X-Git-Url: https://plomlompom.com/repos/?a=blobdiff_plain;f=plomtask%2Fhttp.py;h=d602f07b9baf3c18df19fa88435928d2a33845d6;hb=refs%2Fheads%2Fmaster;hp=417c5a609c49bff6a7b0f6c85cda1be3d9efb0da;hpb=692bfbac8d81ad5f1f0210e550dcabd15c58e8a5;p=plomtask

diff --git a/plomtask/http.py b/plomtask/http.py
index 417c5a6..b7040f7 100644
--- 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
@@ -177,6 +178,38 @@ class TaskHandler(BaseHTTPRequestHandler):
     @staticmethod
     def _request_wrapper(http_method: str, not_found_msg: str
                          ) -> Callable[..., Callable[[TaskHandler], None]]:
+        """Wrapper for do_GET… and do_POST… handlers, to init and clean up.
+
+        Among other things, conditionally cleans all caches, but only on POST
+        requests, as only those are expected to change the states of objects
+        that may be cached, and certainly only those are expected to write any
+        changes to the database. We want to call them as early though as
+        possible here, either exactly after the specific request handler
+        returns successfully, or right after any exception is triggered –
+        otherwise, race conditions become plausible.
+
+        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
+          the cache and affect other objects despite their possibly illegal
+          state
+
+        - even if an object was just saved to the DB, we cannot be sure its
+          current state is completely identical to what we'd get if loading it
+          fresh from the DB (e.g. currently Process.n_owners is only updated
+          when loaded anew via .from_table_row, nor is its state written to
+          the DB by .save; a questionable design choice, but proof that we
+          have no guarantee that objects' .save stores all their states we'd
+          prefer at their most up-to-date.
+        """
+
+        def clear_caches() -> None:
+            for cls in (Day, Todo, Condition, Process, ProcessStep):
+                assert hasattr(cls, 'empty_cache')
+                cls.empty_cache()
+
         def decorator(f: Callable[..., str | None]
                       ) -> Callable[[TaskHandler], None]:
             def wrapper(self: TaskHandler) -> None:
@@ -193,6 +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 redir_target:
                             self.send_response(302)
                             self.send_header('Location', redir_target)
@@ -201,9 +236,8 @@ class TaskHandler(BaseHTTPRequestHandler):
                         msg = f'{not_found_msg}: {self._site}'
                         raise NotFoundException(msg)
                 except HandledException as error:
-                    for cls in (Day, Todo, Condition, Process, ProcessStep):
-                        assert hasattr(cls, 'empty_cache')
-                        cls.empty_cache()
+                    if 'POST' == http_method:
+                        clear_caches()
                     ctx = {'msg': error}
                     self._send_page(ctx, 'msg', error.http_code)
                 finally:
@@ -442,13 +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,