Add DNSBL querying in conditions

utils/dnsbl.go

@@ -0,0 +1,75 @@
+package utils
+
+import (
+	"context"
+	"net"
+	"strconv"
+)
+
+type DNSBL struct {
+	target   string
+	resolver *net.Resolver
+}
+
+func NewDNSBL(target string, resolver *net.Resolver) *DNSBL {
+	if resolver == nil {
+		resolver = net.DefaultResolver
+	}
+	return &DNSBL{
+		target:   target,
+		resolver: resolver,
+	}
+}
+
+var nibbleTable = [16]byte{
+	'0', '1', '2', '3',
+	'4', '5', '6', '7',
+	'8', '9', 'a', 'b',
+	'c', 'd', 'e', 'f',
+}
+
+type DNSBLResponse uint8
+
+func (r DNSBLResponse) Bad() bool {
+	return r != ResponseGood && r != ResponseUnknown
+}
+
+const (
+	ResponseGood    = DNSBLResponse(0)
+	ResponseUnknown = DNSBLResponse(255)
+)
+
+func (bl DNSBL) Lookup(ctx context.Context, ip net.IP) (DNSBLResponse, error) {
+	var target []byte
+	if ip4 := ip.To4(); ip4 != nil {
+		// max length preallocate
+		target = make([]byte, 0, len(bl.target)+1+len(ip4)*4)
+
+		for i := len(ip4) - 1; i >= 0; i-- {
+			target = strconv.AppendUint(target, uint64(ip4[i]), 10)
+			target = append(target, '.')
+		}
+	} else {
+		// IPv6
+		// max length preallocate
+		target = make([]byte, 0, len(bl.target)+1+len(ip)*4)
+
+		for i := len(ip) - 1; i >= 0; i-- {
+			target = append(target, nibbleTable[ip[i]&0xf], '.', ip[i]>>4, '.')
+		}
+	}
+
+	target = append(target, bl.target...)
+
+	ips, err := bl.resolver.LookupIP(ctx, "ip4", string(target))
+	if err != nil {
+		return ResponseUnknown, err
+	}
+
+	for _, ip := range ips {
+		ip4 := ip.To4()
+		return DNSBLResponse(ip4[len(ip4)-1]), nil
+	}
+
+	return ResponseUnknown, nil
+}