jwalterweatherman

README

jWalterWeatherman

Seamless printing to the terminal (stdout) and logging to a io.Writer (file) that’s as easy to use as fmt.Println.

Graphic by JonnyEtc

JWW is primarily a wrapper around the excellent standard log library. It provides a few advantages over using the standard log library alone.

1. Ready to go out of the box.
2. One library for both printing to the terminal and logging (to files).
3. Really easy to log to either a temp file or a file you specify.

I really wanted a very straightforward library that could seamlessly do the following things.

1. Replace all the println, printf, etc statements thoughout my code with something more useful
2. Allow the user to easily control what levels are printed to stdout
3. Allow the user to easily control what levels are logged
4. Provide an easy mechanism (like fmt.Println) to print info to the user which can be easily logged as well
5. Due to 2 & 3 provide easy verbose mode for output and logs
6. Not have any unnecessary initialization cruft. Just use it.

Usage

Step 1. Use it

Put calls throughout your source based on type of feedback. No initialization or setup needs to happen. Just start calling things.

Available Loggers are:

• TRACE
• DEBUG
• INFO
• WARN
• ERROR
• CRITICAL
• FATAL

These each are loggers based on the log standard library and follow the standard usage. Eg.

    import (
        jww "github.com/spf13/jwalterweatherman"
    )

    ...

    if err != nil {

        // This is a pretty serious error and the user should know about
        // it. It will be printed to the terminal as well as logged under the
        // default thresholds.

        jww.ERROR.Println(err)
    }

    if err2 != nil {
        // This error isn’t going to materially change the behavior of the
        // application, but it’s something that may not be what the user
        // expects. Under the default thresholds, Warn will be logged, but
        // not printed to the terminal. 

        jww.WARN.Println(err2)
    }

    // Information that’s relevant to what’s happening, but not very
    // important for the user. Under the default thresholds this will be
    // discarded.

    jww.INFO.Printf("information %q", response)

NOTE: You can also use the library in a non-global setting by creating an instance of a Notebook:

notepad = jww.NewNotepad(jww.LevelInfo, jww.LevelTrace, os.Stdout, ioutil.Discard, "", log.Ldate|log.Ltime)
notepad.WARN.Println("Some warning"")

Why 7 levels?

Maybe you think that 7 levels are too much for any application... and you are probably correct. Just because there are seven levels doesn’t mean that you should be using all 7 levels. Pick the right set for your needs. Remember they only have to mean something to your project.

Step 2. Optionally configure JWW

Under the default thresholds :

• Debug, Trace & Info goto /dev/null
• Warn and above is logged (when a log file/io.Writer is provided)
• Error and above is printed to the terminal (stdout)

Changing the thresholds

The threshold can be changed at any time, but will only affect calls that execute after the change was made.

This is very useful if your application has a verbose mode. Of course you can decide what verbose means to you or even have multiple levels of verbosity.

    import (
        jww "github.com/spf13/jwalterweatherman"
    )

    if Verbose {
        jww.SetLogThreshold(jww.LevelTrace)
        jww.SetStdoutThreshold(jww.LevelInfo)
    }

Note that JWW's own internal output uses log levels as well, so set the log level before making any other calls if you want to see what it's up to.

Setting a log file

JWW can log to any io.Writer:

    jww.SetLogOutput(customWriter) 

More information

This is an early release. I’ve been using it for a while and this is the third interface I’ve tried. I like this one pretty well, but no guarantees that it won’t change a bit.

I wrote this for use in hugo. If you are looking for a static website engine that’s super fast please checkout Hugo.

Documentation

Index

• Variables
• func SetFlags(flags int)
• func SetLogListeners(l ...LogListener)
• func SetLogOutput(handle io.Writer)
• func SetLogThreshold(threshold Threshold)
• func SetPrefix(prefix string)
• func SetStdoutOutput(handle io.Writer)
• func SetStdoutThreshold(threshold Threshold)
• type Counter
  • func (c *Counter) Count() uint64
  • func (c *Counter) Reset()
  • func (c *Counter) Write(p []byte) (n int, err error)
• type Feedback
  • func (fb *Feedback) Print(v ...interface{})
  • func (fb *Feedback) Printf(format string, v ...interface{})
  • func (fb *Feedback) Println(v ...interface{})
• type LogListener
  • func LogCounter(counter *Counter, t1 Threshold) LogListener
• type Notepad
  • func NewNotepad(outThreshold Threshold, logThreshold Threshold, outHandle, logHandle io.Writer, ...) *Notepad
  • func (n *Notepad) GetLogThreshold() Threshold
  • func (n *Notepad) GetStdoutThreshold() Threshold
  • func (n *Notepad) SetFlags(flags int)
  • func (n *Notepad) SetLogOutput(handle io.Writer)
  • func (n *Notepad) SetLogThreshold(threshold Threshold)
  • func (n *Notepad) SetPrefix(prefix string)
  • func (n *Notepad) SetStdoutThreshold(threshold Threshold)
• type Threshold
  • func GetLogThreshold() Threshold
  • func GetStdoutThreshold() Threshold
  • func LogThreshold() Threshold
  • func StdoutThreshold() Threshold
  • func (t Threshold) String() string

