Always send the Host header first

wpull/namevalue.py

@@ -80,10 +80,12 @@ def __iter__(self):
     def __len__(self):
         return len(self._map)
 
-    def add(self, name, value):
+    def add(self, name, value, front=False):
         '''Append the name-value pair to the record.'''
         normalized_name = normalize_name(name, self._normalize_overrides)
         self._map[normalized_name].append(value)
+        if front:
+            self._map.move_to_end(normalized_name, last=False)
 
     def get_list(self, name):
         '''Return all the values for given name.'''

wpull/protocol/http/request.py

@@ -136,7 +136,7 @@ def prepare_for_send(self, full_url=False):
         url_info = self.url_info
 
         if 'Host' not in self.fields:
-            self.fields['Host'] = url_info.hostname_with_port
+            self.fields.add('Host', url_info.hostname_with_port, front=True)
 
         if not full_url:
             if url_info.query:

wpull/protocol/http/request_test.py

@@ -18,6 +18,17 @@ def test_request(self):
              b'\r\n'),
             request.to_bytes()
         )
+        # Host should always be first, and automatically added
+        request = Request('http://example.com/robots.txt')
+        request.fields['Accept'] = 'text/plain'
+        request.prepare_for_send()
+        self.assertEqual(
+            (b'GET /robots.txt HTTP/1.1\r\n'
+             b'Host: example.com\r\n'
+             b'Accept: text/plain\r\n'
+             b'\r\n'),
+            request.to_bytes()
+        )
 
     def test_request_parse(self):
         request = Request()