(core) control the distribution of attachment metadata

Summary:
for users who don't automatically have deep rights
to the document, provide them with attachment metadata only
for rows they have access to. This is a little tricky to
do efficiently. We provide attachment metadata when an
individual table is fetched, rather than on initial document
load, so we don't block that load on a full document scan.
We provide attachment metadata to a client when we see that
we are shipping rows mentioning particular attachments,
without making any effort to keep track of the metadata they
already have.

Test Plan: updated tests

Reviewers: dsagal, jarek

Reviewed By: dsagal, jarek

Differential Revision: https://phab.getgrist.com/D3722

test/server/gristClient.ts

@@ -1,4 +1,6 @@
 import { DocAction } from 'app/common/DocActions';
+import { DocData } from 'app/common/DocData';
+import { SchemaTypes } from 'app/common/schema';
 import { FlexServer } from 'app/server/lib/FlexServer';
 import axios from 'axios';
 import pick = require('lodash/pick');
@@ -28,6 +30,7 @@ export class GristClient {
 
   private _requestId: number = 0;
   private _pending: Array<GristResponse|GristMessage> = [];
+  private _docData?: DocData;  // accumulate tabular info like a real client.
   private _consumer: () => void;
   private _ignoreTrivialActions: boolean = false;
 
@@ -41,6 +44,17 @@ export class GristClient {
         return;
       }
       this._pending.push(msg);
+      if (msg.data?.doc) {
+        this._docData = new DocData(() => {
+          throw new Error('no fetches');
+        }, msg.data.doc);
+      }
+      if (this._docData && msg.type === 'docUserAction') {
+        const docActions = msg.data?.docActions || [];
+        for (const docAction of docActions) {
+          this._docData.receiveAction(docAction);
+        }
+      }
       if (this._consumer) { this._consumer(); }
     };
   }
@@ -65,6 +79,15 @@ export class GristClient {
     return this._pending.length;
   }
 
+  public get docData() {
+    if (!this._docData) { throw new Error('no DocData'); }
+    return this._docData;
+  }
+
+  public getMetaRecords(tableId: keyof SchemaTypes) {
+    return this.docData.getMetaTable(tableId).getRecords();
+  }
+
   public async read(): Promise<any> {
     for (;;) {
       if (this._pending.length) {
@@ -97,6 +120,11 @@ export class GristClient {
     }
   }
 
+  public waitForServer() {
+    // send an arbitrary failing message and wait for response.
+    return this.send('ping');
+  }
+
   // Helper to read the next docUserAction ignoring anything else (e.g. a duplicate clientConnect).
   public async readDocUserAction(): Promise<DocAction[]> {
     while (true) {    // eslint-disable-line no-constant-condition