From ad08117e9daf5d2a34be1ca71a23366f39079990 Mon Sep 17 00:00:00 2001
From: Ryan Liptak <squeek502@hotmail.com>
Date: Sat, 20 Dec 2025 20:15:14 -0800
Subject: [PATCH] Fix sizing of buffer/reservation size for dirReadWindows

---
 lib/std/Io/Dir.zig      | 7 ++++++-
 lib/std/Io/Threaded.zig | 8 +++++---
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/lib/std/Io/Dir.zig b/lib/std/Io/Dir.zig
index 60cdd88453d3f05241207412df41cf6b19688ef0..a84a20167dd82c29dde487f75d738ca992743b25 100644
--- a/lib/std/Io/Dir.zig
+++ b/lib/std/Io/Dir.zig
@@ -105,7 +105,12 @@ pub const Reader = struct {
     pub const min_buffer_len = switch (native_os) {
         .linux => std.mem.alignForward(usize, @sizeOf(std.os.linux.dirent64), 8) +
             std.mem.alignForward(usize, max_name_bytes, 8),
-        .windows => std.mem.alignForward(usize, max_name_bytes, @alignOf(usize)),
+        .windows => len: {
+            const max_info_len = @sizeOf(std.os.windows.FILE_BOTH_DIR_INFORMATION) + std.os.windows.NAME_MAX * 2;
+            const info_align = @alignOf(std.os.windows.FILE_BOTH_DIR_INFORMATION);
+            const reserved_len = std.mem.alignForward(usize, max_name_bytes, info_align) - max_info_len;
+            break :len std.mem.alignForward(usize, reserved_len, info_align) + max_info_len;
+        },
         .wasi => @sizeOf(std.os.wasi.dirent_t) +
             std.mem.alignForward(usize, max_name_bytes, @alignOf(std.os.wasi.dirent_t)),
         else => if (builtin.link_libc) @sizeOf(std.c.dirent) else std.mem.alignForward(usize, max_name_bytes, @alignOf(usize)),
diff --git a/lib/std/Io/Threaded.zig b/lib/std/Io/Threaded.zig
index 182a8f4b6d45ae6561bb8ae6fca88a86d6bbe790..a586ae2b38acafee8df177d8055c382de5cf0010 100644
--- a/lib/std/Io/Threaded.zig
+++ b/lib/std/Io/Threaded.zig
@@ -3757,11 +3757,13 @@ fn dirReadWindows(userdata: ?*anyopaque, dr: *Dir.Reader, buffer: []Dir.Entry) D
     // reserve enough to get us to up to having `3 * NAME_MAX` bytes available when taking into account
     // that we have the ability to write over top of the reserved memory + the full footprint of that
     // particular `FILE_BOTH_DIR_INFORMATION`.
-    const reserve_needed = w.NAME_MAX - @sizeOf(w.FILE_BOTH_DIR_INFORMATION);
-    const unreserved_start = std.mem.alignForward(usize, reserve_needed, @alignOf(usize));
+    const max_info_len = @sizeOf(w.FILE_BOTH_DIR_INFORMATION) + w.NAME_MAX * 2;
+    const info_align = @alignOf(w.FILE_BOTH_DIR_INFORMATION);
+    const reserve_needed = std.mem.alignForward(usize, Dir.max_name_bytes, info_align) - max_info_len;
+    const unreserved_start = std.mem.alignForward(usize, reserve_needed, info_align);
     const unreserved_buffer = dr.buffer[unreserved_start..];
     // This is enforced by `Dir.Reader`
-    assert(unreserved_buffer.len >= @sizeOf(w.FILE_BOTH_DIR_INFORMATION) + w.NAME_MAX * 2);
+    assert(unreserved_buffer.len >= max_info_len);
 
     var name_index: usize = 0;
     var buffer_index: usize = 0;
-- 
2.54.0