Add Slack support

vendor/github.com/nlopes/slack/websocket_proxy.go

@@ -0,0 +1,83 @@
+package slack
+
+import (
+	"crypto/tls"
+	"errors"
+	"net"
+	"net/http"
+	"net/http/httputil"
+	"net/url"
+	"os"
+	"strings"
+
+	"golang.org/x/net/websocket"
+)
+
+// Taken and reworked from: https://gist.github.com/madmo/8548738
+func websocketHTTPConnect(proxy, urlString string) (net.Conn, error) {
+	p, err := net.Dial("tcp", proxy)
+	if err != nil {
+		return nil, err
+	}
+
+	turl, err := url.Parse(urlString)
+	if err != nil {
+		return nil, err
+	}
+
+	req := http.Request{
+		Method: "CONNECT",
+		URL:    &url.URL{},
+		Host:   turl.Host,
+	}
+
+	cc := httputil.NewProxyClientConn(p, nil)
+	cc.Do(&req)
+	if err != nil && err != httputil.ErrPersistEOF {
+		return nil, err
+	}
+
+	rwc, _ := cc.Hijack()
+
+	return rwc, nil
+}
+
+func websocketProxyDial(urlString, origin string) (ws *websocket.Conn, err error) {
+	if os.Getenv("HTTP_PROXY") == "" {
+		return websocket.Dial(urlString, "", origin)
+	}
+
+	purl, err := url.Parse(os.Getenv("HTTP_PROXY"))
+	if err != nil {
+		return nil, err
+	}
+
+	config, err := websocket.NewConfig(urlString, origin)
+	if err != nil {
+		return nil, err
+	}
+
+	client, err := websocketHTTPConnect(purl.Host, urlString)
+	if err != nil {
+		return nil, err
+	}
+
+	switch config.Location.Scheme {
+	case "ws":
+	case "wss":
+		tlsClient := tls.Client(client, &tls.Config{
+			ServerName: strings.Split(config.Location.Host, ":")[0],
+		})
+		err := tlsClient.Handshake()
+		if err != nil {
+			tlsClient.Close()
+			return nil, err
+		}
+		client = tlsClient
+
+	default:
+		return nil, errors.New("invalid websocket schema")
+	}
+
+	return websocket.NewClient(config, client)
+}