Log errors captured by the JSON api

One thing that we were lacking was actually logging any errors which
occurred with a JSON api endpoint. This simply cargo cults, copies, the
logic that Rails already uses for errors. The logic has changed slightly
for Rails 5, but since we are not targeting that just yet we'll stick
with the latest Rails 4.2.6 version.

We need to log the error before we render the JSON as our middleware's
return value from `call` is used as the response. There isn't much
special to note about the logging itself. All of the complex logic comes
from Rails, mostly to ensure it focuses on app related errors, stripping
out Rails framework details, when possible.

Author: cupakromer

lib/kracken/json_api/public_exceptions.rb

@@ -1,7 +1,37 @@
 module Kracken
   module JsonApi
+    # Error logging methods used by `ActionDispatch::DebugExceptions`
+    # https://github.com/rails/rails/blob/v4.2.6/actionpack/lib/action_dispatch/middleware/debug_exceptions.rb
+    module ErrorLogging
+      def log_error(env, wrapper)
+        logger = logger(env)
+        return unless logger
+
+        exception = wrapper.exception
+
+        trace = wrapper.application_trace
+        trace = wrapper.framework_trace if trace.empty?
+
+        ActiveSupport::Deprecation.silence do
+          message = "\n#{exception.class} (#{exception.message}):\n"
+          message << exception.annoted_source_code.to_s if exception.respond_to?(:annoted_source_code)
+          message << "  " << trace.join("\n  ")
+          logger.fatal("#{message}\n\n")
+        end
+      end
+
+      def logger(env)
+        env['action_dispatch.logger'] || stderr_logger
+      end
+
+      def stderr_logger
+        @stderr_logger ||= ActiveSupport::Logger.new($stderr)
+      end
+    end
+
     class PublicExceptions
-      attr_reader :app
+      include ErrorLogging
+
       def initialize(app)
         @app = app
       end
@@ -29,7 +59,9 @@ def capture_error(env)
 
         response
       rescue Exception => exception
-        render_json_error(ExceptionWrapper.new(env, exception))
+        wrapper = ExceptionWrapper.new(env, exception)
+        log_error(env, wrapper)
+        render_json_error(wrapper)
       end
 
       if Rails.env.production?