Fix /proc/net/dev column parsing.

This fixes https://github.com/prometheus/node_exporter/issues/73

collector/fixtures/net-dev

@@ -3,6 +3,7 @@ Inter-|   Receive                                                |  Transmit
   tun0:    1888      24    0    0    0     0          0         0    67120     934    0    0    0     0       0          0
 veth4B09XN:     648       8    0    0    0     0          0         0  1943284   10640    0    0    0     0       0          0
     lo: 435303245 1832522    0    0    0     0          0         0 435303245 1832522    0    0    0     0       0          0
+  eth0:68210035552 520993275    0    0    0     0          0         0 9315587528 43451486    0    0    0     0       0          0
 lxcbr0:       0       0    0    0    0     0          0         0  2630299   28339    0    0    0     0       0          0
  wlan0: 10437182923 13899359    0    0    0     0          0         0 2851649360 11726200    0    0    0     0       0          0
 docker0: 64910168 1065585    0    0    0     0          0         0 2681662018 1929779    0    0    0     0       0          0

collector/netdev.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"regexp"
 	"strconv"
 	"strings"
 
@@ -18,6 +19,10 @@ const (
 	netDevSubsystem = "network"
 )
 
+var (
+	fieldSep = regexp.MustCompile("[ :] *")
+)
+
 type netDevCollector struct {
 	config  Config
 	metrics map[string]*prometheus.GaugeVec
@@ -95,13 +100,14 @@ func parseNetDevStats(r io.Reader) (map[string]map[string]map[string]string, err
 	}
 	header := strings.Fields(parts[1])
 	for scanner.Scan() {
-		parts := strings.Fields(string(scanner.Text()))
+		line := strings.TrimLeft(string(scanner.Text()), " ")
+		parts := fieldSep.Split(line, -1)
 		if len(parts) != 2*len(header)+1 {
 			return nil, fmt.Errorf("Invalid line in %s: %s",
 				procNetDev, scanner.Text())
 		}
 
-		dev := parts[0][:len(parts[0])-1]
+		dev := parts[0][:len(parts[0])]
 		receive, err := parseNetDevLine(parts[1:len(header)+1], header)
 		if err != nil {
 			return nil, err

collector/netdev_test.go

@@ -21,6 +21,10 @@ func TestNetDevStats(t *testing.T) {
 		t.Errorf("want netstat wlan0 bytes %s, got %s", want, got)
 	}
 
+	if want, got := "68210035552", netStats["receive"]["eth0"]["bytes"]; want != got {
+		t.Errorf("want netstat eth0 bytes %s, got %s", want, got)
+	}
+
 	if want, got := "934", netStats["transmit"]["tun0"]["packets"]; want != got {
 		t.Errorf("want netstat tun0 packets %s, got %s", want, got)
 	}