Warn before opening a very large JSON value in the data grid (#9868)

docs/en_US/release_notes_9_16.rst

@@ -43,6 +43,7 @@ Bug fixes
   | `Issue #9595 <https://github.com/pgadmin-org/pgadmin4/issues/9595>`_ -  Fix missing ALTER ... SET DEFAULT statements for inherited columns in the generated table SQL/EDIT script.
   | `Issue #9677 <https://github.com/pgadmin-org/pgadmin4/issues/9677>`_ -  Fix the Unlogged table toggle in table properties not generating any ALTER TABLE ... SET LOGGED/UNLOGGED statement.
   | `Issue #9828 <https://github.com/pgadmin-org/pgadmin4/issues/9828>`_ -  Fix tool calls failing against OpenAI-compatible providers that emit empty/null name, arguments, or id fields in streaming continuation deltas.
+  | `Issue #9868 <https://github.com/pgadmin-org/pgadmin4/issues/9868>`_ -  Warn before opening a very large JSON/JSONB value in the data grid cell editor, which could freeze pgAdmin, and let the user choose whether to proceed.
   | `Issue #9875 <https://github.com/pgadmin-org/pgadmin4/issues/9875>`_ -  Fixed an issue where EXPLAIN and EXPLAIN ANALYZE failed to execute when blank lines separated clauses in the SQL query.
   | `Issue #9810 <https://github.com/pgadmin-org/pgadmin4/issues/9810>`_ -  Use the ServerManager's passfile for the credential gate in connect() so the check matches the passfile actually used for the connection, and warn on conflicting passfile/passexec settings.
   | `Issue #9892 <https://github.com/pgadmin-org/pgadmin4/issues/9892>`_ -  Fix blank difference counts on the top-level group rows in Schema Diff.

web/pgadmin/tools/sqleditor/static/js/components/QueryToolDataGrid/Editors.jsx

@@ -15,6 +15,7 @@ import CloseIcon from '@mui/icons-material/Close';
 import gettext from 'sources/gettext';
 import JSONBigNumber from 'json-bignumber';
 import JsonEditor from '../../../../../../static/js/components/JsonEditor';
+import { shouldWarnForLargeJSON } from './json_editor_warning';
 import PropTypes from 'prop-types';
 import { RowInfoContext } from '.';
 import { usePgAdmin } from '../../../../../../static/js/PgAdminProvider';
@@ -388,7 +389,7 @@ export function CheckboxEditor({row, column, onRowChange, onClose}) {
 }
 CheckboxEditor.propTypes = EditorPropTypes;
 
-export function JsonTextEditor({row, column, onRowChange, onClose}) {
+function JsonTextEditorContent({row, column, onRowChange, onClose}) {
 
   const pgAdmin = usePgAdmin();
 
@@ -475,4 +476,42 @@ export function JsonTextEditor({row, column, onRowChange, onClose}) {
     </Portal>
   );
 }
+JsonTextEditorContent.propTypes = EditorPropTypes;
+
+// Wraps the JSON editor with a guard that warns before opening a very large
+// value. Rendering/parsing a huge JSON document blocks the main thread and can
+// freeze pgAdmin, so for large cells we render nothing until the user confirms
+// (#9868). The editor uses commitOnOutsideClick: false, so showing the confirm
+// dialog does not dismiss the editor.
+export function JsonTextEditor(props) {
+  const { row, column, onClose } = props;
+  const pgAdmin = usePgAdmin();
+  const [proceed, setProceed] = React.useState(
+    () => !shouldWarnForLargeJSON(row[column.key])
+  );
+
+  React.useEffect(() => {
+    if (proceed) return;
+    // notifier.confirm() fires its cancel callback whenever the dialog
+    // closes, including when the user clicks OK. Track the confirmation so
+    // we only close the cell editor on an actual cancel and not after the
+    // user chose to continue (#9868).
+    let confirmed = false;
+    pgAdmin.Browser.notifier.confirm(
+      gettext('Large data'),
+      gettext('This cell contains a large amount of data. Opening it in the JSON editor may make pgAdmin slow or unresponsive. Do you want to continue?'),
+      () => {
+        confirmed = true;
+        setProceed(true);
+      },
+      () => {
+        if (confirmed) return;
+        onClose(false);
+      },
+    );
+  }, []);
+
+  if (!proceed) return null;
+  return <JsonTextEditorContent {...props} />;
+}
 JsonTextEditor.propTypes = EditorPropTypes;

web/pgadmin/tools/sqleditor/static/js/components/QueryToolDataGrid/json_editor_warning.js

@@ -0,0 +1,21 @@
+/////////////////////////////////////////////////////////////
+//
+// pgAdmin 4 - PostgreSQL Tools
+//
+// Copyright (C) 2013 - 2026, The pgAdmin Development Team
+// This software is released under the PostgreSQL Licence
+//
+//////////////////////////////////////////////////////////////
+
+// Opening a very large JSON/JSONB value in the cell editor parses, pretty-
+// prints and renders the whole document on the main thread, which can make
+// pgAdmin slow or completely unresponsive. Above this size (in characters) we
+// warn the user and let them decide whether to proceed. See issue #9868.
+export const LARGE_JSON_WARNING_LENGTH = 1024 * 1024;
+
+// Returns true when the raw cell value is large enough that opening it in the
+// JSON editor warrants a confirmation prompt. Only string values are measured;
+// the cheap length check avoids serializing the value just to size it.
+export function shouldWarnForLargeJSON(value, threshold = LARGE_JSON_WARNING_LENGTH) {
+  return typeof value === 'string' && value.length > threshold;
+}

