add rate limiting per engine

searx/plugins/engine_rate_limiter.py

@@ -0,0 +1,79 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+# lint: pylint
+# pyright: basic
+"""Rate limit outgoing requests per engine
+
+Enable ``settings.yml``:
+
+- ``redis.url: ...`` check the value, see :ref:`settings redis`
+- ``rate_limit: ...`` max_requests and interval, as specified below
+- ``max_requests: ...`` max number of requests for that engine per interval
+- ``interval: ...`` number of seconds before rate limiting resets (optional, by default 1 second)
+"""
+
+import hmac
+
+from searx import settings
+from searx.engines import engines
+from searx.shared import redisdb
+
+name = "Engine rate limiter"
+description = "Limit the number of outgoing requests per engine"
+default_on = True
+preference_section = 'service'
+
+
+def check_rate_limiter(engine_name, limit, interval):
+    redis_client = redisdb.client()
+    lua_script = """
+    local engine = KEYS[1]
+    local limit = ARGV[1]
+    local interval = ARGV[2]
+
+    local count = redis.call('GET', engine)
+    if count and count > limit then
+        return count
+    else
+        local newCount = redis.call('INCR', engine)
+        if newCount == 1 then
+            redis.call('EXPIRE', engine, interval)
+        end
+        return newCount
+    end
+    """
+    script_sha = redis_client.script_load(lua_script)
+
+    secret_key_bytes = bytes(settings['server']['secret_key'], encoding='utf-8')
+    m = hmac.new(secret_key_bytes, digestmod='sha256')
+    m.update(bytes(engine_name, encoding='utf-8'))
+    key = m.digest()
+
+    requestsCounter = redis_client.evalsha(script_sha, 1, key, limit, interval)
+    return int(requestsCounter)
+
+
+def below_rate_limit(engine_name):
+    engine = engines[engine_name]
+    max_requests = engine.rate_limit['max_requests']
+    interval = engine.rate_limit['interval']
+
+    if max_requests == float('inf'):
+        return True
+    if max_requests >= check_rate_limiter(engine_name, max_requests, interval):
+        return True
+    logger.debug(f"{engine_name} exceeded rate limit of {max_requests} requests per {interval} seconds")  # pylint: disable=undefined-variable
+    return False
+
+
+def pre_search(_, search):
+    allowed_engines = list(filter(lambda e: below_rate_limit(e.name), search.search_query.engineref_list))
+    search.search_query.engineref_list = allowed_engines
+    return bool(allowed_engines)
+
+
+def init(*args, **kwargs):  # pylint: disable=unused-argument
+    logger.debug("init engine rate limiter DB")  # pylint: disable=undefined-variable
+    if not redisdb.init():
+        logger.error("init engine rate limiter DB failed!!!")  # pylint: disable=undefined-variable
+        return False
+    return True