Allow to freeze and dup Rackstash::Flows collections

lib/rackstash/flows.rb

@@ -103,6 +103,16 @@ module Rackstash
       end
     end
 
+    # Prevents further modifications to the flows list. A `RuntimeError` will be
+    # raised if you attempt to add, delete, or overwrite flows in the list.
+    # There is no way to unfreeze a frozen object.
+    #
+    # @return [self]
+    def freeze
+      @flows.freeze
+      super
+    end
+
     # @return [String] a string representation of `self`
     def inspect
       id_str = Object.instance_method(:to_s).bind(self).call[2..-2]
@@ -192,8 +202,17 @@ module Rackstash
       @flows.to_s
     end
 
+    protected
+
+    attr_reader :flows
+
     private
 
+    def initialize_copy(other)
+      @flows = other.flows.dup
+      super
+    end
+
     # Create a deep duplicate of an event hash. It is assumed that the input
     # event follows the normalized structure as generated by
     # {Fields::Hash#to_h}.

spec/rackstash/flows_spec.rb

@@ -122,6 +122,41 @@ describe Rackstash::Flows do
     end
   end
 
+  describe '#dup' do
+    it 'dups the flows' do
+      flows << a_flow
+      copied = flows.dup
+
+      expect(copied).to be_instance_of described_class
+      expect(copied.length).to eql 1
+      expect(copied).to_not equal flows
+    end
+
+    it 'separates the flows' do
+      flows << a_flow
+
+      copied = flows.dup
+      copied << a_flow
+
+      expect(copied.first).to equal flows.first
+
+      expect(flows.length).to eql 1
+      expect(copied.length).to eql 2
+    end
+  end
+
+  describe '#freeze' do
+    it 'freezes the object' do
+      expect(flows.freeze).to equal flows
+      expect(flows).to be_frozen
+    end
+
+    it 'denies all further changes' do
+      flows.freeze
+      expect { flows << a_flow }.to raise_error(RuntimeError)
+    end
+  end
+
   describe '#reopen' do
     it 'calls reopen on all flows' do
       [a_flow, a_flow].each do |flow|