[enh] introduce Engine class

Previously engines were defined in modules, which where then
stapled with logger, supported_languages & language_aliases
via monkey patching in searx/engines/__init__.py.

Monkey patching is obviously a bad practice since it confuses
humans as well as static type checkers. But there were more problems:

* there were no type hints for the method input and output types

* the request method did not even make a clear distinction between input
  and output (abusing a single "params" dictionary for both)

This commit introduces a new class-based architecture for engines,
in a backwards-compatiable manner: allowing old-style module engines
to be used along witn new-style class-based engines.

docs/admin/engines/configured_engines.rst

@@ -48,12 +48,14 @@ Explanation of the :ref:`general engine configuration` shown in the table
 
       {% for mod in engines %}
 
+      {% set mod_name = mod['__name__'] or mod.__module__ %}
+
       * - `{{mod.name}} <{{mod.about and mod.about.website}}>`_
         - ``!{{mod.shortcut}}``
-        - {%- if 'searx.engines.' + mod.__name__ in documented_modules %}
-          :py:mod:`~searx.engines.{{mod.__name__}}`
+        - {%- if 'searx.engines.' + mod_name in documented_modules %}
+          :py:mod:`~searx.engines.{{mod_name}}`
           {%- else %}
-          :origin:`{{mod.__name__}} <searx/engines/{{mod.__name__}}.py>`
+          :origin:`{{mod_name}} <searx/engines/{{mod_name}}.py>`
           {%- endif %}
         - {{(mod.disabled and "y") or ""}}
           {%- if mod.about and  mod.about.language %}

searx/engine.py

@@ -0,0 +1,100 @@
+# pyright: strict
+from logging import Logger
+from typing import Iterable, List, NamedTuple, Optional, Dict, Union
+from typing_extensions import Literal, TypedDict, NotRequired
+from dataclasses import dataclass
+
+from httpx import Response
+
+
+class Engine:
+    categories: Optional[List[str]]
+    paging = False
+    time_range_support = False
+    supported_languages: List[str]
+    language_aliases: Dict[str, str]
+    about: 'About'
+
+    def __init__(self, logger: Logger) -> None:
+        self.logger = logger
+
+
+class About(TypedDict, total=False):
+    website: str
+    wikidata_id: Optional[str]
+    official_api_documentation: Optional[str]
+    use_official_api: bool
+    require_api_key: bool
+    results: Literal["HTML", "JSON"]
+    language: NotRequired[str]
+
+
+class OnlineEngine(Engine):
+    def request(self, query: str, ctx: 'QueryContext') -> 'OnlineRequest':
+        raise NotImplementedError()
+
+    def response(self, response: Response) -> List['Result']:
+        raise NotImplementedError()
+
+
+class QueryContext(NamedTuple):
+    category: str
+    """current category"""
+    safesearch: Literal[0, 1, 2]
+    """desired content safety (normal, moderate, strict)"""
+    time_range: Optional[Literal['day', 'week', 'month', 'year']]
+    """current time range (if any)"""
+    pageno: int
+    """current page number"""
+    language: str
+    """specific language code like ``en_US``, or ``all`` if unspecified"""
+
+
+@dataclass
+class OnlineRequest:
+    url: str
+    """requested URL"""
+    method: Literal['GET', 'POST'] = 'GET'
+    """HTTP request method"""
+    headers: Optional[Dict[str, str]] = None
+    """HTTP headers"""
+    data: Optional[Dict[str, str]] = None
+    """data to be sent as the HTTP body"""
+    cookies: Optional[Dict[str, str]] = None
+    """HTTP cookies"""
+    verify: bool = True
+    """Assert that the TLS certificate is valid"""
+    allow_redirects: bool = True
+    """follow redirects"""
+    max_redirects: Optional[int] = None
+    """maximum redirects, hard limit"""
+    soft_max_redirects: Optional[int] = None
+    """maximum redirects, soft limit. Record an error but don't stop the engine"""
+    raise_for_httperror: bool = True
+    """raise an exception if the HTTP code of response is >= 300"""
+
+    def set_header(self, name: str, value: str):
+        if self.headers is None:
+            self.headers = {}
+        self.headers[name] = value
+
+
+Result = Union['StandardResult', 'InfoBox']
+
+
+@dataclass
+class StandardResult:
+    url: str
+    title: str
+    content: str = ''
+
+
+@dataclass
+class InfoBox(StandardResult):
+    img_src: Optional[str] = None
+    links: Iterable['Link'] = ()
+
+
+class Link(TypedDict):
+    title: str
+    url: str

