将GoLang中的Dial与特定的本地地址一起使用

Question

I need to be able selecting from which IP address my HTTP request should be sent. In my code right now, for DNS caching i'm using the following according to this:

defaultTransport.DialContext = func(ctx context.Context, network string, addr string) (conn net.Conn, err error) {
    separator := strings.LastIndex(addr, ":")
    ips, err := r.LookupHost(ctx, addr[:separator])
    if err != nil {
        return nil, err
    }
    for _, ip := range ips {
        conn, err = net.Dial(network, ip+addr[separator:])
        if err == nil {
            break
        }
    }
    return
}

In order to specify the local address, the only way i found is by using the following:

defaultTransport.DialContext = (&net.Dialer{
    LocalAddr: localAddr,
}).DialContext

How can i achieve combining the above?

Answer 1

You could wrap the local address dialer that you want to use, and delegate the actual calls to it?

localAddrDialier := &net.Dialer{
    LocalAddr: localAddr,
}

// trimmed...

defaultTransport.DialContext = func(ctx context.Context, network string, addr string) (conn net.Conn, err error) {
    separator := strings.LastIndex(addr, ":")
    ips, err := r.LookupHost(ctx, addr[:separator])
    if err != nil {
        return nil, err
    }
    for _, ip := range ips {
        // use the localAddrDialer here for the _actual_ request?
        conn, err = localAddrDialer.DialContext(ctx, network, ip+addr[separator:])
        if err == nil {
            break
        }
    }
    return
}

Or vice-versa, according to which if the net.Dialer's you want to make the actual call