add an endpoint for doing SQL selects (#641)

* add an endpoint for doing SQL selects

This adds an endpoint for doing SQL selects directly on a Grist document. Other kinds of statements are not supported. There is a default timeout of a second on queries.

This follows loosely an API design by Alex Hall.

Co-authored-by: jarek <jaroslaw.sadzinski@gmail.com>

app/server/lib/ActiveDoc.ts

@@ -914,6 +914,11 @@ export class ActiveDoc extends EventEmitter {
     return this._granularAccess.canCopyEverything(docSession);
   }
 
+  // Check if user has rights to read everything in this doc.
+  public async canCopyEverything(docSession: OptDocSession) {
+    return this._granularAccess.canCopyEverything(docSession);
+  }
+
   // Check if it is appropriate for the user to be treated as an owner of
   // the document for granular access purposes when in "prefork" mode
   // (meaning a document has been opened with the intent to fork it, but

app/server/lib/AppSettings.ts

@@ -96,6 +96,17 @@ export class AppSettings {
     return result;
   }
 
+  /**
+   * As for readInt() but fail if nothing was found.
+   */
+  public requireInt(query: AppSettingQuery): number {
+    const result = this.readInt(query);
+    if (result === undefined) {
+      throw new Error(`missing environment variable: ${query.envVar}`);
+    }
+    return result;
+  }
+
   /**
    * As for read() but type (and store, and report) the result as
    * a boolean.
@@ -107,6 +118,17 @@ export class AppSettings {
     return result;
   }
 
+  /**
+   * As for read() but type (and store, and report) the result as
+   * an integer (well, a number).
+   */
+  public readInt(query: AppSettingQuery): number|undefined {
+    this.readString(query);
+    const result = this.getAsInt();
+    this._value = result;
+    return result;
+  }
+
   /* set this setting 'manually' */
   public set(value: JSONValue): void {
     this._value = value;

app/server/lib/DocApi.ts

@@ -32,6 +32,7 @@ import {
   TableOperationsPlatform
 } from 'app/plugin/TableOperationsImpl';
 import {ActiveDoc, colIdToRef as colIdToReference, tableIdToRef} from "app/server/lib/ActiveDoc";
+import {appSettings} from "app/server/lib/AppSettings";
 import {sendForCompletion} from 'app/server/lib/Assistance';
 import {
   assertAccess,
@@ -96,16 +97,25 @@ const MAX_PARALLEL_REQUESTS_PER_DOC = 10;
 // then the _dailyUsage cache may become unreliable and users may be able to exceed their allocated requests.
 const MAX_ACTIVE_DOCS_USAGE_CACHE = 1000;
 
+// Maximum duration of a call to /sql. Does not apply to internal calls to SQLite.
+const MAX_CUSTOM_SQL_MSEC = appSettings.section('integrations')
+  .section('sql').flag('timeout').requireInt({
+    envVar: 'GRIST_SQL_TIMEOUT_MSEC',
+    defaultValue: 1000,
+  });
+
 type WithDocHandler = (activeDoc: ActiveDoc, req: RequestWithLogin, resp: Response) => Promise<void>;
 
 // Schema validators for api endpoints that creates or updates records.
 const {
   RecordsPatch, RecordsPost, RecordsPut,
   ColumnsPost, ColumnsPatch, ColumnsPut,
+  SqlPost,
   TablesPost, TablesPatch,
 } = t.createCheckers(DocApiTypesTI, GristDataTI);
 
-for (const checker of [RecordsPatch, RecordsPost, RecordsPut, ColumnsPost, ColumnsPatch, TablesPost, TablesPatch]) {
+for (const checker of [RecordsPatch, RecordsPost, RecordsPut, ColumnsPost, ColumnsPatch,
+                       SqlPost, TablesPost, TablesPatch]) {
   checker.setReportedPath("body");
 }
 
@@ -518,6 +528,27 @@ export class DocWorkerApi {
       })
     );
 
