diff --git a/src/network/core/CMakeLists.txt b/src/network/core/CMakeLists.txt
index 37cc3e1954..bf713be99c 100644
--- a/src/network/core/CMakeLists.txt
+++ b/src/network/core/CMakeLists.txt
@@ -8,6 +8,7 @@ add_files(
     game_info.h
     host.cpp
     host.h
+    os_abstraction.cpp
     os_abstraction.h
     packet.cpp
     packet.h
diff --git a/src/network/core/address.cpp b/src/network/core/address.cpp
index c5e920b1ef..fe7bd6e50f 100644
--- a/src/network/core/address.cpp
+++ b/src/network/core/address.cpp
@@ -316,7 +316,7 @@ static SOCKET ConnectLoopProc(addrinfo *runp)
 
 	SOCKET sock = socket(runp->ai_family, runp->ai_socktype, runp->ai_protocol);
 	if (sock == INVALID_SOCKET) {
-		DEBUG(net, 1, "[%s] could not create %s socket: %s", type, family, NetworkGetLastErrorString());
+		DEBUG(net, 1, "[%s] could not create %s socket: %s", type, family, NetworkError::GetLast().AsString());
 		return INVALID_SOCKET;
 	}
 
@@ -326,12 +326,12 @@ static SOCKET ConnectLoopProc(addrinfo *runp)
 #ifdef __EMSCRIPTEN__
 	/* Emscripten is asynchronous, and as such a connect() is still in
 	 * progress by the time the call returns. */
-	if (err != 0 && errno != EINPROGRESS)
+	if (err != 0 && !NetworkError::GetLast().IsConnectInProgress())
 #else
 	if (err != 0)
 #endif
 	{
-		DEBUG(net, 1, "[%s] could not connect %s socket: %s", type, family, NetworkGetLastErrorString());
+		DEBUG(net, 1, "[%s] could not connect %s socket: %s", type, family, NetworkError::GetLast().AsString());
 		closesocket(sock);
 		return INVALID_SOCKET;
 	}
@@ -369,7 +369,7 @@ static SOCKET ListenLoopProc(addrinfo *runp)
 
 	SOCKET sock = socket(runp->ai_family, runp->ai_socktype, runp->ai_protocol);
 	if (sock == INVALID_SOCKET) {
-		DEBUG(net, 0, "[%s] could not create %s socket on port %s: %s", type, family, address, NetworkGetLastErrorString());
+		DEBUG(net, 0, "[%s] could not create %s socket on port %s: %s", type, family, address, NetworkError::GetLast().AsString());
 		return INVALID_SOCKET;
 	}
 
@@ -380,24 +380,24 @@ static SOCKET ListenLoopProc(addrinfo *runp)
 	int on = 1;
 	/* The (const char*) cast is needed for windows!! */
 	if (setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (const char*)&on, sizeof(on)) == -1) {
-		DEBUG(net, 3, "[%s] could not set reusable %s sockets for port %s: %s", type, family, address, NetworkGetLastErrorString());
+		DEBUG(net, 3, "[%s] could not set reusable %s sockets for port %s: %s", type, family, address, NetworkError::GetLast().AsString());
 	}
 
 #ifndef __OS2__
 	if (runp->ai_family == AF_INET6 &&
 			setsockopt(sock, IPPROTO_IPV6, IPV6_V6ONLY, (const char*)&on, sizeof(on)) == -1) {
-		DEBUG(net, 3, "[%s] could not disable IPv4 over IPv6 on port %s: %s", type, address, NetworkGetLastErrorString());
+		DEBUG(net, 3, "[%s] could not disable IPv4 over IPv6 on port %s: %s", type, address, NetworkError::GetLast().AsString());
 	}
 #endif
 
 	if (bind(sock, runp->ai_addr, (int)runp->ai_addrlen) != 0) {
-		DEBUG(net, 1, "[%s] could not bind on %s port %s: %s", type, family, address, NetworkGetLastErrorString());
+		DEBUG(net, 1, "[%s] could not bind on %s port %s: %s", type, family, address, NetworkError::GetLast().AsString());
 		closesocket(sock);
 		return INVALID_SOCKET;
 	}
 
 	if (runp->ai_socktype != SOCK_DGRAM && listen(sock, 1) != 0) {
-		DEBUG(net, 1, "[%s] could not listen at %s port %s: %s", type, family, address, NetworkGetLastErrorString());
+		DEBUG(net, 1, "[%s] could not listen at %s port %s: %s", type, family, address, NetworkError::GetLast().AsString());
 		closesocket(sock);
 		return INVALID_SOCKET;
 	}
diff --git a/src/network/core/core.cpp b/src/network/core/core.cpp
index 5c12cb2242..563deae963 100644
--- a/src/network/core/core.cpp
+++ b/src/network/core/core.cpp
@@ -13,7 +13,6 @@
 #include "../../debug.h"
 #include "os_abstraction.h"
 #include "packet.h"
-#include "../../string_func.h"
 
