> On 9 Jan 2021, at 9:50 am, Amit Saha <amitsaha...@gmail.com> wrote:
>
> Say I have created a RequestWithContext:
>
> r, err := http.NewRequestWithContext(ctx, "GET",
> "http://127.0.0.1:8080/healthcheck";, nil)
>
> Now, I make the request in the context of *another* HTTP request handling
> function:
>
> Func myHandler(w http.ResponseWriter, r *http.Request) {
> ...
>
> resp, err := client.Do(r)
> if err != nil {
> http.Error(w, err.Error(), http.StatusInternalServerError)
> }
> return
> }
> …
> }
>
>
> When I cancel this context, the above http.Error() call triggers a
> superfluous write header message.
> I dug down a bit and I can see that when the context is cancelled, the
> finishRequest() function
> (https://golang.org/src/net/http/server.go?h=finishRequest#L1613) is called
> which essentially writes a 200 status code. Hence, when the code above goes
> to write an error, it gets the superfluous writeHeader message.
>
> I then updated my code above to be:
>
> resp, err := client.Do(r)
> if err != nil {
> if err != context.Canceled {
> http.Error(w, err.Error(), http.StatusInternalServerError)
> }
> return
> }
>
> Wondering if anyone has any thoughts on this pattern and if there is any
> reason why we complete the full lifecycle of finsihRequest() on context
> cancellation even if it is going to fail somewhere down the line since in
> this case, the client has already disconnected?
I missed the complete handler function which will make the query more sensible:
func getData(ctx context.Context, w http.ResponseWriter) {
done := make(chan bool)
client := http.Client{}
go func() {
r, err := http.NewRequestWithContext(ctx, "GET",
"http://127.0.0.1:8080/healthcheck";, nil)
if err != nil {
http.Error(w, err.Error(),
http.StatusInternalServerError)
return
}
resp, err := client.Do(r)
if err != nil && err != context.Canceled {
http.Error(w, err.Error(),
http.StatusInternalServerError)
}
return
}
defer resp.Body.Close()
io.Copy(w, resp.Body)
done <- true
}()
select {
case <-done:
return
case <-ctx.Done():
log.Printf("api: client disconnected.")
return # This return triggers the finishRequest() function call
to be made
}
}
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