ipam/host-local: add ResolvConf argument for DNS configuration

This adds the option `resolvConf` to the host-local IPAM configuration.
If specified, the plugin will try to parse the file as a resolv.conf(5)
type file and return it in the DNS response.

plugins/ipam/host-local/dns_test.go

@@ -0,0 +1,80 @@
+// Copyright 2016 CNI 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 main
+
+import (
+	"io/ioutil"
+	"os"
+
+	"github.com/containernetworking/cni/pkg/types"
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("parsing resolv.conf", func() {
+	It("parses a simple resolv.conf file", func() {
+		contents := `
+		nameserver 192.0.2.0
+		nameserver 192.0.2.1
+		`
+		dns, err := parse(contents)
+		Expect(err).NotTo(HaveOccurred())
+		Expect(*dns).Should(Equal(types.DNS{Nameservers: []string{"192.0.2.0", "192.0.2.1"}}))
+	})
+	It("ignores comments", func() {
+		dns, err := parse(`
+nameserver 192.0.2.0
+;nameserver 192.0.2.1
+`)
+		Expect(err).NotTo(HaveOccurred())
+		Expect(*dns).Should(Equal(types.DNS{Nameservers: []string{"192.0.2.0"}}))
+	})
+	It("parses all fields", func() {
+		dns, err := parse(`
+nameserver 192.0.2.0
+nameserver 192.0.2.2
+domain example.com
+;nameserver comment
+#nameserver comment
+search example.net example.org
+search example.gov
+options one two three
+options four
+`)
+		Expect(err).NotTo(HaveOccurred())
+		Expect(*dns).Should(Equal(types.DNS{
+			Nameservers: []string{"192.0.2.0", "192.0.2.2"},
+			Domain:      "example.com",
+			Search:      []string{"example.net", "example.org", "example.gov"},
+			Options:     []string{"one", "two", "three", "four"},
+		}))
+	})
+})
+
+func parse(contents string) (*types.DNS, error) {
+	f, err := ioutil.TempFile("", "host_local_resolv")
+	defer f.Close()
+	defer os.Remove(f.Name())
+
+	if err != nil {
+		return nil, err
+	}
+
+	if _, err := f.WriteString(contents); err != nil {
+		return nil, err
+	}
+
+	return parseResolvConf(f.Name())
+}