Merge pull request #3242 from ranjib/chef_handler

[RFC-039] chef handler dsl

6 files changed, 183 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 5cf4f95af5..458ac82467 100644
--- a/lib/chef/chef_class.rb
+++ b/lib/chef/chef_class.rb
@@ -52,7 +52,14 @@ class Chef
     #
     attr_reader :run_context
 
+    # Register an event handler with user specified block
     #
+    # @return[Chef::EventDispatch::Base] handler object
+    def event_handler(&block)
+      dsl = Chef::EventDispatch::DSL.new('Chef client DSL')
+      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..c6f21c9b45
--- /dev/null
+++ b/lib/chef/event_dispatch/dsl.rb
@@ -0,0 +1,64 @@
+#
+# 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
+      attr_reader :handler
+
+      def initialize(name)
+        klass = Class.new(Chef::EventDispatch::Base) do
+          attr_reader :name
+        end
+        @handler = klass.new
+        @handler.instance_variable_set(:@name, name)
+
+        # Use event.register API to add anonymous handler if Chef.run_context
+        # and associated event dispatcher is set, else fallback to
+        # Chef::Config[:hanlder]
+        if Chef.run_context && Chef.run_context.events
+          Chef::Log.debug("Registering handler '#{name}' using events api")
+          Chef.run_context.events.register(handler)
+        else
+          Chef::Log.debug("Registering handler '#{name}' using global config")
+          Chef::Config[:event_handlers] << handler
+        end
+      end
+
+      # 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.define_singleton_method(event_type) do |*args|
+          instance_exec(*args, &block)
+        end
+      end
+
+      private
+      def validate!(event_type)
+        all_event_types = (Chef::EventDispatch::Base.instance_methods - Object.instance_methods)
+        raise Chef::Exceptions::InvalidEventType, "Invalid event type: #{event_type}" unless all_event_types.include?(event_type)
+      end
+    end
+  end
+end
diff --git a/lib/chef/exceptions.rb b/lib/chef/exceptions.rb
index d5c4c4832b..e2e36e8162 100644
--- a/lib/chef/exceptions.rb
+++ b/lib/chef/exceptions.rb
@@ -103,6 +103,7 @@ class Chef
     class ProviderNotFound < RuntimeError; end
     NoProviderAvailable = ProviderNotFound
     class VerificationNotFound < RuntimeError; end
+    class InvalidEventType < ArgumentError; end
     class MultipleIdentityError < RuntimeError; end
 
     # Can't find a Resource of this type that is valid on this platform.
diff --git a/spec/unit/chef_class_spec.rb b/spec/unit/chef_class_spec.rb
index 2528246be6..d6bf74572e 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::InvalidEventType)
+    end
+  end
 end
diff --git a/spec/unit/event_dispatch/dsl_spec.rb b/spec/unit/event_dispatch/dsl_spec.rb
new file mode 100644
index 0000000000..f467ea81ea
--- /dev/null
+++ b/spec/unit/event_dispatch/dsl_spec.rb
@@ -0,0 +1,87 @@
+#
+# 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 'spec_helper'
+require 'chef/event_dispatch/dsl'
+
+describe Chef::EventDispatch::DSL do
+  let(:events) do
+    Chef::EventDispatch::Dispatcher.new
+  end
+
+  let(:run_context) do
+    Chef::RunContext.new(Chef::Node.new, nil, events)
+  end
+
+  before do
+    Chef.set_run_context(run_context)
+  end
+
+  after do
+    Chef.reset!
+  end
+
+  subject{ described_class.new('test') }
+
+  it 'set handler name' do
+    subject.on(:run_started) {}
+    expect(events.subscribers.first.name).to eq('test')
+  end
+
+  it 'raise error when invalid event type is supplied' do
+    expect do
+      subject.on(:foo_bar) {}
+    end.to raise_error(Chef::Exceptions::InvalidEventType)
+  end
+
+  it 'register user hooks against valid event type' do
+    subject.on(:run_failed) {'testhook'}
+    expect(events.subscribers.first.run_failed).to eq('testhook')
+  end
+
+  it 'preserve state across event hooks' do
+    calls = []
+    Chef.event_handler do
+      on :resource_updated do
+        calls << :updated
+      end
+      on :resource_action_start do
+        calls << :started
+      end
+    end
+    resource = Chef::Resource::RubyBlock.new('foo', run_context)
+    resource.block { }
+    resource.run_action(:run)
+    expect(calls).to eq([:started, :updated])
+  end
+
+  it 'preserve instance variables across handler callbacks' do
+    Chef.event_handler do
+      on :resource_action_start do
+        @ivar = [1]
+      end
+      on :resource_updated do
+        @ivar << 2
+      end
+    end
+    resource = Chef::Resource::RubyBlock.new('foo', run_context)
+    resource.block { }
+    resource.run_action(:run)
+    expect(events.subscribers.first.instance_variable_get(:@ivar)).to eq([1, 2])
+  end
+end