text: /**
   * @file
   *
   * IPv6 address scopes, zones, and scoping policy.
   *
   * This header provides the means to implement support for IPv6 address scopes,
   * as per RFC 4007. An address scope can be either global or more constrained.
   * In lwIP, we say that an address "has a scope" or "is scoped" when its scope
   * is constrained, in which case the address is meaningful only in a specific
   * "zone." For unicast addresses, only link-local addresses have a scope; in
   * that case, the scope is the link. For multicast addresses, there are various
   * scopes defined by RFC 4007 and others. For any constrained scope, a system
   * must establish a (potentially one-to-many) mapping between zones and local
   * interfaces. For example, a link-local address is valid on only one link (its
   * zone). That link may be attached to one or more local interfaces. The
   * decisions on which scopes are constrained and the mapping between zones and
   * interfaces is together what we refer to as the "scoping policy" - more on
   * this in a bit.
   *
   * In lwIP, each IPv6 address has an associated zone index. This zone index may
   * be set to "no zone" (IP6_NO_ZONE, 0) or an actual zone. We say that an
   * address "has a zone" or "is zoned" when its zone index is *not* set to "no
   * zone." In lwIP, in principle, each address should be "properly zoned," which
   * means that if the address has a zone if and only if has a scope. As such, it
   * is a rule that an unscoped (e.g., global) address must never have a zone.
   * Even though one could argue that there is always one zone even for global
   * scopes, this rule exists for implementation simplicity. Violation of the
   * rule will trigger assertions or otherwise result in undesired behavior.
   *
   * Backward compatibility prevents us from requiring that applications always
   * provide properly zoned addresses. We do enforce the rule that the in the
   * lwIP link layer (everything below netif->output_ip6() and in particular ND6)
   * *all* addresses are properly zoned. Thus, on the output paths down the
   * stack, various places deal with the case of addresses that lack a zone.
   * Some of them are best-effort for efficiency (e.g. the PCB bind and connect
   * API calls' attempts to add missing zones); ultimately the IPv6 output
   * handler (@ref ip6_output_if_src) will set a zone if necessary.
   *
   * Aside from dealing with scoped addresses lacking a zone, a proper IPv6
   * implementation must also ensure that a packet with a scoped source and/or
   * destination address does not leave its zone. This is currently implemented
   * in the input and forward functions. However, for output, these checks are
   * deliberately omitted in order to keep the implementation lightweight. The
   * routing algorithm in @ref ip6_route will take decisions such that it will
   * not cause zone violations unless the application sets bad addresses, though.
   *
   * In terms of scoping policy, lwIP implements the default policy from RFC 4007
   * using macros in this file. This policy considers link-local unicast
   * addresses and (only) interface-local and link-local multicast addresses as
   * having a scope. For all these addresses, the zone is equal to the interface.
   * As shown below in this file, it is possible to implement a custom policy.
   */
  
  /*
   * Copyright (c) 2017 The MINIX 3 Project.
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without modification,
   * are permitted provided that the following conditions are met:
   *
   * 1. Redistributions of source code must retain the above copyright notice,
   *    this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright notice,
   *    this list of conditions and the following disclaimer in the documentation
   *    and/or other materials provided with the distribution.
   * 3. The name of the author may not be used to endorse or promote products
   *    derived from this software without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
   * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
   * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
   * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
   * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
   * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
   * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
   * OF SUCH DAMAGE.
   *
   * This file is part of the lwIP TCP/IP stack.
   *
   * Author: David van Moolenbroek <david@minix3.org>
   *
   */
  #ifndef LWIP_HDR_IP6_ZONE_H
  #define LWIP_HDR_IP6_ZONE_H
  
  #ifdef __cplusplus
  extern "C" {
  #endif
  
  /**
   * @defgroup ip6_zones IPv6 Zones
   * @ingroup ip6
   * @{
   */
  
  #if LWIP_IPV6  /* don't build if not configured for use in lwipopts.h */
  
  /** Identifier for "no zone". */
  #define IP6_NO_ZONE 0
  
  #if LWIP_IPV6_SCOPES
  
  /** Zone initializer for static IPv6 address initialization, including comma. */
  #define IPADDR6_ZONE_INIT , IP6_NO_ZONE
  
  /** Return the zone index of the given IPv6 address; possibly "no zone". */
  #define ip6_addr_zone(ip6addr) ((ip6addr)->zone)
  
  /** Does the given IPv6 address have a zone set? (0/1) */
  #define ip6_addr_has_zone(ip6addr) (ip6_addr_zone(ip6addr) != IP6_NO_ZONE)
  
  /** Set the zone field of an IPv6 address to a particular value. */
  #define ip6_addr_set_zone(ip6addr, zone_idx) ((ip6addr)->zone = (zone_idx))
  
