# Purpose

`Vlog` extends the structured log JSONHandler with sending logs to a VictoriaLogs instance for central logging.

Logs are first queued to a buffered channel processed by go-routine loop which transform and send the log to the server.

In case of network error, queue getting full - anything that doesn't get a HTTP 200 from VictoriaLogs; logs get stored to disk to be processed at intervals.

Streams are set to separate application runs to instances of it running on different servers.

# Usage

```golang
package main

import (
	// External
	"git.gibonuddevalla.se/go/vlog"

	// Standard
	"log/slog"
	"os"
	"time"
)

func main() {
	opts := slog.HandlerOptions{
		Level: slog.LevelInfo, // Minimum level to display.
	}

	handler := vlog.New(
		os.Stdout,
		opts,
		"/tmp/vlog_spool",     // Spool directory when logs can't be sent.
		"https://log.hum.se/", // URL to VictoriaLogs instance.
		"vlog",                // Application name.
		"srv01",               // System/server that runs the instance.
		"dev",                 // Instance name.
	)

	log := slog.New(handler)

	for {
		log.Warn("server", "foo", "bar", "baz", 123)
		time.Sleep(time.Second * 1)
	}

}
```

# Logging stream

The stream is created with:
1) application name.
1) system name running the software.
1) instance name (like dev or prod).
1) run, which is automated to YYMMDD_HHMMSS when application is started.

These are prefixed with `log`, see JSON data below.

# Logging data

Application log attributes (`foo`, `baz` in the example code) are added to the top level log entry.

The vlog library adds go build information (git repo and such) and a runtime trace when sending logs with level `warn`, `warn` or `error`.

The `info` level is excepted to this since it would probably be used the most for regular data that wouldn't lead to any troubleshooting. Making the trace eats a bit of performance.

```json
{
  "_time": "2026-02-14T08:43:02.760194943Z",
  "_stream_id": "0000000000000000926515688d74d64c8facef73b36a02b5",
  "_stream": "{log.application=\"vlog\",log.instance=\"dev\",log.run=\"260214_094242\",log.system=\"srv01\"}",
  "_msg": "server",
  "baz": "123",
  "foo": "bar",
  "log.application": "vlog",
  "log.instance": "dev",
  "log.level": "WARN",
  "log.run": "260214_094242",
  "log.system": "srv01",
  "log.build": "{\"GoVersion\":\"go1.25.4\",\"Path\":\"hum\",\"Main\":{\"Path\":\"hum\",\"Version\":\"(devel)\"},\"Deps\":[{\"Path\":\"git.gibonuddevalla.se/go/vlog\",\"Version\":\"(devel)\"}],\"Settings\":[{\"Key\":\"-buildmode\",\"Value\":\"exe\"},{\"Key\":\"-compiler\",\"Value\":\"gc\"},{\"Key\":\"CGO_ENABLED\",\"Value\":\"1\"},{\"Key\":\"CGO_CFLAGS\"},{\"Key\":\"CGO_CPPFLAGS\"},{\"Key\":\"CGO_CXXFLAGS\"},{\"Key\":\"CGO_LDFLAGS\"},{\"Key\":\"GOARCH\",\"Value\":\"amd64\"},{\"Key\":\"GOOS\",\"Value\":\"linux\"},{\"Key\":\"GOAMD64\",\"Value\":\"v1\"}]}",
  "log.trace": "goroutine 1 [running]:\nruntime/debug.Stack()\n\t/usr/local/go/src/runtime/debug/stack.go:26 +0x5e\ngit.gibonuddevalla.se/go/vlog.(*VictoriaHandler).queue(_, {{0xc25c2b45ad4fa77f, 0x4a9205feb, 0x9bf140}, {0x7339a5, 0x6}, 0x4, 0x65125f, {{{0x73345d, 0x3}, ...}, ...}, ...})\n\t/tmp/foo/vlog/lib.go:146 +0x65\ngit.gibonuddevalla.se/go/vlog.VictoriaHandler.Handle({0xc000074080, {0x7335b3, 0x4}, {0x733793, 0x5}, {0x733466, 0x3}, {0x73842d, 0x14}, {0x7aec30, ...}, ...}, ...)\n\t/tmp/foo/vlog/lib.go:75 +0x65\nlog/slog.(*Logger).log(0xc0000f3f30, {0x7aebf8?, 0x9e03c0?}, 0x4, {0x7339a5, 0x6}, {0xc0000f3ef0, 0x4, 0x4})\n\t/usr/local/go/src/log/slog/logger.go:256 +0x208\nlog/slog.(*Logger).Warn(...)\n\t/usr/local/go/src/log/slog/logger.go:219\nmain.main()\n\t/tmp/foo/hum/main.go:31 +0x1a6\n"
}
```