Log

This is the simplest logging for Go.

Level Management

Use the level package and MinLevel/SetMinLevel.

// Set minimum level Warn to default logger.
log.SetMinLevel(level.Warn)

log.Debug("debug") // Output nothing
log.Warn("warn") // Output `warn`

Output Format Customization

You can customize the output format easily. Let's use Format/SetFormat to set the output format into the logger.

SetFormat(format.JSON)
logger.Info("info")
// Output:
// {"level":"INFO","message":"info","time":"2019-10-22T16:50:17.637733482+09:00"}

SetFormat(format.JSONPretty)
logger.Info("info")
// Output:
// {
//   "level": "INFO",
//   "message": "info",
//   "time": "2019-10-22T16:49:00.253014475+09:00"
// }

This repository supports only 2 formats that are plain JSON and pretty JSON.

however, you can make a new format that is along func(map[string]interface{}) string. After creating it, just needed to use Format/SetFormat to set it into the logger.

Common Output Field (Metadata)

If you use some querying service for searching specific logs like BigQuery, CloudWatch Logs Insight, Elasticsearch and other more, Metadata/SetMetadata can be used to set additional pieces of information to be able to search conveniently. For instance, Service ID, HTTP Request ID, the id of user signed in, EC2 instance-id and other more.

logger := log.New(
    log.Metadata(map[string]interface{}{
        "uesr_id":    "86f32b8b-ec0d-479f-aed1-1070aa54cecf",
        "request_id": "943ad105-7543-11e6-a9ac-65e093327849",
    }),
    log.FlattenMetadata(true),
    log.Format(format.JSONPretty),
)

logger.Info("info")
// Output:
// {
//   "level": "INFO",
//   "message": "info",
//   "request_id": "943ad105-7543-11e6-a9ac-65e093327849",
//   "time": "2019-10-22T17:02:02.748123389+09:00",
//   "uesr_id": "86f32b8b-ec0d-479f-aed1-1070aa54cecf"
// }

Example

package main

import (
    "errors"

    "github.com/kyfk/log"
    "github.com/kyfk/log/format"
    "github.com/kyfk/log/level"
)

func main() {
    logger := log.New(
        log.MinLevel(level.Warn),
        log.Format(format.JSONPretty),
        log.Metadata(map[string]interface{}{
            "service":    "book",
            "uesr_id":    "86f32b8b-ec0d-479f-aed1-1070aa54cecf",
            "request_id": "943ad105-7543-11e6-a9ac-65e093327849",
            "path":       "/operator/hello",
            // more other metadatas
        }),
        log.FlattenMetadata(true),
    )

    logger.Debug("debug")
    logger.Info("info")
    logger.Warn("warn")
    logger.Error(errors.New("error"))
}

// Output:
//
// {
//   "level": "WARN",
//   "message": "warn",
//   "path": "/operator/hello",
//   "request_id": "943ad105-7543-11e6-a9ac-65e093327849",
//   "service": "book",
//   "time": "2019-10-22T16:28:04.180385072+09:00",
//   "trace": [
//     "main.main /home/koya/go/src/github.com/kyfk/log/example/main.go:26",
//     "runtime.main /home/koya/go/src/github.com/golang/go/src/runtime/proc.go:203",
//     "runtime.goexit /home/koya/go/src/github.com/golang/go/src/runtime/asm_amd64.s:1357"
//   ],
//   "uesr_id": "86f32b8b-ec0d-479f-aed1-1070aa54cecf"
// }
// {
//   "error": "*errors.fundamental: error",
//   "level": "ERROR",
//   "path": "/operator/hello",
//   "request_id": "943ad105-7543-11e6-a9ac-65e093327849",
//   "service": "book",
//   "time": "2019-10-22T16:28:04.180589439+09:00",
//   "trace": [
//     "main.main /home/koya/go/src/github.com/kyfk/log/example/main.go:27",
//     "runtime.main /home/koya/go/src/github.com/golang/go/src/runtime/proc.go:203",
//     "runtime.goexit /home/koya/go/src/github.com/golang/go/src/runtime/asm_amd64.s:1357"
//   ],
//   "uesr_id": "86f32b8b-ec0d-479f-aed1-1070aa54cecf"
// }