[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>

1 files changed, 44 insertions, 47 deletions

diff --git a/searx/engines/duckduckgo.py b/searx/engines/duckduckgo.py
index 450cd9cf8..62e1603a6 100644
--- a/searx/engines/duckduckgo.py
+++ b/searx/engines/duckduckgo.py
@@ -6,16 +6,17 @@ DuckDuckGo WEB
 
 from __future__ import annotations
 
-from typing import TYPE_CHECKING
+import json
 import re
+import typing
+
 from urllib.parse import quote_plus
-import json
+
 import babel
 import lxml.html
 
 from searx import (
     locales,
-    redislib,
     external_bang,
 )
 from searx.utils import (
@@ -25,12 +26,12 @@ from searx.utils import (
     extract_text,
 )
 from searx.network import get  # see https://github.com/searxng/searxng/issues/762
-from searx import redisdb
 from searx.enginelib.traits import EngineTraits
+from searx.enginelib import EngineCache
 from searx.exceptions import SearxEngineCaptchaException
 from searx.result_types import EngineResults
 
-if TYPE_CHECKING:
+if typing.TYPE_CHECKING:
     import logging
 
     logger: logging.Logger
@@ -61,28 +62,18 @@ url = "https://html.duckduckgo.com/html"
 
 time_range_dict = {'day': 'd', 'week': 'w', 'month': 'm', 'year': 'y'}
 form_data = {'v': 'l', 'api': 'd.js', 'o': 'json'}
-__CACHE = []
 
+CACHE: EngineCache
+"""Persistent (SQLite) key/value cache that deletes its values after ``expire``
+seconds."""
 
-def _cache_key(query: str, region: str):
-    return 'SearXNG_ddg_web_vqd' + redislib.secret_hash(f"{query}//{region}")
 
-
-def cache_vqd(query: str, region: str, value: str):
-    """Caches a ``vqd`` value from a query."""
-    c = redisdb.client()
-    if c:
-        logger.debug("VALKEY cache vqd value: %s (%s)", value, region)
-        c.set(_cache_key(query, region), value, ex=600)
-
-    else:
-        logger.debug("MEM cache vqd value: %s (%s)", value, region)
-        if len(__CACHE) > 100:  # cache vqd from last 100 queries
-            __CACHE.pop(0)
-        __CACHE.append((_cache_key(query, region), value))
+def init(_):  # pylint: disable=unused-argument
+    global CACHE  # pylint: disable=global-statement
+    CACHE = EngineCache("duckduckgo")  # type:ignore
 
 
-def get_vqd(query: str, region: str, force_request: bool = False):
+def get_vqd(query: str, region: str, force_request: bool = False) -> str:
     """Returns the ``vqd`` that fits to the *query*.
 
     :param query: The query term
@@ -114,31 +105,34 @@ def get_vqd(query: str, region: str, force_request: bool = False):
     seems the block list is a sliding window: to get my IP rid from the bot list
     I had to cool down my IP for 1h (send no requests from that IP to DDG).
     """
-    key = _cache_key(query, region)
-
-    c = redisdb.client()
-    if c:
-        value = c.get(key)
-        if value or value == b'':
-            value = value.decode('utf-8')  # type: ignore
-            logger.debug("re-use CACHED vqd value: %s", value)
-            return value
+    key = CACHE.secret_hash(f"{query}//{region}")
+    value = CACHE.get(key=key)
+    if value is not None and not force_request:
+        logger.debug("vqd: re-use cached value: %s", value)
+        return value
+
+    logger.debug("vqd: request value from from duckduckgo.com")
+    resp = get(f'https://duckduckgo.com/?q={quote_plus(query)}')
+    if resp.status_code == 200:  # type: ignore
+        value = extr(resp.text, 'vqd="', '"')  # type: ignore
+        if value:
+            logger.debug("vqd value from duckduckgo.com request: '%s'", value)
+        else:
+            logger.error("vqd: can't parse value from ddg response (return empty string)")
+            return ""
+    else:
+        logger.error("vqd: got HTTP %s from duckduckgo.com", resp.status_code)
 
-    for k, value in __CACHE:
-        if k == key:
-            logger.debug("MEM re-use CACHED vqd value: %s", value)
-            return value
+    if value:
+        CACHE.set(key=key, value=value)
+    else:
+        logger.error("vqd value from duckduckgo.com ", resp.status_code)
+    return value
 
-    if force_request:
-        resp = get(f'https://duckduckgo.com/?q={quote_plus(query)}')
-        if resp.status_code == 200:  # type: ignore
-            value = extr(resp.text, 'vqd="', '"')  # type: ignore
-            if value:
-                logger.debug("vqd value from DDG request: %s", value)
-                cache_vqd(query, region, value)
-                return value
 
-    return None
+def set_vqd(query: str, region: str, value: str):
+    key = CACHE.secret_hash(f"{query}//{region}")
+    CACHE.set(key=key, value=value, expire=3600)
 
 
 def get_ddg_lang(eng_traits: EngineTraits, sxng_locale, default='en_US'):
@@ -373,8 +367,11 @@ def response(resp) -> EngineResults:
         # some locales (at least China) does not have a "next page" button
         form = form[0]
         form_vqd = eval_xpath(form, '//input[@name="vqd"]/@value')[0]
-
-        cache_vqd(resp.search_params['data']['q'], resp.search_params['data']['kl'], form_vqd)
+        set_vqd(
+            query=resp.search_params['data']['q'],
+            region=resp.search_params['data']['kl'],
+            value=str(form_vqd),
+        )
 
     # just select "web-result" and ignore results of class "result--ad result--ad--small"
     for div_result in eval_xpath(doc, '//div[@id="links"]/div[contains(@class, "web-result")]'):
@@ -401,7 +398,7 @@ def response(resp) -> EngineResults:
         results.add(
             results.types.Answer(
                 answer=zero_click,
-                url=eval_xpath_getindex(doc, '//div[@id="zero_click_abstract"]/a/@href', 0),
+                url=eval_xpath_getindex(doc, '//div[@id="zero_click_abstract"]/a/@href', 0),  # type: ignore
             )
         )