log XI is a structured 12-factor app logger built for speed and happy development.
- Simpler. Sane no-configuration defaults out of the box.
- Faster. See benchmarks vs logrus and log15.
- Structured. Key-value pairs are enforced. Logs JSON in production.
- Configurable. Enable/disalbe Loggers and levels via env vars.
- Friendlier. Happy, colorful and developer friendly logger in terminal.
- Helpul. Traces, warnings and errors are emphasized with file, line number and callstack.
- Efficient. Has level guards to avoid cost of building complex arguments.
Go 1.3+
go get -u github.com/mgutz/logxi/v1
import "github.com/mgutz/logxi/v1"
// create package variable for Logger interface
var logger log.Logger
func main() {
// use default logger
who := "mario"
log.Info("Hello", "who", who)
// create a logger with a unique identifier which
// can be enabled from environment variables
logger = log.New("pkg")
// specify a writer, use NewConcurrentWriter if it is not concurrent
// safe
modelLogger = log.NewLogger(log.NewConcurrentWriter(os.Stdout), "models")
db, err := sql.Open("postgres", "dbname=testdb")
if err != nil {
modelLogger.Error("Could not open database", "err", err)
}
fruit := "apple"
languages := []string{"go", "javascript"}
if log.IsDebug() {
// use key-value pairs after message
logger.Debug("OK", "fruit", fruit, "languages", languages)
}
}logxi defaults to showing warnings and above. To view all logs
LOGXI=* go run main.go
This logger package
-
Is fast in production environment
A logger should be efficient and minimize performance tax. logxi encodes JSON 2X faster than logrus and log15 with primitive types. When diagnosing a problem in production, troubleshooting often means enabling small trace data in
DebugandInfostatements for some period of time.# primitive types BenchmarkLogxi 100000 20021 ns/op 2477 B/op 66 allocs/op BenchmarkLogrus 30000 46372 ns/op 8991 B/op 196 allocs/op BenchmarkLog15 20000 62974 ns/op 9244 B/op 236 allocs/op # nested object BenchmarkLogxiComplex 30000 44448 ns/op 6416 B/op 190 allocs/op BenchmarkLogrusComplex 20000 65006 ns/op 12231 B/op 278 allocs/op BenchmarkLog15Complex 20000 92880 ns/op 13172 B/op 311 allocs/op -
Is developer friendly in the terminal. The HappyDevFormatter is colorful, prints file and line numbers for traces, warnings and errors. Arguments are printed in the order they are coded. Errors print the call stack.
HappyDevFormatteris not too concerned with performance and delegates to JSONFormatter internally. -
Logs machine parsable output in production environments. The default formatter for non terminals is
JSONFormatter.TextFormattermay also be used which is MUCH faster than JSON but there is no guarantee it can be easily parsed. -
Has level guards to avoid the cost of building arguments. Get in the habit of using guards.
if log.IsDebug() { log.Debug("some ", "key1", expensive()) } -
Conforms to a logging interface so it can be replaced.
type Logger interface { Trace(msg string, args ...interface{}) Debug(msg string, args ...interface{}) Info(msg string, args ...interface{}) Warn(msg string, args ...interface{}) error Error(msg string, args ...interface{}) error Fatal(msg string, args ...interface{}) Log(level int, msg string, args []interface{}) SetLevel(int) IsTrace() bool IsDebug() bool IsInfo() bool IsWarn() bool // Error, Fatal not needed, those SHOULD always be logged } -
Standardizes on key-value pair argument sequence
log.Debug("inside Fn()", "key1", value1, "key2", value2)
// instead of this log.WithFields(logrus.Fields{"m": "pkg", "key1": value1, "key2": value2}).Debug("inside fn()")
logxi logs `FIX_IMBALANCED_PAIRS =>` if key-value pairs are imbalanced
`log.Warn and log.Error` are special cases and return error:
```go
return log.Error(msg) //=> fmt.Errorf(msg)
return log.Error(msg, "err", err) //=> err
-
Supports Color Schemes (256 colors)
log.Newcreates a logger that supports color schemeslogger := log.New("mylog")To customize scheme
# emphasize errors with white text on red background LOGXI_COLORS="ERR=white:red" yourapp # emphasize errors with pink = 200 on 256 colors table LOGXI_COLORS="ERR=200" yourapp -
Is suppressable in unit tests
func TestErrNotFound() { log.Suppress(true) defer log.Suppress(false) ... }
## Configuration
### Enabling/Disabling Loggers
By default logxi logs entries whose level is `LevelWarn` or above when
using a terminal. For non-terminals, entries with level `LevelError` and
above are logged.
