Retry signing the request if too slow (#363)

There are cases where the cryptographic operation to sign the request
takes unusually long. One example is when using a hardware such as the
YubiKey which is busy signing other stuff.

The Serveradmin server is pretty strict and would reject these as expired
for security reasons.

To gracefully handle temporary congestion in the signing we log an error
and retry the operation up to Settings.tries.

adminapi/request.py

@@ -2,7 +2,7 @@
 
 Copyright (c) 2019 InnoGames GmbH
 """
-
+import logging
 import os
 from hashlib import sha1
 import hmac
@@ -41,6 +41,9 @@
 )
 
 
+logger = logging.getLogger(__name__)
+
+
 def load_private_key_file(private_key_path):
     """Try to load a private ssh key from disk
 
@@ -69,6 +72,7 @@ class Settings:
     timeout = 60.0
     tries = 3
     sleep_interval = 5
+    grace_period = 15  # <= serveradmin.api.decorators.TIMESTAMP_GRACE_PERIOD
 
 
 def calc_message(timestamp, data=None):
@@ -137,7 +141,7 @@ def send_request(endpoint, get_params=None, post_params=None):
     return json.loads(response.read().decode())
 
 
-def _build_request(endpoint, get_params, post_params):
+def _build_request(endpoint, get_params, post_params, retry=1):
     """Wrap request data in an urllib Request instance
 
     Aside from preparing the get and post data for transport, this function
@@ -184,6 +188,15 @@ def _build_request(endpoint, get_params, post_params):
         headers['X-PublicKeys'] = ','.join(key_signatures.keys())
         headers['X-Signatures'] = ','.join(key_signatures.values())
 
+    time_spent_signing = int(time.time()) - timestamp
+    if time_spent_signing > Settings.grace_period:
+        if retry <= Settings.tries:
+            logger.error(
+                f'Signing the requests took {time_spent_signing} seconds! '
+                'Serveradmin would reject this request. Maybe your signing '
+                f'soft-/hardware is congested ? Retry {retry}/{Settings.tries}.')
+            return _build_request(endpoint, get_params, post_params, retry+1)
+
     if not Settings.base_url:
         raise ConfigurationError(
             'Environment variable SERVERADMIN_BASE_URL not set'