IsLocalHost: support host:port

Without this patch IsLocalHost does not work for URLs with port specified i.e. it works for `http://localhost` but does not work for `http://localhost:80` or `http://localhost:10000`.

Fixes #487

dispatcher.go

@@ -97,15 +97,22 @@ func ReqHostIs(hosts ...string) ReqConditionFunc {
 	}
 }
 
-var localHostIpv4 = regexp.MustCompile(`127\.0\.0\.\d+`)
-
-// IsLocalHost checks whether the destination host is explicitly local host
-// (buggy, there can be IPv6 addresses it doesn't catch)
+// IsLocalHost checks whether the destination host is localhost.
 var IsLocalHost ReqConditionFunc = func(req *http.Request, ctx *ProxyCtx) bool {
-	return req.URL.Host == "::1" ||
-		req.URL.Host == "0:0:0:0:0:0:0:1" ||
-		localHostIpv4.MatchString(req.URL.Host) ||
-		req.URL.Host == "localhost"
+	h := req.URL.Hostname()
+	if h == "localhost" {
+		return true
+	}
+	if ip := net.ParseIP(h); ip != nil {
+		return ip.IsLoopback()
+	}
+
+	// In case of IPv6 without a port number Hostname() sometimes returns the invalid value.
+	if ip := net.ParseIP(req.URL.Host); ip != nil {
+		return ip.IsLoopback()
+	}
+
+	return false
 }
 
 // UrlMatches returns a ReqCondition testing whether the destination URL

dispatcher_test.go

@@ -0,0 +1,47 @@
+package goproxy
+
+import (
+	"net"
+	"net/http"
+	"strings"
+	"testing"
+)
+
+func TestIsLocalHost(t *testing.T) {
+	hosts := []string{
+		"localhost",
+		"127.0.0.1",
+		"127.0.0.7",
+		"::ffff:127.0.0.1",
+		"::ffff:127.0.0.7",
+		"::1",
+		"0:0:0:0:0:0:0:1",
+	}
+	ports := []string{
+		"",
+		"80",
+		"443",
+	}
+
+	for _, host := range hosts {
+		for _, port := range ports {
+			if port == "" && strings.HasPrefix(host, "::ffff:") {
+				continue
+			}
+
+			addr := host
+			if port != "" {
+				addr = net.JoinHostPort(host, port)
+			}
+			t.Run(addr, func(t *testing.T) {
+				req, err := http.NewRequest("GET", "http://"+addr, http.NoBody)
+				if err != nil {
+					t.Fatal(err)
+				}
+				if !IsLocalHost(req, nil) {
+					t.Fatal("expected true")
+				}
+			})
+		}
+	}
+}