 #include "../../safeguards.h"
 
@@ -48,20 +47,3 @@ void NetworkCoreShutdown()
 	WSACleanup();
 #endif
 }
-
-#if defined(_WIN32)
-/**
- * Return the string representation of the given error from the OS's network functions.
- * @param error The error number (from \c NetworkGetLastError()).
- * @return The error message, potentially an empty string but never \c nullptr.
- */
-const char *NetworkGetErrorString(int error)
-{
-	static char buffer[512];
-	if (FormatMessageA(FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS, NULL, error,
-			MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), buffer, sizeof(buffer), NULL) == 0) {
-		seprintf(buffer, lastof(buffer), "Unknown error %d", error);
-	}
-	return buffer;
-}
-#endif /* defined(_WIN32) */
diff --git a/src/network/core/os_abstraction.cpp b/src/network/core/os_abstraction.cpp
new file mode 100644
index 0000000000..75f2224eb0
--- /dev/null
+++ b/src/network/core/os_abstraction.cpp
@@ -0,0 +1,125 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/**
+ * @file os_abstraction.cpp OS specific implementations of functions of the OS abstraction layer for network stuff.
+ *
+ * The general idea is to have simple abstracting functions for things that
+ * require different implementations for different environments.
+ * In here the functions, and their documentation, are defined only once
+ * and the implementation contains the #ifdefs to change the implementation.
+ * Since Windows is usually different that is usually the first case, after
+ * that the behaviour is usually Unix/BSD-like with occasional variation.
+ */
+
+#include "stdafx.h"
+#include "os_abstraction.h"
+#include "../../string_func.h"
+#include <mutex>
+
+#include "../../safeguards.h"
+
+/**
+ * Construct the network error with the given error code.
+ * @param error The error code.
+ */
+NetworkError::NetworkError(int error) : error(error)
+{
+}
+
+/**
+ * Check whether this error describes that the operation would block.
+ * @return True iff the operation would block.
+ */
+bool NetworkError::WouldBlock() const
+{
+#if defined(_WIN32)
+	return this->error == WSAEWOULDBLOCK;
+#else
+	/* Usually EWOULDBLOCK and EAGAIN are the same, but sometimes they are not
+	 * and the POSIX.1 specification states that either should be checked. */
+	return this->error == EWOULDBLOCK || this->error == EAGAIN;
+#endif
+}
+
+/**
+ * Check whether this error describes a connection reset.
+ * @return True iff the connection is reset.
+ */
+bool NetworkError::IsConnectionReset() const
+{
+#if defined(_WIN32)
+	return this->error == WSAECONNRESET;
+#else
+	return this->error == ECONNRESET;
+#endif
+}
+
+/**
+ * Check whether this error describes a connect is in progress.
+ * @return True iff the connect is already in progress.
+ */
+bool NetworkError::IsConnectInProgress() const
+{
+#if defined(_WIN32)
+	return this->error == WSAEWOULDBLOCK;
+#else
+	return this->error == EINPROGRESS;
+#endif
+}
+
+/**
+ * Get the string representation of the error message.
+ * @return The string representation that will get overwritten by next calls.
+ */
+const char *NetworkError::AsString() const
+{
+	if (this->message.empty()) {
+#if defined(_WIN32)
+		char buffer[512];
+		if (FormatMessageA(FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS, NULL, this->error,
+			MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), buffer, sizeof(buffer), NULL) == 0) {
+			seprintf(buffer, lastof(buffer), "Unknown error %d", this->error);
+		}
+		this->message.assign(buffer);
+#else
+		/* Make strerror thread safe by locking access to it. There is a thread safe strerror_r, however
+		 * the non-POSIX variant is available due to defining _GNU_SOURCE meaning it is not portable.
+		 * The problem with the non-POSIX variant is that it does not necessarily fill the buffer with
+		 * the error message but can also return a pointer to a static bit of memory, whereas the POSIX
+		 * variant always fills the buffer. This makes the behaviour too erratic to work with. */
+		static std::mutex mutex;
+		std::lock_guard<std::mutex> guard(mutex);
+		this->message.assign(strerror(this->error));
+#endif
+	}
+	return this->message.c_str();
+}
+
+/**
+ * Check whether an error was actually set.
+ * @return True iff an error was set.
+ */
+bool NetworkError::HasError() const
+{
+	return this->error != 0;
+}
+
+/**
+ * Get the last network error.
+ * @return The network error.
+ */
+/* static */ NetworkError NetworkError::GetLast()
+{
+#if defined(_WIN32)
+	return NetworkError(WSAGetLastError());
+#elif defined(__OS2__)
+	return NetworkError(sock_errno());
+#else
+	return NetworkError(errno);
+#endif
+}
diff --git a/src/network/core/os_abstraction.h b/src/network/core/os_abstraction.h
index 7af3fd163e..4164dff983 100644
--- a/src/network/core/os_abstraction.h
+++ b/src/network/core/os_abstraction.h
@@ -14,6 +14,28 @@
 #ifndef NETWORK_CORE_OS_ABSTRACTION_H
 #define NETWORK_CORE_OS_ABSTRACTION_H
 
