udp.c

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/*
 * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
 * 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: Adam Dunkels <adam@sics.se>
 *
 */


/* udp.c
 *
 * The code for the User Datagram Protocol UDP & UDPLite (RFC 3828).
 *
 */

/* @todo Check the use of '(struct udp_pcb).chksum_len_rx'!
 */

#include "lwip/opt.h"

#if LWIP_UDP /* don't build if not configured for use in lwipopts.h */

#include "lwip/udp.h"
#include "lwip/def.h"
#include "lwip/memp.h"
#include "lwip/inet_chksum.h"
#include "lwip/ip_addr.h"
#include "lwip/netif.h"
#include "lwip/icmp.h"
#include "lwip/stats.h"
#include "lwip/snmp.h"
#include "arch/perf.h"
#include "lwip/dhcp.h"

#include <string.h>

/* The list of UDP PCBs */
/* exported in udp.h (was static) */
struct udp_pcb *udp_pcbs;

void
udp_input(struct pbuf *p, struct netif *inp)
{
  struct udp_hdr *udphdr;
  struct udp_pcb *pcb, *prev;
  struct udp_pcb *uncon_pcb;
  struct ip_hdr *iphdr;
  u16_t src, dest;
  u8_t local_match;
  u8_t broadcast;

  PERF_START;

  UDP_STATS_INC(udp.recv);

  iphdr = (struct ip_hdr *)p->payload;

  /* Check minimum length (IP header + UDP header)
   * and move payload pointer to UDP header */
  if (p->tot_len < (IPH_HL(iphdr) * 4 + UDP_HLEN) || pbuf_header(p, -(s16_t)(IPH_HL(iphdr) * 4))) {
    /* drop short packets */
    LWIP_DEBUGF(UDP_DEBUG,
                ("udp_input: short UDP datagram (%"U16_F" bytes) discarded\n", p->tot_len));
    UDP_STATS_INC(udp.lenerr);
    UDP_STATS_INC(udp.drop);
    snmp_inc_udpinerrors();
    pbuf_free(p);
    goto end;
  }

  udphdr = (struct udp_hdr *)p->payload;

  /* is broadcast packet ? */
  broadcast = ip_addr_isbroadcast(&current_iphdr_dest, inp);

  LWIP_DEBUGF(UDP_DEBUG, ("udp_input: received datagram of length %"U16_F"\n", p->tot_len));

  /* convert src and dest ports to host byte order */
  src = ntohs(udphdr->src);
  dest = ntohs(udphdr->dest);

  udp_debug_print(udphdr);

  /* print the UDP source and destination */
  LWIP_DEBUGF(UDP_DEBUG,
              ("udp (%"U16_F".%"U16_F".%"U16_F".%"U16_F", %"U16_F") <-- "
               "(%"U16_F".%"U16_F".%"U16_F".%"U16_F", %"U16_F")\n",
               ip4_addr1_16(&iphdr->dest), ip4_addr2_16(&iphdr->dest),
               ip4_addr3_16(&iphdr->dest), ip4_addr4_16(&iphdr->dest), ntohs(udphdr->dest),
               ip4_addr1_16(&iphdr->src), ip4_addr2_16(&iphdr->src),
               ip4_addr3_16(&iphdr->src), ip4_addr4_16(&iphdr->src), ntohs(udphdr->src)));

