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// Package stdlog provides simple and fast logging to the standard output
// (stdout) and is optimized for programs launched via a shell or cron. It can
// also be used to log to a file by redirecting the standard output to a file.
// This package is thread-safe.
//
// Basic examples:
//
// logger := stdlog.GetFromFlags()
// logger.Info("Connecting to the server...")
// logger.Errorf("Connection failed: %q", err)
//
// Will output:
//
// 2014-04-02 18:09:15.862 INFO Connecting to the API...
// 2014-04-02 18:10:14.347 ERROR Connection failed (Server is unavailable).
//
// Log*() functions can be used to avoid evaluating arguments when it is
// expensive and unnecessary:
//
// logger.Debug("Memory usage: %s", getMemoryUsage())
// if LogDebug() { logger.Debug("Memory usage: %s", getMemoryUsage()) }
//
// If debug logging is off the getMemoryUsage() will be executed on the first
// line while it will not be executed on the second line.
//
// List of command-line arguments:
//
// -log=info
// Log events at or above this level are logged.
// -stderr=false
// Logs are written to standard error (stderr) instead of standard
// output.
// -flushlog=none
// Until this level is reached nothing is output and logs are stored
// in the memory. Once a log event is at or above this level, it
// outputs all logs in memory as well as the future log events. This
// feature should not be used with long-running processes.
//
// The available levels are the eight ones described in RFC 5424 (debug, info,
// notice, warning, error, critical, alert, emergency) and none.
//
// Some use cases:
// - By default, all logs except debug ones are output to the stdout. Which
// is useful to follow the execution of a program launched via a shell.
// - A program launched by a crontab where the variable `MAILTO` is set
// with `-debug -flushlog=error` will send all logs generated by the
// program only if an error happens. When there is no error the email
// will not be sent.
// - `my_program > /var/log/my_program/my_program-$(date+%Y-%m-%d-%H%M%S).log`
// will create a log file in /var/log/my_program each time it is run.
package stdlog
import (
"flag"
"fmt"
"io"
"os"
"github.com/alexcesaro/log"
"github.com/alexcesaro/log/buflog"
"github.com/alexcesaro/log/golog"
)
var (
logger log.Logger
thresholdName *string
logToStderr *bool
flushThresholdName *string
)
// GetFromFlags returns the logger defined by the command-line flags. This
// function runs flag.Parse() if it has not been run yet.
func GetFromFlags() log.Logger {
if logger != nil {
return logger
}
if !flag.Parsed() {
flag.Parse()
}
threshold := getLevelFromName(*thresholdName)
thresholdName = nil
out := getStream(*logToStderr)
logToStderr = nil
flushThreshold := getLevelFromName(*flushThresholdName)
flushThresholdName = nil
if flushThreshold == log.None {
logger = golog.New(out, threshold)
} else {
logger = buflog.New(out, threshold, flushThreshold)
}
return logger
}
func init() {
thresholdName = flag.String("log", "info", "sets the logging threshold")
logToStderr = flag.Bool("stderr", false, "outputs to standard error (stderr)")
flushThresholdName = flag.String("flushlog", "none", "sets the flush trigger level")
}
func getLevelFromName(levelName string) (level log.Level) {
switch levelName {
case "debug":
level = log.Debug
case "info":
level = log.Info
case "notice":
level = log.Notice
case "warning":
level = log.Warning
case "error":
level = log.Error
case "critical":
level = log.Critical
case "alert":
level = log.Alert
case "emergency":
level = log.Emergency
case "none":
level = log.None
default:
fmt.Fprintf(os.Stderr, "Invalid level value %q, allowed values are: debug, info, notice, warning, error, critical, alert, emergency and none\n", levelName)
os.Exit(2)
}
return
}
// Stubbed out for testing.
var getStream = func(logToStderr bool) io.Writer {
if logToStderr {
return os.Stderr
}
return os.Stdout
}
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