[mod] engines: migration of the individual cache solutions to EngineCache

The EngineCache class replaces all previously individual solutions for caches in
the context of the engines.

- demo_offline.py
- duckduckgo.py
- radio_browser.py
- soundcloud.py
- startpage.py
- wolframalpha_api.py
- wolframalpha_noapi.py

Search term to test most of the modified engines::

    !ddg !rb !sc !sp !wa test

    !ddg !rb !sc !sp !wa foo

For introspection of the DB, jump into developer environment and run command to
show cache state::

    $ ./manage pyenv.cmd bash --norc --noprofile
    (py3) python -m searx.enginelib cache state

    cache tables and key/values
    ===========================
    [demo_offline        ] 2025-04-22 11:32:50 count        --> (int) 4
    [startpage           ] 2025-04-22 12:32:30 SC_CODE      --> (str) fSOBnhEMlDfE20
    [duckduckgo          ] 2025-04-22 12:32:31 4dff493e.... --> (str) 4-128634958369380006627592672385352473325
    [duckduckgo          ] 2025-04-22 12:40:06 3e2583e2.... --> (str) 4-263126175288871260472289814259666848451
    [radio_browser       ] 2025-04-23 11:33:08 servers      --> (list) ['https://de2.api.radio-browser.info',  ...]
    [soundcloud          ] 2025-04-29 11:40:06 guest_client_id --> (str) EjkRJG0BLNEZquRiPZYdNtJdyGtTuHdp
    [wolframalpha        ] 2025-04-22 12:40:06 code         --> (str) 5aa79f86205ad26188e0e26e28fb7ae7
    number of tables: 6
    number of key/value pairs: 7

In the "cache tables and key/values" section, the table name (engine name) is at
first position on the second there is the calculated expire date and on the
third and fourth position the key/value is shown.

About duckduckgo: The *vqd coode* of ddg depends on the query term and therefore
the key is a hash value of the query term (to not to store the raw query term).

In the "properties of ENGINES_CACHE" section all properties of the SQLiteAppl /
ExpireCache and their last modification date are shown::

    properties of ENGINES_CACHE
    ===========================
    [last modified: 2025-04-22 11:32:27] DB_SCHEMA           : 1
    [last modified: 2025-04-22 11:32:27] LAST_MAINTENANCE    :
    [last modified: 2025-04-22 11:32:27] crypt_hash          : ca612e3566fdfd7cf7efe2b1c9349f461158d07cb78a3750e5c5be686aa8ebdc
    [last modified: 2025-04-22 11:32:30] CACHE-TABLE--demo_offline: demo_offline
    [last modified: 2025-04-22 11:32:30] CACHE-TABLE--startpage: startpage
    [last modified: 2025-04-22 11:32:31] CACHE-TABLE--duckduckgo: duckduckgo
    [last modified: 2025-04-22 11:33:08] CACHE-TABLE--radio_browser: radio_browser
    [last modified: 2025-04-22 11:40:06] CACHE-TABLE--soundcloud: soundcloud
    [last modified: 2025-04-22 11:40:06] CACHE-TABLE--wolframalpha: wolframalpha

These properties provide information about the state of the ExpireCache and
control the behavior.  For example, the maintenance intervals are controlled by
the last modification date of the LAST_MAINTENANCE property and the hash value
of the password can be used to detect whether the password has been changed (in
this case the DB entries can no longer be decrypted and the entire cache must be
discarded).

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/engines/startpage.py

@@ -84,7 +84,6 @@ from typing import TYPE_CHECKING, Any
 from collections import OrderedDict
 import re
 from unicodedata import normalize, combining
-from time import time
 from datetime import datetime, timedelta
 from json import loads
 
@@ -97,6 +96,7 @@ from searx.network import get  # see https://github.com/searxng/searxng/issues/7
 from searx.exceptions import SearxEngineCaptchaException
 from searx.locales import region_tag
 from searx.enginelib.traits import EngineTraits
+from searx.enginelib import EngineCache
 
 if TYPE_CHECKING:
     import logging
@@ -159,10 +159,21 @@ search_form_xpath = '//form[@id="search"]'
     </form>
 """
 
-# timestamp of the last fetch of 'sc' code
-sc_code_ts = 0
-sc_code = ''
-sc_code_cache_sec = 30
+
+CACHE: EngineCache
+"""Persistent (SQLite) key/value cache that deletes its values after ``expire``
+seconds."""
+
+
+def init(_):
+    global CACHE  # pylint: disable=global-statement
+
+    # hint: all three startpage engines (WEB, Images & News) can/should use the
+    # same sc_code ..
+    CACHE = EngineCache("startpage")  # type:ignore
+
+
+sc_code_cache_sec = 3600
 """Time in seconds the sc-code is cached in memory :py:obj:`get_sc_code`."""
 
 
@@ -176,14 +187,10 @@ def get_sc_code(searxng_locale, params):
 
     Startpage's search form generates a new sc-code on each request.  This
     function scrap a new sc-code from Startpage's home page every
-    :py:obj:`sc_code_cache_sec` seconds.
+    :py:obj:`sc_code_cache_sec` seconds."""
 
-    """
-
-    global sc_code_ts, sc_code  # pylint: disable=global-statement
-
-    if sc_code and (time() < (sc_code_ts + sc_code_cache_sec)):
-        logger.debug("get_sc_code: reuse '%s'", sc_code)
+    sc_code = CACHE.get("SC_CODE", "")
+    if sc_code:
         return sc_code
 
     headers = {**params['headers']}
@@ -233,8 +240,9 @@ def get_sc_code(searxng_locale, params):
             message="get_sc_code: [PR-695] query new sc time-stamp failed! (%s)" % resp.url,  # type: ignore
         ) from exc
 
-    sc_code_ts = time()
+    sc_code = str(sc_code)
     logger.debug("get_sc_code: new value is: %s", sc_code)
+    CACHE.set(key="SC_CODE", value=sc_code, expire=sc_code_cache_sec)
     return sc_code