searx/engines/__init__.py

@@ -20,6 +20,11 @@ from searx import logger, settings
 from searx.data import ENGINES_LANGUAGES
 from searx.network import get
 from searx.utils import load_module, gen_useragent, find_language_aliases
+from searx.engine import Engine
+
+_NEXTGEN_ENGINES = {
+}
+"""maps module names to class names for engines that are implemented using the new class-based approach"""
 
 
 logger = logger.getChild('engines')
@@ -121,6 +126,11 @@ def load_engine(engine_data: dict) -> Optional[ConfiguredEngine]:
         logger.exception('Cannot load engine "{}"'.format(engine_module))
         return None
 
+    if engine_data['engine'] in _NEXTGEN_ENGINES:
+        engine = getattr(engine, _NEXTGEN_ENGINES[engine_data['engine']])(
+            logger=logger.getChild(engine_name),
+        )
+
     update_engine_attributes(engine, engine_data)
     set_language_attributes(engine)
     update_attributes_for_tor(engine)
@@ -204,10 +214,11 @@ def _get_supported_languages(engine: ConfiguredEngine) -> Collection[str]:
 
 
 def set_language_attributes(engine: ConfiguredEngine):
-    engine.supported_languages = _get_supported_languages(engine)
+    if not isinstance(engine, Engine):
+        engine.supported_languages = _get_supported_languages(engine)
 
-    # find custom aliases for non standard language codes
-    engine.language_aliases.update(find_language_aliases(engine.supported_languages))
+        # find custom aliases for non standard language codes
+        engine.language_aliases.update(find_language_aliases(engine.supported_languages))
 
     # language_support
     engine.language_support = len(engine.supported_languages) > 0

searx/results.py

@@ -6,6 +6,7 @@ from typing import List, NamedTuple, Set
 from urllib.parse import urlparse, unquote
 
 from searx import logger
+from searx.engine import InfoBox, StandardResult
 from searx.engines import engines
 from searx.metrics import histogram_observe, counter_add, count_error
 
@@ -195,6 +196,17 @@ class ResultContainer:
         standard_result_count = 0
         error_msgs = set()
         for result in list(results):
+            if isinstance(result, InfoBox):
+                result = {
+                    'infobox': result.title,
+                    'id': result.url,
+                    'content': result.content,
+                    'img_src': result.img_src,
+                    'urls': result.links,
+                }
+            elif isinstance(result, StandardResult):
+                result = result.__dict__
+
             result['engine'] = engine_name
             if 'suggestion' in result and self.on_result(result):
                 self.suggestions.add(result['suggestion'])

searx/search/processors/online.py

@@ -17,6 +17,7 @@ from searx.exceptions import (
     SearxEngineTooManyRequestsException,
 )
 from searx.metrics.error_recorder import count_error
+from searx.engine import OnlineEngine, QueryContext
 from .abstract import EngineProcessor
 
 
@@ -114,7 +115,21 @@ class OnlineProcessor(EngineProcessor):
     def _search_basic(self, query, params):
         # update request parameters dependent on
         # search-engine (contained in engines folder)
-        self.engine.request(query, params)
+        if isinstance(self.engine, OnlineEngine):
+            params.update(
+                self.engine.request(
+                    query,
+                    QueryContext(
+                        category=params['category'],
+                        safesearch=params['safesearch'],
+                        time_range=params['time_range'],
+                        pageno=params['pageno'],
+                        language=params['language'],
+                    ),
+                ).__dict__
+            )
+        else:
+            self.engine.request(query, params)
 
         # ignoring empty urls
         if params['url'] is None: