The ctxhttp.Do method contains a race condition when the context is cancelled before the client.Do performed in a go routine returns. The http.Response is discarded, leaving its Body opened and thus leading to sockets left in CLOSE_WAIT state.

To reproduce the issue, run this on Linux (can't reproduce on osx, I'm not sure why):

package main

import (
    "fmt"

    "golang.org/x/net/context"
    "golang.org/x/net/context/ctxhttp"
)

func main() {
    ctx, cancel := context.WithCancel(context.Background())
    cancel()
    resp, err := ctxhttp.Get(ctx, nil, "http://httpbin.org/get")
    fmt.Printf("%v, %v\n", resp, err)
    <-make(chan struct{})
}

The output is:

<nil>, context canceled

As the res is nil, I have no way for the caller to close the resp.Body.

Then look at netstat -lan | grep CLOSE_WAIT, you will see a new socket lying down forever.