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feat: Improve error message on connection failure [2.X] #4208

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Merged
simon-lemay-unity merged 1 commit into from
Oct 23, 2026
Merged

feat: Improve error message on connection failure [2.X] #4208

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36 changes: 35 additions & 1 deletion com.unity.netcode.gameobjects/Runtime/Transports/UTP/UnityTransport.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1144,7 +1144,7 @@
// means a clean disconnect that doesn't require logging.
if (!m_Driver.Listening && m_ServerClientId == default)
{
Debug.LogError("Failed to connect to server.");
LogClientConnectionFailureMessage();
}

// Set the disconnect event error code
Expand Down Expand Up @@ -1172,6 +1172,40 @@
return false;
}

private void LogClientConnectionFailureMessage()
{
if (OnCurrentTopology() == NetworkTopologyTypes.ClientServer)
{
var reasons = new List<string> { "Server/host is not running." };

if (m_ProtocolType == ProtocolType.RelayUnityTransport && !m_UseWebSockets)
{
reasons.Add("Relay port might be blocked on your network. Try using WebSockets.");
if (m_RelayServerData.IsSecure != 0)
{
reasons.Add("DTLS might be blocked on your network. Try using UDP or WebSockets.");
}
}

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else if (m_ProtocolType != ProtocolType.RelayUnityTransport)
{
reasons.Add($"Server/host might not be reachable. Try \"ping {ConnectionData.Address}\" in a terminal.");
reasons.Add("The firewall on the server/host might be blocking the connection attempts.");
if (m_UseEncryption && !m_UseWebSockets)

@u-pr u-pr Bot Oct 22, 2026

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P2

In browser builds with UseWebSockets false and UseEncryption true, failed direct connections incorrectly report DTLS as a possible cause. CreateDriver forces WebSocketNetworkInterface under UNITY_WEBGL && !UNITY_EDITOR, even when UseWebSockets is false. The connection therefore uses TLS over WebSockets, and recommending WebSockets sends users toward a protocol already in use. The Relay diagnostic has the same flag mismatch. Base these conditions on the effective protocol, including the WebGL fallback.

🤖 Helpful? 👍/👎

{
reasons.Add("DTLS might be blocked on your network. Try using WebSockets.");
}

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}

const string prefix = "\n\t- ";
Debug.LogError("Failed to connect to server. Possible reasons:" + prefix + string.Join(prefix, reasons));
}
else
{

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// If using DA the SDK should have logged an actual useful error.
Debug.LogError("Failed to connect to server.");
}

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}

/// <summary>
/// Handles accepting new connections and processing transport events.
/// </summary>
Expand Down
3 changes: 2 additions & 1 deletion com.unity.netcode.gameobjects/Tests/Runtime/Connection/ClientOnlyConnectionTests.cs
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Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
using System.Collections;
using System.Text.RegularExpressions;
using NUnit.Framework;
using Unity.Netcode.TestHelpers.Runtime;
using Unity.Netcode.Transports.UTP;
Expand Down Expand Up @@ -48,7 +49,7 @@ public IEnumerator ClientFailsToConnect()
m_ClientNetworkManager.StartClient();

// Unity Transport throws an error when it times out
LogAssert.Expect(LogType.Error, "Failed to connect to server.");
LogAssert.Expect(LogType.Error, new Regex("^Failed to connect to server\\."));
yield return NetcodeIntegrationTest.WaitForConditionOrTimeOut(() => m_WasDisconnected, m_TimeoutHelper);
Assert.False(m_TimeoutHelper.TimedOut, "Timed out waiting for client to timeout waiting to connect!");

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