Do not alter real (non-stubbed) request headers when handling em-http…

…-request requests.

lib/webmock/http_lib_adapters/em_http_request_adapter.rb

@@ -101,7 +101,7 @@ def setup(response, uri, error = nil)
 
       def connection_completed
         @state = :response_header
-        send_request(request_signature.headers, request_signature.body)
+        send_request(*headers_and_body_processed_by_middleware)
       end
 
       def send_request(head, body)
@@ -168,12 +168,18 @@ def build_webmock_response
         webmock_response
       end
 
-      def build_request_signature
-        headers, body = build_request, @req.body
-
-        @conn.middleware.select {|m| m.respond_to?(:request) }.each do |m|
-          headers, body = m.request(self, headers, body)
+      def headers_and_body_processed_by_middleware
+        @headers_and_body_processed_by_middleware ||= begin
+          head, body = build_request, @req.body
+          @conn.middleware.each do |m|
+            head, body = m.request(self, head, body) if m.respond_to?(:request)
+          end
+          [head, body]
         end
+      end
+
+      def build_request_signature
+        headers, body = headers_and_body_processed_by_middleware
 
         method = @req.method
         uri = @req.uri.clone

spec/acceptance/em_http_request/em_http_request_spec.rb

@@ -149,6 +149,18 @@ def response(resp)
           before { WebMock.allow_net_connect! }
           include_examples "em-http-request middleware/after_request hook integration"
 
+          it "doesn't modify headers" do
+            EM.run do
+              conn = EventMachine::HttpRequest.new(webmock_server_url)
+              http = conn.post(head: { 'content-length' => '4' }, body: 'test')
+              expect(conn).to receive(:send_data).with(/POST \/ HTTP\/1.1\r\nContent-Length: 4\r\nConnection: close\r\nHost: localhost:\d+\r\nUser-Agent: EventMachine HttpClient\r\nAccept-Encoding: gzip, compressed\r\n\r\n/).and_call_original
+              expect(conn).to receive(:send_data).with('test')
+              http.callback do
+                EM.stop
+              end
+            end
+          end
+
           it "only calls request middleware once" do
             middleware = Class.new do
               def self.called!