#if LWIP_DHCP
  pcb = NULL;
  /* when LWIP_DHCP is active, packets to DHCP_CLIENT_PORT may only be processed by
     the dhcp module, no other UDP pcb may use the local UDP port DHCP_CLIENT_PORT */
  if (dest == DHCP_CLIENT_PORT) {
    /* all packets for DHCP_CLIENT_PORT not coming from DHCP_SERVER_PORT are dropped! */
    if (src == DHCP_SERVER_PORT) {
      if ((inp->dhcp != NULL) && (inp->dhcp->pcb != NULL)) {
        /* accept the packe if 
           (- broadcast or directed to us) -> DHCP is link-layer-addressed, local ip is always ANY!
           - inp->dhcp->pcb->remote == ANY or iphdr->src */
        if ((ip_addr_isany(&inp->dhcp->pcb->remote_ip) ||
           ip_addr_cmp(&(inp->dhcp->pcb->remote_ip), &current_iphdr_src))) {
          pcb = inp->dhcp->pcb;
        }
      }
    }
  } else
#endif /* LWIP_DHCP */
  {
    prev = NULL;
    local_match = 0;
    uncon_pcb = NULL;
    /* Iterate through the UDP pcb list for a matching pcb.
     * 'Perfect match' pcbs (connected to the remote port & ip address) are
     * preferred. If no perfect match is found, the first unconnected pcb that
     * matches the local port and ip address gets the datagram. */
    for (pcb = udp_pcbs; pcb != NULL; pcb = pcb->next) {
      local_match = 0;
      /* print the PCB local and remote address */
      LWIP_DEBUGF(UDP_DEBUG,
                  ("pcb (%"U16_F".%"U16_F".%"U16_F".%"U16_F", %"U16_F") --- "
                   "(%"U16_F".%"U16_F".%"U16_F".%"U16_F", %"U16_F")\n",
                   ip4_addr1_16(&pcb->local_ip), ip4_addr2_16(&pcb->local_ip),
                   ip4_addr3_16(&pcb->local_ip), ip4_addr4_16(&pcb->local_ip), pcb->local_port,
                   ip4_addr1_16(&pcb->remote_ip), ip4_addr2_16(&pcb->remote_ip),
                   ip4_addr3_16(&pcb->remote_ip), ip4_addr4_16(&pcb->remote_ip), pcb->remote_port));

      /* compare PCB local addr+port to UDP destination addr+port */
      if ((pcb->local_port == dest) &&
          ((!broadcast && ip_addr_isany(&pcb->local_ip)) ||
           ip_addr_cmp(&(pcb->local_ip), &current_iphdr_dest) ||
#if LWIP_IGMP
           ip_addr_ismulticast(&current_iphdr_dest) ||
#endif /* LWIP_IGMP */
#if IP_SOF_BROADCAST_RECV
           (broadcast && (pcb->so_options & SOF_BROADCAST)))) {
#else  /* IP_SOF_BROADCAST_RECV */
           (broadcast))) {
#endif /* IP_SOF_BROADCAST_RECV */
        local_match = 1;
        if ((uncon_pcb == NULL) && 
            ((pcb->flags & UDP_FLAGS_CONNECTED) == 0)) {
          /* the first unconnected matching PCB */
          uncon_pcb = pcb;
        }
      }
      /* compare PCB remote addr+port to UDP source addr+port */
      if ((local_match != 0) &&
          (pcb->remote_port == src) &&
          (ip_addr_isany(&pcb->remote_ip) ||
           ip_addr_cmp(&(pcb->remote_ip), &current_iphdr_src))) {
        /* the first fully matching PCB */
        if (prev != NULL) {
          /* move the pcb to the front of udp_pcbs so that is
             found faster next time */
          prev->next = pcb->next;
          pcb->next = udp_pcbs;
          udp_pcbs = pcb;
        } else {
          UDP_STATS_INC(udp.cachehit);
        }
        break;
      }
      prev = pcb;
    }
    /* no fully matching pcb found? then look for an unconnected pcb */
    if (pcb == NULL) {
      pcb = uncon_pcb;
    }
  }