+    // A GET /sql endpoint that takes a query like ?q=select+*+from+Table1
+    // Not very useful, apart from testing - see the POST endpoint for
+    // serious use.
+    // If SQL statements that modify the DB are ever supported, they should
+    // not be permitted by this endpoint.
+    this._app.get(
+      '/api/docs/:docId/sql', canView,
+      withDoc(async (activeDoc, req, res) => {
+        const sql = stringParam(req.query.q, 'q');
+        await this._runSql(activeDoc, req, res, { sql });
+      }));
+
+    // A POST /sql endpoint, accepting a body like:
+    // { "sql": "select * from Table1 where name = ?", "args": ["Paul"] }
+    // Only SELECT statements are currently supported.
+    this._app.post(
+      '/api/docs/:docId/sql', canView, validate(SqlPost),
+      withDoc(async (activeDoc, req, res) => {
+        await this._runSql(activeDoc, req, res, req.body);
+      }));
+
     // Create columns in a table, given as records of the _grist_Tables_column metatable.
     this._app.post('/api/docs/:docId/tables/:tableId/columns', canEdit, validate(ColumnsPost),
       withDoc(async (activeDoc, req, res) => {
@@ -1502,6 +1533,73 @@ export class DocWorkerApi {
     await this._dbManager.flushSingleDocAuthCache(scope, docId);
     await this._docManager.interruptDocClients(docId);
   }
+
+  private async _runSql(activeDoc: ActiveDoc, req: RequestWithLogin, res: Response,
+      options: Types.SqlPost) {
+    if (!await activeDoc.canCopyEverything(docSessionFromRequest(req))) {
+      throw new ApiError('insufficient document access', 403);
+    }
+    const statement = options.sql;
+    // A very loose test, just for early error message
+    if (!(statement.toLowerCase().includes('select'))) {
+      throw new ApiError('only select statements are supported', 400);
+    }
+    const sqlOptions = activeDoc.docStorage.getOptions();
+    if (!sqlOptions?.canInterrupt || !sqlOptions?.bindableMethodsProcessOneStatement) {
+      throw new ApiError('The available SQLite wrapper is not adequate', 500);
+    }
+    const timeout =
+        Math.max(0, Math.min(MAX_CUSTOM_SQL_MSEC,
+                             optIntegerParam(options.timeout) || MAX_CUSTOM_SQL_MSEC));
+    // Wrap in a select to commit to the SELECT branch of SQLite
+    // grammar. Note ; isn't a problem.
+    //
+    // The underlying SQLite functions used will only process the
+    // first statement in the supplied text. For node-sqlite3, the
+    // remainder is placed in a "tail string" ignored by that library.
+    // So a Robert'); DROP TABLE Students;-- style attack isn't applicable.
+    //
+    // Since Grist is used with multiple SQLite wrappers, not just
+    // node-sqlite3, we have added a bindableMethodsProcessOneStatement
+    // flag that will need adding for each wrapper, and this endpoint
+    // will not operate unless that flag is set to true.
+    //
+    // The text is wrapped in select * from (USER SUPPLIED TEXT) which
+    // puts SQLite unconditionally onto the SELECT branch of its
+    // grammar. It is straightforward to break out of such a wrapper
+    // with multiple statements, but again, only the first statement
+    // is processed.
+    const wrappedStatement = `select * from (${statement})`;
+    const interrupt = setTimeout(async () => {
+      await activeDoc.docStorage.interrupt();
+    }, timeout);
+    try {
+      const records = await activeDoc.docStorage.all(wrappedStatement,
+                                                     ...(options.args || []));
+      res.status(200).json({
+        statement,
+        records: records.map(
+          rec => ({
+            fields: rec,
+          })
+        ),
+      });
+    } catch (e) {
+      if (e?.code === 'SQLITE_INTERRUPT') {
+        res.status(400).json({
+          error: "a slow statement resulted in a database interrupt",
+        });
+      } else if (e?.code === 'SQLITE_ERROR') {
+        res.status(400).json({
+          error: e?.message,
+        });
+      } else {
+        throw e;
+      }
+    } finally {
+      clearTimeout(interrupt);
+    }
+  }
 }
 
 export function addDocApiRoutes(

app/server/lib/DocStorage.ts

@@ -31,6 +31,7 @@ import {ISQLiteDB, MigrationHooks, OpenMode, PreparedStatement, quoteIdent,
 import chunk = require('lodash/chunk');
 import cloneDeep = require('lodash/cloneDeep');
 import groupBy = require('lodash/groupBy');
+import { MinDBOptions } from './SqliteCommon';
 
 
 // Run with environment variable NODE_DEBUG=db (may include additional comma-separated sections)
@@ -1419,6 +1420,14 @@ export class DocStorage implements ISQLiteDB, OnDemandStorage {
     }
   }
 
