Chunked http response with go routines

[hasangenc...@gmail.com]

flusher, ok := w.(http.Flusher)

// w.wr is io.Writer here

for _, gateway := range app.Gateway {

 go func(w http.ResponseWriter) {

    // w.wr is nil here

    tmpl, err := template.New(gateway.Name).Parse(gateway.Content)
  
    if err != nil {
       panic("An Error occured when parsing html")
       return
    }

    tmpl.Execute(w, "")
 
    defer flusher.Flush()
 }()

}

Why w.wr is nil inside the function ? When i use function as non routine it works fine but i want to use the function as go routine.

[Burak Serdar]

This isn't valid code. The goroutine is declared with a w arg, but it
is not called with the parameter.

Assuming you intended to pass the w declared outside the for loop: is
it possible that the whole thing is inside another for-loop, and w is
the loop variable?

for _,w:=range ... {
// your code here
}

If that's the case, just add a w:=w at the top of the for loop:

for _,w:=range ... {
w:=w
// your code here
}

If that's not the case, maybe posting code that compiles might help.

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[Hasan Genc]

Sorry, I made a mistake when copy paste :)

Actually we can assume above code as 

go func() {

 ...

}

Because I want to reference of w variable which is the type of http.ResponseWrite.

My actual problem is w.wr is nil inside go routine. I can post the code today but I can not access the code right now.

On Monday, July 15, 2019 at 9:32:54 PM UTC+3, Burak Serdar wrote:

> To unsubscribe from this group and stop receiving emails from it, send an email to golan...@googlegroups.com.

[Hasan Genc]

This is my original code.

outside of the go routine w variable is

But inside the go routine

I don't understand why. Anyone can help about this ? 

func Make(w http.ResponseWriter, r *http.Request, app App) {
   runtime.GOMAXPROCS(4)

   flusher, ok := w.(http.Flusher)

   if !ok {
      panic("expected http.ResponseWriter to be an http.Flusher")
   }

   w.Header().Set("X-Content-Type-Options", "nosniff")

   tmpl, err := template.New("app").Parse(app.Page.Content)

   if err != nil {
      panic("An Error occured when parsing html")
      return
   }

   err = tmpl.Execute(w, "")

   if err != nil {
      panic("Error in Template.Execute")
   }

   flusher.Flush()

   for _, gateway := range app.Gateway {

      go func(gateway Gateway) {

         tmpl, err := template.New(gateway.Name).Parse(gateway.Content)

         if err != nil {
            panic("An Error occured when parsing html")
         }

         err = tmpl.Execute(w, "")

         if err != nil {
            panic(err)
         }

         defer flusher.Flush()
      }(gateway)
   }

}

[Jakob Borg]

At a guess, because your goroutine is running after the response handler has returned, and at that point the ResponseWriter isn’t valid any more. 

//jb

On 16 Jul 2019, at 20:03, Hasan Genc <hasangenc...@gmail.com> wrote:

This is my original code.

outside of the go routine w variable is

<Screen Shot 2019-07-16 at 20.57.35.png>

But inside the go routine

<Screen Shot 2019-07-16 at 20.58.17.png>

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<Screen Shot 2019-07-16 at 20.57.35.png>

<Screen Shot 2019-07-16 at 20.58.17.png>

[Burak Serdar]

On Tue, Jul 16, 2019 at 12:03 PM Hasan Genc <hasangenc...@gmail.com> wrote:

This is my original code.

Multiple things are wrong with this code:

 * You are writing to a stream from multiple goroutines with no synchronization.

 * You are not waiting for the goroutines to complete before returning. Once the http handler returns, the response is written and the stream is closed.

If you really want to use goroutines for this task, process the templates in separate goroutines, collect the output via channels and write to the output stream from the handler's goroutine.

 

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