client: Discovery via SRV lookups

Based on code from discovery/srv.go.  The returns the target as DNS
returns it. In the case of SSL, certs are tied to the hostname and not
the IP address generally.

Solves #2547

client/srv_test.go

@@ -0,0 +1,102 @@
+// Copyright 2015 CoreOS, Inc.
+//
+// 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 client
+
+import (
+	"errors"
+	"net"
+	"reflect"
+	"testing"
+)
+
+func TestSRVDiscover(t *testing.T) {
+	defer func() { lookupSRV = net.LookupSRV }()
+
+	tests := []struct {
+		withSSL    []*net.SRV
+		withoutSSL []*net.SRV
+		expected   []string
+	}{
+		{
+			[]*net.SRV{},
+			[]*net.SRV{},
+			[]string{},
+		},
+		{
+			[]*net.SRV{
+				&net.SRV{Target: "10.0.0.1", Port: 2480},
+				&net.SRV{Target: "10.0.0.2", Port: 2480},
+				&net.SRV{Target: "10.0.0.3", Port: 2480},
+			},
+			[]*net.SRV{},
+			[]string{"https://10.0.0.1:2480", "https://10.0.0.2:2480", "https://10.0.0.3:2480"},
+		},
+		{
+			[]*net.SRV{
+				&net.SRV{Target: "10.0.0.1", Port: 2480},
+				&net.SRV{Target: "10.0.0.2", Port: 2480},
+				&net.SRV{Target: "10.0.0.3", Port: 2480},
+			},
+			[]*net.SRV{
+				&net.SRV{Target: "10.0.0.1", Port: 7001},
+			},
+			[]string{"https://10.0.0.1:2480", "https://10.0.0.2:2480", "https://10.0.0.3:2480", "http://10.0.0.1:7001"},
+		},
+		{
+			[]*net.SRV{
+				&net.SRV{Target: "10.0.0.1", Port: 2480},
+				&net.SRV{Target: "10.0.0.2", Port: 2480},
+				&net.SRV{Target: "10.0.0.3", Port: 2480},
+			},
+			[]*net.SRV{
+				&net.SRV{Target: "10.0.0.1", Port: 7001},
+			},
+			[]string{"https://10.0.0.1:2480", "https://10.0.0.2:2480", "https://10.0.0.3:2480", "http://10.0.0.1:7001"},
+		},
+		{
+			[]*net.SRV{
+				&net.SRV{Target: "a.example.com", Port: 2480},
+				&net.SRV{Target: "b.example.com", Port: 2480},
+				&net.SRV{Target: "c.example.com", Port: 2480},
+			},
+			[]*net.SRV{},
+			[]string{"https://a.example.com:2480", "https://b.example.com:2480", "https://c.example.com:2480"},
+		},
+	}
+
+	for i, tt := range tests {
+		lookupSRV = func(service string, proto string, domain string) (string, []*net.SRV, error) {
+			if service == "etcd-server-ssl" {
+				return "", tt.withSSL, nil
+			}
+			if service == "etcd-server" {
+				return "", tt.withoutSSL, nil
+			}
+			return "", nil, errors.New("Unkown service in mock")
+		}
+
+		d := NewSRVDiscover()
+
+		endpoints, err := d.Discover("example.com")
+		if err != nil {
+			t.Fatalf("%d: err: %#v", i, err)
+		}
+
+		if !reflect.DeepEqual(endpoints, tt.expected) {
+			t.Errorf("#%d: endpoints = %v, want %v", i, endpoints, tt.expected)
+		}
+
+	}
+}