Fillmore Labs Async (Experimental)

The async package provides interfaces and utilities for writing asynchronous code in Go.

Motivation

This is an experimental package which has a similar API as fillmore-labs.com/promise, but is implemented with a structure instead.

Usage

Assuming you have a synchronous function func getMyIP(ctx context.Context) (string, error) returning your external IP address (see GetMyIP for an example).

Now you can do

	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
	defer cancel()

	query := func() (string, error) {
		return getMyIP(ctx) // Capture context with timeout
	}
	future := async.NewAsync(query)

and elsewhere in your program, even in a different goroutine

	if ip, err := future.Await(ctx); err == nil {
		slog.Info("Found IP", "ip", ip)
	} else {
		slog.Error("Failed to fetch IP", "error", err)
	}

decoupling query construction from result processing.

GetMyIP

Sample code to retrieve your IP address:

const serverURL = "https://httpbin.org/ip"

func getMyIP(ctx context.Context) (string, error) {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, serverURL, nil)
	if err != nil {
		return "", err
	}
	req.Header.Set("Accept", "application/json")

	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		return "", err
	}
	defer func() { _ = resp.Body.Close() }()

	ipResponse := struct {
		Origin string `json:"origin"`
	}{}
	err = json.NewDecoder(resp.Body).Decode(&ipResponse)

	return ipResponse.Origin, err
}

Links

• Futures and Promises in the English Wikipedia