# simplelog

## Summary

simplelog is an opinionated logging package designed to facilitate easy and
structured logging in Go applications with an absolute minimum of
boilerplate.

The idea is that you can add a single import line which replaces the
stdlib `log/slog` default handler, and solve the 90% case for logging.

## Current Status

Released v1.0.0 2024-06-14.  Works as intended.  No known bugs.

## Features

-   if output is a tty, outputs pretty color logs
-   if output is not a tty, outputs json
-   supports delivering each log message via a webhook
-   emits every `slog` attribute: those passed to a log call, those
    accumulated with `WithAttrs`, and those qualified by `WithGroup`.
    `slog.Group` values nest, and `slog.LogValuer` values are resolved. In
    json output attributes are object fields (groups become nested objects);
    in console output they are appended as `key=value` pairs, with grouped
    keys written as `group.key=value`. See
    [Attribute output](#attribute-output) for the details worth knowing

## Planned Features

-   supports delivering logs via tcp RELP (e.g. to remote rsyslog using imrelp)

## Installation

To use simplelog, first ensure your project is set up with Go modules:

```bash
go mod init your_project_name
```

Then, add SimpleLog to your project:

```bash
go get sneak.berlin/go/simplelog
```

## Usage

Below is an example of how to use SimpleLog in a Go application. This
example is provided in the form of a `main.go` file, which demonstrates
logging at various levels using structured logging syntax.

```go
package main

import (
	"log/slog"
	_ "sneak.berlin/go/simplelog"
)

func main() {

    // log structured data with slog as usual:
	slog.Info("User login attempt", slog.String("user", "JohnDoe"), slog.Int("attempt", 3))
	slog.Warn("Configuration mismatch", slog.String("expected", "config.json"), slog.String("found", "config.dev.json"))
	slog.Error("Failed to save data", slog.String("reason", "permission denied"))
}
```

## Attribute output

Attributes reach every handler: the ones passed to the log call, the ones
accumulated with `WithAttrs`, and the ones qualified by the groups open at
the time they were attached. `slog.Group` values nest, and
`slog.LogValuer` values are resolved to the value they stand for. A few
behaviours are worth knowing before you rely on them.

**Your values are never modified.** Whatever you log is read and rendered,
never written to. A map or a slice you pass to `slog.Any` comes back from
the logger exactly as you handed it over, even when a group later uses the
same key.

**Durations are nanoseconds in json, and readable on the console.** The
json and webhook payloads emit a `slog.Duration` as a number of
nanoseconds, matching `slog.NewJSONHandler`, so a consumer can compare and
aggregate the field without parsing it. The console line emits the same
duration as `3s`, matching `slog.NewTextHandler`, because a person reads
it.

**The json payload is an object, with the consequences an object has.**
The record's own fields are named `Time`, `Level`, `Message` and `PC`, and
they own those names: an attribute keyed after one of them is dropped from
the json and webhook output. A key logged more than once keeps its last
value there for the same reason, with one exception: when both are
`slog.Group` values sharing a key, the two groups are merged into one
object holding the members of both, rather than the second replacing the
first. Neither the collision nor the merge applies to the console output,
which is a line of text: every pair appears, in order. If you need a field
called `message`, pick a key that does not collide - the collision is
silent.

**Empty things follow the `slog.Handler` contract.** An empty `Attr` is
ignored, an empty group is elided along with its key, a group with an
empty key is inlined into its parent, and `WithGroup("")` returns the
handler unchanged.

## License

[WTFPL](./LICENSE)