server2.go

package main

import (
    "context"
    "encoding/json"
    "github.com/juju/errors"
    "github.com/thehivecorporation/log"
    "net/http"
    "time"
)

type res struct {
    Success bool
}

func main() {
    http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
        err := potentiallySlowOperation(r.Context(), 5)
        if err != nil {
            log.WithError(err).Error("Error while 'processing'")
            w.WriteHeader(500)
            return
        }

        byt, err := json.Marshal(res{Success: true})
        if err != nil {
            w.WriteHeader(500)
            return
        }

        w.Write(byt)
    })

    http.ListenAndServe(":8080", nil)
}

func potentiallySlowOperation(ctx context.Context, s time.Duration) error {
    log.Infof("'Processing' for %d seconds", s)

    now := time.Now()
    defer func(now time.Time) {
        log.WithField("elapsed", time.Since(now)).Info("Returning")
    }(now)

    select {
    case <-time.After(time.Second * s):
        log.Info("Processing done")
    case <-ctx.Done():
        return errors.New("Context cancelled")
    }

    return nil
}