From 5e6eff81b6f7f18b3dd24bec03ea71f009a3e938 Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Wed, 26 Jun 2019 13:27:48 +0200
Subject: tun: windows: inform wintun of maximum buffer length for writes

---
 tun/tun_windows.go | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tun/tun_windows.go b/tun/tun_windows.go
index 05fc3df..1de74e6 100644
--- a/tun/tun_windows.go
+++ b/tun/tun_windows.go
@@ -141,6 +141,12 @@ func (tun *NativeTun) openTUN() error {
 			}
 			return err
 		}
+		firstSize := (*uint32)(unsafe.Pointer(&tun.wrBuff.data[0]))
+		saved := *firstSize
+		*firstSize = 0
+		// Set the maximum buffer length with an invalid write.
+		tun.tunFileWrite.Write(tun.wrBuff.data[:])
+		*firstSize = saved
 	}
 	return nil
 }
-- 
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