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bpo-42044: Write all bytes to the console in unbuffered mode on Windows #26678

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bpo-42044: Write all bytes to the console in unbuffered mode on Windows #26678

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bpo-42044: Write all bytes to the console in unbuffered mode on Windows
fabioz Jun 11, 2021
3fff6b4
bpo-42044: Code-review
fabioz Jul 5, 2021
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Windows/2021-06-11-15-13-08.bpo-42044.Jnky9u.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
When the io is flushed in unbuffered mode in Windows, all bytes are now
properly written to the console.
15 changes: 5 additions & 10 deletions Modules/_io/winconsoleio.c
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Original file line number Diff line number Diff line change
Expand Up @@ -978,16 +978,6 @@ _io__WindowsConsoleIO_write_impl(winconsoleio *self, Py_buffer *b)

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;
wlen = MultiByteToWideChar(CP_UTF8, 0, b->buf, len, NULL, 0);
}
Py_END_ALLOW_THREADS

if (!wlen)
Expand All @@ -998,6 +988,11 @@ _io__WindowsConsoleIO_write_impl(winconsoleio *self, Py_buffer *b)
Py_BEGIN_ALLOW_THREADS
wlen = MultiByteToWideChar(CP_UTF8, 0, b->buf, len, wbuf, wlen);
if (wlen) {
/* Note that it's possible that this would fail to print big strings
* on Windows 7 (before Windows 8 LPC-based pseudo-files were used
* for I/O and would be limited to a 64 KiB heap).
* As Windows 7 is currently unsupported, that's Ok.
*/
res = WriteConsoleW(handle, wbuf, wlen, &n, NULL);
if (res && n < wlen) {
/* Wrote fewer characters than expected, which means our
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