  /* Check checksum if this is a match or if it was directed at us. */
  if (pcb != NULL || ip_addr_cmp(&inp->ip_addr, &current_iphdr_dest)) {
    LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_TRACE, ("udp_input: calculating checksum\n"));
#if LWIP_UDPLITE
    if (IPH_PROTO(iphdr) == IP_PROTO_UDPLITE) {
      /* Do the UDP Lite checksum */
#if CHECKSUM_CHECK_UDP
      u16_t chklen = ntohs(udphdr->len);
      if (chklen < sizeof(struct udp_hdr)) {
        if (chklen == 0) {
          /* For UDP-Lite, checksum length of 0 means checksum
             over the complete packet (See RFC 3828 chap. 3.1) */
          chklen = p->tot_len;
        } else {
          /* At least the UDP-Lite header must be covered by the
             checksum! (Again, see RFC 3828 chap. 3.1) */
          UDP_STATS_INC(udp.chkerr);
          UDP_STATS_INC(udp.drop);
          snmp_inc_udpinerrors();
          pbuf_free(p);
          goto end;
        }
      }
      if (inet_chksum_pseudo_partial(p, &current_iphdr_src, &current_iphdr_dest,
                             IP_PROTO_UDPLITE, p->tot_len, chklen) != 0) {
       LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
                   ("udp_input: UDP Lite datagram discarded due to failing checksum\n"));
        UDP_STATS_INC(udp.chkerr);
        UDP_STATS_INC(udp.drop);
        snmp_inc_udpinerrors();
        pbuf_free(p);
        goto end;
      }
#endif /* CHECKSUM_CHECK_UDP */
    } else
#endif /* LWIP_UDPLITE */
    {
#if CHECKSUM_CHECK_UDP
      if (udphdr->chksum != 0) {
        if (inet_chksum_pseudo(p, ip_current_src_addr(), ip_current_dest_addr(),
                               IP_PROTO_UDP, p->tot_len) != 0) {
          LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
                      ("udp_input: UDP datagram discarded due to failing checksum\n"));
          UDP_STATS_INC(udp.chkerr);
          UDP_STATS_INC(udp.drop);
          snmp_inc_udpinerrors();
          pbuf_free(p);
          goto end;
        }
      }
#endif /* CHECKSUM_CHECK_UDP */
    }
    if(pbuf_header(p, -UDP_HLEN)) {
      /* Can we cope with this failing? Just assert for now */
      LWIP_ASSERT("pbuf_header failed\n", 0);
      UDP_STATS_INC(udp.drop);
      snmp_inc_udpinerrors();
      pbuf_free(p);
      goto end;
    }
    if (pcb != NULL) {
      snmp_inc_udpindatagrams();
#if SO_REUSE && SO_REUSE_RXTOALL
      if ((broadcast || ip_addr_ismulticast(&current_iphdr_dest)) &&
          ((pcb->so_options & SOF_REUSEADDR) != 0)) {
        /* pass broadcast- or multicast packets to all multicast pcbs
           if SOF_REUSEADDR is set on the first match */
        struct udp_pcb *mpcb;
        u8_t p_header_changed = 0;
        for (mpcb = udp_pcbs; mpcb != NULL; mpcb = mpcb->next) {
          if (mpcb != pcb) {
            /* compare PCB local addr+port to UDP destination addr+port */
            if ((mpcb->local_port == dest) &&
                ((!broadcast && ip_addr_isany(&mpcb->local_ip)) ||
                 ip_addr_cmp(&(mpcb->local_ip), &current_iphdr_dest) ||
#if LWIP_IGMP
                 ip_addr_ismulticast(&current_iphdr_dest) ||
#endif /* LWIP_IGMP */
#if IP_SOF_BROADCAST_RECV
                 (broadcast && (mpcb->so_options & SOF_BROADCAST)))) {
#else  /* IP_SOF_BROADCAST_RECV */
                 (broadcast))) {
#endif /* IP_SOF_BROADCAST_RECV */
              /* pass a copy of the packet to all local matches */
              if (mpcb->recv != NULL) {
                struct pbuf *q;
                /* for that, move payload to IP header again */
                if (p_header_changed == 0) {
                  pbuf_header(p, (s16_t)((IPH_HL(iphdr) * 4) + UDP_HLEN));
                  p_header_changed = 1;
                }
                q = pbuf_alloc(PBUF_RAW, p->tot_len, PBUF_RAM);
                if (q != NULL) {
                  err_t err = pbuf_copy(q, p);
                  if (err == ERR_OK) {
                    /* move payload to UDP data */
                    pbuf_header(q, -(s16_t)((IPH_HL(iphdr) * 4) + UDP_HLEN));
                    mpcb->recv(mpcb->recv_arg, mpcb, q, ip_current_src_addr(), src);
                  }
                }
              }
            }
          }
        }
        if (p_header_changed) {
          /* and move payload to UDP data again */
          pbuf_header(p, -(s16_t)((IPH_HL(iphdr) * 4) + UDP_HLEN));
        }
      }
#endif /* SO_REUSE && SO_REUSE_RXTOALL */
      /* callback */
      if (pcb->recv != NULL) {
        /* now the recv function is responsible for freeing p */
        pcb->recv(pcb->recv_arg, pcb, p, ip_current_src_addr(), src);
      } else {
        /* no recv function registered? then we have to free the pbuf! */
        pbuf_free(p);
        goto end;
      }
    } else {
      LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_TRACE, ("udp_input: not for us.\n"));

