.gristDoc.get().docData.sendAction(['UpdateRecord', '_grist_Views_section', 1, {shareOptions: '{"publish": true, "form": true}'}])
gristDocPageModel.gristDoc.get().docData.getMetaTable('_grist_Pages').getRecords()
gristDocPageModel.gristDoc.get().docData.sendAction(['UpdateRecord', '_grist_Pages', 1, {shareRef: 1}])
```
For a share to be effective, at least one page needs to have its shareRef set to the rowId of the share, and at least one widget on one of those pages needs to have its shareOptions set to {"publish": "true", "form": "true"} (meaning turn on sharing, and include form sharing), and the share itself needs {"publish": true} on its options.
I think special shares are kind of incompatible with public sharing, since by their nature (allowing access to all endpoints) they easily expose the docId, and changing that would be hard.
Test Plan: tests added
Reviewers: dsagal, georgegevoian
Reviewed By: dsagal, georgegevoian
Subscribers: jarek, dsagal
Differential Revision: https://phab.getgrist.com/D4144
