I guess testing on windows passes.

include/spdlog/details/tcp_client-windows.h

@@ -58,6 +58,60 @@ public:
 
     SOCKET fd() const { return socket_; }
 
+    int connect_socket_with_timeout(SOCKET sockfd,
+                                    const struct sockaddr *addr,
+                                    int addrlen,
+                                    const timeval &tv) {
+        // Blocking if no timeout
+        if (tv.tv_sec == 0 && tv.tv_usec == 0) {
+            int rv = ::connect(sockfd, addr, addrlen);
+            if (rv == SOCKET_ERROR && WSAGetLastError() == WSAEISCONN) return 0;
+            return rv;
+        }
+
+        // Set non-blocking
+        u_long mode = 1UL;
+        ::ioctlsocket(sockfd, FIONBIO, &mode);
+
+        int rv = ::connect(sockfd, addr, addrlen);
+        int last_error = WSAGetLastError();
+        if (rv == 0 || last_error == WSAEISCONN) {
+            mode = 0UL;
+            ::ioctlsocket(sockfd, FIONBIO, &mode);
+            return 0;
+        }
+        if (last_error != WSAEWOULDBLOCK) {
+            mode = 0UL;
+            ::ioctlsocket(sockfd, FIONBIO, &mode);
+            return SOCKET_ERROR;
+        }
+
+        // Wait for writability
+        fd_set wfds;
+        FD_ZERO(&wfds);
+        FD_SET(sockfd, &wfds);
+
+        rv = ::select(0, nullptr, &wfds, nullptr, &tv);
+        mode = 0UL;
+        ::ioctlsocket(sockfd, FIONBIO, &mode);
+
+        if (rv <= 0) {
+            // timeout or error
+            if (rv == 0) WSASetLastError(WSAETIMEDOUT);
+            return SOCKET_ERROR;
+        }
+
+        // Check socket for errors
+        int so_error = 0;
+        int len = sizeof(so_error);
+        ::getsockopt(sockfd, SOL_SOCKET, SO_ERROR, (char *)&so_error, &len);
+        if (so_error != 0 && so_error != WSAEISCONN) {
+            WSASetLastError(so_error);
+            return SOCKET_ERROR;
+        }
+        return 0;
+    }
+
     // try to connect or throw on failure
     void connect(const std::string &host, int port, int timeout_ms) {
         if (is_connected()) {
@@ -71,6 +125,10 @@ public:
         hints.ai_flags = AI_NUMERICSERV;  // port passed as as numeric value
         hints.ai_protocol = 0;
 
+        timeval tv;
+        tv.tv_sec = timeout_ms / 1000;
+        tv.tv_usec = (timeout_ms % 1000) * 1000;
+
         auto port_str = std::to_string(port);
         struct addrinfo *addrinfo_result;
         auto rv = ::getaddrinfo(host.c_str(), port_str.c_str(), &hints, &addrinfo_result);
@@ -82,7 +140,6 @@ public:
         }
 
         // Try each address until we successfully connect(2).
-
         for (auto *rp = addrinfo_result; rp != nullptr; rp = rp->ai_next) {
             socket_ = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
             if (socket_ == INVALID_SOCKET) {
@@ -90,47 +147,11 @@ public:
                 WSACleanup();
                 continue;
             }
-            // set non-blocking if timeout specified
-            u_long mode = (timeout_ms > 0) ? 1UL : 0UL;
-            ::ioctlsocket(socket_, FIONBIO, &mode);
-
-            rv = ::connect(socket_, rp->ai_addr, (int)rp->ai_addrlen);
-            if (rv == SOCKET_ERROR) {
-                last_error = WSAGetLastError();
-                if (timeout_ms > 0 && last_error == WSAEWOULDBLOCK) {
-                    fd_set wfds;
-                    FD_ZERO(&wfds);
-                    FD_SET(socket_, &wfds);
-                    timeval tv;
-                    tv.tv_sec = timeout_ms / 1000;
-                    tv.tv_usec = (timeout_ms % 1000) * 1000;
-                    rv = ::select(0, nullptr, &wfds, nullptr, &tv);
-                    if (rv > 0) {
-                        int so_error = 0;
-                        int len = sizeof(so_error);
-                        ::getsockopt(socket_, SOL_SOCKET, SO_ERROR, (char *)&so_error, &len);
-                        if (so_error == 0)
-                            rv = 0;
-                        else {
-                            last_error = so_error;
-                            rv = SOCKET_ERROR;
-                        }
-                    } else {
-                        last_error = (rv == 0 ? WSAETIMEDOUT : WSAGetLastError());
-                        rv = SOCKET_ERROR;
-                    }
-                }
-            }
-
-            // restore blocking mode
-            mode = 0UL;
-            ::ioctlsocket(socket_, FIONBIO, &mode);
-
-            if (rv == 0) {
+            if (connect_socket_with_timeout(socket_, rp->ai_addr, (int)rp->ai_addrlen, tv) == 0) {
                 last_error = 0;
                 break;
             }
-
+            last_error = WSAGetLastError();
             ::closesocket(socket_);
             socket_ = INVALID_SOCKET;
         }
@@ -139,10 +160,11 @@ public:
             WSACleanup();
             throw_winsock_error_("connect failed", last_error);
         }
-
+        if (timeout_ms > 0) {
             DWORD tv = static_cast<DWORD>(timeout_ms);
             ::setsockopt(socket_, SOL_SOCKET, SO_RCVTIMEO, (const char *)&tv, sizeof(tv));
             ::setsockopt(socket_, SOL_SOCKET, SO_SNDTIMEO, (const char *)&tv, sizeof(tv));
+        }
 
         // set TCP_NODELAY
         int enable_flag = 1;

include/spdlog/details/tcp_client.h

@@ -151,9 +151,11 @@ public:
             throw_spdlog_ex("::connect failed", last_errno);
         }
 
+        if (timeout_ms > 0) {
             // Set timeouts for send and recv
             ::setsockopt(socket_, SOL_SOCKET, SO_RCVTIMEO, (const char *)&tv, sizeof(tv));
             ::setsockopt(socket_, SOL_SOCKET, SO_SNDTIMEO, (const char *)&tv, sizeof(tv));
+        }
 
         // set TCP_NODELAY
         int enable_flag = 1;

include/spdlog/sinks/tcp_sink.h

@@ -31,7 +31,7 @@ namespace sinks {
 struct tcp_sink_config {
     std::string server_host;
     int server_port;
-    int timeout_ms = 0;
+    int timeout_ms = 0; // The timeout for all 3 major socket operations that is connect, send, and recv
     bool lazy_connect = false;  // if true connect on first log call instead of on construction
 
     tcp_sink_config(std::string host, int port)