Update asyncfile.nim: support write to > 2GB file on Windows (#25105)

foldl · web-flow · commit 4f09675d8a9b · 2025-09-10T15:37:09.000+02:00
`DWORD` is defined as `int32`, so `DWORD(...)` would not work as
expected. When writing to files larger than 2GB, exception occurs:

```
unhandled exception: value out of range: 4294967295 notin -2147483648 .. 2147483647 [RangeDefect]
```

This PR is a quick fix for this.

P.S. Why `DWORD` is defined as `int32`?
diff --git a/lib/pure/asyncfile.nim b/lib/pure/asyncfile.nim
@@ -428,7 +428,7 @@ proc write*(f: AsyncFile, data: string): Future[void] =
           dealloc buffer
           buffer = nil
     )
-    ol.offset = DWORD(f.offset and 0xffffffff)
+    ol.offset = cast[DWORD](f.offset and 0xffffffff)
     ol.offsetHigh = DWORD(f.offset shr 32)
     f.offset.inc(data.len)
 

Original file line number	Diff line number	Diff line change
`@@ -428,7 +428,7 @@ proc write*(f: AsyncFile, data: string): Future[void] =`
`428`	`428`	`dealloc buffer`
`429`	`429`	`buffer = nil`
`430`	`430`	`)`
`431`		`- ol.offset = DWORD(f.offset and 0xffffffff)`
	`431`	`+ ol.offset = cast[DWORD](f.offset and 0xffffffff)`
`432`	`432`	`ol.offsetHigh = DWORD(f.offset shr 32)`
`433`	`433`	`f.offset.inc(data.len)`
`434`	`434`