I have recently updated the way I handle errors in Go. In some ways, I’ve come full circle back to where I started, in others, I think I’ve evolved. When I initially wrote my errors post in June of 2021, I had come up with a hybrid of Rob Pike’s upspin errors and Dave Cheney’s https://github.com/pkg/errors package. This hybrid works well, however, in December 2021 https://github.com/pkg/errors was archived and, generally, the Go community seems to have opted for a simpler option of adding proper error context and wrapping errors. For instance, https://earthly.dev/blog/golang-errors/ was one of the more popular blog posts from 2022 and features this approach.

I decided I would return to error wrapping also, but wanted to standardize my approach similar to what Rob Pike did in his article using an op constant:

In typical use, calls to errors.E will arise multiple times within a method, so we define a constant, conventionally called op, that will be passed to all E calls within the method:

func (s *Server) Delete(ref upspin.Reference) error { const op errors.Op = “server.Delete” …

Then through the method we use the constant to prefix each call (although the actual ordering of arguments is irrelevant, by convention op goes first):

if err := authorize(user); err != nil { return errors.E(op, user, errors.Permission, err) }

Where I differ, is that I need to present the op stack in structured logging vs. the upspin approach of string formatting with nested indentation.

I created an OpStack function to recursively unwrap all errors wrapped inside a given error and pull out the op for each error, returning the full list of ops as a slice of string.

// OpStack returns the op stack information for an error
func OpStack(err error) []string {
    type o struct {
        Op    string
        Order int
    }

    e := err
    i := 0
    var os []o

    // loop through all wrapped errors and add to struct
    // order will be from top to bottom of stack
    for errors.Unwrap(e) != nil {
        var errsError *Error
        if errors.As(e, &errsError) {
            if errsError.Op != "" {
                op := o{Op: string(errsError.Op), Order: i}
                os = append(os, op)
            }
        }
        e = errors.Unwrap(e)
        i++
    }

    // reverse the order of the stack (bottom to top)
    sort.Slice(os, func(i, j int) bool { return os[i].Order > os[j].Order })

    // pull out just the stack info, now in reversed order
    var ops []string
    for _, op := range os {
        ops = append(ops, op.Op)
    }

    return ops
}

I then use this function when logging errors from my API.

        ops := OpStack(e)
        if len(ops) > 0 {
            j, _ := json.Marshal(ops)
            // log the error with the op stack
            lgr.Error().RawJSON("stack", j).Err(e.Err).
                Int("http_statuscode", httpStatusCode).
                Str("Kind", e.Kind.String()).
                Str("Parameter", string(e.Param)).
                Str("Code", string(e.Code)).
                Msg(errMsg)

This ends up producing a “pseudo stack” that is easy to look at and understand in structured logging.

{
   "level": "error",
   "remote_ip": "127.0.0.1:60382",
   "user_agent": "PostmanRuntime/7.30.1",
   "request_id": "cfgihljuns2hhjb77tq0",
   "stack": [
      "diygoapi/Movie.IsValid",
      "service/MovieService.Create"
   ],
   "error": "title is required",
   "http_statuscode": 400,
   "Kind": "input validation error",
   "Parameter": "title",
   "Code": "",
   "time": 1675700438,
   "severity": "ERROR",
   "message": "error response sent to client"
}

I refactored my diygoapi project to now use this method by default. I have setup the project to still allow for error tracing using https://github.com/pkg/errors, but it’s optional and needs to be set to do so on startup or using a service. I have updated the README details for errors here and if you want to understand how to turn on the stack tracing using flags or environment variables, you can look here.

404 Error Illustration by Pixeltrue from Ouch!