From 92af10a0feef6fa053207030822c6372134f8f94 Mon Sep 17 00:00:00 2001
From: Tim Hockin <thockin@google.com>
Date: Sat, 13 Feb 2016 15:37:42 -0800
Subject: [PATCH] Extract hostname from (hostname.domainname)

This approach allows the user to provide a FQDN as hostname if that is what
they want in their container, or to provide distinct host and domain parts.  In
both cases we will correctly extract the first token for /etc/hosts.

Signed-off-by: Tim Hockin <thockin@google.com>
---
 libnetwork/etchosts/etchosts.go      | 12 ++++++++++--
 libnetwork/etchosts/etchosts_test.go | 22 ++++++++++++++++++++++
 2 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/libnetwork/etchosts/etchosts.go b/libnetwork/etchosts/etchosts.go
index 5f68372b90..99ea5dec77 100644
--- a/libnetwork/etchosts/etchosts.go
+++ b/libnetwork/etchosts/etchosts.go
@@ -8,6 +8,7 @@ import (
 	"io/ioutil"
 	"os"
 	"regexp"
+	"strings"
 	"sync"
 )
 
@@ -78,10 +79,17 @@ func Build(path, IP, hostname, domainname string, extraContent []Record) error {
 		//set main record
 		var mainRec Record
 		mainRec.IP = IP
+		// User might have provided a FQDN in hostname or split it across hostname
+		// and domainname.  We want the FQDN and the bare hostname.
+		fqdn := hostname
 		if domainname != "" {
-			mainRec.Hosts = fmt.Sprintf("%s.%s %s", hostname, domainname, hostname)
+			fqdn = fmt.Sprintf("%s.%s", fqdn, domainname)
+		}
+		parts := strings.SplitN(fqdn, ".", 2)
+		if len(parts) == 2 {
+			mainRec.Hosts = fmt.Sprintf("%s %s", fqdn, parts[0])
 		} else {
-			mainRec.Hosts = hostname
+			mainRec.Hosts = fqdn
 		}
 		if _, err := mainRec.WriteTo(content); err != nil {
 			return err
diff --git a/libnetwork/etchosts/etchosts_test.go b/libnetwork/etchosts/etchosts_test.go
index 2a0a4f6d68..f897096da5 100644
--- a/libnetwork/etchosts/etchosts_test.go
+++ b/libnetwork/etchosts/etchosts_test.go
@@ -81,6 +81,28 @@ func TestBuildHostname(t *testing.T) {
 	}
 }
 
+func TestBuildHostnameFQDN(t *testing.T) {
+	file, err := ioutil.TempFile("", "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.Remove(file.Name())
+
+	err = Build(file.Name(), "10.11.12.13", "testhostname.testdomainname.com", "", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	content, err := ioutil.ReadFile(file.Name())
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if expected := "10.11.12.13\ttesthostname.testdomainname.com testhostname\n"; !bytes.Contains(content, []byte(expected)) {
+		t.Fatalf("Expected to find '%s' got '%s'", expected, content)
+	}
+}
+
 func TestBuildNoIP(t *testing.T) {
 	file, err := ioutil.TempFile("", "")
 	if err != nil {