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README.md

Golang Errors with Stack Trace and Source Fragments

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Tired of uninformative error output? Probably this will be more convenient:

Output

Example

package main

import (
	"io/ioutil"

	"github.com/ztrue/tracerr"
)

func main() {
	if err := read(); err != nil {
		tracerr.PrintSourceColor(err)
	}
}

func read() error {
	return readNonExistent()
}

func readNonExistent() error {
	_, err := ioutil.ReadFile("/tmp/non_existent_file")
	// Add stack trace to existing error, no matter if it's nil.
	return tracerr.Wrap(err)
}

Find more executable examples in examples dir.

How to Use

Import

import "github.com/ztrue/tracerr"

Create New Error

err := tracerr.New("some error")

Or:

err := tracerr.Errorf("some error %d", num)

Add Stack Trace to Existing Error

If err is nil then it still be nil with no stack trace added.

err = tracerr.Wrap(err)

Print Error and Stack Trace

Stack trace will be printed only if err is of type tracerr.Error, otherwise just error text will be shown.

This will print error message and stack trace if any:

tracerr.Print(err)

This will add source code:

tracerr.PrintSource(err)

It's able to set up number of lines of code to display for each frame, which is 6 by default:

tracerr.PrintSource(err, 9)

Or to set up number of lines before and after traced line:

tracerr.PrintSource(err, 5, 2)

The same, but with color, which is much more useful:

tracerr.PrintSourceColor(err)
tracerr.PrintSourceColor(err, 9)
tracerr.PrintSourceColor(err, 5, 2)

Save Output to Variable

It's also able to save output to variable instead of printing it, which works the same way:

text := tracerr.Sprint(err)
text := tracerr.SprintSource(err)
text := tracerr.SprintSource(err, 9)
text := tracerr.SprintSource(err, 5, 2)

Get Stack Trace

Stack trace will be empty if err is not an instance of tracerr.Error.

frames := tracerr.StackTrace(err)

Or if err is of type tracerr.Error:

frames := err.StackTrace()

Get Original Error

Unwrapped error will be nil if err is nil and will be the same error if err is not an instance of tracerr.Error.

err = tracerr.Unwrap(err)

Or if err is of type tracerr.Error:

err = err.Unwrap()

Performance

Stack trace causes a performance overhead, depending on a stack trace depth. This can be insignificant in a number of situations (such as HTTP request handling), however, avoid of adding a stack trace for really hot spots where a high number of errors created frequently, this can be inefficient.

Benchmarks done on a MacBook Pro 2015 with go 1.11.

Benchmarks for creating a new error with a stack trace of different depth:

BenchmarkNew/5    200000    5646 ns/op    976 B/op   4 allocs/op
BenchmarkNew/10   200000   11565 ns/op    976 B/op   4 allocs/op
BenchmarkNew/20    50000   25629 ns/op    976 B/op   4 allocs/op
BenchmarkNew/40    20000   65833 ns/op   2768 B/op   5 allocs/op
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