FEATURE: avatar proxy happens in background

This ensures that even if it is slow to download avatars site will
continue to work

Also simplifies hijack pattern

lib/hijack.rb

@@ -5,58 +5,10 @@
 # free up a unicorn worker while the remote IO is happening
 module Hijack
 
-  class FakeResponse
-    attr_reader :headers
-    def initialize
-      @headers = {}
-    end
-  end
-
-  class Binder
-    attr_reader :content_type, :body, :status, :response
-
-    def initialize
-      @content_type = 'text/plain'
-      @status = 500
-      @body = ""
-      @response = FakeResponse.new
-    end
-
-    def immutable_for(duration)
-      response.headers['Cache-Control'] = "max-age=#{duration}, public, immutable"
-    end
-
-    def render(opts)
-      if opts[:status]
-        @status = opts[:status].to_i
-      else
-        @status = 200
-      end
-
-      if opts.key?(:body)
-        @body = opts[:body].to_s
-      end
-
-      if opts.key?(:content_type)
-        @content_type = opts[:content_type]
-      end
-
-      if opts.key?(:plain)
-        @content_type = 'text/plain; charset=utf-8'
-        @body = opts[:plain].to_s
-      end
-
-      if opts.key?(:json)
-        @content_type = 'application/json; charset=utf-8'
-        @body = opts[:json]
-        unless String === @body
-          @body = @body.to_json
-        end
-      end
-    end
-  end
-
   def hijack(&blk)
+    controller_class = self.class
+    request = self.request
+
     if hijack = request.env['rack.hijack']
       io = hijack.call
 
@@ -67,26 +19,41 @@ module Hijack
           # before doing any work
           io.write "HTTP/1.1 "
 
-          binder = Binder.new
+          # this trick avoids double render, also avoids any litter that the controller hooks
+          # place on the response
+          instance = controller_class.new
+          response = ActionDispatch::Response.new
+          instance.response = response
+          instance.request = request
+
           begin
-            binder.instance_eval(&blk)
+            instance.instance_eval(&blk)
           rescue => e
             Rails.logger.warn("Failed to process hijacked response correctly #{e}")
           end
 
-          headers = binder.response.headers
-          headers['Content-Length'] = binder.body.bytesize
-          headers['Content-Type'] = binder.content_type
+          unless instance.response_body
+            instance.status = 500
+          end
+
+          response.commit!
+
+          body = response.body
+
+          headers = response.headers
+          headers['Content-Length'] = body.bytesize
+          headers['Content-Type'] = response.content_type || "text/plain"
           headers['Connection'] = "close"
 
-          io.write "#{binder.status} OK\r\n"
+          status_string = Rack::Utils::HTTP_STATUS_CODES[instance.status.to_i] || "Unknown"
+          io.write "#{instance.status} #{status_string}\r\n"
 
           headers.each do |name, val|
             io.write "#{name}: #{val}\r\n"
           end
 
           io.write "\r\n"
-          io.write binder.body
+          io.write body
           io.close
         rescue Errno::EPIPE, IOError
           # happens if client terminated before we responded, ignore
@@ -95,18 +62,7 @@ module Hijack
       # not leaked out, we use 418 ... I am a teapot to denote that we are hijacked
       render plain: "", status: 418
     else
-      binder = Binder.new
-      binder.instance_eval(&blk)
-
-      binder.response.headers.each do |name, val|
-        response.headers[name] = val
-      end
-
-      render(
-        body: binder.body,
-        content_type: binder.content_type,
-        status: binder.status
-      )
+      blk.call
     end
   end
 end