gh-101881: Support (non-)blocking read/write functions on Windows pipes (GH-101882)

* fileutils: handle non-blocking pipe IO on Windows

Handle erroring operations on non-blocking pipes by reading the _doserrno code.
Limit writes on non-blocking pipes that are too large.

* Support blocking functions on Windows

Use the GetNamedPipeHandleState and SetNamedPipeHandleState Win32 API functions to add support for os.get_blocking and os.set_blocking.

Doc/library/os.rst

@@ -1091,13 +1091,17 @@ as internal buffering of data.
 
    See also :func:`set_blocking` and :meth:`socket.socket.setblocking`.
 
-   .. availability:: Unix.
+   .. availability:: Unix, Windows.
 
       The function is limited on Emscripten and WASI, see
       :ref:`wasm-availability` for more information.
 
+      On Windows, this function is limited to pipes.
+
    .. versionadded:: 3.5
 
+   .. versionchanged:: 3.12
+      Added support for pipes on Windows.
 
 .. function:: isatty(fd, /)
 
@@ -1565,13 +1569,17 @@ or `the MSDN <https://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx>`_ on Windo
 
    See also :func:`get_blocking` and :meth:`socket.socket.setblocking`.
 
-   .. availability:: Unix.
+   .. availability:: Unix, Windows.
 
       The function is limited on Emscripten and WASI, see
       :ref:`wasm-availability` for more information.
 
+      On Windows, this function is limited to pipes.
+
    .. versionadded:: 3.5
 
+   .. versionchanged:: 3.12
+      Added support for pipes on Windows.
 
 .. data:: SF_NODISKIO
           SF_MNOWAIT

Include/internal/pycore_fileutils.h

@@ -160,11 +160,11 @@ PyAPI_FUNC(int) _Py_set_inheritable_async_safe(int fd, int inheritable,
 
 PyAPI_FUNC(int) _Py_dup(int fd);
 
-#ifndef MS_WINDOWS
 PyAPI_FUNC(int) _Py_get_blocking(int fd);
 
 PyAPI_FUNC(int) _Py_set_blocking(int fd, int blocking);
-#else   /* MS_WINDOWS */
+
+#ifdef MS_WINDOWS
 PyAPI_FUNC(void*) _Py_get_osfhandle_noraise(int fd);
 
 PyAPI_FUNC(void*) _Py_get_osfhandle(int fd);

Lib/test/test_os.py

@@ -4099,6 +4099,7 @@ class PathTConverterTests(unittest.TestCase):
 @unittest.skipUnless(hasattr(os, 'get_blocking'),
                      'needs os.get_blocking() and os.set_blocking()')
 @unittest.skipIf(support.is_emscripten, "Cannot unset blocking flag")
+@unittest.skipIf(sys.platform == 'win32', 'Windows only supports blocking on pipes')
 class BlockingTests(unittest.TestCase):
     def test_blocking(self):
         fd = os.open(__file__, os.O_RDONLY)

Misc/NEWS.d/next/Windows/2023-02-13-18-05-49.gh-issue-101881._TnHzN.rst

@@ -0,0 +1 @@
+Add support for the os.get_blocking() and os.set_blocking() functions on Windows.

Misc/NEWS.d/next/Windows/2023-02-15-11-08-10.gh-issue-101881.fScr3m.rst

@@ -0,0 +1 @@
+Handle read and write operations on non-blocking pipes properly on Windows.

Modules/clinic/posixmodule.c.h

@@ -10402,8 +10402,6 @@ exit:
 
 #endif /* defined(MS_WINDOWS) */
 
-#if !defined(MS_WINDOWS)
-
 PyDoc_STRVAR(os_get_blocking__doc__,
 "get_blocking($module, fd, /)\n"
 "--\n"
@@ -10439,10 +10437,6 @@ exit:
     return return_value;
 }
 
-#endif /* !defined(MS_WINDOWS) */
-
-#if !defined(MS_WINDOWS)
-
 PyDoc_STRVAR(os_set_blocking__doc__,
 "set_blocking($module, fd, blocking, /)\n"
 "--\n"
@@ -10482,8 +10476,6 @@ exit:
     return return_value;
 }
 
-#endif /* !defined(MS_WINDOWS) */
-
 PyDoc_STRVAR(os_DirEntry_is_symlink__doc__,
 "is_symlink($self, /)\n"
 "--\n"
@@ -11789,14 +11781,6 @@ exit:
     #define OS_SET_HANDLE_INHERITABLE_METHODDEF
 #endif /* !defined(OS_SET_HANDLE_INHERITABLE_METHODDEF) */
 
-#ifndef OS_GET_BLOCKING_METHODDEF
-    #define OS_GET_BLOCKING_METHODDEF
-#endif /* !defined(OS_GET_BLOCKING_METHODDEF) */
-
-#ifndef OS_SET_BLOCKING_METHODDEF
-    #define OS_SET_BLOCKING_METHODDEF
-#endif /* !defined(OS_SET_BLOCKING_METHODDEF) */
-
 #ifndef OS_GETRANDOM_METHODDEF
     #define OS_GETRANDOM_METHODDEF
 #endif /* !defined(OS_GETRANDOM_METHODDEF) */
@@ -11812,4 +11796,4 @@ exit:
 #ifndef OS_WAITSTATUS_TO_EXITCODE_METHODDEF
     #define OS_WAITSTATUS_TO_EXITCODE_METHODDEF
 #endif /* !defined(OS_WAITSTATUS_TO_EXITCODE_METHODDEF) */
-/*[clinic end generated code: output=a3f76228b549e8ec input=a9049054013a1b77]*/
+/*[clinic end generated code: output=1b0eb6a76b1a0e28 input=a9049054013a1b77]*/

