Support custom headers in freddy.deliver

Headers are the main point for including message metadata in AMQP.
Headers are already in use to propagate traces.
Allow library users to add arbitrary headers themselves.

README.md

@@ -55,6 +55,11 @@ The message heading specify the `content-encoding` indicating the compression al
 freddy.deliver(destination, message, compress: 'zlib')
 ```
 
+#### Metadata through headers
+
+Send a message with arbitrary message metadata included in the message headers
+freddy.deliver(destination, message, headers: {'my-key' => 'my-value'})
+
 ### Request delivery
 
 #### Expiring messages

lib/freddy.rb

@@ -166,6 +166,8 @@ def tap_into(pattern_or_patterns, options = {}, &callback)
   #   won't be discarded if timeout it set to 0 (default).
   # @option options [String] :compress (nil)
   #   - 'zlib' - compresses the payload with zlib
+  # @option options [Hash] :headers (nil)
+  #   Arbitrary headers to add as message metadata
   # @return [void]
   #
   # @example
@@ -176,6 +178,7 @@ def deliver(destination, payload, options = {})
     opts = {}
     opts[:expiration] = (timeout * 1000).to_i if timeout.positive?
     opts[:content_encoding] = compression_algorithm if compression_algorithm
+    opts[:headers] = options[:headers] if options[:headers]
 
     @send_and_forget_producer.produce(destination, payload, opts)
   end

spec/freddy/freddy_spec.rb

@@ -7,6 +7,13 @@
   let(:destination2) { random_destination }
   let(:payload)      { { pay: 'load' } }
 
+  before do
+    @bunny = Bunny.new(config)
+    @bunny.start()
+  end
+
+  after { @bunny.close }
+
   after { freddy.close }
 
   def respond_to(&block)
@@ -72,6 +79,23 @@ def respond_to(&block)
         expect(@tapped_message).to eq(payload)
       end
     end
+
+    it 'accepts custom headers' do
+      queue = exclusive_subscribe do |_info, metadata, _payload|
+        @metadata = metadata
+      end
+      freddy.deliver(queue, payload, headers: {'foo' => 'bar'})
+
+      wait_for { @metadata }
+      expect(@metadata[:headers]).to include({'foo' => 'bar'})
+    end
+  end
+
+  def exclusive_subscribe(&block)
+    channel = @bunny.create_channel
+    queue = channel.queue('', exclusive: true)
+    queue.subscribe(&block)
+    queue.name
   end
 
   context 'when making a synchronized request' do