+#include <string>
+
+/**
+ * Abstraction of a network error where all implementation details of the
+ * error codes are encapsulated in this class and the abstraction layer.
+ */
+class NetworkError {
+private:
+	int error;                   ///< The underlying error number from errno or WSAGetLastError.
+	mutable std::string message; ///< The string representation of the error (set on first call to #AsString).
+public:
+	NetworkError(int error);
+
+	bool HasError() const;
+	bool WouldBlock() const;
+	bool IsConnectionReset() const;
+	bool IsConnectInProgress() const;
+	const char *AsString() const;
+
+	static NetworkError GetLast();
+};
+
 /* Include standard stuff per OS */
 
 /* Windows stuff */
@@ -23,19 +45,6 @@
 #include <ws2tcpip.h>
 #include <windows.h>
 
-/**
- * Get the last error code from any of the OS's network functions.
- * What it returns and when it is reset, is implementation defined.
- * @return The last error code.
- */
-#define NetworkGetLastError() WSAGetLastError()
-#undef EWOULDBLOCK
-#define EWOULDBLOCK WSAEWOULDBLOCK
-#undef ECONNRESET
-#define ECONNRESET WSAECONNRESET
-
-const char *NetworkGetErrorString(int error);
-
 /* Windows has some different names for some types */
 typedef unsigned long in_addr_t;
 
@@ -61,8 +70,6 @@ typedef unsigned long in_addr_t;
 #	define INVALID_SOCKET -1
 #	define ioctlsocket ioctl
 #	define closesocket close
-#	define NetworkGetLastError() (errno)
-#	define NetworkGetErrorString(error) (strerror(error))
 /* Need this for FIONREAD on solaris */
 #	define BSD_COMP
 
@@ -112,8 +119,6 @@ typedef unsigned long in_addr_t;
 #	define INVALID_SOCKET -1
 #	define ioctlsocket ioctl
 #	define closesocket close
-#	define NetworkGetLastError() (sock_errno())
-#	define NetworkGetErrorString(error) (strerror(error))
 
 /* Includes needed for OS/2 systems */
 #	include <types.h>
@@ -185,15 +190,6 @@ static inline socklen_t FixAddrLenForEmscripten(struct sockaddr_storage &address
 }
 #endif
 
-/**
- * Return the string representation of the last error from the OS's network functions.
- * @return The error message, potentially an empty string but never \c nullptr.
- */
-static inline const char *NetworkGetLastErrorString()
-{
-	return NetworkGetErrorString(NetworkGetLastError());
-}
-
 /**
  * Try to set the socket into non-blocking mode.
  * @param d The socket to set the non-blocking more for.
@@ -230,6 +226,20 @@ static inline bool SetNoDelay(SOCKET d)
 #endif
 }
 
