I really like tracing but

[snmpboy]

When I used tracing, I realized that the error! macro was pretty picky. What you tried to log had to have the Value trait. To get around that I did this:

if let Ok(formatted_xml) = formatter(&string) {
        file.write_all(&*formatted_xml).unwrap_or_else(|error| {
            let msg = error.to_string();
            error!(msg, "Problem writing file: {}", msg);
        });
    };

Is that ok? From what I understand, I just made an allocation using to_string(). Am I right? I also see recommendations but about reducing allocations but I am not sure what is meant by that.

[kornel]

That's generally expected, since errors rarely implement any other form of serializing them.

Reducing allocations usually helps make code faster, but that applies to cases where the code is performance-sensitive (you're allocating millions of things), and/or where there are easy obvious ways to avoid allocations.

In this case the error handling code is on the less-used code path, and it's just one string.

[scottmcm]

That would be bad for a verbose! log where it often would be turned off and you're be doing the .to_string() for nothing. If it's something that deserves to be an error!, then presumably it's going to actually go somewhere, and thus as kornel said, it's fine.

[CAD97]

For tracing's macros specifically, you can capture a value's Debug representation by writing ?error and Display by writing %error.

Separately, as a style thing, if you include something as structured data, you generally shouldn't also put it into the string message. Your current error! might potentially be logged as something like

ERROR: Problem writing file: access denied
    .msg = "access denied"

(made up log syntax), and almost all tracing log sinks will record the structured data you give it, making its presence in the primary error message redundant.

[snmpboy]

I am not sure I follow about redundancy. Right now an example of the log file is like so:

{"v":0,"name":"ncclient","msg":"executing statement s184 with parameters: ["cfp2-or-qsfp28", "20-30-31-39-2d-30-37-38-2d-30-35-38-20-41-30-31-df-10-01-11-11-00-10-00-00-00-00-00-00-00-00", "FTLC9555REPM3-E5", "X6PB7T1", "1/1/c15", 2024-10-17T01:07:57.500683943Z, 5, "qsfp28-connector"]","level":20,"hostname":"87826decf1e2","pid":1,"time":"2024-10-17T01:07:57.533699616Z","target":"log","line":null,"file":null,"log.file":"/usr/local/cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-postgres-0.7.12/src/query.rs","log.module_path":"tokio_postgres::query","log.target":"tokio_postgres::query","log.line":46}
{"v":0,"name":"ncclient","msg":"Database error: db error: ERROR: value too long for type character varying(60)","level":50,"hostname":"87826decf1e2","pid":1,"time":"2024-10-17T01:07:57.534173928Z","target":"vip_poll","line":230,"file":"src/main.rs"}