To quickly see all entries use short form
# enable all, disable log named foo
LOGXI=*,-foo yourapp
To better control logs in production, use long form which allows
for granular control of levels
# the above statement is equivalent to this
LOGXI=*=DBG,foo=OFF yourapp
`DBG` should obviously not be used in production unless for
troubleshooting. See `LevelAtoi` in `logger.go` for values.
For example, there is a problem in the data access layer
in production.
# Set all to Error and set data related packages to Debug
LOGXI=*=ERR,models=DBG,dat*=DBG,api=DBG yourapp
### Format
The format may be set via `LOGXI_FORMAT` environment
variable. Valid values are `"happy", "text", "JSON", "LTSV"`
# Use JSON in production with custom time
LOGXI_FORMAT=JSON,t=2006-01-02T15:04:05.000000-0700 yourapp
The "happy" formatter has more options
* pretty - puts each key-value pair indented on its own line
"happy" default to fitting key-value pair onto the same line. If
result characters are longer than `maxcol` then the pair will be
put on the next line and indented
* maxcol - maximum number of columns before forcing a key to be on its
own line. If you want everything on a single line, set this to high
value like 1000. Default is 80.
* context - the number of context lines to print on source. Set to -1
to see only file:lineno. Default is 2.
### Color Schemes
The color scheme may be set with `LOGXI_COLORS` environment variable. For
example, the default dark scheme is emulated like this
# on non-Windows, see Windows support below
export LOGXI_COLORS=key=cyan+h,value,misc=blue+h,source=magenta,TRC,DBG,WRN=yellow,INF=green,ERR=red+h
yourapp
# color only errors
LOGXI_COLORS=ERR=red yourapp
See [ansi](https://github.com/mgutz/ansi) package for styling. An empty
value, like "value" and "DBG" above means use default foreground and
background on terminal.
Keys
* \* - default color
* TRC - trace color
* DBG - debug color
* WRN - warn color
* INF - info color
* ERR - error color
* message - message color
* key - key color
* value - value color unless WRN or ERR
* misc - time and log name color
* source - source context color (excluding error line)
#### Windows
Use [ConEmu-Maximus5](https://github.com/Maximus5/ConEmu).
Read this page about [256 colors](https://code.google.com/p/conemu-maximus5/wiki/Xterm256Colors).
Colors in PowerShell and Command Prompt _work_ but not very pretty.
## Extending
What about hooks? There are least two ways to do this
* Implement your own `io.Writer` to write to external services. Be sure to set
the formatter to JSON to faciliate decoding with Go's built-in streaming
decoder.
* Create an external filter. See `v1/cmd/filter` as an example.
What about log rotation? 12 factor apps only concern themselves with
STDOUT. Use shell redirection operators to write to a file.
There are many utilities to rotate logs which accept STDIN as input. They can
do many things like send alerts, etc. The two obvious choices are Apache's `rotatelogs`
utility and `lograte`.
```sh
yourapp | rotatelogs yourapp 86400
# install godo task runner
go get -u gopkg.in/godo.v2/cmd/godo
# install dependencies
godo install -v
# run test
godo test
# run bench with allocs (requires manual cleanup of output)
godo bench-allocs
MIT License