From 3be7ee750fd0d31d6e995140025e0d18e6aa788e Mon Sep 17 00:00:00 2001
From: fanquake <fanquake@gmail.com>
Date: Tue, 28 Jun 2022 17:37:32 +0100
Subject: [PATCH] compat: document error-code mapping

See:
https://docs.microsoft.com/en-us/windows/win32/winsock/windows-sockets-error-codes-2
---
 src/compat/compat.h | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/compat/compat.h b/src/compat/compat.h
index 633aa6f3b57..670da9a6313 100644
--- a/src/compat/compat.h
+++ b/src/compat/compat.h
@@ -37,9 +37,12 @@
 #include <unistd.h>
 #endif
 
+// We map Linux / BSD error functions and codes, to the equivalent
+// Windows definitions, and use the WSA* names throughout our code.
+// Note that glibc defines EWOULDBLOCK as EAGAIN (see errno.h).
 #ifndef WIN32
 typedef unsigned int SOCKET;
-#include <errno.h>
+#include <cerrno>
 #define WSAGetLastError()   errno
 #define WSAEINVAL           EINVAL
 #define WSAEWOULDBLOCK      EWOULDBLOCK
@@ -51,14 +54,13 @@ typedef unsigned int SOCKET;
 #define INVALID_SOCKET      (SOCKET)(~0)
 #define SOCKET_ERROR        -1
 #else
-#ifndef WSAEAGAIN
+// WSAEAGAIN doesn't exist on Windows
 #ifdef EAGAIN
 #define WSAEAGAIN EAGAIN
 #else
 #define WSAEAGAIN WSAEWOULDBLOCK
 #endif
 #endif
-#endif
 
 // Windows doesn't define S_IRUSR or S_IWUSR. We define both
 // here, with the same values as glibc (see stat.h).