fix #1842

Warn about banning a single IPv6 address

irc/flatip/flatip.go

 	return cidr.IP == maskedIP
 }
 
+func (cidr IPNet) Size() (ones, bits int) {
+	if cidr.IP.IsIPv4() {
+		return int(cidr.PrefixLen) - 96, 32
+	} else {
+		return int(cidr.PrefixLen), 128
+	}
+}
+
 // FromNetIPnet converts a net.IPNet into an IPNet.
 func FromNetIPNet(network net.IPNet) (result IPNet) {
 	ones, _ := network.Mask.Size()

irc/flatip/flatip_test.go

 
 import (
 	"bytes"
+	"fmt"
 	"math/rand"
 	"net"
+	"reflect"
 	"testing"
 	"time"
 )
 	}
 }
 
+func assertEqual(found, expected interface{}) {
+	if !reflect.DeepEqual(found, expected) {
+		panic(fmt.Sprintf("expected %#v, found %#v", expected, found))
+	}
+}
+
+func TestSize(t *testing.T) {
+	_, net, err := ParseCIDR("8.8.8.8/24")
+	if err != nil {
+		panic(err)
+	}
+	ones, bits := net.Size()
+	assertEqual(ones, 24)
+	assertEqual(bits, 32)
+
+	_, net, err = ParseCIDR("2001::0db8/64")
+	if err != nil {
+		panic(err)
+	}
+	ones, bits = net.Size()
+	assertEqual(ones, 64)
+	assertEqual(bits, 128)
+
+	_, net, err = ParseCIDR("2001::0db8/96")
+	if err != nil {
+		panic(err)
+	}
+	ones, bits = net.Size()
+	assertEqual(ones, 96)
+	assertEqual(bits, 128)
+}
+
 func TestMasking(t *testing.T) {
 	for _, ipstr := range testIPStrs {
 		doMaskingTest(easyParseIP(ipstr), t)

irc/uban.go

 }
 
 func ubanInfoCIDR(client *Client, target ubanTarget, rb *ResponseBuffer) {
-	if target.cidr.PrefixLen == 128 {
+	config := client.server.Config()
+	// show connection limiter/throttler state if this CIDR is entirely
+	// contained in a single limiter/throttler bucket:
+	ones, bits := target.cidr.Size()
+	showLimiter := (bits == 32 && ones >= config.Server.IPLimits.CidrLenIPv4) ||
+		(bits == 128 && ones >= config.Server.IPLimits.CidrLenIPv6)
+	sendMaskWarning := (bits == 128 && ones > config.Server.IPLimits.CidrLenIPv6)
+	if showLimiter {
 		netName, status := client.server.connectionLimiter.Status(target.cidr.IP)
 		if status.Exempt {
 			rb.Notice(fmt.Sprintf(client.t("IP %s is exempt from connection limits"), target.cidr.IP.String()))
 			rb.Notice(line)
 		}
 	}
+	if sendMaskWarning {
+		rb.Notice(fmt.Sprintf(client.t("Note: try evaluating a wider IPv6 CIDR like %s/%d"),
+			target.cidr.IP.String(), config.Server.IPLimits.CidrLenIPv6))
+	}
 }
 
 func ubanInfoNickmask(client *Client, target ubanTarget, rb *ResponseBuffer) {