Add support for ipv6 subnet in ipStrategy

pkg/ip/strategy.go

@@ -3,6 +3,7 @@ package ip
 import (
 	"net"
 	"net/http"
+	"net/netip"
 	"strings"
 )
 
@@ -16,7 +17,10 @@ type Strategy interface {
 }
 
 // RemoteAddrStrategy a strategy that always return the remote address.
-type RemoteAddrStrategy struct{}
+type RemoteAddrStrategy struct {
+	// IPv6Subnet instructs the strategy to return the first IP of the subnet where IP belongs.
+	IPv6Subnet *int
+}
 
 // GetIP returns the selected IP.
 func (s *RemoteAddrStrategy) GetIP(req *http.Request) string {
@@ -24,15 +28,22 @@ func (s *RemoteAddrStrategy) GetIP(req *http.Request) string {
 	if err != nil {
 		return req.RemoteAddr
 	}
+
+	if s.IPv6Subnet != nil {
+		return getIPv6SubnetIP(ip, *s.IPv6Subnet)
+	}
+
 	return ip
 }
 
 // DepthStrategy a strategy based on the depth inside the X-Forwarded-For from right to left.
 type DepthStrategy struct {
 	Depth int
+	// IPv6Subnet instructs the strategy to return the first IP of the subnet where IP belongs.
+	IPv6Subnet *int
 }
 
-// GetIP return the selected IP.
+// GetIP returns the selected IP.
 func (s *DepthStrategy) GetIP(req *http.Request) string {
 	xff := req.Header.Get(xForwardedFor)
 	xffs := strings.Split(xff, ",")
@@ -40,7 +51,14 @@ func (s *DepthStrategy) GetIP(req *http.Request) string {
 	if len(xffs) < s.Depth {
 		return ""
 	}
-	return strings.TrimSpace(xffs[len(xffs)-s.Depth])
+
+	ip := strings.TrimSpace(xffs[len(xffs)-s.Depth])
+
+	if s.IPv6Subnet != nil {
+		return getIPv6SubnetIP(ip, *s.IPv6Subnet)
+	}
+
+	return ip
 }
 
 // PoolStrategy is a strategy based on an IP Checker.
@@ -72,3 +90,23 @@ func (s *PoolStrategy) GetIP(req *http.Request) string {
 
 	return ""
 }
+
+// getIPv6SubnetIP returns the IPv6 subnet IP.
+// It returns the original IP when it is not an IPv6, or if parsing the IP has failed with an error.
+func getIPv6SubnetIP(ip string, ipv6Subnet int) string {
+	addr, err := netip.ParseAddr(ip)
+	if err != nil {
+		return ip
+	}
+
+	if !addr.Is6() {
+		return ip
+	}
+
+	prefix, err := addr.Prefix(ipv6Subnet)
+	if err != nil {
+		return ip
+	}
+
+	return prefix.Addr().String()
+}