Wrapping Go errors with caller info

I find Go’s error handling refreshingly simple & clear. Nowadays, all I do is wrap my errors using fmt.Errorf with some additional context. The pattern I tend to use most of the time just includes a function/method name, like so:

func someFunction() error {
	err := someStruct{}.someMethod()
	return fmt.Errorf("someFunction: %w", err)
}

type someStruct struct {
}

func (ss someStruct) someMethod() error {
	return fmt.Errorf("someMethod: %w", errors.New("boom"))
}

If I now call someFunction, the error - when logged or printed - will look like this: someFunction: someMethod: boom. This gives just enough context to figure out what happened, and where.

I thought to myself - this can be wrapped in a helper function, to automatically take the caller name and do this wrapping for me.

Here’s an implementation:

func WrapWithCaller(err error) error {
	pc, _, _, ok := runtime.Caller(1)
	if !ok {
		return fmt.Errorf("%v: %w", "unknown", err)
	}
	fn := runtime.FuncForPC(pc).Name()
	pkgFunc := path.Base(fn)
	return fmt.Errorf("%v: %w", pkgFunc, err)
}

We can now use it like so:

func someFunction() error {
	err := someStruct{}.someMethod()
	return WrapWithCaller(err)
}

type someStruct struct {
}

func (ss someStruct) someMethod() error {
	return WrapWithCaller(errors.New("boom"))
}

And it will return the following: main.someFunction: main.someStruct.someMethod: boom. Keep in mind that this will have performance overhead:

func Benchmark_WrapWithCaller(b *testing.B) {
	err := errors.New("boom")
	for i := 0; i < b.N; i++ {
		_ = WrapWithCaller(err)
	}
}
// Result:
// Benchmark_WrapWithCaller-10    	 2801312	       427.0 ns/op	     344 B/op	       5 allocs/op

func Benchmark_FmtErrorf(b *testing.B) {
	err := errors.New("boom")
	for i := 0; i < b.N; i++ {
		_ = fmt.Errorf("FmtErrorf: %w", err)
	}
}

// Result:
// Benchmark_FmtErrorf-10    	13475013	        87.19 ns/op	      48 B/op	       2 allocs/op

So it’s 4-5 times slower than a simple wrap using fmt.Errorf.

One benefit of using WrapWithCaller is that refactoring is easier - you change the function/method name and don’t need to bother yourself with changing the string in the fmt.Errorf. The performance hit is likely not an issue for most programs, unless you’re wrapping tons of errors in hot loops or something like that.

I’m a bit torn if I want to add this helper to my codebases and use it everywhere - seems like an extra dependency with little benefit, but I’ll have to give it a spin before I decide if this is something I’m ready to accept. Time will tell. Thanks for reading!