implements NetIOCounters() on FreeBSD.

README.rst

@@ -102,7 +102,7 @@ Current Status
   - disk_partitions (linux, freebsd, windows)
   - disk_io_counters (linux)
   - disk_usage (linux, freebsd, windows)
-  - net_io_counters (linux, windows)
+  - net_io_counters (linux, freebsd, windows)
   - boot_time (linux, freebsd, windows(but little broken))
   - users (linux, freebsd)
   - pids (linux, freebsd)

net_freebsd.go

@@ -3,9 +3,43 @@
 package gopsutil
 
 import (
-	"errors"
+	"os/exec"
+	"strings"
 )
 
 func NetIOCounters(pernic bool) ([]NetIOCountersStat, error) {
-	return nil, errors.New("not implemented yet")
+	out, err := exec.Command("/usr/bin/netstat", "-ibdn").Output()
+	if err != nil {
+		return nil, err
+	}
+
+	lines := strings.Split(string(out), "\n")
+	ret := make([]NetIOCountersStat, 0, len(lines)-1)
+
+	for _, line := range lines {
+		values := strings.Fields(line)
+		if len(values) < 1 || values[0] == "Name" {
+			continue
+		}
+		base := 1
+		// sometimes Address is ommitted
+		if len(values) < 13 {
+			base = 0
+		}
+
+		n := NetIOCountersStat{
+			Name:        values[0],
+			PacketsRecv: mustParseUint64(values[base+3]),
+			Errin:       mustParseUint64(values[base+4]),
+			Dropin:      mustParseUint64(values[base+5]),
+			BytesRecv:   mustParseUint64(values[base+6]),
+			PacketsSent: mustParseUint64(values[base+7]),
+			Errout:      mustParseUint64(values[base+8]),
+			BytesSent:   mustParseUint64(values[base+9]),
+			Dropout:     mustParseUint64(values[base+11]),
+		}
+		ret = append(ret, n)
+	}
+
+	return ret, nil
 }