rebase Initial support for parsing /proc/net/arp #105 from @skottler

Signed-off-by: Christoph Maser <christoph.maser+github@gmail.com>

arp.go

@@ -0,0 +1,84 @@
+// Copyright 2019 The Prometheus 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 procfs
+
+import (
+	"fmt"
+	"io/ioutil"
+	"net"
+	"strings"
+)
+
+// ARPEntry contains a single row of the columnar data represented in
+// /proc/net/arp.
+type ARPEntry struct {
+	// IP address
+	IPAddr net.IP
+	// MAC address
+	HWAddr net.HardwareAddr
+	// Name of the device
+	Device string
+}
+
+// GatherARPEntries retrieves all the ARP entries, parse the relevant columns,
+// and then return a slice of ARPEntry's.
+func (fs FS) GatherARPEntries() ([]ARPEntry, error) {
+	data, err := ioutil.ReadFile(fs.proc.Path("net/arp"))
+	if err != nil {
+		return nil, fmt.Errorf("error reading arp %s: %s", fs.proc.Path("net/arp"), err)
+	}
+
+	return parseARPEntries(data)
+}
+
+func parseARPEntries(data []byte) ([]ARPEntry, error) {
+	lines := strings.Split(string(data), "\n")
+	entries := make([]ARPEntry, 0)
+	var err error
+
+	for _, line := range lines {
+		columns := strings.Fields(line)
+		width := len(columns)
+		expectedDataWidth := 6
+		expectedHeaderWidth := 9
+
+		if width == expectedHeaderWidth || width == 0 {
+			continue
+		} else if width == expectedDataWidth {
+			entry, err := parseARPEntry(columns)
+			if err != nil {
+				return []ARPEntry{}, fmt.Errorf("failed to parse ARP entry: %s", err)
+			}
+			entries = append(entries, entry)
+		} else {
+			return []ARPEntry{}, fmt.Errorf("%d columns were detected, but %d were expected", width, expectedDataWidth)
+		}
+
+	}
+
+	return entries, err
+}
+
+func parseARPEntry(columns []string) (ARPEntry, error) {
+	ip := net.ParseIP(columns[0])
+	mac := net.HardwareAddr(columns[3])
+
+	entry := ARPEntry{
+		IPAddr: ip,
+		HWAddr: mac,
+		Device: columns[5],
+	}
+
+	return entry, nil
+}

arp_test.go

@@ -0,0 +1,43 @@
+// Copyright 2019 The Prometheus 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 procfs
+
+import (
+	"net"
+	"testing"
+)
+
+func TestARP(t *testing.T) {
+	fs, err := NewFS(procTestFixtures)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	arpFile, err := fs.GatherARPEntries()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if want, got := "192.168.224.1", arpFile[0].IPAddr.String(); want != got {
+		t.Errorf("want 192.168.224.1, got %s", got)
+	}
+
+	if want, got := net.HardwareAddr("00:50:56:c0:00:08").String(), arpFile[0].HWAddr.String(); want != got {
+		t.Errorf("want 00:50:56:c0:00:08, got %s", got)
+	}
+
+	if want, got := "ens33", arpFile[0].Device; want != got {
+		t.Errorf("want ens33, got %s", got)
+	}
+}

fixtures.ttar

@@ -482,6 +482,12 @@ Mode: 644
 Directory: fixtures/proc/net
 Mode: 755
 # ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Path: fixtures/proc/net/arp
+Lines: 2
+IP address       HW type     Flags       HW address            Mask     Device
+192.168.224.1    0x1         0x2         00:50:56:c0:00:08     *        ens33
+Mode: 664
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 Path: fixtures/proc/net/dev
 Lines: 6
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