Fix #273 (#277), adding FIREWALL_OUTBOUND_SUBNETS

internal/params/routing.go

@@ -0,0 +1,31 @@
+package params
+
+import (
+	"fmt"
+	"net"
+	"strings"
+)
+
+// GetOutboundSubnets obtains the CIDR subnets from the comma separated list of the
+// environment variable FIREWALL_OUTBOUND_SUBNETS.
+func (r *reader) GetOutboundSubnets() (outboundSubnets []net.IPNet, err error) {
+	const key = "FIREWALL_OUTBOUND_SUBNETS"
+	s, err := r.envParams.GetEnv(key)
+	if err != nil {
+		return nil, err
+	} else if s == "" {
+		return nil, nil
+	}
+	subnets := strings.Split(s, ",")
+	for _, subnet := range subnets {
+		_, cidr, err := net.ParseCIDR(subnet)
+		if err != nil {
+			return nil, fmt.Errorf("cannot parse outbound subnet %q from environment variable with key %s: %w", subnet, key, err)
+		} else if cidr == nil {
+			return nil, fmt.Errorf("cannot parse outbound subnet %q from environment variable with key %s: subnet is nil",
+				subnet, key)
+		}
+		outboundSubnets = append(outboundSubnets, *cidr)
+	}
+	return outboundSubnets, nil
+}