Force Host header to be first in ClientRequest

CHANGES/3265.bugfix

@@ -0,0 +1 @@
+Ensure Host header is added first to ClientRequest to better replicate browser

CONTRIBUTORS.txt

@@ -1,6 +1,7 @@
 - Contributors -
 ----------------
 A. Jesse Jiryu Davis
+Adam Cooper
 Adam Mills
 Adrián Chaves
 Alec Hanefeld

aiohttp/client_reqrep.py

@@ -305,6 +305,15 @@ def update_headers(self, headers):
             for key, value in headers:
                 self.headers.add(key, value)
 
+        # add host
+        if hdrs.HOST not in self.headers:
+            netloc = self.url.raw_host
+            if helpers.is_ipv6_address(netloc):
+                netloc = '[{}]'.format(netloc)
+            if not self.url.is_default_port():
+                netloc += ':' + str(self.url.port)
+            self.headers[hdrs.HOST] = netloc
+
     def update_auto_headers(self, skip_auto_headers):
         self.skip_auto_headers = CIMultiDict(
             (hdr, None) for hdr in sorted(skip_auto_headers))
@@ -315,15 +324,6 @@ def update_auto_headers(self, skip_auto_headers):
             if hdr not in used_headers:
                 self.headers.add(hdr, val)
 
-        # add host
-        if hdrs.HOST not in used_headers:
-            netloc = self.url.raw_host
-            if helpers.is_ipv6_address(netloc):
-                netloc = '[{}]'.format(netloc)
-            if not self.url.is_default_port():
-                netloc += ':' + str(self.url.port)
-            self.headers[hdrs.HOST] = netloc
-
         if hdrs.USER_AGENT not in used_headers:
             self.headers[hdrs.USER_AGENT] = SERVER_SOFTWARE
 

tests/test_client_functional.py

@@ -497,6 +497,18 @@ async def handler(request):
     resp.close()
 
 
+async def test_host_header_first(aiohttp_client) -> None:
+    async def handler(request):
+        assert list(request.headers)[0] == hdrs.HOST
+        return web.Response()
+
+    app = web.Application()
+    app.router.add_route('GET', '/', handler)
+    client = await aiohttp_client(app)
+    resp = await client.get('/')
+    assert resp.status == 200
+
+
 async def test_empty_header_values(aiohttp_client) -> None:
     async def handler(request):
         resp = web.Response()

tests/test_client_request.py

@@ -210,6 +210,11 @@ def test_hostname_err(make_request) -> None:
         make_request('get', 'http://:8080/')
 
 
+def test_host_header_host_first(make_request) -> None:
+    req = make_request('get', 'http://python.org/')
+    assert list(req.headers)[0] == 'Host'
+
+
 def test_host_header_host_without_port(make_request) -> None:
     req = make_request('get', 'http://python.org/')
     assert req.headers['HOST'] == 'python.org'