[mod] botdetection - improve ip_limit and link_token methods

- counting requests in LONG_WINDOW and BURST_WINDOW is not needed when the
  request is validated by the link_token method [1]

- renew a ping-key on validation [2], this is needed for infinite scrolling,
  where no new token (CSS) is loaded. / this does not fix the BURST_MAX issue in
  the vanilla limiter

- normalize the counter names of the ip_limit method to 'ip_limit.*'

- just integrate the ip_limit method straight forward in the limiter plugin /
  non intermediate code --> ip_limit now returns None or a werkzeug.Response
  object that can be passed by the plugin to the flask application / non
  intermediate code that returns a tuple

[1] https://github.com/searxng/searxng/pull/2357#issuecomment-1566113277
[2] https://github.com/searxng/searxng/pull/2357#discussion_r1208542206
[3] https://github.com/searxng/searxng/pull/2357#issuecomment-1566125979

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

1 files changed, 93 insertions, 0 deletions

diff --git a/searx/botdetection/_helpers.py b/searx/botdetection/_helpers.py
new file mode 100644
index 000000000..b034b980b
--- /dev/null
+++ b/searx/botdetection/_helpers.py
@@ -0,0 +1,93 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+# lint: pylint
+# pylint: disable=missing-module-docstring, invalid-name
+
+from typing import Optional
+import flask
+import werkzeug
+
+from searx import logger
+
+logger = logger.getChild('botdetection')
+
+
+def dump_request(request: flask.Request):
+    return (
+        "%s: %s" % (get_real_ip(request), request.path)
+        + " || X-Forwarded-For: %s" % request.headers.get('X-Forwarded-For')
+        + " || X-Real-IP: %s" % request.headers.get('X-Real-IP')
+        + " || form: %s" % request.form
+        + " || Accept: %s" % request.headers.get('Accept')
+        + " || Accept-Language: %s" % request.headers.get('Accept-Language')
+        + " || Accept-Encoding: %s" % request.headers.get('Accept-Encoding')
+        + " || Content-Type: %s" % request.headers.get('Content-Type')
+        + " || Content-Length: %s" % request.headers.get('Content-Length')
+        + " || Connection: %s" % request.headers.get('Connection')
+        + " || User-Agent: %s" % request.headers.get('User-Agent')
+    )
+
+
+def too_many_requests(request: flask.Request, log_msg: str) -> Optional[werkzeug.Response]:
+    log_prefix = 'BLOCK %s: ' % get_real_ip(request)
+    logger.debug(log_prefix + log_msg)
+    return flask.make_response(('Too Many Requests', 429))
+
+
+def get_real_ip(request: flask.Request) -> str:
+    """Returns real IP of the request.  Since not all proxies set all the HTTP
+    headers and incoming headers can be faked it may happen that the IP cannot
+    be determined correctly.
+
+    .. sidebar:: :py:obj:`flask.Request.remote_addr`
+
+       SearXNG uses Werkzeug's ProxyFix_ (with it default ``x_for=1``).
+
+    This function tries to get the remote IP in the order listed below,
+    additional some tests are done and if inconsistencies or errors are
+    detected, they are logged.
+
+    The remote IP of the request is taken from (first match):
+
+    - X-Forwarded-For_ header
+    - `X-real-IP header <https://github.com/searxng/searxng/issues/1237#issuecomment-1147564516>`__
+    - :py:obj:`flask.Request.remote_addr`
+
+    .. _ProxyFix:
+       https://werkzeug.palletsprojects.com/middleware/proxy_fix/
+
+    .. _X-Forwarded-For:
+      https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Forwarded-For
+
+    """
+
+    forwarded_for = request.headers.get("X-Forwarded-For")
+    real_ip = request.headers.get('X-Real-IP')
+    remote_addr = request.remote_addr
+    logger.debug("X-Forwarded-For: %s || X-Real-IP: %s || request.remote_addr: %s", forwarded_for, real_ip, remote_addr)
+
+    if not forwarded_for:
+        logger.error("X-Forwarded-For header is not set!")
+    else:
+        from .limiter import get_cfg  # pylint: disable=import-outside-toplevel, cyclic-import
+
+        forwarded_for = [x.strip() for x in forwarded_for.split(',')]
+        x_for: int = get_cfg()['real_ip.x_for']
+        forwarded_for = forwarded_for[-min(len(forwarded_for), x_for)]
+
+    if not real_ip:
+        logger.error("X-Real-IP header is not set!")
+
+    if forwarded_for and real_ip and forwarded_for != real_ip:
+        logger.warning("IP from X-Real-IP (%s) is not equal to IP from X-Forwarded-For (%s)", real_ip, forwarded_for)
+
+    if forwarded_for and remote_addr and forwarded_for != remote_addr:
+        logger.warning(
+            "IP from WSGI environment (%s) is not equal to IP from X-Forwarded-For (%s)", remote_addr, forwarded_for
+        )
+
+    if real_ip and remote_addr and real_ip != remote_addr:
+        logger.warning("IP from WSGI environment (%s) is not equal to IP from X-Real-IP (%s)", remote_addr, real_ip)
+
+    request_ip = forwarded_for or real_ip or remote_addr or '0.0.0.0'
+    logger.debug("get_real_ip() -> %s", request_ip)
+    return request_ip