Why Does Go's `http` Package Miss Cancellation Signals in POST Requests with Bodies?

Go http package: Capture Cancellation Signal in Requests with Bodies

Question: Why does the Go http package fail to capture cancellation signals for POST requests with bodies?

Answer: Go's http server reads the request body to detect when the client closes the connection. Until the body is read, no checks for closed connections are made.

Therefore, to handle this correctly, read the request body as soon as possible, even if it's not needed in the request handling logic.

Solution:

func handler(w http.ResponseWriter, r *http.Request) {
    go func(done <-chan struct{}) {
        <-done
        fmt.Println("message", "client connection has gone away, request got cancelled")
    }(r.Context().Done())

    io.Copy(ioutil.Discard, r.Body) // Read the body to detect the closed connection
    time.Sleep(30 * time.Second)
    fmt.Fprintf(w, "Hi there, I love %s!\n", r.URL.Path[1:])
}

When the client closes the connection early, this code will detect it and cancel any ongoing work.

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