Split utils/general.py

This puts backend specific code in either the builder or scheduler
subpackage. This puts API specific code in the new web subpackage.
Lastly, any code shared between the API and backend is placed in the
common subpackage.

module_build_service/builder/base.py

@@ -7,11 +7,10 @@ import dogpile.cache
 from abc import ABCMeta, abstractmethod
 from requests.exceptions import ConnectionError
 
-from module_build_service import conf, log
+from module_build_service import conf, log, models
 from module_build_service.common.retry import retry
 from module_build_service.models import BUILD_STATES
 from module_build_service.resolver import GenericResolver
-from module_build_service.utils import create_dogpile_key_generator_func
 
 
 """
@@ -30,6 +29,37 @@ Koji workflow
 """
 
 
+def create_dogpile_key_generator_func(skip_first_n_args=0):
+    """
+    Creates dogpile key_generator function with additional features:
+
+    - when models.ModuleBuild is an argument of method cached by dogpile-cache,
+      the ModuleBuild.id is used as a key. Therefore it is possible to cache
+      data per particular module build, while normally, it would be per
+      ModuleBuild.__str__() output, which contains also batch and other data
+      which changes during the build of a module.
+    - it is able to skip first N arguments of a cached method. This is useful
+      when the db.session is part of cached method call, and the caching should
+      work no matter what session instance is passed to cached method argument.
+    """
+
+    def key_generator(namespace, fn):
+        fname = fn.__name__
+
+        def generate_key(*arg, **kwarg):
+            key_template = fname + "_"
+            for s in arg[skip_first_n_args:]:
+                if type(s) == models.ModuleBuild:
+                    key_template += str(s.id)
+                else:
+                    key_template += str(s) + "_"
+            return key_template
+
+        return generate_key
+
+    return key_generator
+
+
 class GenericBuilder(six.with_metaclass(ABCMeta)):
     """
     External Api for builders