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Bug #11172

Updated by naruse (Yui NARUSE) about 4 years ago

Windowsでopen("hoge.txt", "ab+")すると、開いたファイルの既存の内容が読めません。
File::APPEND|File::CREAT|File::RDWR|File::BINARYでも同様です。

Unixでは読める上に、a+の時、つまり_openを使う場合も読めるので、意図しない挙動でしょう。

```
diff --git a/win32/win32.c b/win32/win32.c
index 55e0d2e..57d9df4 100644
--- a/win32/win32.c
+++ b/win32/win32.c
@@ -6476,12 +6476,16 @@ rb_w32_close(int fd)
}

static int
-setup_overlapped(OVERLAPPED *ol, int fd)
+setup_overlapped(OVERLAPPED *ol, int fd, int iswrite)
{
memset(ol, 0, sizeof(*ol));
if (!(_osfile(fd) & (FDEV | FPIPE))) {
LONG high = 0;
- DWORD method = _osfile(fd) & FAPPEND ? FILE_END : FILE_CURRENT;
+ /* On mode:a, it can write only FILE_END.
+ * On mode:a+, though it can write only FILE_END,
+ * it can read from everywhere.
+ */
+ DWORD method = ((_osfile(fd) & FAPPEND) && iswrite) ? FILE_END : FILE_CURRENT;
DWORD low = SetFilePointer((HANDLE)_osfhnd(fd), 0, &high, method);
#ifndef INVALID_SET_FILE_POINTER
#define INVALID_SET_FILE_POINTER ((DWORD)-1)
@@ -6578,7 +6582,7 @@ rb_w32_read(int fd, void *buf, size_t size)

/* if have cancel_io, use Overlapped I/O */
if (cancel_io) {
- if (setup_overlapped(&ol, fd)) {
+ if (setup_overlapped(&ol, fd, FALSE)) {
rb_acrt_lowio_unlock_fh(fd);
return -1;
}
@@ -6708,7 +6712,7 @@ rb_w32_write(int fd, const void *buf, size_t size)

/* if have cancel_io, use Overlapped I/O */
if (cancel_io) {
- if (setup_overlapped(&ol, fd)) {
+ if (setup_overlapped(&ol, fd, TRUE)) {
rb_acrt_lowio_unlock_fh(fd);
return -1;
}
```

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