How can I make io.Reader stop reading?

[Alexander Menzhinsky]

When implementing a proxy server I would like to stop reading from a connection when another is closed. I use the io.Copy but basically it uses the Read function.

go io.Copy(connOne, connTwo)

Is it possible?

[Peter Waller]

If connTwo is closed, Read will return io.EOF, and io.Copy will return. (With no error, because copy runs until io.EOF is reached).

If that's not happening for you, can you give an example to reproduce?

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[Daniel Theophanes]

You can also use it.CopyContext and cancel the ctx.

[Alexander Menzhinsky]

func forward(src net.Conn, network, address string, timeout time.Duration) {
 defer src.Close()


 dst, err := net.DialTimeout(network, address, timeout)
 if err != nil {
 log.Printf("dial err: %s", err)
 return
 }


 defer dst.Close()


 cpErr := make(chan error)


 go cp(cpErr, src, dst)
 go cp(cpErr, dst, src)


 select {
 case err = <-cpErr:
 if err != nil {
 log.Printf("copy err: %v", err)
 }
 }


 log.Printf("disconnect: %s", src.RemoteAddr())
}


func cp(c chan error, w io.Writer, r io.Reader) {
 _, err := io.Copy(w, r)
 c <- err


 fmt.Println("cp end")
}

Seems like it doesn't work, io.Copy() still block its goroutine

On Wednesday, 16 November 2016 18:09:40 UTC+3, Peter Waller wrote:

If connTwo is closed, Read will return io.EOF, and io.Copy will return. (With no error, because copy runs until io.EOF is reached).

If that's not happening for you, can you give an example to reproduce?

On 16 November 2016 at 14:49, Alexander Menzhinsky <amenz...@gmail.com> wrote:

When implementing a proxy server I would like to stop reading from a connection when another is closed. I use the io.Copy but basically it uses the Read function.

go io.Copy(connOne, connTwo)

Is it possible?

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[Alexander Menzhinsky]

Do you mean io.CopyContext? I wasn't able to find it. 

[Peter Waller]

Your original email was ambiguous and said "when a connection is closed", so I gave an answer for when `connTwo` is closed. But your actual question was "when `connOne`" is closed, if I'm understanding correctly given the program you posted. So given the program above, if `dst` is closed you should observe that one goroutine has terminated, correct? Then the question is, "what about that other goroutine"?

The problem is that that other goroutine's Copy is sat in a loop like this:

for {

  read bytes from src (blocked here)

  write bytes to dst

}

`src` in this case has not been closed, so the only way you will notice if `dst` has closed is if you read from `src`, either by closing `src` and returning (via io.EOF) or reading bytes from `src` which then get written to `dst` and cause a "the network connection is broken" style of error, which io.Copy will return.

TL;DR: when the io.Copy(A, B) finishes, call A.Close() and the io.Copy(B, A) will terminate. Calling A.Close() is like forwarding the B.Read()'s io.EOF error.

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[Hoots The Owl]

As far as I understood, Daniel means something like that https://gowalker.org/github.com/northbright/ctx/ctxcopy

среда, 16 ноября 2016 г., 19:22:56 UTC+3 пользователь Alexander Menzhinsky написал:

[Peter Waller]

As far as I understand, that seems unlikely to solve the problem of the Read() function being blocked, if that is what is happening here.

--

[Alexander Menzhinsky]

I was able to solve the problem with the SetReadDeadline function. 

I check every n second some flag or channel whether to stop reading or not. In case you use net sockets and your reader is closed by other goroutine, the Read function will fail the next for loop iteration with the "reading from closed connection" error. 

for {

err := r.SetReadDeadline(time.Now().Add(5 * time.Second))

if err != nil {

return err

}

_, err = r.Read(buf)

if netErr, ok := err.(net.Error); ok && netErr.Timeout() {

// check whether t

continue

}

// ...

}

[Munding]

There's only one way(SetReadDeadline to timeout) to stop reading？