502 Bad Gateway: net/http GET failed with IPSec Tunnel

When making remote GET requests with net/http package through IPSec Tunnel(VPN) on windows, GET request failed with response code 502 Bad Gateway. However request with same headers, uri, method sent by curl works greatly. The go source code looks like:

	var req *http.Request
	req, err = http.NewRequest('GET', *uri, reader)
	if nil != err {
		level.Warn(log).Log("msg", "Unable to create request", "err", err, "uri", uri)
		return nil, err
	}
	if nil != req.Body {
		defer req.Body.Close()
	}
	for h, v := range opts.Headers {
		req.Header.Add(h, *v)
	}

	client := http.Client{}
	if nil != err {
		return nil, err
	}
	res, err := client.Do(req)
	if nil != err {
		level.Warn(log).Log("msg", "Unable to send request", "err", err, "uri", uri)
		return nil, err
	}
	defer res.Body.Close()

	buf, err := io.ReadAll(res.Body)
	if nil != err {
		level.Warn(log).Log("msg", "Unable to read response", "err", err, "uri", uri, "status", res.Status, "status_code", res.StatusCode)
		return nil, err
	}

After capturing and analysising the traffic, I found the request sent by curl can be captured normally on VPN Interface but GET request sent from go(net/http) lost.

Then I guess it probably because the framework seleted wrong interface to send the packet.

So I tried to find out proper local network interface and specify its LocalAddr to send my GET request as following:

func Client(u string) (*http.Client, error) {
	uri, err := url.Parse(u)
	if nil != err {
		return nil, err
	}
    host := uri.Host
	port := uri.Port()
	if Empty == port {
		if uri.Scheme == "http" {
			host = host + ":80"
		} else if uri.Scheme == "https" {
			host = host + ":443"
		}
	}
	conn, err := net.Dial("tcp", host)
	if nil != err {
		return nil, err
	}
	addr := conn.LocalAddr().(*net.TCPAddr)
    // **make sure using random port as local port**
	addr.Port = 0

	dialer := &net.Dialer{LocalAddr: addr}
	dialContext := func(ctx context.Context, network, addr string) (net.Conn, error) {
		conn, err := dialer.Dial(network, addr)
		return conn, err
	}

	transport := &http.Transport{DialContext: dialContext}
	client := &http.Client{
		Transport: transport,
	}
	return client, nil
}

And after repacing client with Client function, GET request final works.

client := &http.Client{} => client, err := Client(uri)

Then my question is why golang doesn't select proper local network interface to send request automatically?

After debugging the net.dial#DialContext, I found the address has been changed to my proxy address in Visual Studio Code settings. And my proxy server won't be able to handle my application requests.

When I removed the proxy setting, net.dial works as expected.

What matters

I'm using vscode to work with TypeScript/Java/Golang... and this is the first time I encounter a proxy issue on Developing Application in vscode IDE. In other words, I never thought the IDE proxy will work on the work it builds. Since extensions or IDE itself use this proxy settings is reasonable but my golang project debugging use it too that really confused me a lot.