#if LWIP_ICMP
      /* No match was found, send ICMP destination port unreachable unless
         destination address was broadcast/multicast. */
      if (!broadcast &&
          !ip_addr_ismulticast(&current_iphdr_dest)) {
        /* move payload pointer back to ip header */
        pbuf_header(p, (IPH_HL(iphdr) * 4) + UDP_HLEN);
        LWIP_ASSERT("p->payload == iphdr", (p->payload == iphdr));
        icmp_dest_unreach(p, ICMP_DUR_PORT);
      }
#endif /* LWIP_ICMP */
      UDP_STATS_INC(udp.proterr);
      UDP_STATS_INC(udp.drop);
      snmp_inc_udpnoports();
      pbuf_free(p);
    }
  } else {
    pbuf_free(p);
  }
end:
  PERF_STOP("udp_input");
}

err_t
udp_send(struct udp_pcb *pcb, struct pbuf *p)
{
  /* send to the packet using remote ip and port stored in the pcb */
  return udp_sendto(pcb, p, &pcb->remote_ip, pcb->remote_port);
}

#if LWIP_CHECKSUM_ON_COPY

err_t
udp_send_chksum(struct udp_pcb *pcb, struct pbuf *p,
                u8_t have_chksum, u16_t chksum)
{
  /* send to the packet using remote ip and port stored in the pcb */
  return udp_sendto_chksum(pcb, p, &pcb->remote_ip, pcb->remote_port,
    have_chksum, chksum);
}
#endif /* LWIP_CHECKSUM_ON_COPY */

err_t
udp_sendto(struct udp_pcb *pcb, struct pbuf *p,
  ip_addr_t *dst_ip, u16_t dst_port)
{
#if LWIP_CHECKSUM_ON_COPY
  return udp_sendto_chksum(pcb, p, dst_ip, dst_port, 0, 0);
}

err_t
udp_sendto_chksum(struct udp_pcb *pcb, struct pbuf *p, ip_addr_t *dst_ip,
                  u16_t dst_port, u8_t have_chksum, u16_t chksum)
{
#endif /* LWIP_CHECKSUM_ON_COPY */
  struct netif *netif;

  LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_TRACE, ("udp_send\n"));

  /* find the outgoing network interface for this packet */
#if LWIP_IGMP
  netif = ip_route((ip_addr_ismulticast(dst_ip))?(&(pcb->multicast_ip)):(dst_ip));
#else
  netif = ip_route(dst_ip);
#endif /* LWIP_IGMP */

