bpo-31945: Configurable blocksize in HTTP(S)Connection (#4279)

blocksize was hardcoded to 8192, preventing efficient upload when using
file-like body. Add blocksize argument to __init__, so users can
configure the blocksize to fit their needs.

I tested this uploading data from /dev/zero to a web server dropping the
received data, to test the overhead of the HTTPConnection.send() with a
file-like object.

Here is an example 10g upload with the default buffer size (8192):

$ time ~/src/cpython/release/python upload-httplib.py 10 https://localhost:8000/
Uploaded 10.00g in 17.53 seconds (584.00m/s)

real	0m17.574s
user	0m8.887s
sys	0m5.971s

Same with 512k blocksize:

$ time ~/src/cpython/release/python upload-httplib.py 10 https://localhost:8000/
Uploaded 10.00g in 6.60 seconds (1551.15m/s)

real	0m6.641s
user	0m3.426s
sys	0m2.162s

In real world usage the difference will be smaller, depending on the
local and remote storage and the network.

See https://github.com/nirs/http-bench for more info.

Lib/test/test_httplib.py

@@ -756,6 +756,29 @@ class BasicTest(TestCase):
         conn.request('GET', '/foo', body(), {'Content-Length': '11'})
         self.assertEqual(sock.data, expected)
 
+    def test_blocksize_request(self):
+        """Check that request() respects the configured block size."""
+        blocksize = 8  # For easy debugging.
+        conn = client.HTTPConnection('example.com', blocksize=blocksize)
+        sock = FakeSocket(None)
+        conn.sock = sock
+        expected = b"a" * blocksize + b"b"
+        conn.request("PUT", "/", io.BytesIO(expected), {"Content-Length": "9"})
+        self.assertEqual(sock.sendall_calls, 3)
+        body = sock.data.split(b"\r\n\r\n", 1)[1]
+        self.assertEqual(body, expected)
+
+    def test_blocksize_send(self):
+        """Check that send() respects the configured block size."""
+        blocksize = 8  # For easy debugging.
+        conn = client.HTTPConnection('example.com', blocksize=blocksize)
+        sock = FakeSocket(None)
+        conn.sock = sock
+        expected = b"a" * blocksize + b"b"
+        conn.send(io.BytesIO(expected))
+        self.assertEqual(sock.sendall_calls, 2)
+        self.assertEqual(sock.data, expected)
+
     def test_send_type_error(self):
         # See: Issue #12676
         conn = client.HTTPConnection('example.com')