glog

Go's modified log package with an option to set a loglevel, which will filter the output of logs based on that. (This is a lame attempt to modify GO's original log package (version 1.6.2)), and the logic borrowed from Sirupsen package.

Why

I was trying to find a way to log filename and line number using logrus for obvious debugging purpose, but I failed to get a workaround. I am not using advanced features of logrus like SetFormatter or hooks. Go's native log package already provides a feature to log filename and line numbers but it lacks setting a loglevel for filtering logs. I just borrowed and incorporated the idea of using a loglevel. Newly added methods for *Logger like (Error|Warn|Info|Debug)ln(), (Error|Warn|Info|Debug)f() and (Error|Warn|Info|Debug)() will only output logs based on the configured loglevel with the helper function SetLogLevel(). Accepted log levels are ErrorLevel, WarnLevel, InfoLevel and DebugLevel which are of values int 0, 1, 2, 3 respectively.

Default value of loglevel at the time of initing the *Logger is set to the lowest level, which is ErrorLevel.

Breaking change because of using pointer to loglevel

Use

require github.com/nohupped/glog v0.0.0-20200102070319-ef78151f855d

in the go.mod file to continue using the older version that uses int as loglevel instead of *uint.

• why? To have the convenience of using this logger in init() functions and have a global variable that can be modified without calling the SetStandardLogLevel or similar functions in every importing sub-packages.

Eg: Package foo/blah

package blah
import (
     // "flag"
    log "github.com/nohupped/glog"
)

// Loglevel is the logging handler
var Loglevel *uint

func init() {
    // loglevel := flag.Uint("loglevel", uint(glog.InfoLevel), "Loglevel.")
    // flag.Parse()
    // Don't do the above 2 lines in init functions. This will mess with go's testing because of https://github.com/golang/go/issues/33774.
    // flag.Parse() and init() functions doesn't go well.
    if Loglevel == nil {
        l := log.ErrorLevel
        Loglevel = &l
    }
    log.SetFlags(log.Lshortfile | log.Ldate | log.Ltime)
    log.SetStandardLogLevel(Loglevel)
    log.Infof("Setting loglevel to %d", log.InfoLevel)
}

and in package foo,

package main

import(
    "foo/blah"
)
func main(){
    loglevel := flag.Uint("loglevel", log.InfoLevel, "Loglevel.")
    flag.Parse()
    *blah.Loglevel = *loglevel // Dereference and modify the pointer value to update the loglevel globally on all the packages that imports foo/blah.
}

Now, for another sub-package foo/extreme_computation,

package extreme_computation
import(
    _ "foo/blah"
    log "github.com/nohupped/glog"
)

func PvsNP() {

}

it will see the updated loglevel from the main although the initial loglevel was set in blah, and this is because of the var Loglevel *uint

Reference when setting loglevel

logger.SetLogLevel(log.ErrorLevel) will log only Errors using the method log.Error*(). Any calls to log.Warn*(), log.Info*() and log.Debug*() will not be logged unless the loglevel is changed.

logger.SetLogLevel(log.WarnLevel) will log Errors and Warnings. Rest are not logged.

logger.SetLogLevel(log.InfoLevel) will log Errors, Warnings and Info. Rest are not logged.

logger.SetLogLevel(log.DebugLevel) will log Errors, Warnings, Info and Debug.

Note: To disable logging line numbers and file names, set the logger's flag similar to logger := log.New(&buf, "logger: ", log.Ldate) instead of log.Lshortfile or similar flags.

Example

package main

import (
    "bytes"
    "fmt"
    log "github.com/nohupped/glog"
)

func main() {
    var buf bytes.Buffer
    logger := log.New(&buf, "logger: ", log.Lshortfile)
    // Below two lines to set logging to file
    //file, _ := os.OpenFile("/tmp/testlog.log", os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0666)
    //logger.SetOutput(file)
    strfn := "Errorf()!"
    logger.Errorf("Hello, this is %d Error from %s", 1, strfn)
    logger.Error("Hello, this is 1 Error from Error()!")
    logger.Warnln("Hello, This is from Warnln!") // This will not print because the default loglevel when initiating logger is set to ErrorLevel.
    il := log.InfoLevel
    logger.SetLogLevel(&iL)
    logger.Errorln("Hello, This is Error from Errorln!")
    logger.Warnln("Hello, This is Warn from Warnln!")
    logger.Infoln("Hello, This is Info from Infoln!")
    logger.Debugln("Hello, This is Debug from Debugln!") // This will not print because loglevel is set to InfoLevel
    dl := log.DebugLevel
    log.SetStandardLogLevel(&dl) // set std loglevel. This will NOT set the *Logger struct's loglevel.
    log.SetFlags(log.Lshortfile) // set flags to log. This will add short filename and line number.
    log.Debugf("This is from %s", strfn)
    log.Printf("%d error from %s", 1, "Error function")
    log.Warnf("%d error from %s", 1, "Error function")
    fmt.Println(&buf)

    fmt.Print(&buf)

    // Output:
    // logger: main.go:19: ERROR: Hello, this is 1 Error from Errorf()!
    // logger: main.go:20: ERROR: Hello, this is 1 Error from Error()!
    // logger: main.go:23: ERROR: Hello, This is Error from Errorln!
    // logger: main.go:24: WARN: Hello, This is Warn from Warnln!
    // logger: main.go:25: INFO: Hello, This is Info from Infoln!

* Line numbers may vary.