A simple function tracer for Go
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Function tracing in golang.


go get github.com/sabhiram/go-tracey

Basic usage

file: foo.go

package main

import (

// Setup global enter exit trace functions (default options)
var G, O = tracey.New(nil)
// Or...
// var Exit, Enter = tracey.New(nil)

func foo(i int) {
    // $FN will get replaced with the function's name
    defer G(O("$FN(%d)", i))
    if i != 0 {
        foo(i - 1)

func main() {
    defer G(O())
go run foo.go
[ 0]ENTER: main
[ 1]  ENTER: foo(2)
[ 2]    ENTER: foo(1)
[ 3]      ENTER: foo(0)
[ 3]      EXIT:  foo(0)
[ 2]    EXIT:  foo(1)
[ 1]  EXIT:  foo(2)
[ 0]EXIT:  main

Configurable options

// These options represent the various settings which tracey exposes.
// A pointer to this structure is expected to be passed into the
// `tracey.New(...)` function below.
type Options struct {

    // Setting "DisableTracing" to "true" will cause tracey to return
    // no-op'd functions for both exit() and enter(). The default value
    // for this is "false" which enables tracing.
    DisableTracing      bool

    // Setting the "CustomLogger" to nil will cause tracey to log to
    // os.Stdout. Otherwise, this is a pointer to an object as returned
    // from `log.New(...)`.
    CustomLogger        *log.Logger

    // Setting "DisableDepthValue" to "true" will cause tracey to not
    // prepend the printed function's depth to enter() and exit() messages.
    // The default value is "false", which logs the depth value.
    DisableDepthValue   bool

    // Setting "DisableNesting" to "true" will cause tracey to not indent
    // any messages from nested functions. The default value is "false"
    // which enables nesting by prepending "SpacesPerIndent" number of
    // spaces per level nested.
    DisableNesting      bool
    SpacesPerIndent     int    `default:"2"`

    // Setting "EnterMessage" or "ExitMessage" will override the default
    // value of "Enter: " and "EXIT:  " respectively.
    EnterMessage        string `default:"ENTER: "`
    ExitMessage         string `default:"EXIT:  "`

Advanced usage

Tracey's Enter() receives a variadic list interfaces: ...interface{}. This allows us to pass in a variable number of types. However, the first of such is expected to be a format string, otherwise the function just logs the function's name. If a format string is specified with a $FN token, then said token is replaced for the actual function's name.

var G,O = tracey.New(nil)
//var Exit, Enter = tracey.New(nil)

func Foo() {
    defer G(O("$FN is awesome %d %s", 3, "four"))

Will produce: Foo is awesome 3 four when Foo() is logged.

Anonymous functions:

Non-named functions are given a generic name of "func.N" where N is the N-th unnamed function in a given file. If we wish to log these explicitly, we can just give them a suitable name using the format string. For instance:

var G,O = tracey.New(nil)
//var Exit, Enter = tracey.New(nil)

func main() {
    defer G(O())
    func() {
        defer G(O("InnerFunction"))

Will produce:

[ 0]ENTER: main
  [ 1]ENTER: InnerFunction
  [ 1]EXIT : InnerFunction
[ 0]EXIT : main

Custom logger

TODO: Example Custom Logger

For the time being, please check out the tracey_test.go file. All the tests create a custom logger out of a []byte so we can compare whats written out to what we expect to output.

Want to help out?

I appreciate any and all feedback. All pull requests and commits will be run against Travis-CI, and results will be forwarded to Coveralls.io.

Here is the CI page for the project: Build Status

And coverage here: Coverage Status

To run tests:

cd $GOPATH/src/github.com/sabhiram/go-tracey
go test -v

Link to tests for the lazy