Context Timeout in GoLang

Question

Implemented a context timeout in Go APIs using

context.WithTimeout(context,time)

Expectation is that if I set it to 10 seconds and if the API happens to run longer, it should stop and return Timeout error. However, if I add a sleep in between , the API still runs and gives 200 output. Is there any solution to this other than manually checking at random points for the time elapsed ? Looks like context.WithTimeout() doesnt solve its purpose.

Answer 1

So, this is a minimum code to exemplify how the context.WithTimeout can work:

server.go

package main

import (
    "fmt"
    "net/http"
    "time"
)

func main() {
    http.HandleFunc("/bad", badResponse)
    http.HandleFunc("/nice", niceResponse)
    
    http.ListenAndServe(":8099", nil)
}

// badResponse is a procedure that takes too much time
func badResponse(w http.ResponseWriter, r *http.Request) {
    fmt.Println("got request, it may take too long to answer")
    time.Sleep(3 * time.Second)
    fmt.Fprintf(w, "bad response!")
}

// niceResponse is a procedure that respond in time
func niceResponse(w http.ResponseWriter, r *http.Request) {
    fmt.Println("got request, will return fast")
    fmt.Fprintf(w, "nice response!")
}

client.go

package main

import (
    "context"
    "io/ioutil"
    "log"
    "net/http"
    "time"
)

func main () {
  req, err := http.NewRequest(http.MethodGet, "http://localhost:8099/bad", nil)
  if err != nil {
    log.Fatal(err)
  }
  ctx, cancel := context.WithTimeout(context.Background(), 10*time.Millisecond)
  defer cancel()

  req = req.WithContext(ctx)
  c := &http.Client{}
  res, err := c.Do(req)
  if err != nil {
    log.Fatal(err)
  }
  defer res.Body.Close()

  out, err := ioutil.ReadAll(res.Body)
  if err != nil {
    log.Fatal(err)
  }

  log.Println(string(out))
}

In the example above the client must fail because the timeout is lower than the client server delay.