SLog - Golang Super Simple Logging

Usage:

package main

import (
    "github.com/quan-to/slog"
    "time"
)

var log = slog.Scope("MAIN")


func Call0(i slog.Instance, arg0 string) {
    l := i.SubScope("Call0").WithFields(map[string]interface{}{
        "arg0": arg0,
    })
    l.Await("Doing some work")
    time.Sleep(time.Second)
    l.Done("Finished some work")
    l.Note("Not sure what I'm doing...")
    l.Info("Calling Call1")
    Call1(l, "call1arg")
    l.Done("Exiting")
}

func Call1(i slog.Instance, huebr string) {
    l := i.SubScope("Call1").WithFields(map[string]interface{}{
        "huebr": huebr,
    })
    l.Info("Calling Call2")
    Call2(l, "abcde")
    l.Warn("Call 1 finished")
}

func Call2(i slog.Instance, pop string) {
    l := i.SubScope("Call2").WithFields(map[string]interface{}{
        "pop": pop,
    })

    l.IO("Doing some IO")
    l.Error("I'm useless. Please fix-me")
}

func main() {
    slog.SetScopeLength(40) // Expand Scope pad length

    log = log.Tag("REQ001") // Tag current as REQ001

    log.Info("Starting program")

    Call0(log, "MyArg0")

    Call1(log, "Call1Arg")
    Call2(log, "Call2Arg")
}

Output:

Log Pattern

There are 2 types of outputs: Pipe Delimited Text (default) and JSON.
To change the type of output, call the function SetLogFormat:

slog.SetLogFormat(JSON)

Pipe Delimited Text

The slog output is expected to be like this:

2019-09-16T15:35:52-03:00 | I | IO    | REQ001 | MAIN > Call0 > Call1 > Call2             | test.go:38 | Doing some IO  | {"arg0":"MyArg0","huebr":"call1arg","pop":"abcde"}

There are some fields that are optional (like filename/line number) but it should always follow the same pattern:

DATETIME | LEVEL | OPERATION | TAG | SCOPE | [FILENAME:LINE NUMBER] | MESSAGE | LOG FIELDS

• DATETIME => An ISO Datetime when the log is displayed
• LEVEL => The level of the log line
  • I => INFO - Shows an information usually to track what's happening inside an application
  • W => WARN - Shows an warning regarding something that went in a way that might require some attention
  • E => ERROR - Shows an application error that can be expected or not
  • D => DEBUG - Shows some debug information to help tracking issues
  • F => FATAL - Shows an error that will quit the application in that point
• TAG => Line log tag. Use this for tracking related log lines. For example with a HTTP Request ID
• SCOPE => The scope of the current log. Use this to trace the chain of calls inside the application. For example in a context change
• FILENAME: LINE NUMBER => OPTIONAL When ShowLines is enabled, it will show the filename and the line number of the caller of the slog library. Use this on debug mode to see which piece of code called the log library. Disabled by default
• MESSAGE => The message
• LOG FIELDS => When an instance is created using WithFields call, the fields will be serialized to either JSON or Key-Value depending on the configuration of the log instance. Defaults to JSON

JSON

The output is expected to be in this format:

{
  "level":"info",
  "op":"MSG",
  "msg":"Processing rule 123",
  "scope":"PriceCalc",
  "tag":"RULE_ENGINE",
  "time":"2020-02-07T15:36:20-03:00",
  "customField01":"123"
}

The fields are the same as from Pipe Delimited Text and work the same way, except that the Key-Value option is not available for the LOG FIELDS.

Operations Usage

The library implements the concept of operation type. This describes which type of operation the log line represents.

• IO => Anytime you do a I/O Operation such as Database or File Read/Write
• AWAIT => Anytime you will do a asynchronous operation that will block the flow
• DONE => After any AWAIT operation you should always use a DONE to log that the operation that did the AWAIT log line has finished.
• NOTE => Also know as Verbose, that operation is used when you're just letting the log reader some note about the operation
• MSG => Common messages such like normal information (which does not fit in other operations)

There are some syntax sugars to make easy to use Log Levels with Log Operations together:

• Warning Messages
  • WarnDone => Same as log.Operation(DONE).Warn(message)
  • WarnNote => Same as log.Operation(NOTE).Warn(message)
  • WarnAwait => Same as log.Operation(AWAIT).Warn(message)
  • WarnSuccess => Same as log.Operation(DONE).Warn(message)
  • WarnIO => Same as log.Operation(IO).Warn(message)
• Error Messages
  • ErrorDone => Same as log.Operation(DONE).Error(message)
  • ErrorNote => Same as log.Operation(NOTE).Error(message)
  • ErrorAwait => Same as log.Operation(AWAIT).Error(message)
  • ErrorSuccess => Same as log.Operation(DONE).Error(message)
  • ErrorIO => Same as log.Operation(IO).Error(message)
• Debug Messages
  • DebugDone => Same as log.Operation(DONE).Debug(message)
  • DebugNote => Same as log.Operation(NOTE).Debug(message)
  • DebugAwait => Same as log.Operation(AWAIT).Debug(message)
  • DebugSuccess => Same as log.Operation(DONE).Debug(message)
  • DebugIO => Same as log.Operation(IO).Debug(message)

Use these syntax sugars whenever is possible, instead of calling Operation(X).Level directly.

Multiline Logs

If a multiline log is displayed, the library will correctly ident all the messages:

2019-09-16T15:39:42-03:00 | I | MSG   | REQ001 | MAIN  | Multiline call
                                                         Thats the second line
                                                         Thats the third line  | {}

Use Patterns

• After calling a Await, you should always call a Done or Success
• Don't add extensive fields to WithFields as it will pollute the log
• Avoid multiline logs as this make parsing hard.
• Avoid using pipes | in your log message or fields
• Instead of Operation(AWAIT).Warn use WarnAwait
• Use Tag to indentify calls in the same flow (for example on a HTTP Request)
• All LogInstance calls returns a new LogInstance with the modified data. It will never change it's parent data making it completely immutable.