From c9ed143956863cbf98a207b3c23983899282a875 Mon Sep 17 00:00:00 2001
From: Carsten Andrich <carsten.andrich@tu-ilmenau.de>
Date: Wed, 29 Apr 2020 15:28:54 +0200
Subject: [PATCH] set COMMTIMEOUTS for POSIX-like read timeout behavior

---
 serial-windows/src/com.rs | 13 +++++++++++--
 serial-windows/src/ffi.rs |  2 ++
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/serial-windows/src/com.rs b/serial-windows/src/com.rs
index ba1b0cb..fa5b2fd 100644
--- a/serial-windows/src/com.rs
+++ b/serial-windows/src/com.rs
@@ -167,10 +167,19 @@ impl SerialDevice for COMPort {
     fn set_timeout(&mut self, timeout: Duration) -> core::Result<()> {
         let milliseconds = timeout.as_secs() * 1000 + timeout.subsec_nanos() as u64 / 1_000_000;
 
+        // populate COMMTIMEOUTS struct
+        // https://docs.microsoft.com/en-us/windows/win32/devio/time-outs
+        // https://docs.microsoft.com/en-us/windows/win32/api/winbase/ns-winbase-commtimeouts
         let timeouts = COMMTIMEOUTS {
-            ReadIntervalTimeout: 0,
-            ReadTotalTimeoutMultiplier: 0,
+            // return as soon as bytes become available (like POSIX would) and
+            // block up to given duration otherwise
+            // https://docs.microsoft.com/en-us/windows/win32/api/winbase/ns-winbase-commtimeouts#remarks
+            ReadIntervalTimeout: MAXDWORD,
+            ReadTotalTimeoutMultiplier: MAXDWORD,
             ReadTotalTimeoutConstant: milliseconds as DWORD,
+            // block without timeout until write is complete
+            // MAXDWORD is *not* a reserved WriteTotalTimeoutMultiplier
+            // value, i.e., setting it incurs a long write timeout
             WriteTotalTimeoutMultiplier: 0,
             WriteTotalTimeoutConstant: 0,
         };
diff --git a/serial-windows/src/ffi.rs b/serial-windows/src/ffi.rs
index c2fc98a..dd08eb2 100644
--- a/serial-windows/src/ffi.rs
+++ b/serial-windows/src/ffi.rs
@@ -18,6 +18,8 @@ pub type LPWSTR = *mut WCHAR;
 
 pub type HANDLE = *mut LPVOID;
 
+pub const MAXDWORD: DWORD = 0xFFFFFFFF;
+
 pub const GENERIC_READ: DWORD = 0x80000000;
 pub const GENERIC_WRITE: DWORD = 0x40000000;
 pub const OPEN_EXISTING: DWORD = 3;