Feature: Allows logging of errors that raised in adapter or other mid…

…dleware.

docs/middleware/response/logger.md

@@ -84,9 +84,10 @@ end
 
 ### Customize the formatter
 
-You can also provide a custom formatter to control how requests and responses are logged.
+You can also provide a custom formatter to control how requests, responses and errors are logged.
 Any custom formatter MUST implement the `request` and `response` method, with one argument which
 will be passed being the Faraday environment.
+Any custom formatter CAN implement the `error` method, with one argument which will be passed being the Faraday error.
 If you make your formatter inheriting from `Faraday::Logging::Formatter`,
 then the methods `debug`, `info`, `warn`, `error` and `fatal` are automatically delegated to the logger.
 
@@ -101,6 +102,11 @@ class MyFormatter < Faraday::Logging::Formatter
     # Build a custom message using `env`
     info('Response') { 'Response Received' }
   end
+
+  def error(error)
+    # Build a custom message using `error`
+    info('Error') { 'Error Raised' }
+  end
 end
 
 conn = Faraday.new(url: 'http://httpbingo.org/api_key=s3cr3t') do |faraday|

lib/faraday/logging/formatter.rb

@@ -35,6 +35,14 @@ def response(env)
         log_body('response', env[:body]) if env[:body] && log_body?(:response)
       end
 
+      def error(error)
+        error_log = proc { error.full_message }
+        public_send(log_level, 'error', &error_log)
+
+        log_headers('error', error.response_headers) if log_headers?(:error)
+        log_body('error', error.response_body) if error.response_body && log_body?(:error)
+      end
+
       def filter(filter_word, filter_replacement)
         @filter.push([filter_word, filter_replacement])
       end

lib/faraday/middleware.rb

@@ -17,6 +17,9 @@ def call(env)
       app.call(env).on_complete do |environment|
         on_complete(environment) if respond_to?(:on_complete)
       end
+    rescue StandardError => e
+      on_error(e) if respond_to?(:on_error)
+      raise
     end
 
     def close

lib/faraday/response/logger.rb

@@ -26,6 +26,10 @@ def call(env)
       def on_complete(env)
         @formatter.response(env)
       end
+
+      def on_error(error)
+        @formatter.error(error) if @formatter.respond_to?(:error)
+      end
     end
   end
 end

spec/faraday/middleware_spec.rb

@@ -33,6 +33,24 @@ def on_request(env)
     end
   end
 
+  describe '#on_error' do
+    subject do
+      Class.new(described_class) do
+        def on_error(error)
+          # do nothing
+        end
+      end.new(app)
+    end
+
+    it 'is called by #call' do
+      expect(app).to receive(:call).and_raise(Faraday::ConnectionFailed)
+      is_expected.to receive(:call).and_call_original
+      is_expected.to receive(:on_error)
+
+      expect { subject.call(double) }.to raise_error(Faraday::ConnectionFailed)
+    end
+  end
+
   describe '#close' do
     context "with app that doesn't support \#close" do
       it 'should issue warning' do

spec/faraday/response/logger_spec.rb

@@ -64,6 +64,15 @@
       expect(formatter).to receive(:response).with(an_instance_of(Faraday::Env))
       conn.get '/hello'
     end
+
+    context 'when no route' do
+      it 'delegates logging to the formatter' do
+        expect(formatter).to receive(:request).with(an_instance_of(Faraday::Env))
+        expect(formatter).to receive(:error).with(an_instance_of(Faraday::Adapter::Test::Stubs::NotFound))
+
+        expect { conn.get '/noroute' }.to raise_error(Faraday::Adapter::Test::Stubs::NotFound)
+      end
+    end
   end
 
   context 'with custom formatter' do