Fix issues with Content-Length after explicit forward [#159]

lib/sinatra/base.rb

@@ -49,7 +49,7 @@ module Sinatra
       else
         body = @body || []
         body = [body] if body.respond_to? :to_str
-        if header["Content-Length"].nil? && body.respond_to?(:to_ary)
+        if body.respond_to?(:to_ary)
           header["Content-Length"] = body.to_ary.
             inject(0) { |len, part| len + part.bytesize }.to_s
         end
@@ -345,9 +345,9 @@ module Sinatra
       invoke { error_block!(response.status) }
 
       # never respond with a body on HEAD requests
-      @response.body = [] if @env['REQUEST_METHOD'] == 'HEAD'
+      status, header, body = @response.finish
-
+      body = [] if @env['REQUEST_METHOD'] == 'HEAD'
-      @response.finish
+      [status, header, body]
     end
 
     # Access options defined with Base.set.

test/base_test.rb

@@ -108,5 +108,23 @@ describe "Sinatra::Base as Rack middleware" do
     assert_equal 210, response.status
     assert_equal 'true', response['X-Downstream']
     assert_equal 'Hello after explicit forward', response.body
+    assert_equal '28', response['Content-Length']
+  end
+
+  app_content_length = lambda {|env|
+    [200, {'Content-Length' => '16'}, 'From downstream!']}
+  class TestMiddlewareContentLength < Sinatra::Base
+    get '/forward' do
+      res = forward
+      'From after explicit forward!'
+    end
+  end
+
+  middleware_content_length = TestMiddlewareContentLength.new(app_content_length)
+  request_content_length = Rack::MockRequest.new(middleware_content_length)
+
+  it "sets content length for last response" do
+    response = request_content_length.get('/forward')
+    assert_equal '28', response['Content-Length']
   end
 end