Fixed ARP table MAC address parsing, added Flags field (prometheus#414)

* fixed arp table mac address parsing

- Added ARPEntry.Flags field related to entry flags
- Added ARPEntry.IsComplete() to check if entry is complete
- Fixed mac address parsing and error handling
- Test improved with incomplete entry information
Closes prometheus#413.

Signed-off-by: Serhii Zasenko <sergii@zasenko.name>

* Arp flag const names cleanup

Signed-off-by: Serhii Zasenko <sergii@zasenko.name>

arp.go

@@ -17,9 +17,26 @@ import (
 	"fmt"
 	"io/ioutil"
 	"net"
+	"strconv"
 	"strings"
 )
 
+// Learned from include/uapi/linux/if_arp.h
+const (
+	// completed entry (ha valid)
+	ATFComplete = 0x02
+	// permanent entry
+	ATFPermanent = 0x04
+	// Publish entry
+	ATFPublish = 0x08
+	// Has requested trailers
+	ATFUseTrailers = 0x10
+	// Obsoleted: Want to use a netmask (only for proxy entries)
+	ATFNetmask = 0x20
+	// Don't answer this addresses
+	ATFDontPublish = 0x40
+)
+
 // ARPEntry contains a single row of the columnar data represented in
 // /proc/net/arp.
 type ARPEntry struct {
@@ -29,6 +46,8 @@ type ARPEntry struct {
 	HWAddr net.HardwareAddr
 	// Name of the device
 	Device string
+	// Flags
+	Flags byte
 }
 
 // GatherARPEntries retrieves all the ARP entries, parse the relevant columns,
@@ -72,14 +91,26 @@ func parseARPEntries(data []byte) ([]ARPEntry, error) {
 }
 
 func parseARPEntry(columns []string) (ARPEntry, error) {
+	entry := ARPEntry{Device: columns[5]}
 	ip := net.ParseIP(columns[0])
-	mac := net.HardwareAddr(columns[3])
+	entry.IPAddr = ip
+
+	if mac, err := net.ParseMAC(columns[3]); err == nil {
+		entry.HWAddr = mac
+	} else {
+		return ARPEntry{}, err
+	}
 
-	entry := ARPEntry{
-		IPAddr: ip,
-		HWAddr: mac,
-		Device: columns[5],
+	if flags, err := strconv.ParseUint(columns[2], 0, 8); err == nil {
+		entry.Flags = byte(flags)
+	} else {
+		return ARPEntry{}, err
 	}
 
 	return entry, nil
 }
+
+// IsComplete returns true if ARP entry is marked with complete flag
+func (entry *ARPEntry) IsComplete() bool {
+	return entry.Flags&ATFComplete != 0
+}

arp_test.go

@@ -33,11 +33,35 @@ func TestARP(t *testing.T) {
 		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 := "00:50:56:c0:00:08", arpFile[0].HWAddr.String(); want != got {
+		t.Errorf("want %s, got %s", want, got)
 	}
 
 	if want, got := "ens33", arpFile[0].Device; want != got {
 		t.Errorf("want ens33, got %s", got)
 	}
+
+	if want, got := true, arpFile[0].IsComplete(); want != got {
+		t.Errorf("want %t, got %t", want, got)
+	}
+
+	if want, got := "192.168.224.2", arpFile[1].IPAddr.String(); want != got {
+		t.Errorf("want 192.168.224.2, got %s", got)
+	}
+
+	if want, got := make(net.HardwareAddr, 6).String(), arpFile[1].HWAddr.String(); want != got {
+		t.Errorf("expected empty MAC, got %s", got)
+	}
+
+	if want, got := "ens33", arpFile[1].Device; want != got {
+		t.Errorf("want %s, got %s", want, got)
+	}
+
+	if want, got := byte(0x0), arpFile[1].Flags; want != got {
+		t.Errorf("want %b, got %b", want, got)
+	}
+
+	if want, got := false, arpFile[1].IsComplete(); want != got {
+		t.Errorf("want %t, got %t", want, got)
+	}
 }

fixtures.ttar

@@ -2084,9 +2084,10 @@ Directory: fixtures/proc/net
 Mode: 755
 # ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 Path: fixtures/proc/net/arp
-Lines: 2
+Lines: 3
 IP address       HW type     Flags       HW address            Mask     Device
 192.168.224.1    0x1         0x2         00:50:56:c0:00:08     *        ens33
+192.168.224.2    0x1         0x0         00:00:00:00:00:00     *        ens33
 Mode: 664
 # ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 Path: fixtures/proc/net/dev