add resource_resolver and resource_priority_map

also wire them up through the Chef class.

1 files changed, 101 insertions, 0 deletions

diff --git a/lib/chef/resource_resolver.rb b/lib/chef/resource_resolver.rb
new file mode 100644
index 0000000000..ff9d7aeb9f
--- /dev/null
+++ b/lib/chef/resource_resolver.rb
@@ -0,0 +1,101 @@
+#
+# Author:: Lamont Granquist (<lamont@chef.io>)
+# Copyright:: Copyright (c) 2015 Chef Software, Inc.
+# License:: Apache License, Version 2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+require 'chef/exceptions'
+require 'chef/platform/resource_priority_map'
+
+class Chef
+  class ResourceResolver
+
+    attr_reader :node
+    attr_reader :resource
+    attr_reader :action
+
+    def initialize(node, resource)
+      @node = node
+      @resource = resource
+    end
+
+    # return a deterministically sorted list of Chef::Resource subclasses
+    def resources
+      @resources ||= Chef::Resource.descendants
+    end
+
+    def resolve
+      maybe_dynamic_resource_resolution(resource) ||
+        maybe_chef_platform_lookup(resource)
+    end
+
+    # this cut looks at if the resource can handle the resource type on the node
+    def enabled_handlers
+      @enabled_handlers ||=
+        resources.select do |klass|
+          klass.provides?(node, resource)
+        end.sort {|a,b| a.to_s <=> b.to_s }
+      @enabled_handlers
+    end
+
+    private
+
+    # try dynamically finding a resource based on querying the resources to see what they support
+    def maybe_dynamic_resource_resolution(resource)
+      # log this so we know what resources will work for the generic resource on the node (early cut)
+      Chef::Log.debug "resources for generic #{resource} resource enabled on node include: #{enabled_handlers}"
+
+      # if none of the resources specifically support the resource, we still need to pick one of the resources that are
+      # enabled on the node to handle the why-run use case.
+      handlers = enabled_handlers
+
+      if handlers.count >= 2
+        # this magic stack ranks the resources by where they appear in the resource_priority_map
+        priority_list = [ get_priority_array(node, resource) ].flatten.compact
+        handlers = handlers.sort_by { |x| i = priority_list.index x; i.nil? ? Float::INFINITY : i }
+        if priority_list.index(handlers.first).nil?
+          # if we had more than one and we picked one with a precidence of infinity that means that the resource_priority_map
+          # entry for this resource is missing -- we should probably raise here and force resolution of the ambiguity.
+          Chef::Log.warn "Ambiguous resource precedence: #{handlers}, please use Chef.set_resource_priority_array to provide determinism"
+        end
+        handlers = [ handlers.first ]
+      end
+
+      Chef::Log.debug "resources that survived replacement include: #{handlers}"
+
+      raise Chef::Exceptions::AmbiguousResourceResolution.new(resource, handlers) if handlers.count >= 2
+
+      Chef::Log.debug "dynamic resource resolver FAILED to resolve a resouce" if handlers.empty?
+
+      return nil if handlers.empty?
+
+      handlers[0]
+    end
+
+    # try the old static lookup of resources by mangling name to resource klass
+    def maybe_chef_platform_lookup(resource)
+      Chef::Resource.resource_matching_short_name(resource)
+    end
+
+    # dep injection hooks
+    def get_priority_array(node, resource_name)
+      resource_priority_map.get_priority_array(node, resource_name)
+    end
+
+    def resource_priority_map
+      Chef::Platform::ResourcePriorityMap.instance
+    end
+  end
+end