  /* no outgoing network interface could be found? */
  if (netif == NULL) {
    LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("udp_send: No route to %"U16_F".%"U16_F".%"U16_F".%"U16_F"\n",
      ip4_addr1_16(dst_ip), ip4_addr2_16(dst_ip), ip4_addr3_16(dst_ip), ip4_addr4_16(dst_ip)));
    UDP_STATS_INC(udp.rterr);
    return ERR_RTE;
  }
#if LWIP_CHECKSUM_ON_COPY
  return udp_sendto_if_chksum(pcb, p, dst_ip, dst_port, netif, have_chksum, chksum);
#else /* LWIP_CHECKSUM_ON_COPY */
  return udp_sendto_if(pcb, p, dst_ip, dst_port, netif);
#endif /* LWIP_CHECKSUM_ON_COPY */
}

err_t
udp_sendto_if(struct udp_pcb *pcb, struct pbuf *p,
  ip_addr_t *dst_ip, u16_t dst_port, struct netif *netif)
{
#if LWIP_CHECKSUM_ON_COPY
  return udp_sendto_if_chksum(pcb, p, dst_ip, dst_port, netif, 0, 0);
}

err_t
udp_sendto_if_chksum(struct udp_pcb *pcb, struct pbuf *p, ip_addr_t *dst_ip,
                     u16_t dst_port, struct netif *netif, u8_t have_chksum,
                     u16_t chksum)
{
#endif /* LWIP_CHECKSUM_ON_COPY */
  struct udp_hdr *udphdr;
  ip_addr_t *src_ip;
  err_t err;
  struct pbuf *q; /* q will be sent down the stack */

#if IP_SOF_BROADCAST
  /* broadcast filter? */
  if ( ((pcb->so_options & SOF_BROADCAST) == 0) && ip_addr_isbroadcast(dst_ip, netif) ) {
    LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
      ("udp_sendto_if: SOF_BROADCAST not enabled on pcb %p\n", (void *)pcb));
    return ERR_VAL;
  }
#endif /* IP_SOF_BROADCAST */

  /* if the PCB is not yet bound to a port, bind it here */
  if (pcb->local_port == 0) {
    LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_TRACE, ("udp_send: not yet bound to a port, binding now\n"));
    err = udp_bind(pcb, &pcb->local_ip, pcb->local_port);
    if (err != ERR_OK) {
      LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS, ("udp_send: forced port bind failed\n"));
      return err;
    }
  }

  /* not enough space to add an UDP header to first pbuf in given p chain? */
  if (pbuf_header(p, UDP_HLEN)) {
    /* allocate header in a separate new pbuf */
    q = pbuf_alloc(PBUF_IP, UDP_HLEN, PBUF_RAM);
    /* new header pbuf could not be allocated? */
    if (q == NULL) {
      LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS, ("udp_send: could not allocate header\n"));
      return ERR_MEM;
    }
    if (p->tot_len != 0) {
      /* chain header q in front of given pbuf p (only if p contains data) */
      pbuf_chain(q, p);
    }
    /* first pbuf q points to header pbuf */
    LWIP_DEBUGF(UDP_DEBUG,
                ("udp_send: added header pbuf %p before given pbuf %p\n", (void *)q, (void *)p));
  } else {
    /* adding space for header within p succeeded */
    /* first pbuf q equals given pbuf */
    q = p;
    LWIP_DEBUGF(UDP_DEBUG, ("udp_send: added header in given pbuf %p\n", (void *)p));
  }
  LWIP_ASSERT("check that first pbuf can hold struct udp_hdr",
              (q->len >= sizeof(struct udp_hdr)));
  /* q now represents the packet to be sent */
  udphdr = (struct udp_hdr *)q->payload;
  udphdr->src = htons(pcb->local_port);
  udphdr->dest = htons(dst_port);
  /* in UDP, 0 checksum means 'no checksum' */
  udphdr->chksum = 0x0000; 

