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Slog Package

In Go 1.21 (June 2023), the log/slog package was added to the standard library to support structured logging. There was much rejoicing.

There are several third-party logging libraries, like:

Most predate log/slog, and unless you have very specific needs, log/slog is probably all you need these days. Compare a standard log message:

2023/10/01 12:00:00 This is a log message

To a structured log/slog message:

2024-01-15T10:30:45.123Z INFO msg="user login successful" user_id=12345 username=john_doe ip_address=192.168.1.100 duration_ms=245

Handlers

The log/slog package introduces handlers, which accept arbitrary key-value pairs and format them into a log record. Two built-in handlers are:

The log/slog.New function takes a handler as an argument, and returns a logger instance that can be used to log messages:

logger := slog.New(slog.NewTextHandler(os.Stderr, nil))

Then we can use it like this:

logger.Info("This is an info message")

The structured logger doesn't support formatting methods like Infof, so use fmt.Sprintf when needed:

logger.Info(fmt.Sprintf("Failed to open file %s: %s", filename, err))

Switch Linko to structured logging with slog.

Update your logger type to *slog.Logger, using slog.NewTextHandler. You can use nil handler options for now.
Update the rest of the app to use the new logger type. Replace existing Print/Printf calls with Info calls.

Use fmt.Sprintf to format strings as needed. slog doesn't have Infof or similar methods.
Make sure all packages compile.

Restart your server:

go run .

Run and submit the CLI tests from the root of the Linko repo.