From 86d7c47c0ab6239c261e368b184e6d2c86c60252 Mon Sep 17 00:00:00 2001
From: tmshn <tmshn@r.recruit.co.jp>
Date: Wed, 19 Apr 2017 20:26:49 +0900
Subject: [PATCH] Change cidrhost() to get IP from end of the range when
 negative number given Ref: https://github.com/apparentlymart/go-cidr/pull/2

---
 config/interpolate_funcs_test.go                  | 15 +++++++++++++++
 .../apparentlymart/go-cidr/cidr/cidr.go           |  9 ++++++++-
 vendor/vendor.json                                |  5 +++--
 .../docs/configuration/interpolation.html.md      |  6 ++++--
 4 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/config/interpolate_funcs_test.go b/config/interpolate_funcs_test.go
index 78816b6dd8..801be6dbb3 100644
--- a/config/interpolate_funcs_test.go
+++ b/config/interpolate_funcs_test.go
@@ -541,11 +541,26 @@ func TestInterpolateFuncCidrHost(t *testing.T) {
 				"192.168.1.5",
 				false,
 			},
+			{
+				`${cidrhost("192.168.1.0/24", -5)}`,
+				"192.168.1.251",
+				false,
+			},
+			{
+				`${cidrhost("192.168.1.0/24", -256)}`,
+				"192.168.1.0",
+				false,
+			},
 			{
 				`${cidrhost("192.168.1.0/30", 255)}`,
 				nil,
 				true, // 255 doesn't fit in two bits
 			},
+			{
+				`${cidrhost("192.168.1.0/30", -255)}`,
+				nil,
+				true, // 255 doesn't fit in two bits
+			},
 			{
 				`${cidrhost("not-a-cidr", 6)}`,
 				nil,
diff --git a/vendor/github.com/apparentlymart/go-cidr/cidr/cidr.go b/vendor/github.com/apparentlymart/go-cidr/cidr/cidr.go
index 1583d6382b..a31cdec773 100644
--- a/vendor/github.com/apparentlymart/go-cidr/cidr/cidr.go
+++ b/vendor/github.com/apparentlymart/go-cidr/cidr/cidr.go
@@ -61,7 +61,14 @@ func Host(base *net.IPNet, num int) (net.IP, error) {
 	hostLen := addrLen - parentLen
 
 	maxHostNum := uint64(1<<uint64(hostLen)) - 1
-	if uint64(num) > maxHostNum {
+
+	numUint64 := uint64(num)
+	if num < 0 {
+		numUint64 = uint64(-num) - 1
+		num = int(maxHostNum - numUint64)
+	}
+
+	if numUint64 > maxHostNum {
 		return nil, fmt.Errorf("prefix of %d does not accommodate a host numbered %d", parentLen, num)
 	}
 
diff --git a/vendor/vendor.json b/vendor/vendor.json
index b4fd8b29d6..e6ff9097cb 100644
--- a/vendor/vendor.json
+++ b/vendor/vendor.json
@@ -446,9 +446,10 @@
 			"revisionTime": "2016-08-22T23:00:20Z"
 		},
 		{
-			"checksumSHA1": "kn+zdUr5TNsoAX8BgjOaWYtMT5U=",
+			"checksumSHA1": "FIL83loX9V9APvGQIjJpbxq53F0=",
 			"path": "github.com/apparentlymart/go-cidr/cidr",
-			"revision": "a3ebdb999b831ecb6ab8a226e31b07b2b9061c47"
+			"revision": "7e4b007599d4e2076d9a81be723b3912852dda2c",
+			"revisionTime": "2017-04-18T07:21:50Z"
 		},
 		{
 			"checksumSHA1": "yicZ9OtLcy3iCgraWO015yeoO5E=",
diff --git a/website/source/docs/configuration/interpolation.html.md b/website/source/docs/configuration/interpolation.html.md
index 5958aef709..1b4b69c5c0 100644
--- a/website/source/docs/configuration/interpolation.html.md
+++ b/website/source/docs/configuration/interpolation.html.md
@@ -157,8 +157,10 @@ The supported built-in functions are:
   * `chomp(string)` - Removes trailing newlines from the given string.
 
   * `cidrhost(iprange, hostnum)` - Takes an IP address range in CIDR notation
-    and creates an IP address with the given host number. For example,
-    `cidrhost("10.0.0.0/8", 2)` returns `10.0.0.2`.
+    and creates an IP address with the given host number. If given host
+    number is negative, the count starts from the end of the range.
+    For example, `cidrhost("10.0.0.0/8", 2)` returns `10.0.0.2` and
+    `cidrhost("10.0.0.0/8", -2)` returns `10.255.255.254`.
 
   * `cidrnetmask(iprange)` - Takes an IP address range in CIDR notation
     and returns the address-formatted subnet mask format that some