  /* Multicast Loop? */
#if LWIP_IGMP
  if (ip_addr_ismulticast(dst_ip) && ((pcb->flags & UDP_FLAGS_MULTICAST_LOOP) != 0)) {
    q->flags |= PBUF_FLAG_MCASTLOOP;
  }
#endif /* LWIP_IGMP */


  /* PCB local address is IP_ANY_ADDR? */
  if (ip_addr_isany(&pcb->local_ip)) {
    /* use outgoing network interface IP address as source address */
    src_ip = &(netif->ip_addr);
  } else {
    /* check if UDP PCB local IP address is correct
     * this could be an old address if netif->ip_addr has changed */
    if (!ip_addr_cmp(&(pcb->local_ip), &(netif->ip_addr))) {
      /* local_ip doesn't match, drop the packet */
      if (q != p) {
        /* free the header pbuf */
        pbuf_free(q);
        q = NULL;
        /* p is still referenced by the caller, and will live on */
      }
      return ERR_VAL;
    }
    /* use UDP PCB local IP address as source address */
    src_ip = &(pcb->local_ip);
  }

  LWIP_DEBUGF(UDP_DEBUG, ("udp_send: sending datagram of length %"U16_F"\n", q->tot_len));

#if LWIP_UDPLITE
  /* UDP Lite protocol? */
  if (pcb->flags & UDP_FLAGS_UDPLITE) {
    u16_t chklen, chklen_hdr;
    LWIP_DEBUGF(UDP_DEBUG, ("udp_send: UDP LITE packet length %"U16_F"\n", q->tot_len));
    /* set UDP message length in UDP header */
    chklen_hdr = chklen = pcb->chksum_len_tx;
    if ((chklen < sizeof(struct udp_hdr)) || (chklen > q->tot_len)) {
      if (chklen != 0) {
        LWIP_DEBUGF(UDP_DEBUG, ("udp_send: UDP LITE pcb->chksum_len is illegal: %"U16_F"\n", chklen));
      }
      /* For UDP-Lite, checksum length of 0 means checksum
         over the complete packet. (See RFC 3828 chap. 3.1)
         At least the UDP-Lite header must be covered by the
         checksum, therefore, if chksum_len has an illegal
         value, we generate the checksum over the complete
         packet to be safe. */
      chklen_hdr = 0;
      chklen = q->tot_len;
    }
    udphdr->len = htons(chklen_hdr);
    /* calculate checksum */
#if CHECKSUM_GEN_UDP
    udphdr->chksum = inet_chksum_pseudo_partial(q, src_ip, dst_ip,
      IP_PROTO_UDPLITE, q->tot_len,
#if !LWIP_CHECKSUM_ON_COPY
      chklen);
#else /* !LWIP_CHECKSUM_ON_COPY */
      (have_chksum ? UDP_HLEN : chklen));
    if (have_chksum) {
      u32_t acc;
      acc = udphdr->chksum + (u16_t)~(chksum);
      udphdr->chksum = FOLD_U32T(acc);
    }
#endif /* !LWIP_CHECKSUM_ON_COPY */

