server3.go

package main

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

type res struct {
    Success bool
    Err     string
}

func main() {
    http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
        var response res

        err := potentiallySlowOperation(r.Context(), 5)
        if err != nil {
            log.WithError(err).Error("Error while 'processing'")
            response = res{Success: false, Err: err.Error()}
        } else {
            response = res{Success: true}
        }

        byt, err := json.Marshal(response)
        if err != nil {
            w.WriteHeader(http.StatusInternalServerError)
            return
        }

        if !response.Success {
            w.WriteHeader(http.StatusInternalServerError)
        }
        w.Write(byt)
    })

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

var slow = false

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)

    var waitingTimeCh <-chan time.Time
    if slow {
        waitingTimeCh = time.After(time.Minute * 5 * 60)
        slow = false
    } else {
        waitingTimeCh = time.After(time.Second * s)
        slow = true
    }

    newCtx, cancelFun := context.WithTimeout(ctx, time.Second*6)
    defer cancelFun()

    select {
    case <-waitingTimeCh:
        log.Info("Processing done")
    case <-newCtx.Done():
        return errors.New("Context cancelled")
    }

    return nil
}