package main

import (
	"context"
	"crypto/tls"
	"github.com/gorilla/websocket"
	"log"
	"net"
	"net/http"
	"net/url"
)

const (
	// Local or remote HTTP proxy.
	proxyUrl = "http://127.0.0.1:8888"

	// Websocket endpoint for testing
	websocketUrl = "wss://echo.websocket.events/"
)

func main() {
	p, _ := url.Parse(proxyUrl)

	dialer := websocket.Dialer{
		Proxy:             http.ProxyURL(p),
		EnableCompression: true,
		NetDialTLSContext: func(ctx context.Context, network, addr string) (net.Conn, error) {
			// TCP dial
			netConn, err := net.Dial(network, addr)
			if err != nil {
				return nil, err
			}

			// 'NetDialTLSContext' also gets called during the proxy CONNECT for some reason (at this point 'network' equals "TCP" and 'addr' equals "127.0.0.1:8888")
			// The HTTP proxy doesn't support HTTPS however, so I return the established TCP connection early.
			// If I don't do this check, the connection hangs forever (tested with several proxies).
			// This feels kinda hacky though, not sure if this is the correct approach...
			if p.Host == addr {
				return netConn, err
			}

			// Example TLS handshake
			tlsConn := tls.Client(netConn, &tls.Config{ServerName: "echo.websocket.events", InsecureSkipVerify: true})
			if err = tlsConn.Handshake(); err != nil {
				return nil, err
			}

			return tlsConn, nil
		},
	}

	conn, _, err := dialer.Dial(websocketUrl, nil)
	if err != nil {
		log.Fatalln(err)
	}

	log.Println(conn.LocalAddr())
	// ...
}