Simply use non-zero timeout.

Author: serhiy-storchaka

Lib/http/server.py

@@ -1288,16 +1288,16 @@ def run_cgi(self):
                                  env = env
                                  )
             if self.command.lower() == "post" and nbytes > 0:
-                cursize = min(nbytes, _MIN_READ_BUF_SIZE)
-                data = self.rfile.read(cursize)
-                while (len(data) == cursize < nbytes and
-                       select.select([self.rfile._sock], [], [], 0)[0]):
+                cursize = 0
+                data = self.rfile.read(min(nbytes, _MIN_READ_BUF_SIZE))
+                while (len(data) < nbytes and len(data) != cursize and
+                       select.select([self.rfile._sock], [], [], self.timeout)[0]):
+                    cursize = len(data)
                     # This is a geometric increase in read size (never more
                     # than doubling our the current length of data per loop
                     # iteration).
                     delta = min(cursize, nbytes - cursize)
                     data += self.rfile.read(delta)
-                    cursize += delta
             else:
                 data = None
             # throw away additional data [see bug #427345]

Lib/test/test_httpservers.py

@@ -1132,11 +1132,12 @@ def test_large_content_length(self):
             self.assertEqual(res.read(), b'%d %d' % (size, size) + self.linesep)
 
     def test_large_content_length_truncated(self):
-        for w in range(18, 65):
-            size = 1 << w
-            headers = {'Content-Length' : str(size)}
-            res = self.request('/cgi-bin/file1.py', 'POST', b'x', headers)
-            self.assertEqual(res.read(), b'Hello World' + self.linesep)
+        with support.swap_attr(self.request_handler, 'timeout', 0.001):
+            for w in range(18, 65):
+                size = 1 << w
+                headers = {'Content-Length' : str(size)}
+                res = self.request('/cgi-bin/file1.py', 'POST', b'x', headers)
+                self.assertEqual(res.read(), b'Hello World' + self.linesep)
 
     def test_invaliduri(self):
         res = self.request('/cgi-bin/invalid')