Field truncation

[andrewbanchich]

Feature Request

For large fields, tracing instrumentation can make logs pretty hard to read. It would be really nice to have some setting for the instrument macro that would truncate fields longer than a given value.

[hawkw]

I would probably implement something like this at the subscriber level, perhaps as a wrapper for the FormatFields trait (which determines how tracing-subscriber::fmt formats fields on spans and events).

There are some existing wrappers for changing field visitor behavior in the tracing_subscriber::field module, so I think it would be quite reasonable to add some kind of truncation wrapper there as well.

I don't have the time to implement something like this in the near future, but I'd definitely accept a pull request, and I'm happy to provide some guidance if you're interested in implementing this.

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As a potential alternative solution or workaround, I would also point out that the #[instrument] macro does have the capability to skip recording some arguments to a function as fields. So, if there are specific arguments to an #[instrument]ed function that are always long, you could use this to skip those fields entirely.

Truncation is probably a nicer solution, since it could be configured globally rather than per-function, and would allow a field to still be displayed completely if it's not too long. But, using #[instrument(skip(...))] may be a good interim solution, depending on your use case.

[andrewbanchich]

I don't have the time to implement something like this in the near future, but I'd definitely accept a pull request, and I'm happy to provide some guidance if you're interested in implementing this.

Great, thanks! I'll give it a shot.

[kadenlnelson]

I'm not sure what the original user story is here but I'm curious how an end user would configure/enable/disable truncation.

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Let me know if this is not within scope; Say a user wishes to disable truncation as a one time debug configuration. Does truncation get disabled for everything or for a specific module/fn/line/etc...

Devils advocate; Does the LoE required to implement and configure this feature request outweigh advocating for users to re-evaluate the Level at which they're emitting events? ie, concise events could be logged at INFO and the user could turn up the verbosity with RUSTC_LOG if desired. This echos my question earlier about what the configuration would look like for this feature.

[Sagebati]

Hi,

I'm interested in implementing this issue if not already done, what would be an example of wrappers in the field module ?