[RFC-039] chef handler dsl

5 files changed, 77 insertions, 1 deletions

diff --git a/lib/chef.rb b/lib/chef.rb
index 6bce976439..1a0b802adb 100644
--- a/lib/chef.rb
+++ b/lib/chef.rb
@@ -31,5 +31,5 @@ require 'chef/daemon'
 require 'chef/run_status'
 require 'chef/handler'
 require 'chef/handler/json_file'
-
+require 'chef/event_dispatch/dsl'
 require 'chef/chef_class'
diff --git a/lib/chef/chef_class.rb b/lib/chef/chef_class.rb
index d3f7ee55c7..60dd5efef4 100644
--- a/lib/chef/chef_class.rb
+++ b/lib/chef/chef_class.rb
@@ -43,6 +43,12 @@ class Chef
     # @return [Chef::RunContext] run_context of the chef-client run
     attr_reader :run_context
 
+    # Adds an event handler with user defined block
+    def event_handler(&block)
+      dsl = Chef::EventDispatch::DSL.new
+      dsl.instance_eval(&block)
+    end
+
     # Get the array of providers associated with a resource_name for the current node
     #
     # @param resource_name [Symbol] name of the resource as a symbol
diff --git a/lib/chef/event_dispatch/dsl.rb b/lib/chef/event_dispatch/dsl.rb
new file mode 100644
index 0000000000..f61ea90580
--- /dev/null
+++ b/lib/chef/event_dispatch/dsl.rb
@@ -0,0 +1,46 @@
+#
+# Author:: Ranjib Dey (<ranjib@linux.com>)
+# Copyright:: Copyright (c) 2015 Ranjib Dey
+# 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/event_dispatch/base'
+require 'chef/exceptions'
+require 'chef/config'
+
+class Chef
+  module EventDispatch
+    class DSL
+      # Adds a new event handler derived from base handler
+      # with user defined block against a chef event
+      #
+      # @return [Chef::EventDispatch::Base] a base handler object
+      def on(event_type, &block)
+        validate!(event_type)
+        handler = Chef::EventDispatch::Base.new
+        handler.define_singleton_method(event_type) do |*args|
+          block.call(args)
+        end
+        Chef::Config[:event_handlers] << handler
+        handler
+      end
+
+      private
+      def validate!(event_type)
+        all_event_types = (Chef::EventDispatch::Base.instance_methods - Object.instance_methods)
+        raise Chef::Exceptions::UnknownEventType unless all_event_types.include?(event_type)
+      end
+    end
+  end
+end
diff --git a/lib/chef/exceptions.rb b/lib/chef/exceptions.rb
index eea6a2f239..0b7b1634ad 100644
--- a/lib/chef/exceptions.rb
+++ b/lib/chef/exceptions.rb
@@ -91,6 +91,7 @@ class Chef
     class InvalidResourceReference < RuntimeError; end
     class ResourceNotFound < RuntimeError; end
     class VerificationNotFound < RuntimeError; end
+    class UnknownEventType < ArgumentError; end
 
     # Can't find a Resource of this type that is valid on this platform.
     class NoSuchResourceType < NameError
diff --git a/spec/unit/chef_class_spec.rb b/spec/unit/chef_class_spec.rb
index 2528246be6..65a637dcbb 100644
--- a/spec/unit/chef_class_spec.rb
+++ b/spec/unit/chef_class_spec.rb
@@ -88,4 +88,27 @@ describe "Chef class" do
       expect(Chef.node).to eql(node)
     end
   end
+
+  context '#event_handler' do
+    it 'adds a new handler' do
+      x = 1
+      Chef.event_handler do
+        on :converge_start do
+          x = 2
+        end
+      end
+      expect(Chef::Config[:event_handlers]).to_not be_empty
+      Chef::Config[:event_handlers].first.send(:converge_start)
+      expect(x).to eq(2)
+    end
+
+    it 'raise error if unknown event type is passed' do
+      expect do
+        Chef.event_handler do
+          on :yolo do
+          end
+        end
+      end.to raise_error(Chef::Exceptions::UnknownEventType)
+    end
+  end
 end