pythongh-121940: Stop checking isatty on Windows write()

cmaloney · cmaloney · commit 9a734da89622 · 2024-07-17T15:11:00.000-07:00
This check was added for bpo-11395 in 2011. Versions of Windows before Windows 8 required the check as write size to a tty was limited ( python#55604 (comment)). Based on PEP 11, the last Windows 8 support ended in 2023, so this is no longer needed on any currently supported windows platforms. That large writes to console succeed is tested by test_os.test_write_windows_console, which passes in my testing on Windows 11. It's possible there are still objects on windows which error on a write too large, this leaves in place some code to handle (ex. Pipes and ENOSPC). Write can also still be interrupted and resumed (EAGAIN, etc). If there are other Windows objects or platform files which limit write size, callers should wrap the `os.write` function.
diff --git a/Misc/NEWS.d/next/Windows/2024-07-17-15-07-24.gh-issue-121940.M70eyc.rst b/Misc/NEWS.d/next/Windows/2024-07-17-15-07-24.gh-issue-121940.M70eyc.rst
@@ -0,0 +1,4 @@
+``os.write`` on Windows no longer limits or splits up writes to console
+objects. The behavior was initially added to address bpo-11395 in 2011 as a
+workaround for the OS returning an error with too large of a write call to
+a console.
diff --git a/Modules/_io/winconsoleio.c b/Modules/_io/winconsoleio.c
@@ -134,23 +134,6 @@ char _PyIO_get_console_type(PyObject *path_or_fd) {
     return m;
 }
 
-static DWORD
-_find_last_utf8_boundary(const char *buf, DWORD len)
-{
-    /* This function never returns 0, returns the original len instead */
-    DWORD count = 1;
-    if (len == 0 || (buf[len - 1] & 0x80) == 0) {
-        return len;
-    }
-    for (;; count++) {
-        if (count > 3 || count >= len) {
-            return len;
-        }
-        if ((buf[len - count] & 0xc0) != 0x80) {
-            return len - count;
-        }
-    }
-}
 
 /*[clinic input]
 module _io
@@ -1023,18 +1006,6 @@ _io__WindowsConsoleIO_write_impl(winconsoleio *self, PyTypeObject *cls,
 
     Py_BEGIN_ALLOW_THREADS
     wlen = MultiByteToWideChar(CP_UTF8, 0, b->buf, len, NULL, 0);
-
-    /* issue11395 there is an unspecified upper bound on how many bytes
-       can be written at once. We cap at 32k - the caller will have to
-       handle partial writes.
-       Since we don't know how many input bytes are being ignored, we
-       have to reduce and recalculate. */
-    while (wlen > 32766 / sizeof(wchar_t)) {
-        len /= 2;
-        /* Fix for github issues gh-110913 and gh-82052. */
-        len = _find_last_utf8_boundary(b->buf, len);
-        wlen = MultiByteToWideChar(CP_UTF8, 0, b->buf, len, NULL, 0);
-    }
     Py_END_ALLOW_THREADS
 
     if (!wlen)
diff --git a/Python/fileutils.c b/Python/fileutils.c
@@ -1922,26 +1922,6 @@ _Py_write_impl(int fd, const void *buf, size_t count, int gil_held)
     int async_err = 0;
 
     _Py_BEGIN_SUPPRESS_IPH
-#ifdef MS_WINDOWS
-    if (count > 32767) {
-        /* Issue #11395: the Windows console returns an error (12: not
-           enough space error) on writing into stdout if stdout mode is
-           binary and the length is greater than 66,000 bytes (or less,
-           depending on heap usage). */
-        if (gil_held) {
-            Py_BEGIN_ALLOW_THREADS
-            if (isatty(fd)) {
-                count = 32767;
-            }
-            Py_END_ALLOW_THREADS
-        } else {
-            if (isatty(fd)) {
-                count = 32767;
-            }
-        }
-    }
-
-#endif
     if (count > _PY_WRITE_MAX) {
         count = _PY_WRITE_MAX;
     }