+/**
+ * Get the error from a socket, if any.
+ * @param d The socket to get the error from.
+ * @return The errno on the socket.
+ */
+static inline NetworkError GetSocketError(SOCKET d)
+{
+	int err;
+	socklen_t len = sizeof(err);
+	getsockopt(d, SOL_SOCKET, SO_ERROR, (char *)&err, &len);
+
+	return NetworkError(err);
+}
+
 /* Make sure these structures have the size we expect them to be */
 static_assert(sizeof(in_addr)  ==  4); ///< IPv4 addresses should be 4 bytes.
 static_assert(sizeof(in6_addr) == 16); ///< IPv6 addresses should be 16 bytes.
diff --git a/src/network/core/tcp.cpp b/src/network/core/tcp.cpp
index 91aa226bf0..c5de84d369 100644
--- a/src/network/core/tcp.cpp
+++ b/src/network/core/tcp.cpp
@@ -105,11 +105,11 @@ SendPacketsState NetworkTCPSocketHandler::SendPackets(bool closing_down)
 	while (p != nullptr) {
 		res = send(this->sock, (const char*)p->buffer + p->pos, p->size - p->pos, 0);
 		if (res == -1) {
-			int err = NetworkGetLastError();
-			if (err != EWOULDBLOCK) {
+			NetworkError err = NetworkError::GetLast();
+			if (!err.WouldBlock()) {
 				/* Something went wrong.. close client! */
 				if (!closing_down) {
-					DEBUG(net, 0, "send failed with error %s", NetworkGetErrorString(err));
+					DEBUG(net, 0, "send failed with error %s", err.AsString());
 					this->CloseConnection();
 				}
 				return SPS_CLOSED;
@@ -160,10 +160,10 @@ Packet *NetworkTCPSocketHandler::ReceivePacket()
 		/* Read the size of the packet */
 			res = recv(this->sock, (char*)p->buffer + p->pos, sizeof(PacketSize) - p->pos, 0);
 			if (res == -1) {
-				int err = NetworkGetLastError();
-				if (err != EWOULDBLOCK) {
-					/* Something went wrong... (ECONNRESET is connection reset by peer) */
-					if (err != ECONNRESET) DEBUG(net, 0, "recv failed with error %s", NetworkGetErrorString(err));
+				NetworkError err = NetworkError::GetLast();
+				if (!err.WouldBlock()) {
+					/* Something went wrong... */
+					if (!err.IsConnectionReset()) DEBUG(net, 0, "recv failed with error %s", err.AsString());
 					this->CloseConnection();
 					return nullptr;
 				}
@@ -191,10 +191,10 @@ Packet *NetworkTCPSocketHandler::ReceivePacket()
 	while (p->pos < p->size) {
 		res = recv(this->sock, (char*)p->buffer + p->pos, p->size - p->pos, 0);
 		if (res == -1) {
-			int err = NetworkGetLastError();
-			if (err != EWOULDBLOCK) {
-				/* Something went wrong... (ECONNRESET is connection reset by peer) */
-				if (err != ECONNRESET) DEBUG(net, 0, "recv failed with error %s", NetworkGetErrorString(err));
+			NetworkError err = NetworkError::GetLast();
+			if (!err.WouldBlock()) {
+				/* Something went wrong... */
+				if (!err.IsConnectionReset()) DEBUG(net, 0, "recv failed with error %s", err.AsString());
 				this->CloseConnection();
 				return nullptr;
 			}
diff --git a/src/network/core/tcp_http.cpp b/src/network/core/tcp_http.cpp
index 9fc6d2f869..8b9b37eedb 100644
--- a/src/network/core/tcp_http.cpp
+++ b/src/network/core/tcp_http.cpp
@@ -231,10 +231,10 @@ int NetworkHTTPSocketHandler::Receive()
 	for (;;) {
 		ssize_t res = recv(this->sock, (char *)this->recv_buffer + this->recv_pos, lengthof(this->recv_buffer) - this->recv_pos, 0);
 		if (res == -1) {
-			int err = NetworkGetLastError();
-			if (err != EWOULDBLOCK) {
-				/* Something went wrong... (ECONNRESET is connection reset by peer) */
-				if (err != ECONNRESET) DEBUG(net, 0, "recv failed with error %s", NetworkGetErrorString(err));
+			NetworkError err = NetworkError::GetLast();
+			if (!err.WouldBlock()) {
+				/* Something went wrong... */
+				if (!err.IsConnectionReset()) DEBUG(net, 0, "recv failed with error %s", err.AsString());
 				return -1;
 			}
 			/* Connection would block, so stop for now */
diff --git a/src/network/core/tcp_listen.h b/src/network/core/tcp_listen.h
index 86311823c7..1bfdd3d78f 100644
--- a/src/network/core/tcp_listen.h
+++ b/src/network/core/tcp_listen.h
@@ -64,7 +64,7 @@ public:
 					DEBUG(net, 1, "[%s] Banned ip tried to join (%s), refused", Tsocket::GetName(), entry.c_str());
 
