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net/http: CancelRequest twice on the same request panics #10405

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yichengq opened this issue Apr 10, 2015 · 1 comment

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commented Apr 10, 2015

If i call CancelRequest twice on the same request, CancelRequest will panic because of close a closed channel at here:
https://golang.org/src/net/http/transport.go#L517

I argue that CancelRequest should not panic here:

  1. There is no need to panic when cancelling a cancelled request. And no document says that is not allowed.
  2. It is hard to ensure a request is canceled without CancelRequest retry:
    go func() { c <- f(client.Do(req)) }()
    select {
    case <-ctx.Done():
        tr.CancelRequest(req)
        <-c // Wait for f to return.
        return ctx.Err()
    case err := <-c:
        return err
    }

(code from https://blog.golang.org/context)
It is possible that the request is canceled before Do is called, and it needs CancelRequest retry to ensure it is canceled.

from https://github.com/coreos/go-etcd/issues/197

@bradfitz bradfitz self-assigned this Apr 10, 2015

@bradfitz bradfitz added this to the Go1.5 milestone Apr 10, 2015

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commented Apr 20, 2015

@bradfitz bradfitz closed this in b016eba Apr 20, 2015

@golang golang locked and limited conversation to collaborators Jun 25, 2016

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