Add reject anon middleware

internal/middleware/reject_anon.go

@@ -0,0 +1,99 @@
+// Middleware designed to reject requests from anon users unless from 'safe'
+// IP addresses
+
+package middleware
+
+import (
+	"errors"
+	"fmt"
+	"log"
+	"net"
+	"net/http"
+	"strings"
+)
+
+type netList []net.IPNet
+
+var safeCIDRs = [...]string{"192.168.0.0/23", "10.0.0.0/24", "2001:8b0:f70:546d::/64"}
+
+var safeOriginNets netList
+
+const ipHeader = "x-forwarded-for"
+
+func init() {
+	safeOriginNets = make([]net.IPNet, 0, len(safeCIDRs))
+	for _, cidr := range safeCIDRs {
+		_, net, err := net.ParseCIDR(cidr)
+
+		if err != nil {
+			log.Printf("ignoring invalid cidr: %s", err)
+			continue
+		}
+
+		safeOriginNets = append(safeOriginNets, *net)
+	}
+}
+
+func (n *netList) Contains(ip net.IP) bool {
+	for _, net := range *n {
+		if contains := net.Contains(ip); contains {
+			return true
+		}
+	}
+	return false
+}
+
+func RejectAnonMiddleware(redirect string, next http.Handler) http.Handler {
+	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
+}