ENH: core: switch to off_t and lseek in Python 3 file seeks

This removes dependency on CRT implementation details (whether
fflush/fclose actually seeks the underlying raw file handle or not).

Also, check seek error statuses.

numpy/core/include/numpy/npy_3kcompat.h

@@ -146,11 +146,11 @@ PyUnicode_Concat2(PyObject **left, PyObject *right)
  * Get a FILE* handle to the file represented by the Python object
  */
 static NPY_INLINE FILE*
-npy_PyFile_Dup(PyObject *file, char *mode, Py_ssize_t *orig_pos)
+npy_PyFile_Dup(PyObject *file, char *mode, npy_off_t *orig_pos)
 {
     int fd, fd2;
     PyObject *ret, *os;
-    Py_ssize_t pos;
+    npy_off_t pos;
     FILE *handle;
 
     /* Flush first to ensure things end up in the file in the correct order */
@@ -191,6 +191,10 @@ npy_PyFile_Dup(PyObject *file, char *mode, Py_ssize_t *orig_pos)
 
     /* Record the original raw file handle position */
     *orig_pos = npy_ftell(handle);
+    if (*orig_pos == -1) {
+        PyErr_SetString(PyExc_IOError, "obtaining file position failed");
+        return -1;
+    }
 
     /* Seek raw handle to the Python-side position */
     ret = PyObject_CallMethod(file, "tell", "");
@@ -204,30 +208,45 @@ npy_PyFile_Dup(PyObject *file, char *mode, Py_ssize_t *orig_pos)
         fclose(handle);
         return NULL;
     }
-    npy_fseek(handle, pos, SEEK_SET);
+    if (npy_fseek(handle, pos, SEEK_SET) == -1) {
+        PyErr_SetString(PyExc_IOError, "seeking file failed");
+        return -1;
+    }
     return handle;
 }
 
 /*
  * Close the dup-ed file handle, and seek the Python one to the current position
  */
 static NPY_INLINE int
-npy_PyFile_DupClose(PyObject *file, FILE* handle, Py_ssize_t orig_pos)
+npy_PyFile_DupClose(PyObject *file, FILE* handle, npy_off_t orig_pos)
 {
+    int fd;
     PyObject *ret;
-    Py_ssize_t position;
+    npy_off_t position;
 
     position = npy_ftell(handle);
 
+    /* Close the FILE* handle */
+    fclose(handle);
+
     /* Restore original file handle position, in order to not confuse
        Python-side data structures */
-    npy_fseek(handle, orig_pos, SEEK_SET);
+    fd = PyObject_AsFileDescriptor(file);
+    if (fd == -1) {
+        return -1;
+    }
+    if (npy_lseek(fd, orig_pos, SEEK_SET) == -1) {
+        PyErr_SetString(PyExc_IOError, "seeking file failed");
+        return -1;
+    }
 
-    /* Flush before closing to sync the raw file handle position */
-    fflush(handle);
-    fclose(handle);
+    if (position == -1) {
+        PyErr_SetString(PyExc_IOError, "obtaining file position failed");
+        return -1;
+    }
 
-    /* Seek Python-side handle to the raw handle position */
+    /* Seek Python-side handle to the FILE* handle position */
     ret = PyObject_CallMethod(file, "seek", NPY_SSIZE_T_PYFMT "i", position, 0);
     if (ret == NULL) {
         return -1;

numpy/core/include/numpy/npy_common.h

@@ -58,11 +58,16 @@
 
 /* Enable 64 bit file position support on win-amd64. Ticket #1660 */
 #if defined(_MSC_VER) && defined(_WIN64) && (_MSC_VER > 1400)
+    #include <io.h>
     #define npy_fseek _fseeki64
     #define npy_ftell _ftelli64
+    #define npy_lseek _lseeki64
+    #define npy_off_t npy_int64
 #else
     #define npy_fseek fseek
     #define npy_ftell ftell
+    #define npy_lseek lseek
+    #define npy_off_t off_t
 #endif
 
 /* enums for detected endianness */

numpy/core/src/multiarray/methods.c

@@ -566,7 +566,7 @@ array_tofile(PyArrayObject *self, PyObject *args, PyObject *kwds)
     FILE *fd;
     char *sep = "";
     char *format = "";
-    Py_ssize_t orig_pos;
+    npy_off_t orig_pos;
     static char *kwlist[] = {"file", "sep", "format", NULL};
 
     if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|ss", kwlist,

numpy/core/src/multiarray/multiarraymodule.c

@@ -1972,7 +1972,7 @@ array_fromfile(PyObject *NPY_UNUSED(ignored), PyObject *args, PyObject *keywds)
     static char *kwlist[] = {"file", "dtype", "count", "sep", NULL};
     PyArray_Descr *type = NULL;
     int own;
-    Py_ssize_t orig_pos;
+    npy_off_t orig_pos;
     FILE *fp;
 
     if (!PyArg_ParseTupleAndKeywords(args, keywds,