[bug] The log generated by setting OTEL_DIAGNOSTICS.json is binary and unreadable

[domholmes]

Package

OpenTelemetry

Package Version

Package Name	Version
OpenTelemetry.Api	1.9.0
OpenTelemetry	1.9.0

Runtime Version

net8.0

Description

Creating a OTEL_DIAGNOSTICS.json in the correct place causes debug log files to be created e.g My.Project.exe.37076.log but they are unreadable

Steps to Reproduce

1. Configure a working ASP.NET core application that exports OpenTelemetary data as expected
2. Add a OTEL_DIAGNOSTICS.json file in the root of the project directory
3. Run the application and generate trace data
4. Attempt to open the log file written in the same directory

Expected Result

The log is a readable text file

Actual Result

The log is unreadable

Additional Context

{
"LogDirectory": ".",
"FileSize": 32768,
"LogLevel": "Error"
}

[xiang17]

What does the log file look like? The file is written circularly in a fixed size block. And initially it was initialized with all NUL characters, so there may seem to have a lot of garbles after the lines of readable logs at file start.

[domholmes]

Hi there. Most editors won't open it, reporting it as binary. Those that do, there are no readable characters at the start, even changing the LogLevel to ensure something should be printed.

[xiang17]

Can you give a minimal sample app that can reproduce the issue?

[domholmes]

Ok so I did some more digging and the problem is that the log isn't overwritten with readable data until the TracerProviderBuilder is manually disposed i.e pressing Ctrl+C on the terminal to end the application and not just killing the debug session with the stop icon in Visual Studio (tracer.Dispose() is never reached).

This is only a problem when manually creating tracers with Sdk.CreateTracerProviderBuilder(). Using builder.Services.AddOpenTelemetry() the logs are written instantly (much more useful).

OtelLogTest.zip

[xiang17]

I couldn't reproduce the issue with your sample app. I ran the test app and it generated expected file.

If you opened the file with Visual Studio Code, you might see warning while opening: "The file is not displayed in the text editor because it is either binary or uses an unsupported text encoding." Select "Open Anyway" and choose the built-in Text Editor.

The file would look like:

I also tried to comment out tracer.Dispose(); line and got expected file. The only difference is that the second line '{0}' Disposed.{TracerProvider} is missing, which is also expected.