Investigating Go issue #15425

client.go

package main

import (
	"crypto/tls"
	"io"
	"io/ioutil"
	"log"
	"net/http"
	"os"
	"strings"
)

func main() {
	serverURL := "https://localhost:1333"
	if envServURL := os.Getenv("SERVER_URL"); envServURL != "" {
		serverURL = envServURL
	}

	certs, err := tls.LoadX509KeyPair("key.crt", "key.key")
	if err != nil {
		log.Fatal(err)
	}
	tr := &http.Transport{
		TLSClientConfig: &tls.Config{
			Certificates:       []tls.Certificate{certs},
			InsecureSkipVerify: true,
		},
	}

	client := &http.Client{
		Transport: tr,
	}

	// Make a GigaByte of data
	sr := strings.NewReader(strings.Repeat("A", 1024*1024*1024))
	req, err := http.NewRequest("POST", serverURL, sr)
	if err != nil {
		log.Fatal(err)
	}
	log.Printf("client.Do next\n")
	res, err := client.Do(req)
	log.Printf("client.Do done\n")
	if err != nil {
		log.Fatal(err)
	}
	n, err := io.Copy(ioutil.Discard, res.Body)
	log.Printf("done Reading the server response's body n=(%v) err=%v\n", n, err)
	_ = res.Body.Close()
}

key.crt

-----BEGIN CERTIFICATE-----
MIIC+TCCAeGgAwIBAgIQTQHa9/kuyl5tMXFsd8Xu9jANBgkqhkiG9w0BAQsFADAS
MRAwDgYDVQQKEwdBY21lIENvMB4XDTE2MDQyNTAzNTY1MVoXDTE3MDQyNTAzNTY1
MVowEjEQMA4GA1UEChMHQWNtZSBDbzCCASIwDQYJKoZIhvcNAQEBBQADggEPADCC
AQoCggEBALi+Ju3eXS5Zaa+AGhfk9vy00PdiDsw0EhgCs29cBjlUHVgsOy6Uo9s5
MiklyefEq0ribIet6tL1g5iy0hPK5CMxvIdr8FosUAODA2n8YZ9rtsSvZ6NQgYDE
XLEBU2WUAXfZHsBpScrAIOH3l0vMLlfMKd+NFNAxVlYpA63DCrIIhKvzzqXOQLXf
+w7ybVyyOwZ5k4IjaV+YbiqtaPq3229eySkFoNuUZQ9oi13q0Z2FxRt7vGY7zIor
A/roy/Jbbp9cXlc7ABvuLr1SmTYgnc8zro+4VMSBtUblR/54dt7hInk+fnN8vDk2
xJci8MhjIVqAqjOaCRkjNcoXQL5buwkCAwEAAaNLMEkwDgYDVR0PAQH/BAQDAgWg
MBMGA1UdJQQMMAoGCCsGAQUFBwMBMAwGA1UdEwEB/wQCMAAwFAYDVR0RBA0wC4IJ
bG9jYWxob3N0MA0GCSqGSIb3DQEBCwUAA4IBAQCqlEWfBvw/bJk2MlFYX9+O+i7p
9vBieYGcLRw6Z1r2qDd27PwneSdzJoxKfSOG4zCceVCPSlB/JJpnlb4uiY7cW1zD
2b9ilK7UodM3wS1Uwd4F2VGt7khDfusAuKzXqKUr90FJ6Hs5ilOSZ03GrkGfzpwX
FEtm5p9fP7SujVl2eFRMQxl3p9R4FgFR0ZFRLUUMSPVsKhB8ts4ExeMpoPRs+at8
/SDEMqAYVXELxyyT1Jpsn526hZfV+ZwTkvDaJWff9IhT71lUVvWQkDGyv08vYo8R
XwVkteSj5vmAr0o+5RDSoY3AiM3kC7XihPde5Y6sEfnII5zbcLeOJ7MgfPqf
-----END CERTIFICATE-----

key.key

-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----

server.go

package main

import (
	"io"
	"io/ioutil"
	"log"
	"net/http"
	"strings"
	"time"
)

func handler(w http.ResponseWriter, r *http.Request) {
	if r.Method == "POST" {
		log.Printf("Received post request whose Headers are %v", r.Header)
		if false {
			io.Copy(ioutil.Discard, r.Body)
		}
		err := r.Body.Close()
		log.Printf("req.Body.Close() here, err=%v\n", err)
		if false {
			time.Sleep(700 * time.Millisecond)
		}
		//http.Error(w, error, code)
		w.WriteHeader(413)

		b, err := io.Copy(w, strings.NewReader(strings.Repeat("XXXXXX", 4192)))
		log.Printf("Wrote %d bytes. Error: %v", b, err)
		return
	}
	w.Header().Set("Content-Type", "text/html")
	w.Write([]byte(`
    <body>
    <script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.0.0-beta1/jquery.min.js"></script>
    <script>
      var reqs = 1;
      $('body').text('Sending ' + reqs + ' requests...');
      function send(i) {
  var el = $('<div class="req">Waiting...</div>').attr('id', i).appendTo('body');
  var data = new FormData();
  data.append('file', new File([new Blob([new Array(5 * 1024 * 1024).join('0')], {type: 'image/jpeg'})], 'test.jpg'));
  var done = false;
  var req = new XMLHttpRequest();
  req.upload.onprogress = function(e) {
    if (!e.lengthComputable || done) return;
    el.text((e.loaded / e.total * 100) + '%');
  }
  req.onreadystatechange = function(e) {
    if (done || req.readyState !== 3) return;
    done = true;
    el.text('Done. Got ' + req.status);
  }
  req.open('POST', '/', true);
  req.send(data);
      }
      for (var i = 0; i < reqs; i++)
  send(i);
    </script>
    </body>
  `))
}

func main() {
	http.HandleFunc("/", handler)
	if err := http.ListenAndServeTLS(":1333", "key.crt", "key.key", nil); err != nil {
		log.Fatal(err)
	}
}