Logging for Networked Games

An overview of Logging for Network Games.

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Logging for Networked Games

Client and Server logs are important for identifying and debugging networking issues. While many networking logs fall into the LogNet category, we recommend checking log categories that are more closely related to specific systems to provide greater insight into any issues.

These categories are not enabled by default and have varying amounts of verbosity that you may need to adjust to gain information about the behavior you're experiencing. The list below provides some recommended categories:

Category

Description

LogNetTraffic

Logs all network traffic when this log variable is set to VeryVerbose.

LogNetPackageMap

Logs information related to how NetGUIDs are Sent, Received, and Acknowledged.

LogNetVersion

Logs information related to Property Replication and RepNotify functions that are used by FRepLayout and FObjectReplicator.

LogNetFastTArray

LogNetDormancy

LogRep

LogRepTraffic

LogRepProperties

Logs information related to the sending and receiving of replicated properties.

PacketHandlerLog

Logs information on the packet handler and its components. These components have their own sub-categories. For example, LogDTLSHandler, OodleNetworkHandlerComponentLog, and LogHandshake.

LogDemo

Logs information on recording and playing back replays. Each replay streamer has a related log category: LogLocalFileReplay, LogSaveGameReplay, LogNullReplay, and LogMemoryReplay.

You can enable these categories and adjust their verbosity by either passing in the command line argument: 

-LogCmds=<LogCategory><Log Verbosity>

using the console command Log: 

<Log Category> <Log Verbosity>,

or by setting them in your project's DefaultEngine.ini. For example: 

[Core.Log]

LogNetPackageMap=Log

LogNetTraffic=Verbose

LogRep=VeryVerbose

When reading logs, the following list can be useful for determining what kind of error occurred.

UEngine::BroadcastNetworkFailure

Printed when a net driver encounters some major error. The log line will include the failure type, the error string, and the description of the net driver that encountered the error. You can see a list of the possible network failures with brief descriptions in the ENetworkFailure enum in EngineBaseTypes.h.

UNetConnection::Close

A description of the connection being closed.

UActorChannel::Close

A LogNetTraffic category that will include the channel index, the Actor for that channel, and the reason it was closed. Checking the logs around these lines can help provide some indication as to why a connection or Actor channel was closed.

The command-line argument -LogTrace=<partial log line> performs stack traces from partial log message strings. For example: -LogTrace=UNetConnection::Close will produce a stack trace whenever UNetConnection::Close is printed to the logs. The command-line argument -DumpRPCs provides the capability to dump RPCs and their parameters, which can be useful for tracking what RPCs are being sent and their parameters.

LogTrace and DumpRPCs both require NetcodeUnitTest to be enabled.

This page was written for a previous version of Unreal Engine and has not been updated for the current Unreal Engine 5.0 release.
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