    /* chksum zero must become 0xffff, as zero means 'no checksum' */
    if (udphdr->chksum == 0x0000) {
      udphdr->chksum = 0xffff;
    }
#endif /* CHECKSUM_GEN_UDP */
    /* output to IP */
    LWIP_DEBUGF(UDP_DEBUG, ("udp_send: ip_output_if (,,,,IP_PROTO_UDPLITE,)\n"));
#if LWIP_NETIF_HWADDRHINT
    netif->addr_hint = &(pcb->addr_hint);
#endif /* LWIP_NETIF_HWADDRHINT*/
    err = ip_output_if(q, src_ip, dst_ip, pcb->ttl, pcb->tos, IP_PROTO_UDPLITE, netif);
#if LWIP_NETIF_HWADDRHINT
    netif->addr_hint = NULL;
#endif /* LWIP_NETIF_HWADDRHINT*/
  } else
#endif /* LWIP_UDPLITE */
  {      /* UDP */
    LWIP_DEBUGF(UDP_DEBUG, ("udp_send: UDP packet length %"U16_F"\n", q->tot_len));
    udphdr->len = htons(q->tot_len);
    /* calculate checksum */
#if CHECKSUM_GEN_UDP
    if ((pcb->flags & UDP_FLAGS_NOCHKSUM) == 0) {
      u16_t udpchksum;
#if LWIP_CHECKSUM_ON_COPY
      if (have_chksum) {
        u32_t acc;
        udpchksum = inet_chksum_pseudo_partial(q, src_ip, dst_ip, IP_PROTO_UDP,
          q->tot_len, UDP_HLEN);
        acc = udpchksum + (u16_t)~(chksum);
        udpchksum = FOLD_U32T(acc);
      } else
#endif /* LWIP_CHECKSUM_ON_COPY */
      {
        udpchksum = inet_chksum_pseudo(q, src_ip, dst_ip, IP_PROTO_UDP, q->tot_len);
      }

      /* chksum zero must become 0xffff, as zero means 'no checksum' */
      if (udpchksum == 0x0000) {
        udpchksum = 0xffff;
      }
      udphdr->chksum = udpchksum;
    }
#endif /* CHECKSUM_GEN_UDP */
    LWIP_DEBUGF(UDP_DEBUG, ("udp_send: UDP checksum 0x%04"X16_F"\n", udphdr->chksum));
    LWIP_DEBUGF(UDP_DEBUG, ("udp_send: ip_output_if (,,,,IP_PROTO_UDP,)\n"));
    /* output to IP */
#if LWIP_NETIF_HWADDRHINT
    netif->addr_hint = &(pcb->addr_hint);
#endif /* LWIP_NETIF_HWADDRHINT*/
    err = ip_output_if(q, src_ip, dst_ip, pcb->ttl, pcb->tos, IP_PROTO_UDP, netif);
#if LWIP_NETIF_HWADDRHINT
    netif->addr_hint = NULL;
#endif /* LWIP_NETIF_HWADDRHINT*/
  }
  /* TODO: must this be increased even if error occured? */
  snmp_inc_udpoutdatagrams();

  /* did we chain a separate header pbuf earlier? */
  if (q != p) {
    /* free the header pbuf */
    pbuf_free(q);
    q = NULL;
    /* p is still referenced by the caller, and will live on */
  }

  UDP_STATS_INC(udp.xmit);
  return err;
}

err_t
udp_bind(struct udp_pcb *pcb, ip_addr_t *ipaddr, u16_t port)
{
  struct udp_pcb *ipcb;
  u8_t rebind;

  LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_TRACE, ("udp_bind(ipaddr = "));
  ip_addr_debug_print(UDP_DEBUG, ipaddr);
  LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_TRACE, (", port = %"U16_F")\n", port));

  rebind = 0;
  /* Check for double bind and rebind of the same pcb */
  for (ipcb = udp_pcbs; ipcb != NULL; ipcb = ipcb->next) {
    /* is this UDP PCB already on active list? */
    if (pcb == ipcb) {
      /* pcb may occur at most once in active list */
      LWIP_ASSERT("rebind == 0", rebind == 0);
      /* pcb already in list, just rebind */
      rebind = 1;
    }

    /* By default, we don't allow to bind to a port that any other udp
       PCB is alread bound to, unless *all* PCBs with that port have tha
       REUSEADDR flag set. */
#if SO_REUSE
    else if (((pcb->so_options & SOF_REUSEADDR) == 0) &&
             ((ipcb->so_options & SOF_REUSEADDR) == 0)) {
#else /* SO_REUSE */
    /* port matches that of PCB in list and REUSEADDR not set -> reject */
    else {
#endif /* SO_REUSE */
      if ((ipcb->local_port == port) &&
          /* IP address matches, or one is IP_ADDR_ANY? */
          (ip_addr_isany(&(ipcb->local_ip)) ||
           ip_addr_isany(ipaddr) ||
           ip_addr_cmp(&(ipcb->local_ip), ipaddr))) {
        /* other PCB already binds to this local IP and port */
        LWIP_DEBUGF(UDP_DEBUG,
                    ("udp_bind: local port %"U16_F" already bound by another pcb\n", port));
        return ERR_USE;
      }
    }
  }

  ip_addr_set(&pcb->local_ip, ipaddr);

