Message template support (@mt in Seq)

[Victor-N-Suadicani]

When logging something like info!("Hello, {username}"), is there any way to retrieve the literal string "Hello, {username}" (i.e. without interpolation) as a message template field?

Background

Seq is a logging search/analysis tool. It supports an @mt field that represents the message template, as documented here. This corresponds to message templates as described on https://messagetemplates.org.

For example, a log event may look like:

{"@t":"2016-06-07T03:44:57.8532799Z","@mt":"Hello, {username}","username":"Alice"}

So instead of containing the full interpreted message (which would be "Hello, Alice"), only the message template and the fields are presented in the log line.

Is there any way to support this using the tracing crate, via layers or event formatting or something like this? My initial guess would be "no" since, as far as I can tell, there is no way to retrieve the message template when using the log macros (like info!("Hello, {username}")), but I'd like confirmation and to hear if anyone has a good idea of how to achieve this in a nice way.

[mladedav]

It's not possible in this way as the message is first created as if you called format!. However, you could do something like info!(username = "Alice", "Hello, {{username}}"); to have the message not interpolated and then you can process it in another system.

[Victor-N-Suadicani]

I thought so. I'll probably settle for wrapping the log macros in my own macros that capture the message template string directly, but I was hoping it was possible without making my own macros. Anyways, thanks!