Add explicit checks for asgi library versions

Refs daphne/#105

channels/apps.py

@@ -2,6 +2,7 @@ from django.apps import AppConfig
 from django.core.exceptions import ImproperlyConfigured
 
 from .binding.base import BindingMetaclass
+from .package_checks import check_all
 
 
 class ChannelsConfig(AppConfig):
@@ -10,13 +11,8 @@ class ChannelsConfig(AppConfig):
     verbose_name = "Channels"
 
     def ready(self):
-        # Check you're not running 1.10 or above
+        # Check versions
-        try:
+        check_all()
-            from django import channels  # NOQA isort:skip
-        except ImportError:
-            pass
-        else:
-            raise ImproperlyConfigured("You have Django 1.10 or above; use the builtin django.channels!")
         # Do django monkeypatches
         from .hacks import monkeypatch_django
         monkeypatch_django()

channels/package_checks.py

@@ -0,0 +1,30 @@
+import importlib
+from distutils.version import StrictVersion
+
+
+required_versions = {
+    "asgi_redis": "1.2.0",
+    "asgi_ipc": "1.3.0",
+}
+
+
+def check_all():
+    """
+    Checks versions of all the possible packages you have installed so that
+    we can easily warn people about incompatible versions.
+
+    This is needed as there are some packages (e.g. asgi_redis) that we cannot
+    declare dependencies on as they are not _required_. People usually remember
+    to upgrade their Channels package so this is where we check.
+    """
+    for package, version in required_versions.items():
+        try:
+            module = importlib.import_module(package)
+        except ImportError:
+            return
+        else:
+            if StrictVersion(version) > StrictVersion(module.__version__):
+                raise RuntimeError("Your version of %s is too old - it must be at least %s" % (
+                    package,
+                    version,
+                ))