Methods to get a private IP

consul/util.go

@@ -1,13 +1,45 @@
 package consul
 
 import (
+	"fmt"
 	"github.com/hashicorp/serf/serf"
+	"net"
 	"os"
 	"path/filepath"
 	"strconv"
 	"strings"
 )
 
+/*
+ * Contains an entry for each private block:
+ * 10.0.0.0/8
+ * 172.16.0.0/12
+ * 192.168/16
+ */
+var privateBlocks []*net.IPNet
+
+func init() {
+	// Add each private block
+	privateBlocks = make([]*net.IPNet, 3)
+	_, block, err := net.ParseCIDR("10.0.0.0/8")
+	if err != nil {
+		panic(fmt.Sprintf("Bad cidr. Got %v", err))
+	}
+	privateBlocks[0] = block
+
+	_, block, err = net.ParseCIDR("172.16.0.0/12")
+	if err != nil {
+		panic(fmt.Sprintf("Bad cidr. Got %v", err))
+	}
+	privateBlocks[1] = block
+
+	_, block, err = net.ParseCIDR("192.168.0.0/16")
+	if err != nil {
+		panic(fmt.Sprintf("Bad cidr. Got %v", err))
+	}
+	privateBlocks[2] = block
+}
+
 // strContains checks if a list contains a string
 func strContains(l []string, s string) bool {
 	for _, v := range l {
@@ -44,3 +76,39 @@ func isConsulServer(m serf.Member) (bool, string, int) {
 
 	return true, datacenter, port
 }
+
+// Returns if the given IP is in a private block
+func isPrivateIP(ip_str string) bool {
+	ip := net.ParseIP(ip_str)
+	for _, priv := range privateBlocks {
+		if priv.Contains(ip) {
+			return true
+		}
+	}
+	return false
+}
+
+// GetPrivateIP is used to return the first private IP address
+// associated with an interface on the machine
+func GetPrivateIP() (*net.IPNet, error) {
+	addresses, err := net.InterfaceAddrs()
+	if err != nil {
+		return nil, fmt.Errorf("Failed to get interface addresses: %v", err)
+	}
+
+	// Find private IPv4 address
+	for _, addr := range addresses {
+		ip, ok := addr.(*net.IPNet)
+		if !ok {
+			continue
+		}
+		if ip.IP.To4() == nil {
+			continue
+		}
+		if !isPrivateIP(ip.IP.String()) {
+			continue
+		}
+		return ip, nil
+	}
+	return nil, fmt.Errorf("No private IP address found")
+}

consul/util_test.go

@@ -13,3 +13,21 @@ func TestStrContains(t *testing.T) {
 		t.Fatalf("should not contain")
 	}
 }
+
+func TestIsPrivateIP(t *testing.T) {
+	if !isPrivateIP("192.168.1.1") {
+		t.Fatalf("bad")
+	}
+	if !isPrivateIP("172.16.45.100") {
+		t.Fatalf("bad")
+	}
+	if !isPrivateIP("10.1.2.3") {
+		t.Fatalf("bad")
+	}
+	if isPrivateIP("8.8.8.8") {
+		t.Fatalf("bad")
+	}
+	if isPrivateIP("127.0.0.1") {
+		t.Fatalf("bad")
+	}
+}