netutil: add little AwaitReachable func

Change-Id: I52af3add776cd57ca91c073e0ec563c50923d40f

pkg/netutil/netutil.go

@@ -0,0 +1,38 @@
+/*
+Copyright 2014 The Camlistore Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package netutil
+
+import (
+	"errors"
+	"net"
+	"time"
+)
+
+// AwaitReachable tries to make a TCP connection to addr regularly.
+// It returns an error if it's unable to make a connection before maxWait.
+func AwaitReachable(addr string, maxWait time.Duration) error {
+	done := time.Now().Add(maxWait)
+	for time.Now().Before(done) {
+		c, err := net.Dial("tcp", addr)
+		if err == nil {
+			c.Close()
+			return nil
+		}
+		time.Sleep(100 * time.Millisecond)
+	}
+	return errors.New("timeout")
+}