web/regression/javascript/sqleditor/json_editor_warning.spec.js

@@ -0,0 +1,134 @@
+/////////////////////////////////////////////////////////////
+//
+// pgAdmin 4 - PostgreSQL Tools
+//
+// Copyright (C) 2013 - 2026, The pgAdmin Development Team
+// This software is released under the PostgreSQL Licence
+//
+//////////////////////////////////////////////////////////////
+
+import { render, screen, act } from '@testing-library/react';
+
+import {
+  LARGE_JSON_WARNING_LENGTH,
+  shouldWarnForLargeJSON,
+} from '../../../pgadmin/tools/sqleditor/static/js/components/QueryToolDataGrid/json_editor_warning';
+
+// Stub the heavy JSON editor so the wrapper can render without CodeMirror.
+jest.mock('../../../pgadmin/static/js/components/JsonEditor', () => ({
+  __esModule: true,
+  default: () => <div data-testid="json-editor" />,
+}));
+
+// Mock the QueryToolDataGrid index so importing Editors does not pull in the
+// whole data grid; Editors only needs RowInfoContext from it.
+jest.mock('../../../pgadmin/tools/sqleditor/static/js/components/QueryToolDataGrid', () => {
+  const ReactActual = require('react');
+  return { RowInfoContext: ReactActual.createContext() };
+});
+
+import Theme from 'sources/Theme';
+import { JsonTextEditor } from '../../../pgadmin/tools/sqleditor/static/js/components/QueryToolDataGrid/Editors';
+import { RowInfoContext } from '../../../pgadmin/tools/sqleditor/static/js/components/QueryToolDataGrid';
+import { PgAdminProvider } from '../../../pgadmin/static/js/PgAdminProvider';
+
+describe('QueryToolDataGrid json_editor_warning', () => {
+  describe('shouldWarnForLargeJSON', () => {
+    it('does not warn for small string values', () => {
+      expect(shouldWarnForLargeJSON('{"a":1}')).toBe(false);
+      expect(shouldWarnForLargeJSON('')).toBe(false);
+    });
+
+    it('warns once a string value exceeds the threshold (#9868)', () => {
+      const big = 'x'.repeat(LARGE_JSON_WARNING_LENGTH + 1);
+      expect(shouldWarnForLargeJSON(big)).toBe(true);
+    });
+
+    it('does not warn exactly at the threshold', () => {
+      const atLimit = 'x'.repeat(LARGE_JSON_WARNING_LENGTH);
+      expect(shouldWarnForLargeJSON(atLimit)).toBe(false);
+    });
+
+    it('respects a custom threshold', () => {
+      expect(shouldWarnForLargeJSON('abcd', 3)).toBe(true);
+      expect(shouldWarnForLargeJSON('abc', 3)).toBe(false);
+    });
+
+    it('does not warn for non-string values', () => {
+      expect(shouldWarnForLargeJSON(null)).toBe(false);
+      expect(shouldWarnForLargeJSON(undefined)).toBe(false);
+      expect(shouldWarnForLargeJSON(12345)).toBe(false);
+      expect(shouldWarnForLargeJSON([1, 2, 3])).toBe(false);
+      expect(shouldWarnForLargeJSON({ a: 1 })).toBe(false);
+    });
+  });
+
+  describe('JsonTextEditor large-value guard', () => {
+    const KEY = 'col';
+    let confirmArgs;
+    let onClose;
+
+    const renderEditor = (value) => {
+      const column = { key: KEY, idx: 0, can_edit: true };
+      const pgAdmin = {
+        Browser: {
+          notifier: {
+            confirm: (title, text, onOk, onCancel) => {
+              confirmArgs = { title, text, onOk, onCancel };
+            },
+            error: jest.fn(),
+          },
+        },
+      };
+      return render(
+        <Theme>
+          <PgAdminProvider value={pgAdmin}>
+            <RowInfoContext.Provider value={{ getCellElement: () => null }}>
+              <JsonTextEditor
+                row={{ [KEY]: value }}
+                column={column}
+                onRowChange={jest.fn()}
+                onClose={onClose}
+              />
+            </RowInfoContext.Provider>
+          </PgAdminProvider>
+        </Theme>
+      );
+    };
+
+    beforeEach(() => {
+      confirmArgs = undefined;
+      onClose = jest.fn();
+    });
+
+    it('opens the editor immediately for small values without confirming', () => {
+      renderEditor('{"a":1}');
+      expect(confirmArgs).toBeUndefined();
+      expect(screen.getByTestId('json-editor')).toBeInTheDocument();
+    });
+
+    it('warns for large values and waits before opening the editor', () => {
+      renderEditor('x'.repeat(LARGE_JSON_WARNING_LENGTH + 1));
+      expect(confirmArgs).toBeDefined();
+      expect(screen.queryByTestId('json-editor')).not.toBeInTheDocument();
+    });
+
+    it('closes the editor when the warning is cancelled', () => {
+      renderEditor('x'.repeat(LARGE_JSON_WARNING_LENGTH + 1));
+      act(() => confirmArgs.onCancel());
+      expect(onClose).toHaveBeenCalledWith(false);
+    });
+
+    it('opens the editor and does not close it when the user continues (#9868)', () => {
+      renderEditor('x'.repeat(LARGE_JSON_WARNING_LENGTH + 1));
+      // notifier.confirm() fires the cancel callback as well as the OK
+      // callback when the user clicks OK; the guard must keep the editor open.
+      act(() => {
+        confirmArgs.onOk();
+        confirmArgs.onCancel();
+      });
+      expect(onClose).not.toHaveBeenCalled();
+      expect(screen.getByTestId('json-editor')).toBeInTheDocument();
+    });
+  });
+});