bpo-34563: Fix for invalid assert on big output of multiprocessing.Pr…

…ocess (pythonGH-9027)

Fix for invalid assert on big output of multiprocessing.Process.

Misc/NEWS.d/next/Library/2018-09-01-20-43-10.bpo-34563.7NQK7B.rst

@@ -0,0 +1 @@
+On Windows, fix multiprocessing.Connection for very large read: fix _winapi.PeekNamedPipe() and _winapi.ReadFile() for read larger than INT_MAX (usually 2^31-1).

Modules/_winapi.c

@@ -1338,7 +1338,7 @@ _winapi_PeekNamedPipe_impl(PyObject *module, HANDLE handle, int size)
         }
         if (_PyBytes_Resize(&buf, nread))
             return NULL;
-        return Py_BuildValue("Nii", buf, navail, nleft);
+        return Py_BuildValue("NII", buf, navail, nleft);
     }
     else {
         Py_BEGIN_ALLOW_THREADS
@@ -1347,22 +1347,22 @@ _winapi_PeekNamedPipe_impl(PyObject *module, HANDLE handle, int size)
         if (!ret) {
             return PyErr_SetExcFromWindowsErr(PyExc_OSError, 0);
         }
-        return Py_BuildValue("ii", navail, nleft);
+        return Py_BuildValue("II", navail, nleft);
     }
 }
 
 /*[clinic input]
 _winapi.ReadFile
 
     handle: HANDLE
-    size: int
+    size: DWORD
     overlapped as use_overlapped: bool(accept={int}) = False
 [clinic start generated code]*/
 
 static PyObject *
-_winapi_ReadFile_impl(PyObject *module, HANDLE handle, int size,
+_winapi_ReadFile_impl(PyObject *module, HANDLE handle, DWORD size,
                       int use_overlapped)
-/*[clinic end generated code: output=492029ca98161d84 input=3f0fde92f74de59a]*/
+/*[clinic end generated code: output=d3d5b44a8201b944 input=08c439d03a11aac5]*/
 {
     DWORD nread;
     PyObject *buf;