502 Bad Gateway: net/http GET failed for IPSec tunnel

php Editor Zimo sometimes encounters a 502 Bad Gateway prompt when using the Internet. This error message means that there is a communication problem between the gateway server and the upstream server, resulting in the request not being completed. One of the possible causes is a net/http GET failure for the IPSec tunnel. Although this error can be confusing, by understanding its cause and how to fix it, we can quickly resolve the issue and continue enjoying the convenience of the Internet.

Question content

Issuing a remote get request through ipsec tunnel (vpn) on windows using the net/http package When , the get request failed and the response code was 502 bad gateway. However, requests sent by curl with the same headers, uri, method work just fine. go The source code is as follows:

    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 analyzing the packet capture of the traffic, it was found that the vpn interface can normally capture the request sent by curl, but get cannot be retrieved from go(net /http)The request sent was lost.

Then I guess it may be because the framework chooses the wrong interface to send the packet.

So I try to find the correct local network interface and specify its localaddr to send my get request like this:

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
}

After replacing client with the client function, the get request finally works.

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

So my question is why golang is not selecting the correct local network interface to automatically send the request?

Solution

After debuggingnet.dial#DialContext, I found that the address has been changed to my Visual Studio Code settings proxy address. My proxy server will not be able to handle my application requests.

When I remove the proxy settings, net.dial works as expected.

important things

I'm using vscode to work with TypeScript/Java/Golang... and this is my first time developing an application in vscode IDE Encountering proxy issues. In other words, I never thought the IDE agent could do the job it was built for. It makes sense since the extension or the IDE itself uses this proxy setting, but my golang project debugging also uses it, which really confuses me.

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