wsgi: Disable Nagle algorithm on client side

When sending a PUT request, the http header may be sent in the first
packet when calling con.endheaders(). When we send the first chunk, the
kernel may delay the send because the header packet was not acked yet.

We have seen PUT requests delayed by 40 milliseconds on the server side.
Typically the server receive the header, and then wait about 40
milliseconds for the message body. The actual work for such request may
take less then a millisecond.

This issue was fixed in python 3.5 by using the TCP_NO_DELAY option
after connecting[1]. I backported this change from python 3.5.

Here is example upload before this change:

$ time ./upload RHEL7_1-001.raw https://host:54322/images/test

real    3m42.144s
user    0m16.240s
sys     0m5.515s

OPTIONS /images/test: [200] 74 [request=0.000859]
PUT /images/test: [200] 0 [request=0.040728, operation=0.039781, read=0.038662, write=0.000838]
PATCH /images/test: [200] 0 [request=0.003775, operation=0.003051, write=0.002775]

The server wait 38 milliseconds for a tiny payload written in 838
microseconds.

Here is the same upload after this change:

$ time ./upload RHEL7_1-001.raw https://host:54322/images/test

real	1m2.492s
user	0m16.232s
sys	0m5.619s

OPTIONS /images/test: [200] 74 [request=0.000972]
PUT /images/test: [200] 0 [request=0.002804, operation=0.001437, read=0.000149, write=0.000841]
PATCH /images/test: [200] 0 [request=0.003511, operation=0.002860, write=0.002646]

Now the server read the payload in 149 microseconds instead of 38
milliseconds, and the entire request was completed in 2.8 milliseconds
instead of 40 milliseconds.

[1] https://bugs.python.org/issue23302

Change-Id: Iebbbceafa0aff5c363e281758daace551f8da8f6
Signed-off-by: Nir Soffer <nsoffer@redhat.com>

examples/upload

@@ -69,6 +69,20 @@ can_zero = False
 can_flush = False
 
 
+class HTTPSConnection(httplib.HTTPSConnection):
+
+    def connect(self):
+        """
+        Using TCP_NO_DELAY avoids delays when sending small payload, such as
+        ovirt PATCH requests.
+
+        This issue was fixed in python 3.5, see:
+        https://bugs.python.org/issue23302
+        """
+        httplib.HTTPSConnection.connect(self)
+        self.sock.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
+
+
 def upload_sparse(con, src):
     """
     Upload a possibly sparse file by sending the data portions using PUT
@@ -218,7 +232,7 @@ context = ssl.create_default_context(
     purpose=ssl.Purpose.SERVER_AUTH, cafile=CERTFILE)
 
 # Check the server capabilities for this image.
-con = httplib.HTTPSConnection(url.netloc, context=context)
+con = HTTPSConnection(url.netloc, context=context)
 with closing(con):
     server_options = options(con, url.path)
     can_flush = "flush" in server_options["features"]
@@ -229,7 +243,7 @@ with closing(con):
 if "unix_socket" in server_options:
     con = uhttp.UnixHTTPConnection(server_options["unix_socket"])
 else:
-    con = httplib.HTTPSConnection(url.netloc, context=context)
+    con = HTTPSConnection(url.netloc, context=context)
 
 # Upload the data. If the server supports "zero", we can upload sparse
 # files more efficiently.