disable SIO_UDP_CONNRESET behaviour for UDP

network.zig

@@ -1268,6 +1268,28 @@ const windows = struct {
             ws2_32.WSA_FLAG_OVERLAPPED,
         );
 
+        // Disable SIO_UDP_CONNRESET behaviour for UDP
+        //
+        // This resolves an issue where "recvfrom" can return a WSAECONNRESET error if a previous send
+        // call failed and resulted in an ICMP Port Unreachable message.
+        // https://github.com/MasterQ32/zig-network/issues/66
+        if (socket_type == std.os.SOCK.DGRAM) {
+            // This was based off the following Go code:
+            // https://github.com/golang/go/blob/5c154986094bcc2fb28909cc5f01c9ba1dd9ddd4/src/internal/poll/fd_windows.go#L338
+            const IOC_IN = 0x80000000;
+            const IOC_VENDOR = 0x18000000;
+            const SIO_UDP_CONNRESET = IOC_IN | IOC_VENDOR | 12;
+            var flag = &[_]u8{ 0, 0, 0, 0 };
+            var ret: u32 = 0;
+            switch (ws2_32.WSAIoctl(sock, SIO_UDP_CONNRESET, flag.ptr, flag.len, null, 0, &ret, null, null)) {
+                0 => {},
+                ws2_32.SOCKET_ERROR => switch (ws2_32.WSAGetLastError()) {
+                    else => |err| return unexpectedWSAError(err),
+                },
+                else => unreachable,
+            }
+        }
+
         if (std.io.is_async and std.event.Loop.instance != null) {
             const loop = std.event.Loop.instance.?;
             _ = try CreateIoCompletionPort(sock, loop.os_data.io_port, undefined, undefined);

testsuite.zig

@@ -1,4 +1,5 @@
 const std = @import("std");
+const builtin = @import("builtin");
 const network = @import("network");
 const expect = std.testing.expect;
 
@@ -35,9 +36,7 @@ test "UDP timeout" {
     var sock = try network.Socket.create(.ipv4, .udp);
     defer sock.close();
     try sock.connect(.{
-        .address = .{
-            .ipv4 = network.Address.IPv4.init(1, 1, 1, 1)
-        },
+        .address = .{ .ipv4 = network.Address.IPv4.init(1, 1, 1, 1) },
         .port = 53,
     });
     try sock.setReadTimeout(3000000); // 3 seconds
@@ -63,3 +62,61 @@ test "IPv4 parse" {
     try std.testing.expectEqual(make(127, 33, 10, 20), try parse("127.33.2580"));
     try std.testing.expectEqual(make(255, 255, 255, 255), try parse("255.255.255.255"));
 }
+
+// https://github.com/MasterQ32/zig-network/issues/66
+test "Windows-only, fix UDP WSAECONNRESET error when calling recvfrom after send failure" {
+    if (builtin.os.tag != .windows) {
+        // Skip if not Windows
+        return;
+    }
+    try network.init();
+    defer network.deinit();
+
+    // setup sockets
+    var server_sock = try network.Socket.create(.ipv4, .udp);
+    defer server_sock.close();
+    try server_sock.setReadTimeout(25 * std.time.us_per_ms);
+    try server_sock.bind(.{
+        .address = network.Address{ .ipv4 = network.Address.IPv4.any },
+        .port = 1234,
+    });
+    var client_sock = try network.Socket.create(.ipv4, .udp);
+    var client_sock_closed = false;
+    defer {
+        if (!client_sock_closed) {
+            client_sock.close();
+            client_sock_closed = true;
+        }
+    }
+    try client_sock.connect(.{
+        .address = .{ .ipv4 = network.Address.IPv4.init(127, 0, 0, 1) },
+        .port = 1234,
+    });
+    try client_sock.setReadTimeout(25 * std.time.us_per_ms);
+
+    // setup buffer
+    const buflen = 32;
+    var msg: [buflen]u8 = undefined;
+
+    // send and read data back and forth
+    _ = try client_sock.send("connect_info");
+    const recvFrom = try server_sock.receiveFrom(msg[0..buflen]);
+    // close the socket to force the WSAECONNRESET error when we send below
+    client_sock.close();
+    client_sock_closed = true;
+    // If we do not disable SIO_UDP_CONNRESET then a failed "send" will be caught when the
+    // next "recvfrom" function is called.
+    //
+    // MDN: https://learn.microsoft.com/en-us/windows/win32/api/winsock/nf-winsock-recvfrom
+    // WSAECONNRESET: "On a UDP-datagram socket this error indicates a previous send operation resulted
+    // in an ICMP Port Unreachable message."
+    _ = try server_sock.sendTo(recvFrom.sender, "data");
+    _ = server_sock.receiveFrom(msg[0..buflen]) catch |err| switch (err) {
+        error.WouldBlock => {
+            // fallthrough, expect this to timeout
+        },
+        else => {
+            return err;
+        },
+    };
+}