  /** Clear the zone field of an IPv6 address, setting it to "no zone". */
  #define ip6_addr_clear_zone(ip6addr) ((ip6addr)->zone = IP6_NO_ZONE)
  
  /** Copy the zone field from the second IPv6 address to the first one. */
  #define ip6_addr_copy_zone(ip6addr1, ip6addr2) ((ip6addr1).zone = (ip6addr2).zone)
  
  /** Is the zone field of the given IPv6 address equal to the given zone index? (0/1) */
  #define ip6_addr_equals_zone(ip6addr, zone_idx) ((ip6addr)->zone == (zone_idx))
  
  /** Are the zone fields of the given IPv6 addresses equal? (0/1)
   * This macro must only be used on IPv6 addresses of the same scope. */
  #define ip6_addr_cmp_zone(ip6addr1, ip6addr2) ((ip6addr1)->zone == (ip6addr2)->zone)
  
  /** Symbolic constants for the 'type' parameters in some of the macros.
   * These exist for efficiency only, allowing the macros to avoid certain tests
   * when the address is known not to be of a certain type. Dead code elimination
   * will do the rest. IP6_MULTICAST is supported but currently not optimized.
   * @see ip6_addr_has_scope, ip6_addr_assign_zone, ip6_addr_lacks_zone.
   */
  enum lwip_ipv6_scope_type
  {
    /** Unknown */
    IP6_UNKNOWN   = 0,
    /** Unicast */
    IP6_UNICAST   = 1,
    /** Multicast */
    IP6_MULTICAST = 2
  };
  
  /** IPV6_CUSTOM_SCOPES: together, the following three macro definitions,
   * @ref ip6_addr_has_scope, @ref ip6_addr_assign_zone, and
   * @ref ip6_addr_test_zone, completely define the lwIP scoping policy.
   * The definitions below implement the default policy from RFC 4007 Sec. 6.
   * Should an implementation desire to implement a different policy, it can
   * define IPV6_CUSTOM_SCOPES to 1 and supply its own definitions for the three
   * macros instead.
   */
  #ifndef IPV6_CUSTOM_SCOPES
  #define IPV6_CUSTOM_SCOPES 0
  #endif /* !IPV6_CUSTOM_SCOPES */
  
  #if !IPV6_CUSTOM_SCOPES
  
  /**
   * Determine whether an IPv6 address has a constrained scope, and as such is
   * meaningful only if accompanied by a zone index to identify the scope's zone.
   * The given address type may be used to eliminate at compile time certain
   * checks that will evaluate to false at run time anyway.
   *
   * This default implementation follows the default model of RFC 4007, where
   * only interface-local and link-local scopes are defined.
   *
   * Even though the unicast loopback address does have an implied link-local
   * scope, in this implementation it does not have an explicitly assigned zone
   * index. As such it should not be tested for in this macro.
   *
   * @param ip6addr the IPv6 address (const); only its address part is examined.
   * @param type address type; see @ref lwip_ipv6_scope_type.
   * @return 1 if the address has a constrained scope, 0 if it does not.
   */
  #define ip6_addr_has_scope(ip6addr, type) \
    (ip6_addr_islinklocal(ip6addr) || (((type) != IP6_UNICAST) && \
     (ip6_addr_ismulticast_iflocal(ip6addr) || \
  	ip6_addr_ismulticast_linklocal(ip6addr))))
  
  /**
   * Assign a zone index to an IPv6 address, based on a network interface. If the
   * given address has a scope, the assigned zone index is that scope's zone of
   * the given netif; otherwise, the assigned zone index is "no zone".
   *
   * This default implementation follows the default model of RFC 4007, where
   * only interface-local and link-local scopes are defined, and the zone index
   * of both of those scopes always equals the index of the network interface.
   * As such, this default implementation need not distinguish between different
   * constrained scopes when assigning the zone.
   *
   * @param ip6addr the IPv6 address; its address part is examined, and its zone
   *                index is assigned.
   * @param type address type; see @ref lwip_ipv6_scope_type.
   * @param netif the network interface (const).
   */
  #define ip6_addr_assign_zone(ip6addr, type, netif) \
  	(ip6_addr_set_zone((ip6addr), \
  	  ip6_addr_has_scope((ip6addr), (type)) ? netif_get_index(netif) : 0))
  
