processors/util: ensure hardware addresses are not duplicated (elasti…

…c#26877)

When a linux host is using a virtual bridge, the mac address of that
interface will be duplicated in the results from net.Interfaces() since a
dummy device will have been created to support the virtual bridge device.
This change ensures that hardware addresses are unique in the returned list.

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

libbeat/processors/util/netinfo.go

@@ -19,6 +19,7 @@ package util
 
 import (
 	"net"
+	"sort"
 
 	"github.com/joeshaw/multierror"
 )
@@ -63,5 +64,25 @@ func GetNetInfo() (ipList []string, hwList []string, err error) {
 		}
 	}
 
-	return ipList, hwList, errs.Err()
+	return ipList, unique(hwList), errs.Err()
+}
+
+// unique returns addrs lexically sorted and with repeated elements
+// omitted.
+func unique(addrs []string) []string {
+	if len(addrs) < 2 {
+		return addrs
+	}
+	sort.Strings(addrs)
+	curr := 0
+	for i, addr := range addrs {
+		if addr == addrs[curr] {
+			continue
+		}
+		curr++
+		if curr < i {
+			addrs[curr], addrs[i] = addrs[i], ""
+		}
+	}
+	return addrs[:curr+1]
 }

libbeat/processors/util/netinfo_test.go

@@ -0,0 +1,56 @@
+// Licensed to Elasticsearch B.V. under one or more contributor
+// license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright
+// ownership. Elasticsearch B.V. licenses this file to you 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 util
+
+import (
+	"reflect"
+	"sort"
+	"testing"
+)
+
+func TestUnique(t *testing.T) {
+	var tests = [][]string{
+		{},
+		{"a"},
+		{"a", "a"},
+		{"a", "b"},
+		{"b", "a"},
+		{"a", "b", "c"},
+		{"c", "b", "a"},
+		{"c", "a", "a", "b", "c", "a"},
+	}
+
+	for i, test := range tests {
+		// Allocating naive implementation of unique.
+		seen := make(map[string]bool)
+		for _, e := range test {
+			seen[e] = true
+		}
+		want := make([]string, 0, len(seen))
+		for e := range seen {
+			want = append(want, e)
+		}
+		sort.Strings(want)
+
+		got := unique(test)
+
+		if !reflect.DeepEqual(got, want) {
+			t.Errorf("unexpected result for test %d: got:%q want:%q", i, got, want)
+		}
+	}
+}