Issue #11172 has been updated by Yui NARUSE.

Description updated

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Bug #11172: Windowsでmode: ab+の時に開いたファイルの内容が読めない
https://bugs.ruby-lang.org/issues/11172#change-52626

* Author: Yui NARUSE
* Status: Assigned
* Priority: Normal
* Assignee: Usaku NAKAMURA
* ruby -v: 
* Backport: 2.0.0: REQUIRED, 2.1: REQUIRED, 2.2: REQUIRED
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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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