xrootd/client: automatically infer xrootd port number

Fixes go-hep#236.

xrootd/client/port.go

@@ -0,0 +1,29 @@
+// Copyright 2018 The go-hep Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package client // import "go-hep.org/x/hep/xrootd/client"
+
+import (
+	"net"
+	"strconv"
+)
+
+func parseAddr(addr string) string {
+	_, _, err := net.SplitHostPort(addr)
+	if err == nil {
+		return addr
+	}
+	switch err := err.(type) {
+	case *net.AddrError:
+		switch err.Err {
+		case "missing port in address":
+			port, e := net.LookupPort("tcp", "rootd")
+			if e != nil {
+				return addr + ":1094"
+			}
+			return addr + ":" + strconv.Itoa(port)
+		}
+	}
+	return addr
+}

xrootd/client/session.go

@@ -51,7 +51,8 @@ func newSession(ctx context.Context, address string, username string, client *Cl
 	ctx, cancel := context.WithCancel(ctx)
 
 	var d net.Dialer
-	conn, err := d.DialContext(ctx, "tcp", address)
+	addr := parseAddr(address)
+	conn, err := d.DialContext(ctx, "tcp", addr)
 	if err != nil {
 		cancel()
 		return nil, err
@@ -63,7 +64,7 @@ func newSession(ctx context.Context, address string, username string, client *Cl
 		mux:       mux.New(),
 		requests:  make(map[xrdproto.StreamID][]byte),
 		client:    client,
-		sessionID: address,
+		sessionID: addr,
 	}
 
 	go sess.consume(ctx)