In GET /process handler, catch malformed ?title_b64= params.

diff --git a/plomtask/http.py b/plomtask/http.py
index 0626b4c1e5aab5bd4bceb0d6594cbaa9da448ae8..b7040f76fa9c3c1d58b0ceedc58fabf02752f616 100644 (file)
--- a/plomtask/http.py
+++ b/plomtask/http.py
@@ -3,6 +3,7 @@ from __future__ import annotations
 from dataclasses import dataclass
 from typing import Any, Callable
 from base64 import b64encode, b64decode
+from binascii import Error as binascii_Exception
 from http.server import BaseHTTPRequestHandler
 from http.server import HTTPServer
 from urllib.parse import urlparse, parse_qs
@@ -187,8 +188,8 @@ class TaskHandler(BaseHTTPRequestHandler):
         returns successfully, or right after any exception is triggered –
         otherwise, race conditions become plausible.
 
-        Note that any POST attempt, even a failed one, may end in problematic
-        inconsistencies:
+        Note that otherwise any POST attempt, even a failed one, may end in
+        problematic inconsistencies:
 
         - if the POST handler experiences an Exception, changes to objects
           won't get written to the DB, but the changed objects may remain in
@@ -225,8 +226,8 @@ class TaskHandler(BaseHTTPRequestHandler):
                     if hasattr(self, handler_name):
                         handler = getattr(self, handler_name)
                         redir_target = f(self, handler)
-                        if 'POST' != http_method:
-                           clear_caches()
+                        if 'POST' == http_method:
+                            clear_caches()
                         if redir_target:
                             self.send_response(302)
                             self.send_header('Location', redir_target)
@@ -235,8 +236,8 @@ class TaskHandler(BaseHTTPRequestHandler):
                         msg = f'{not_found_msg}: {self._site}'
                         raise NotFoundException(msg)
                 except HandledException as error:
-                    if 'POST' != http_method:
-                       clear_caches()
+                    if 'POST' == http_method:
+                        clear_caches()
                     ctx = {'msg': error}
                     self._send_page(ctx, 'msg', error.http_code)
                 finally:
@@ -475,13 +476,18 @@ class TaskHandler(BaseHTTPRequestHandler):
         owned_ids = self._params.get_all_int('has_step')
         title_64 = self._params.get_str('title_b64')
         if title_64:
-            title = b64decode(title_64.encode()).decode()
+            try:
+                title = b64decode(title_64.encode()).decode()
+            except binascii_Exception as exc:
+                msg = 'invalid base64 for ?title_b64='
+                raise BadFormatException(msg) from exc
             process.title.set(title)
+        preset_top_step = None
         owners = process.used_as_step_by(self.conn)
         for step_id in owner_ids:
             owners += [Process.by_id(self.conn, step_id)]
-        preset_top_step = None
         for process_id in owned_ids:
+            Process.by_id(self.conn, process_id)  # to ensure ID exists
             preset_top_step = process_id
         return {'process': process, 'is_new': process.id_ is None,
                 'preset_top_step': preset_top_step,