Modules/posixmodule.c

@@ -13930,7 +13930,6 @@ os_set_handle_inheritable_impl(PyObject *module, intptr_t handle,
 }
 #endif /* MS_WINDOWS */
 
-#ifndef MS_WINDOWS
 /*[clinic input]
 os.get_blocking -> bool
     fd: int
@@ -13978,7 +13977,6 @@ os_set_blocking_impl(PyObject *module, int fd, int blocking)
         return NULL;
     Py_RETURN_NONE;
 }
-#endif   /* !MS_WINDOWS */
 
 
 /*[clinic input]

Python/fileutils.c

@@ -1750,7 +1750,15 @@ _Py_read(int fd, void *buf, size_t count)
         Py_BEGIN_ALLOW_THREADS
         errno = 0;
 #ifdef MS_WINDOWS
+        _doserrno = 0;
         n = read(fd, buf, (int)count);
+        // read() on a non-blocking empty pipe fails with EINVAL, which is
+        // mapped from the Windows error code ERROR_NO_DATA.
+        if (n < 0 && errno == EINVAL) {
+            if (_doserrno == ERROR_NO_DATA) {
+                errno = EAGAIN;
+            }
+        }
 #else
         n = read(fd, buf, count);
 #endif
@@ -1804,6 +1812,7 @@ _Py_write_impl(int fd, const void *buf, size_t count, int gil_held)
             }
         }
     }
+
 #endif
     if (count > _PY_WRITE_MAX) {
         count = _PY_WRITE_MAX;
@@ -1814,7 +1823,18 @@ _Py_write_impl(int fd, const void *buf, size_t count, int gil_held)
             Py_BEGIN_ALLOW_THREADS
             errno = 0;
 #ifdef MS_WINDOWS
-            n = write(fd, buf, (int)count);
+            // write() on a non-blocking pipe fails with ENOSPC on Windows if
+            // the pipe lacks available space for the entire buffer.
+            int c = (int)count;
+            do {
+                _doserrno = 0;
+                n = write(fd, buf, c);
+                if (n >= 0 || errno != ENOSPC || _doserrno != 0) {
+                    break;
+                }
+                errno = EAGAIN;
+                c /= 2;
+            } while (c > 0);
 #else
             n = write(fd, buf, count);
 #endif
@@ -1829,7 +1849,18 @@ _Py_write_impl(int fd, const void *buf, size_t count, int gil_held)
         do {
             errno = 0;
 #ifdef MS_WINDOWS
-            n = write(fd, buf, (int)count);
+            // write() on a non-blocking pipe fails with ENOSPC on Windows if
+            // the pipe lacks available space for the entire buffer.
+            int c = (int)count;
+            do {
+                _doserrno = 0;
+                n = write(fd, buf, c);
+                if (n >= 0 || errno != ENOSPC || _doserrno != 0) {
+                    break;
+                }
+                errno = EAGAIN;
+                c /= 2;
+            } while (c > 0);
 #else
             n = write(fd, buf, count);
 #endif
@@ -2450,6 +2481,64 @@ error:
     return -1;
 }
 #else   /* MS_WINDOWS */
+int
+_Py_get_blocking(int fd)
+{
+    HANDLE handle;
+    DWORD mode;
+    BOOL success;
+
+    handle = _Py_get_osfhandle(fd);
+    if (handle == INVALID_HANDLE_VALUE) {
+        return -1;
+    }
+
+    Py_BEGIN_ALLOW_THREADS
+    success = GetNamedPipeHandleStateW(handle, &mode,
+                                       NULL, NULL, NULL, NULL, 0);
+    Py_END_ALLOW_THREADS
+    
+    if (!success) {
+        PyErr_SetFromWindowsErr(0);
+        return -1;
+    }
+    
+    return !(mode & PIPE_NOWAIT);
+}
+
+int
+_Py_set_blocking(int fd, int blocking)
+{
+    HANDLE handle;
+    DWORD mode;
+    BOOL success;
+
+    handle = _Py_get_osfhandle(fd);
+    if (handle == INVALID_HANDLE_VALUE) {
+        return -1;
+    }
+
+    Py_BEGIN_ALLOW_THREADS
+    success = GetNamedPipeHandleStateW(handle, &mode,
+                                       NULL, NULL, NULL, NULL, 0);
+    if (success) {
+        if (blocking) {
+            mode &= ~PIPE_NOWAIT;
+        }
+        else {
+            mode |= PIPE_NOWAIT;
+        }
+        success = SetNamedPipeHandleState(handle, &mode, NULL, NULL);
+    }
+    Py_END_ALLOW_THREADS
+
+    if (!success) {
+        PyErr_SetFromWindowsErr(0);
+        return -1;
+    }
+    return 0;
+}
+
 void*
 _Py_get_osfhandle_noraise(int fd)
 {