How to include source code in log messages

Sometimes, being able to see the exact code causing an error, is much more helpful than looking at other details around the current HTTP context and similar. If you often find yourself opening Visual Studio or Code to inspect the failing line, embedding source code in errors and log messages will speed up the process. In this article, you will learn how to configure to include source code when logging messages using the Elmah.Io.Client.Extensions.SourceCode NuGet package.

The Elmah.Io.Client.Extensions.SourceCode package requires Elmah.Io.Client version 4.0 or newer.

No matter what integration you are using (with a few exceptions) you are using the Elmah.Io.Client NuGet package to communicate with the API. We have built a range of extensions for this package, to avoid including too many features not related to communicating with the API into the client package. One of them is for including source code when logging messages. Start by installing the Elmah.Io.Client.Extensions.SourceCode NuGet package:

Install-Package Elmah.Io.Client.Extensions.SourceCode
dotnet add package Elmah.Io.Client.Extensions.SourceCode
<PackageReference Include="Elmah.Io.Client.Extensions.SourceCode" Version="5.*" />
paket add Elmah.Io.Client.Extensions.SourceCode

There are currently three ways of including source code with log messages. The first two ways require the Elmah.Io.Client.Extensions.SourceCode package, while the third one can be done manually.

From the file system

This is the most simple approach meant for local development. When logging a stack trace from your local machine, the trace includes the absolute path to the file on your file system, as well as the line causing a log message (typically an error). To set this up, you will need to implement the OnMessage event through the Elmah.Io.Client package. Depending on which integration you are using, the name of that event or action can vary. What you are looking to do is to call the WithSourceCodeFromFileSystem method on log messages you want to include source code. This is an example when using the Elmah.Io.Client directly:

var elmahIoClient = ElmahioAPI.Create("API_KEY");
elmahIoClient.Messages.OnMessage += (sender, e) => e.Message.WithSourceCodeFromFileSystem();

Using an integration like Elmah.Io.AspNetCore uses the same method:

services.AddElmahIo(options =>
    options.OnMessage = msg => msg.WithSourceCodeFromFileSystem();

This will automatically instruct Elmah.Io.Client.Extensions.Source to try and parse any stack trace in the details property and embed the source code.

For an example of how to use the WithSourceCodeFromFileSystem method, check out the following sample: Elmah.Io.Client.Extensions.SourceCode.FileSystem.

From the PDB file

When deploying your code on another environment, you typically don't have the original code available. If you copy your source code to the same absolute path as when building, you can use the file-system approach shown above. If not, embedding the source code in the PDB file can be the option. Before doing so, make sure you include filename and line numbers in stack traces on all environments as shown here: Include filename and line number in stack traces. For the old project template the Debugging information field needs a value of Portable. For the new project template the Debug symbols field needs a value of PDB file, portable across platforms.

To embed source code in the PDB file built alongside your DLL files, include the following property in your csproj file:


Be aware that this will include your original source code in your deployment which may not be a good approach if other people have access to the environment or binary files. Next, call the WithSourceCodeFromPdb method:

var elmahIoClient = ElmahioAPI.Create("API_KEY");
elmahIoClient.Messages.OnMessage += (sender, e) => e.Message.WithSourceCodeFromPdb();

For an example of how to do this from ASP.NET Core, you can use the same approach as specified in the previous section:

services.AddElmahIo(options =>
    options.OnMessage = msg => msg.WithSourceCodeFromPdb();

All of our integrations support a message callback somehow.

For an example of how to use the WithSourceCodeFromPdb method, check out the following sample: Elmah.Io.Client.Extensions.SourceCode.PdbSample for .NET and Elmah.Io.Client.Extensions.SourceCode.NetFrameworkPdb for .NET Framework.


In case you want to include source code manually, you can use the OnMessage event and the Code property on the CreateMessage class:

var elmahIoClient = ElmahioAPI.Create("API_KEY");
elmahIoClient.Messages.OnMessage += (sender, e) =>
    e.Message.Code = FetchCode();

You will need to implement the FetchCode method to return the source code to include. Only 21 lines of code are supported for now.

In case you want to show the correct line numbers, you will need to tell us how the first line number in the provided code matches your original source file as well as the line number causing the error. This is done by adding two Items to the Data dictionary on CreateMessage:

var elmahIoClient = ElmahioAPI.Create("API_KEY");
elmahIoClient.Messages.OnMessage += (sender, e) =>
    e.Message.Code = FetchCode();
    if (e.Message.Data == null) e.Message.Data = new List<Item>();
    e.Message.Data.Add(new Item("X-ELMAHIO-CODESTARTLINE", "42"));
    e.Message.Data.Add(new Item("X-ELMAHIO-CODELINE", "51"));

This will show line number 42 next to the first code line and highlight line number 51 in the UI.


If no source code shows up on log messages, you can start by running through the following checks:

  • Make sure that the log message contains a stack trace in the details field.
  • Make sure that the stack trace contains absolute path filenames and line numbers for the code causing the stack trace.
  • Make sure that you are calling the WithSourceCodeFromPdb or WithSourceCodeFromFileSystem method.
  • Make sure that the Elmah.Io.Client.Extensions.SourceCode.dll file is in your deployed application.
  • Make sure that your project has Portable set in Debugging information or PDB File, portable across platforms set in Debug symbols.
  • For PDB files, make sure that you have included the EmbedAllSources element in your csproj file.
  • Look inside the Data tab on the logged message. It may contain a key named X-ELMAHIO-CODEERROR with a value explaining what went wrong.

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