through error when fediverse server is configured but crypto is missing

modules/fediverse/__init__.py

@@ -1,6 +1,6 @@
 import urllib.parse
 from src import IRCBot, ModuleManager, utils
-from . import ap_actor, ap_server, ap_utils
+from . import ap_actor, ap_security, ap_server, ap_utils
 
 def _format_username(username, instance):
     return "@%s@%s" % (username, instance)
@@ -25,6 +25,9 @@ class Module(ModuleManager.BaseModule):
                 raise ValueError("`tls-key` not provided in bot config")
             if not "tls-certificate" in self.bot.config:
                 raise ValueError("`tls-certificate` not provided in bot config")
+            if not ap_security.has_crypto:
+                raise ValueError("cyprography library is not installed "
+                    "(https://pypi.org/project/cryptography/)")
 
             server_username, instance = ap_utils.split_username(server_username)
             self.server = ap_server.Server(self.bot, self.exports,

modules/fediverse/ap_security.py

@@ -1,12 +1,16 @@
 import base64, typing
+
+try:
     from cryptography.hazmat.primitives import hashes, serialization
     from cryptography.hazmat.primitives.asymmetric import padding, rsa
     from cryptography.hazmat.backends import default_backend
+    has_crypto = True
+except ModuleNotFoundError:
+    has_crypto = False
 
 SIGNATURE_FORMAT = (
     "keyId=\"%s\",headers=\"%s\",signature=\"%s\",algorithm=\"rsa-sha256\"")
 
-
 def _private_key(key_filename: str) -> rsa.RSAPrivateKey:
     with open(key_filename, "rb") as key_file:
         return serialization.load_pem_private_key(