From 1253739fcae5e66b5e7c90080058a7585e245d49 Mon Sep 17 00:00:00 2001
From: mochalins <117967760+mochalins@users.noreply.github.com>
Date: Fri, 17 Jan 2025 16:58:36 +0900
Subject: [PATCH] fix: Windows Poll UB

---
 src/backend/windows.zig | 55 +++++++++++++++++++++++++----------------
 src/serialport.zig      | 12 +++++----
 2 files changed, 41 insertions(+), 26 deletions(-)

diff --git a/src/backend/windows.zig b/src/backend/windows.zig
index 1963202..e673dca 100644
--- a/src/backend/windows.zig
+++ b/src/backend/windows.zig
@@ -22,6 +22,12 @@ pub const BaudRate = enum(windows.DWORD) {
     _,
 };
 
+/// Reused structures necessary between non-blocking poll calls.
+pub const PollContinuation = struct {
+    events: EventMask,
+    overlapped: windows.OVERLAPPED,
+};
+
 pub const ReadError =
     windows.ReadFileError ||
     windows.OpenError ||
@@ -119,25 +125,25 @@ pub fn flush(port: std.fs.File, options: serialport.FlushOptions) !void {
     }
 }
 
-pub fn poll(port: std.fs.File, overlapped_: *?windows.OVERLAPPED) !bool {
+pub fn poll(port: std.fs.File, continuation: *?PollContinuation) !bool {
     var comstat: ComStat = undefined;
     if (ClearCommError(port.handle, null, &comstat) == 0) {
         return windows.unexpectedError(windows.GetLastError());
     }
     if (comstat.cbInQue > 0) return true;
 
-    var events: EventMask = undefined;
-    if (overlapped_.*) |*overlapped| {
+    if (continuation.*) |*cont| {
         if (windows.GetOverlappedResult(
             port.handle,
-            overlapped,
+            &cont.overlapped,
             false,
         ) catch |e| switch (e) {
             error.WouldBlock => return false,
             else => return e,
         } != 0) {
-            overlapped_.* = null;
-            return true;
+            const was_rx = cont.events.RXCHAR;
+            cont.* = null;
+            return was_rx;
         } else {
             switch (windows.GetLastError()) {
                 windows.Win32Error.IO_PENDING => return false,
@@ -145,29 +151,36 @@ pub fn poll(port: std.fs.File, overlapped_: *?windows.OVERLAPPED) !bool {
             }
         }
     } else {
-        overlapped_.* = .{
-            .Internal = 0,
-            .InternalHigh = 0,
-            .DUMMYUNIONNAME = .{
-                .DUMMYSTRUCTNAME = .{
-                    .Offset = 0,
-                    .OffsetHigh = 0,
+        continuation.* = .{
+            .events = undefined,
+            .overlapped = .{
+                .Internal = 0,
+                .InternalHigh = 0,
+                .DUMMYUNIONNAME = .{
+                    .DUMMYSTRUCTNAME = .{
+                        .Offset = 0,
+                        .OffsetHigh = 0,
+                    },
                 },
+                .hEvent = try windows.CreateEventEx(
+                    null,
+                    "",
+                    windows.CREATE_EVENT_MANUAL_RESET,
+                    windows.EVENT_ALL_ACCESS,
+                ),
             },
-            .hEvent = try windows.CreateEventEx(
-                null,
-                "",
-                windows.CREATE_EVENT_MANUAL_RESET,
-                windows.EVENT_ALL_ACCESS,
-            ),
         };
-        if (WaitCommEvent(port.handle, &events, &overlapped_.*.?) == 0) {
+        if (WaitCommEvent(
+            port.handle,
+            &continuation.?.events,
+            &continuation.?.overlapped,
+        ) == 0) {
             switch (windows.GetLastError()) {
                 windows.Win32Error.IO_PENDING => return false,
                 else => |e| return windows.unexpectedError(e),
             }
         }
-        return events.RXCHAR;
+        return continuation.?.events.RXCHAR;
     }
 }
 
diff --git a/src/serialport.zig b/src/serialport.zig
index 517cbcb..38b008e 100644
--- a/src/serialport.zig
+++ b/src/serialport.zig
@@ -29,7 +29,7 @@ const PortImpl = switch (builtin.target.os.tag) {
     },
     .windows => struct {
         file: std.fs.File,
-        poll_overlapped: ?std.os.windows.OVERLAPPED = null,
+        poll_continuation: ?windows.PollContinuation = null,
     },
     else => @compileError("unsupported OS"),
 };
@@ -109,10 +109,12 @@ pub const Port = struct {
     pub fn poll(self: *@This()) !bool {
         switch (comptime builtin.target.os.tag) {
             .linux, .macos => return backend.poll(self._impl.file),
-            .windows => return windows.poll(
-                self._impl.file,
-                &self._impl.poll_overlapped,
-            ),
+            .windows => {
+                return windows.poll(
+                    self._impl.file,
+                    &self._impl.poll_continuation,
+                );
+            },
             else => @compileError("unsupported OS"),
         }
     }