From ae7cf71dcf17aa7e309c62b69fed5a321c4ca5c9 Mon Sep 17 00:00:00 2001
From: "Roger A. Light" <roger@atchoo.org>
Date: Wed, 7 Jan 2026 15:04:06 +0000
Subject: [PATCH] Fix errno setting on Windows

Closes #3424
---
 lib/http_client.c        | 2 +-
 lib/mosquitto_internal.h | 5 +++++
 lib/packet_mosq.c        | 7 +++----
 lib/socks_mosq.c         | 3 +--
 4 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/lib/http_client.c b/lib/http_client.c
index c8dafe72..e7cf4c1a 100644
--- a/lib/http_client.c
+++ b/lib/http_client.c
@@ -131,7 +131,7 @@ int http_c__read(struct mosquitto *mosq)
 		if(read_length == 0){
 			return MOSQ_ERR_CONN_LOST; /* EOF */
 		}
-		WINDOWS_SET_ERRNO();
+		WINDOWS_SET_ERRNO_RW();
 		if(errno == EAGAIN || errno == COMPAT_EWOULDBLOCK){
 			return MOSQ_ERR_SUCCESS;
 		}else{
diff --git a/lib/mosquitto_internal.h b/lib/mosquitto_internal.h
index 3ec9df7f..0beaec31 100644
--- a/lib/mosquitto_internal.h
+++ b/lib/mosquitto_internal.h
@@ -77,11 +77,16 @@ typedef int mosq_sock_t;
 
 #ifdef WIN32
 #  define WINDOWS_SET_ERRNO() \
+		do{ \
+			errno = WSAGetLastError(); \
+		}while(0)
+#  define WINDOWS_SET_ERRNO_RW() \
 		if(errno != EAGAIN){ \
 			errno = WSAGetLastError(); \
 		}
 #else
 #  define WINDOWS_SET_ERRNO()
+#  define WINDOWS_SET_ERRNO_RW()
 #endif
 
 #define SAFE_PRINT(A) (A)?(A):"null"
diff --git a/lib/packet_mosq.c b/lib/packet_mosq.c
index c1587cc9..6adee2bb 100644
--- a/lib/packet_mosq.c
+++ b/lib/packet_mosq.c
@@ -307,8 +307,7 @@ int packet__write(struct mosquitto *mosq)
 				packet->to_process -= (uint32_t)write_length;
 				packet->pos += (uint32_t)write_length;
 			}else{
-				WINDOWS_SET_ERRNO();
-
+				WINDOWS_SET_ERRNO_RW();
 				if(errno == EAGAIN || errno == COMPAT_EWOULDBLOCK
 #ifdef WIN32
 						|| errno == WSAENOTCONN
@@ -377,7 +376,7 @@ static int read_header(struct mosquitto *mosq, ssize_t (*func_read)(struct mosqu
 		if(read_length == 0){
 			return MOSQ_ERR_CONN_LOST; /* EOF */
 		}
-		WINDOWS_SET_ERRNO();
+		WINDOWS_SET_ERRNO_RW();
 		if(errno == EAGAIN || errno == COMPAT_EWOULDBLOCK){
 			return MOSQ_ERR_SUCCESS;
 		}else{
@@ -586,7 +585,7 @@ static int packet__read_single(struct mosquitto *mosq, enum mosquitto_client_sta
 			mosq->in_packet.to_process -= (uint32_t)read_length;
 			mosq->in_packet.pos += (uint32_t)read_length;
 		}else{
-			WINDOWS_SET_ERRNO();
+			WINDOWS_SET_ERRNO_RW();
 			if(errno == EAGAIN || errno == COMPAT_EWOULDBLOCK){
 				if(mosq->in_packet.to_process > 1000){
 					/* Update last_msg_in time if more than 1000 bytes left to
diff --git a/lib/socks_mosq.c b/lib/socks_mosq.c
index 53ced849..759433cf 100644
--- a/lib/socks_mosq.c
+++ b/lib/socks_mosq.c
@@ -64,8 +64,7 @@ Contributors:
 
 static inline int socks5__network_error(struct mosquitto *mosq)
 {
-	WINDOWS_SET_ERRNO();
-
+	WINDOWS_SET_ERRNO_RW();
 	if(errno == EAGAIN || errno == COMPAT_EWOULDBLOCK){
 		return MOSQ_ERR_SUCCESS;
 	}else{