 					if (send(s, (const char*)p.buffer, p.size, 0) < 0) {
-						DEBUG(net, 0, "send failed with error %s", NetworkGetLastErrorString());
+						DEBUG(net, 0, "send failed with error %s", NetworkError::GetLast().AsString());
 					}
 					closesocket(s);
 					break;
@@ -81,7 +81,7 @@ public:
 				p.PrepareToSend();
 
 				if (send(s, (const char*)p.buffer, p.size, 0) < 0) {
-					DEBUG(net, 0, "send failed with error %s", NetworkGetLastErrorString());
+					DEBUG(net, 0, "send failed with error %s", NetworkError::GetLast().AsString());
 				}
 				closesocket(s);
 
diff --git a/src/network/core/udp.cpp b/src/network/core/udp.cpp
index e630f8f777..298b640c81 100644
--- a/src/network/core/udp.cpp
+++ b/src/network/core/udp.cpp
@@ -95,7 +95,7 @@ void NetworkUDPSocketHandler::SendPacket(Packet *p, NetworkAddress *recv, bool a
 			/* Enable broadcast */
 			unsigned long val = 1;
 			if (setsockopt(s.second, SOL_SOCKET, SO_BROADCAST, (char *) &val, sizeof(val)) < 0) {
-				DEBUG(net, 1, "[udp] setting broadcast failed with: %s", NetworkGetLastErrorString());
+				DEBUG(net, 1, "[udp] setting broadcast failed with: %s", NetworkError::GetLast().AsString());
 			}
 		}
 
@@ -104,7 +104,7 @@ void NetworkUDPSocketHandler::SendPacket(Packet *p, NetworkAddress *recv, bool a
 		DEBUG(net, 7, "[udp] sendto(%s)", send.GetAddressAsString().c_str());
 
 		/* Check for any errors, but ignore it otherwise */
-		if (res == -1) DEBUG(net, 1, "[udp] sendto(%s) failed with: %s", send.GetAddressAsString().c_str(), NetworkGetLastErrorString());
+		if (res == -1) DEBUG(net, 1, "[udp] sendto(%s) failed with: %s", send.GetAddressAsString().c_str(), NetworkError::GetLast().AsString());
 
 		if (!all) break;
 	}
diff --git a/src/safeguards.h b/src/safeguards.h
index e3d6c4a3e4..aca461175f 100644
--- a/src/safeguards.h
+++ b/src/safeguards.h
@@ -70,15 +70,15 @@
 #endif
 
 #if defined(NETWORK_CORE_OS_ABSTRACTION_H) && defined(_WIN32)
-/* Use NetworkGetLastError() instead of errno, or do not (indirectly) include network/core/os_abstraction.h.
- * Winsock does not set errno, but one should rather call WSAGetLastError. NetworkGetLastError abstracts that away. */
+/* Use NetworkError::GetLast() instead of errno, or do not (indirectly) include network/core/os_abstraction.h.
+ * Winsock does not set errno, but one should rather call WSAGetLastError. NetworkError::GetLast abstracts that away. */
 #ifdef errno
 #undef errno
 #endif
 #define errno    SAFEGUARD_DO_NOT_USE_THIS_METHOD
 
-/* Use NetworkGetLastErrorString() instead of strerror, or do not (indirectly) include network/core/os_abstraction.h.
- * Winsock errors are not handled by strerror, but one should rather call FormatMessage. NetworkGetLastErrorString abstracts that away. */
+/* Use NetworkError::AsString() instead of strerror, or do not (indirectly) include network/core/os_abstraction.h.
+ * Winsock errors are not handled by strerror, but one should rather call FormatMessage. NetworkError::AsString abstracts that away. */
 #define strerror SAFEGUARD_DO_NOT_USE_THIS_METHOD
 #endif /* defined(NETWORK_CORE_OS_ABSTRACTION_H) && defined(_WIN32) */