fix(admin): the Logs download survives any row and stops at a size it can build

- A failed login writes the name it was tried with, as typed: a control
  character in it made every download holding that row fail, as the
  workbook cannot hold one. Workbooks now write it as \x01; the VM
  report shares the code.
- A download held every matching row in memory: it now takes the newest
  100000, and its About sheet says when the search should be narrowed.

admin/tests/test_logs_page.py

@@ -3,6 +3,7 @@ only, says the year and time zone, links a VM's rows to the VM, and downloads
 what it shows as an Excel workbook."""
 
 from io import BytesIO
+from unittest.mock import patch
 
 from computes.models import Compute
 from django.contrib.auth import get_user_model
@@ -85,3 +86,18 @@ class LogsPageTests(TestCase):
     def test_only_an_administrator_downloads(self):
         self.client.force_login(get_user_model().objects.create_user("lg-user", password="pw"))
         self.assertEqual(self.client.get(reverse("admin:logs_export")).status_code, 403)
+
+    def test_a_control_character_in_a_row_is_shown_not_a_failure(self):
+        # a failed login writes the name it was tried with, as typed
+        Logs.objects.create(user="eve\x01", instance="", message="Login", success=False)
+        response = self.client.get(reverse("admin:logs_export"), {"q": "eve"})
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(load_workbook(BytesIO(response.content)).active.cell(row=2, column=2).value, "eve\\x01")
+
+    def test_the_download_stops_at_its_row_limit_and_says_so(self):
+        with patch("admin.views.EXPORT_ROWS", 3):
+            book = load_workbook(BytesIO(self.client.get(reverse("admin:logs_export")).content))
+        self.assertEqual(book.active.max_row, 4)  # the header and three rows
+        notes = [row[0] for row in book["About"].values]
+        self.assertIn("Only the newest 3 rows: narrow the search for the others", notes)
+

admin/views.py

@@ -260,6 +260,10 @@ def user_unblock(request, pk):
     return redirect("admin:user_list")
 
 
+# rows in one Logs download: the workbook is built in memory
+EXPORT_ROWS = 100000
+
+
 def _logs(request):
     """The Logs rows the search and the failed-only box choose, newest first,
     and the query that chooses them again."""
@@ -299,10 +303,13 @@ def logs_export(request):
     rows, text, failed, _query = _logs(request)
     zone = timezone.get_current_timezone_name()
     header = [f"Date ({zone})", "User", "Host", "VM", "VM UUID", "Message", "Result", "IP"]
+    logs = list(rows[:EXPORT_ROWS + 1])
     data = [[timezone.localtime(log.date).strftime("%Y-%m-%d %H:%M:%S"), log.user, log.host, log.instance,
-             log.instance_uuid, log.message, str(_result(log.success)), log.ip or ""] for log in rows.iterator()]
+             log.instance_uuid, log.message, str(_result(log.success)), log.ip or ""] for log in logs[:EXPORT_ROWS]]
     notes = [f"Search: {text}" if text else "Search: none", "Failed only" if failed else "All results",
              f"Rows: {len(data)}", f"Times in {zone}"]
+    if len(logs) > EXPORT_ROWS:
+        notes.append(f"Only the newest {EXPORT_ROWS} rows: narrow the search for the others")
     response = HttpResponse(workbook("Logs", header, data, "About", notes),
                             content_type="application/vnd.openxmlformats-officedocument.spreadsheetml.sheet")
     name = f"webvirtcloud-logs-{timezone.localtime():%Y%m%d-%H%M%S}.xlsx"

instances/report.py

@@ -3,6 +3,7 @@
 from io import BytesIO
 
 from openpyxl import Workbook
+from openpyxl.cell.cell import ILLEGAL_CHARACTERS_RE
 from openpyxl.styles import Font
 from openpyxl.utils import get_column_letter
 
@@ -17,7 +18,9 @@ def workbook(title, header, rows, notes_title, notes):
     sheet = book.active
     sheet.title = title
     for values in [header, *rows]:
-        sheet.append(values)
+        # a control character (a name typed at a failed login) cannot be in the file: written as \x01
+        sheet.append([ILLEGAL_CHARACTERS_RE.sub(lambda m: f"\\x{ord(m.group()):02x}", value)
+                      if isinstance(value, str) else value for value in values])
     for row in sheet.iter_rows():
         for cell in row:
             if isinstance(cell.value, str):