+  public interrupt(): Promise<void> {
+    return this._getDB().interrupt();
+  }
+
+  public getOptions(): MinDBOptions|undefined {
+    return this._getDB().getOptions();
+  }
+
   public all(sql: string, ...args: any[]): Promise<ResultRow[]> {
     return this._getDB().all(sql, ...args);
   }

app/server/lib/SQLiteDB.ts

@@ -72,7 +72,7 @@ import {timeFormat} from 'app/common/timeFormat';
 import {create} from 'app/server/lib/create';
 import * as docUtils from 'app/server/lib/docUtils';
 import log from 'app/server/lib/log';
-import {MinDB, MinRunResult, PreparedStatement, ResultRow,
+import {MinDB, MinDBOptions, MinRunResult, PreparedStatement, ResultRow,
         SqliteVariant, Statement} from 'app/server/lib/SqliteCommon';
 import {NodeSqliteVariant} from 'app/server/lib/SqliteNode';
 import assert from 'assert';
@@ -258,6 +258,14 @@ export class SQLiteDB implements ISQLiteDB {
   private constructor(protected _db: MinDB, private _dbPath: string) {
   }
 
+  public async interrupt(): Promise<void> {
+    return this._db.interrupt?.();
+  }
+
+  public getOptions(): MinDBOptions|undefined {
+    return this._db.getOptions?.();
+  }
+
   public async all(sql: string, ...args: any[]): Promise<ResultRow[]> {
     const result = await this._db.all(sql, ...args);
     return result;

app/server/lib/SqliteCommon.ts

@@ -12,20 +12,50 @@ import { OpenMode, quoteIdent } from 'app/server/lib/SQLiteDB';
 // eslint-disable-next-line @typescript-eslint/no-empty-interface
 export interface Statement {}
 
+// Some facts about the wrapper implementation.
+export interface MinDBOptions {
+  // is interruption implemented?
+  canInterrupt: boolean;
+
+  // Do all methods apart from exec() process at most one
+  // statement?
+  bindableMethodsProcessOneStatement: boolean;
+}
+
 export interface MinDB {
+  // This method is expected to be able to handle multiple
+  // semicolon-separated statements, as for sqlite3_exec:
+  //   https://www.sqlite.org/c3ref/exec.html
   exec(sql: string): Promise<void>;
+
+  // For all these methods, sql should ultimately be passed
+  // to sqlite3_prepare_v2 or later, and any tail text ignored after
+  // the first complete statement, so only the first statement is
+  // used if there are multiple.
+  //   https://www.sqlite.org/c3ref/prepare.html
   run(sql: string, ...params: any[]): Promise<MinRunResult>;
   get(sql: string, ...params: any[]): Promise<ResultRow|undefined>;
   all(sql: string, ...params: any[]): Promise<ResultRow[]>;
   prepare(sql: string, ...params: any[]): Promise<PreparedStatement>;
   runAndGetId(sql: string, ...params: any[]): Promise<number>;
-  close(): Promise<void>;
   allMarshal(sql: string, ...params: any[]): Promise<Buffer>;
 
+  close(): Promise<void>;
+
   /**
    * Limit the number of ATTACHed databases permitted.
    */
   limitAttach(maxAttach: number): Promise<void>;
+
+  /**
+   * Stop all current queries.
+   */
+  interrupt?(): Promise<void>;
+
+  /**
+   * Get some facts about the wrapper.
+   */
+  getOptions?(): MinDBOptions;
 }
 
 export interface MinRunResult {

app/server/lib/SqliteNode.ts

@@ -1,6 +1,6 @@
 import * as sqlite3 from '@gristlabs/sqlite3';
 import { fromCallback } from 'app/server/lib/serverUtils';
-import { MinDB, PreparedStatement, ResultRow, SqliteVariant } from 'app/server/lib/SqliteCommon';
+import { MinDB, MinDBOptions, PreparedStatement, ResultRow, SqliteVariant } from 'app/server/lib/SqliteCommon';
 import { OpenMode, RunResult } from 'app/server/lib/SQLiteDB';
 
 export class NodeSqliteVariant implements SqliteVariant {
@@ -84,6 +84,17 @@ export class NodeSqlite3DatabaseAdapter implements MinDB {
     this._db.close();
   }
 
+  public async interrupt(): Promise<void> {
+    this._db.interrupt();
+  }
+
+  public getOptions(): MinDBOptions {
+    return {
+      canInterrupt: true,
+      bindableMethodsProcessOneStatement: true,
+    };
+  }
+
   public async allMarshal(sql: string, ...params: any[]): Promise<Buffer> {
     // allMarshal isn't in the typings, because it is our addition to our fork of sqlite3 JS lib.
     return fromCallback(cb => (this._db as any).allMarshal(sql, ...params, cb));