[mod] Revision of the favicon solution

All favicons implementations have been documented and moved to the Python
package:

    searx.favicons

There is a configuration (based on Pydantic) for the favicons and all its
components:

    searx.favicons.config

A solution for caching favicons has been implemented:

    searx.favicon.cache

If the favicon is already in the cache, the returned URL is a data URL [1]
(something like `data:image/png;base64,...`).  By generating a data url from
the FaviconCache, additional HTTP roundtripps via the favicon_proxy are saved:

    favicons.proxy.favicon_url

The favicon proxy service now sets a HTTP header "Cache-Control: max-age=...":

    favicons.proxy.favicon_proxy

The resolvers now also provide the mime type (data, mime):

    searx.favicon.resolvers

[1] https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/Data_URLs

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

searx/favicons/resolvers.py

@@ -0,0 +1,100 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+"""Implementations of the favicon *resolvers* that are available in the favicon
+proxy by default.  A *resolver* is a function that obtains the favicon from an
+external source.  The *resolver* function receives two arguments (``domain,
+timeout``) and returns a tuple ``(data, mime)``.
+
+"""
+
+from __future__ import annotations
+
+__all__ = ["DEFAULT_RESOLVER_MAP", "allesedv", "duckduckgo", "google", "yandex"]
+
+from typing import Callable
+from searx import network
+from searx import logger
+
+DEFAULT_RESOLVER_MAP: dict[str, Callable]
+logger = logger.getChild('favicons.resolvers')
+
+
+def _req_args(**kwargs):
+    # add the request arguments from the searx.network
+    d = {"raise_for_httperror": False}
+    d.update(kwargs)
+    return d
+
+
+def allesedv(domain: str, timeout: int) -> tuple[None | bytes, None | str]:
+    """Favicon Resolver from allesedv.com / https://favicon.allesedv.com/"""
+    data, mime = (None, None)
+    url = f"https://f1.allesedv.com/32/{domain}"
+    logger.debug("fetch favicon from: %s", url)
+
+    # will just return a 200 regardless of the favicon existing or not
+    # sometimes will be correct size, sometimes not
+    response = network.get(url, **_req_args(timeout=timeout))
+    if response and response.status_code == 200:
+        mime = response.headers['Content-Type']
+        if mime != 'image/gif':
+            data = response.content
+    return data, mime
+
+
+def duckduckgo(domain: str, timeout: int) -> tuple[None | bytes, None | str]:
+    """Favicon Resolver from duckduckgo.com / https://blog.jim-nielsen.com/2021/displaying-favicons-for-any-domain/"""
+    data, mime = (None, None)
+    url = f"https://icons.duckduckgo.com/ip2/{domain}.ico"
+    logger.debug("fetch favicon from: %s", url)
+
+    # will return a 404 if the favicon does not exist and a 200 if it does,
+    response = network.get(url, **_req_args(timeout=timeout))
+    if response and response.status_code == 200:
+        # api will respond with a 32x32 png image
+        mime = response.headers['Content-Type']
+        data = response.content
+    return data, mime
+
+
+def google(domain: str, timeout: int) -> tuple[None | bytes, None | str]:
+    """Favicon Resolver from google.com"""
+    data, mime = (None, None)
+
+    # URL https://www.google.com/s2/favicons?sz=32&domain={domain}" will be
+    # redirected (HTTP 301 Moved Permanently) to t1.gstatic.com/faviconV2:
+    url = (
+        f"https://t1.gstatic.com/faviconV2?client=SOCIAL&type=FAVICON&fallback_opts=TYPE,SIZE,URL"
+        f"&url=https://{domain}&size=32"
+    )
+    logger.debug("fetch favicon from: %s", url)
+
+    # will return a 404 if the favicon does not exist and a 200 if it does,
+    response = network.get(url, **_req_args(timeout=timeout))
+    if response and response.status_code == 200:
+        # api will respond with a 32x32 png image
+        mime = response.headers['Content-Type']
+        data = response.content
+    return data, mime
+
+
+def yandex(domain: str, timeout: int) -> tuple[None | bytes, None | str]:
+    """Favicon Resolver from yandex.com"""
+    data, mime = (None, None)
+    url = f"https://favicon.yandex.net/favicon/{domain}"
+    logger.debug("fetch favicon from: %s", url)
+
+    # api will respond with a 16x16 png image, if it doesn't exist, it will be a
+    # 1x1 png image (70 bytes)
+    response = network.get(url, **_req_args(timeout=timeout))
+    if response and response.status_code == 200 and len(response.content) > 70:
+        mime = response.headers['Content-Type']
+        data = response.content
+    return data, mime
+
+
+DEFAULT_RESOLVER_MAP = {
+    "allesedv": allesedv,
+    "duckduckgo": duckduckgo,
+    "google": google,
+    "yandex": yandex,
+}