Add Slack support

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

@@ -0,0 +1,20 @@
+package slack
+
+import (
+	"net"
+	"net/url"
+)
+
+var portMapping = map[string]string{"ws": "80", "wss": "443"}
+
+func websocketizeURLPort(orig string) (string, error) {
+	urlObj, err := url.ParseRequestURI(orig)
+	if err != nil {
+		return "", err
+	}
+	_, _, err = net.SplitHostPort(urlObj.Host)
+	if err != nil {
+		return urlObj.Scheme + "://" + urlObj.Host + ":" + portMapping[urlObj.Scheme] + urlObj.Path, nil
+	}
+	return orig, nil
+}