make utils an internal package

internal/utils/host.go

@@ -0,0 +1,27 @@
+package utils
+
+import (
+	"net/url"
+	"strings"
+)
+
+// HostnameFromAddr determines the hostname in an address string
+func HostnameFromAddr(addr string) (string, error) {
+	p, err := url.Parse(addr)
+	if err != nil {
+		return "", err
+	}
+	h := p.Host
+
+	// copied from https://golang.org/src/net/http/transport.go
+	if hasPort(h) {
+		h = h[:strings.LastIndex(h, ":")]
+	}
+
+	return h, nil
+}
+
+// copied from https://golang.org/src/net/http/http.go
+func hasPort(s string) bool {
+	return strings.LastIndex(s, ":") > strings.LastIndex(s, "]")
+}