  /**
   * Test whether an IPv6 address is "zone-compatible" with a network interface.
   * That is, test whether the network interface is part of the zone associated
   * with the address. For efficiency, this macro is only ever called if the
   * given address is either scoped or zoned, and thus, it need not test this.
   * If an address is scoped but not zoned, or zoned and not scoped, it is
   * considered not zone-compatible with any netif.
   *
   * This default implementation follows the default model of RFC 4007, where
   * only interface-local and link-local scopes are defined, and the zone index
   * of both of those scopes always equals the index of the network interface.
   * As such, there is always only one matching netif for a specific zone index,
   * but all call sites of this macro currently support multiple matching netifs
   * as well (at no additional expense in the common case).
   *
   * @param ip6addr the IPv6 address (const).
   * @param netif the network interface (const).
   * @return 1 if the address is scope-compatible with the netif, 0 if not.
   */
  #define ip6_addr_test_zone(ip6addr, netif) \
  	(ip6_addr_equals_zone((ip6addr), netif_get_index(netif)))
  
  #endif /* !IPV6_CUSTOM_SCOPES */
  
  /** Does the given IPv6 address have a scope, and as such should also have a
   * zone to be meaningful, but does not actually have a zone? (0/1) */
  #define ip6_addr_lacks_zone(ip6addr, type) \
  	(!ip6_addr_has_zone(ip6addr) && ip6_addr_has_scope((ip6addr), (type)))
  
  /**
   * Try to select a zone for a scoped address that does not yet have a zone.
   * Called from PCB bind and connect routines, for two reasons: 1) to save on
   * this (relatively expensive) selection for every individual packet route
   * operation and 2) to allow the application to obtain the selected zone from
   * the PCB as is customary for e.g. getsockname/getpeername BSD socket calls.
   *
   * Ideally, callers would always supply a properly zoned address, in which case
   * this function would not be needed. It exists both for compatibility with the
   * BSD socket API (which accepts zoneless destination addresses) and for
   * backward compatibility with pre-scoping lwIP code.
   *
   * It may be impossible to select a zone, e.g. if there are no netifs.  In that
   * case, the address's zone field will be left as is.
   *
   * @param dest the IPv6 address for which to select and set a zone.
   * @param src source IPv6 address (const); may be equal to dest.
   */
  #define ip6_addr_select_zone(dest, src) do { struct netif *selected_netif; \
    selected_netif = ip6_route((src), (dest)); \
    if (selected_netif != NULL) { \
  	ip6_addr_assign_zone((dest), IP6_UNKNOWN, selected_netif); \
    } } while (0)
  
  /**
   * @}
   */
  
  #else /* LWIP_IPV6_SCOPES */
  
  #define IPADDR6_ZONE_INIT
  #define ip6_addr_zone(ip6addr) (IP6_NO_ZONE)
  #define ip6_addr_has_zone(ip6addr) (0)
  #define ip6_addr_set_zone(ip6addr, zone_idx)
  #define ip6_addr_clear_zone(ip6addr)
  #define ip6_addr_copy_zone(ip6addr1, ip6addr2)
  #define ip6_addr_equals_zone(ip6addr, zone_idx) (1)
  #define ip6_addr_cmp_zone(ip6addr1, ip6addr2) (1)
  #define IPV6_CUSTOM_SCOPES 0
  #define ip6_addr_has_scope(ip6addr, type) (0)
  #define ip6_addr_assign_zone(ip6addr, type, netif)
  #define ip6_addr_test_zone(ip6addr, netif) (1)
  #define ip6_addr_lacks_zone(ip6addr, type) (0)
  #define ip6_addr_select_zone(ip6addr, src)
  
  #endif /* LWIP_IPV6_SCOPES */
  
  #if LWIP_IPV6_SCOPES && LWIP_IPV6_SCOPES_DEBUG
  
  /** Verify that the given IPv6 address is properly zoned. */
  #define IP6_ADDR_ZONECHECK(ip6addr) LWIP_ASSERT("IPv6 zone check failed", \
  	ip6_addr_has_scope(ip6addr, IP6_UNKNOWN) == ip6_addr_has_zone(ip6addr))
  
  /** Verify that the given IPv6 address is properly zoned for the given netif. */
  #define IP6_ADDR_ZONECHECK_NETIF(ip6addr, netif) LWIP_ASSERT("IPv6 netif zone check failed", \
  	ip6_addr_has_scope(ip6addr, IP6_UNKNOWN) ? \
  	(ip6_addr_has_zone(ip6addr) && \
  	 (((netif) == NULL) || ip6_addr_test_zone((ip6addr), (netif)))) : \
  	!ip6_addr_has_zone(ip6addr))
  
  #else /* LWIP_IPV6_SCOPES && LWIP_IPV6_SCOPES_DEBUG */
  
  #define IP6_ADDR_ZONECHECK(ip6addr)
  #define IP6_ADDR_ZONECHECK_NETIF(ip6addr, netif)
  
  #endif /* LWIP_IPV6_SCOPES && LWIP_IPV6_SCOPES_DEBUG */
  
  #endif /* LWIP_IPV6 */
  
  #ifdef __cplusplus
  }
  #endif
  
  #endif /* LWIP_HDR_IP6_ZONE_H */
  