Variables

var (
	TRACE    *log.Logger
	DEBUG    *log.Logger
	INFO     *log.Logger
	WARN     *log.Logger
	ERROR    *log.Logger
	CRITICAL *log.Logger
	FATAL    *log.Logger

	LOG      *log.Logger
	FEEDBACK *Feedback
)

Functions

func SetFlags

func SetFlags(flags int)

SetFlags set the flags for the default logger. "log.Ldate | log.Ltime" by default.

func SetLogListeners

func SetLogListeners(l ...LogListener)

SetLogListeners configures the default logger with one or more log listeners.

func SetLogOutput

func SetLogOutput(handle io.Writer)

SetLogOutput set the log output for the default notepad. Discarded by default.

func SetLogThreshold

func SetLogThreshold(threshold Threshold)

SetLogThreshold set the log threshold for the default notepad. Trace by default.

func SetPrefix

func SetPrefix(prefix string)

SetPrefix set the prefix for the default logger. Empty by default.

func SetStdoutOutput

func SetStdoutOutput(handle io.Writer)

SetStdoutOutput set the stdout output for the default notepad. Default is stdout.

func SetStdoutThreshold

func SetStdoutThreshold(threshold Threshold)

SetStdoutThreshold set the standard output threshold for the default notepad. Info by default.

Types

type Counter

type Counter struct {
	// contains filtered or unexported fields
}

Counter is an io.Writer that increments a counter on Write.

func (*Counter) Count

func (c *Counter) Count() uint64

Count returns the current count.

func (*Counter) Reset

func (c *Counter) Reset()

Reset resets the counter.

func (*Counter) Write

func (c *Counter) Write(p []byte) (n int, err error)

type Feedback

type Feedback struct {
	// contains filtered or unexported fields
}

Feedback writes plainly to the outHandle while logging with the standard extra information (date, file, etc).

func (*Feedback) Print

func (fb *Feedback) Print(v ...interface{})

func (*Feedback) Printf

func (fb *Feedback) Printf(format string, v ...interface{})

func (*Feedback) Println

func (fb *Feedback) Println(v ...interface{})

type LogListener

type LogListener func(t Threshold) io.Writer

A LogListener can ble supplied to a Notepad to listen on log writes for a given threshold. This can be used to capture log events in unit tests and similar. Note that this function will be invoked once for each log threshold. If the given threshold is not of interest to you, return nil. Note that these listeners will receive log events for a given threshold, even if the current configuration says not to log it. That way you can count ERRORs even if you don't print them to the console.

func LogCounter

func LogCounter(counter *Counter, t1 Threshold) LogListener

LogCounter creates a LogListener that counts log statements >= the given threshold.

type Notepad

type Notepad struct {
	TRACE    *log.Logger
	DEBUG    *log.Logger
	INFO     *log.Logger
	WARN     *log.Logger
	ERROR    *log.Logger
	CRITICAL *log.Logger
	FATAL    *log.Logger

	LOG      *log.Logger
	FEEDBACK *Feedback
	// contains filtered or unexported fields
}

Notepad is where you leave a note!

func NewNotepad

func NewNotepad(
	outThreshold Threshold,
	logThreshold Threshold,
	outHandle, logHandle io.Writer,
	prefix string, flags int,
	logListeners ...LogListener,
) *Notepad

NewNotepad creates a new Notepad.

func (*Notepad) GetLogThreshold

func (n *Notepad) GetLogThreshold() Threshold

GetStdoutThreshold returns the defined Treshold for the log logger.

func (*Notepad) GetStdoutThreshold

func (n *Notepad) GetStdoutThreshold() Threshold

GetStdoutThreshold returns the Treshold for the stdout logger.

func (*Notepad) SetFlags

func (n *Notepad) SetFlags(flags int)

SetFlags choose which flags the logger will display (after prefix and message level). See the package log for more informations on this.

func (*Notepad) SetLogOutput

func (n *Notepad) SetLogOutput(handle io.Writer)

SetLogOutput changes the file where log messages are written.

func (*Notepad) SetLogThreshold

func (n *Notepad) SetLogThreshold(threshold Threshold)

SetLogThreshold changes the threshold above which messages are written to the log file.

func (*Notepad) SetPrefix

func (n *Notepad) SetPrefix(prefix string)

SetPrefix changes the prefix used by the notepad. Prefixes are displayed between brackets at the beginning of the line. An empty prefix won't be displayed at all.

func (*Notepad) SetStdoutThreshold

func (n *Notepad) SetStdoutThreshold(threshold Threshold)

SetStdoutThreshold changes the threshold above which messages are written to the standard output.

type Threshold

type Threshold int

const (
	LevelTrace Threshold = iota
	LevelDebug
	LevelInfo
	LevelWarn
	LevelError
	LevelCritical
	LevelFatal
)

func GetLogThreshold

func GetLogThreshold() Threshold

GetStdoutThreshold returns the defined Treshold for the log logger.

func GetStdoutThreshold

func GetStdoutThreshold() Threshold

GetStdoutThreshold returns the Treshold for the stdout logger.

func LogThreshold

func LogThreshold() Threshold

Level returns the current global log threshold.

func StdoutThreshold

func StdoutThreshold() Threshold

Level returns the current global output threshold.

func (Threshold) String

func (t Threshold) String() string