gonotes/internal/middleware/reject_anon.go

// Middleware designed to reject requests from anon users unless from 'safe'
// IP addresses

package middleware

import (
	"errors"
	"fmt"
	"log"
	"net"
	"net/http"
	"strings"

	"forgejo.gwairfelin.com/max/gonotes/internal/conf"
)

type netList []net.IPNet

const ipHeader = "x-forwarded-for"

// Check if any IPNet in the netList contains the given IP
func (n *netList) Contains(ip net.IP) bool {
	for _, net := range *n {
		if contains := net.Contains(ip); contains {
			return true
		}
	}
	return false
}

// Redirect to redirect url any request where the user is anon and the request
// does not appear to come from a safe origin
func RejectAnonMiddleware(redirect string, next http.Handler) http.Handler {
	safeOriginNets := make(netList, 0, len(conf.Conf.AnonCIDRs))

	for _, cidr := range conf.Conf.AnonCIDRs {
		_, net, err := net.ParseCIDR(cidr)

		if err != nil {
			log.Printf("ignoring invalid cidr: %s", err)
			continue
		}

		safeOriginNets = append(safeOriginNets, *net)
	}

	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		user := r.Context().Value(ContextKey("user")).(string)

		originIP, err := getOriginIP(r)

		if err != nil {
			log.Printf("unable to check origin ip: %s", err)
			http.Redirect(w, r, redirect, http.StatusTemporaryRedirect)
			return
		}

		log.Printf("origin ip: %s", originIP)
		safeOrigin := safeOriginNets.Contains(originIP)

		if user == "anon" && !safeOrigin {
			http.Redirect(w, r, redirect, http.StatusTemporaryRedirect)
			return
		}
		next.ServeHTTP(w, r)
	})
}

// Get the origin ip from the x-forwarded-for header, or the source of
// the request if not available
func getOriginIP(r *http.Request) (net.IP, error) {
	sourceIpHeader, ok := r.Header[http.CanonicalHeaderKey(ipHeader)]

	if !ok {
		addrParts := strings.Split(r.RemoteAddr, ":")

		if len(addrParts) == 0 {
			return nil, errors.New("no source ip available")
		}

		ip := net.ParseIP(addrParts[0])
		if ip == nil {
			return nil, fmt.Errorf("ip could not be parsed: %s", addrParts[0])
		}
		return ip, nil
	}

	if len(sourceIpHeader) != 1 {
		return nil, fmt.Errorf("header has more than 1 value: %s=%v", ipHeader, sourceIpHeader)
	}

	ips := strings.Split(sourceIpHeader[0], ",")
	ip := net.ParseIP(ips[0])
	if ip == nil {
		return nil, fmt.Errorf("not parseable as ip: %s", ips[0])
	}

	return ip, nil
}