Allow to set a registered encoder in a Flow by name

lib/rackstash/flow.rb

@@ -188,6 +188,7 @@ module Rackstash
     def encoder(encoder = nil)
       return @encoder if encoder.nil?
       self.encoder = encoder
+      @encoder
     end
 
     # Set the encoder for the log {#adapter}. You can use any object which
@@ -198,8 +199,7 @@ module Rackstash
     #   method
     # @return [#encode] the new `encoder`
     def encoder=(encoder)
-      raise TypeError, 'must provide an encoder' unless encoder.respond_to?(:encode)
-      @encoder = encoder
+      @encoder = Rackstash::Encoder.build(encoder)
     end
 
     # Get or set a separate {Flow} which is used by this flow to write details

spec/rackstash/flow_spec.rb

@@ -221,8 +221,15 @@ RSpec.describe Rackstash::Flow do
       expect(flow.encoder).to equal encoder
     end
 
+    it 'sets an encoder from a spec' do
+      flow.encoder = :raw
+      expect(flow.encoder).to be_a Rackstash::Encoder::Raw
+    end
+
     it 'rejects invalid encoders' do
-      expect { flow.encoder = :foo }.to raise_error TypeError
+      # No registered encoder found
+      expect { flow.encoder = :invalid }.to raise_error KeyError
+
       expect { flow.encoder = 23 }.to raise_error TypeError
       expect { flow.encoder = true }.to raise_error TypeError
       expect { flow.encoder = false }.to raise_error TypeError