  /* no port specified? */
  if (port == 0) {
#ifndef UDP_LOCAL_PORT_RANGE_START
#define UDP_LOCAL_PORT_RANGE_START 4096
#define UDP_LOCAL_PORT_RANGE_END   0x7fff
#endif
    port = UDP_LOCAL_PORT_RANGE_START;
    ipcb = udp_pcbs;
    while ((ipcb != NULL) && (port != UDP_LOCAL_PORT_RANGE_END)) {
      if (ipcb->local_port == port) {
        /* port is already used by another udp_pcb */
        port++;
        /* restart scanning all udp pcbs */
        ipcb = udp_pcbs;
      } else {
        /* go on with next udp pcb */
        ipcb = ipcb->next;
      }
    }
    if (ipcb != NULL) {
      /* no more ports available in local range */
      LWIP_DEBUGF(UDP_DEBUG, ("udp_bind: out of free UDP ports\n"));
      return ERR_USE;
    }
  }
  pcb->local_port = port;
  snmp_insert_udpidx_tree(pcb);
  /* pcb not active yet? */
  if (rebind == 0) {
    /* place the PCB on the active list if not already there */
    pcb->next = udp_pcbs;
    udp_pcbs = pcb;
  }
  LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE,
              ("udp_bind: bound to %"U16_F".%"U16_F".%"U16_F".%"U16_F", port %"U16_F"\n",
               ip4_addr1_16(&pcb->local_ip), ip4_addr2_16(&pcb->local_ip),
               ip4_addr3_16(&pcb->local_ip), ip4_addr4_16(&pcb->local_ip),
               pcb->local_port));
  return ERR_OK;
}
err_t
udp_connect(struct udp_pcb *pcb, ip_addr_t *ipaddr, u16_t port)
{
  struct udp_pcb *ipcb;

  if (pcb->local_port == 0) {
    err_t err = udp_bind(pcb, &pcb->local_ip, pcb->local_port);
    if (err != ERR_OK) {
      return err;
    }
  }

  ip_addr_set(&pcb->remote_ip, ipaddr);
  pcb->remote_port = port;
  pcb->flags |= UDP_FLAGS_CONNECTED;
#ifdef LWIP_UDP_TODO
  /* Nail down local IP for netconn_addr()/getsockname() */
  if (ip_addr_isany(&pcb->local_ip) && !ip_addr_isany(&pcb->remote_ip)) {
    struct netif *netif;

    if ((netif = ip_route(&(pcb->remote_ip))) == NULL) {
      LWIP_DEBUGF(UDP_DEBUG, ("udp_connect: No route to 0x%lx\n", pcb->remote_ip.addr));
      UDP_STATS_INC(udp.rterr);
      return ERR_RTE;
    }
    pcb->local_ip = netif->ip_addr;
  } else if (ip_addr_isany(&pcb->remote_ip)) {
    pcb->local_ip.addr = 0;
  }
#endif
  LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE,
              ("udp_connect: connected to %"U16_F".%"U16_F".%"U16_F".%"U16_F",port %"U16_F"\n",
               ip4_addr1_16(&pcb->local_ip), ip4_addr2_16(&pcb->local_ip),
               ip4_addr3_16(&pcb->local_ip), ip4_addr4_16(&pcb->local_ip),
               pcb->local_port));

  /* Insert UDP PCB into the list of active UDP PCBs. */
  for (ipcb = udp_pcbs; ipcb != NULL; ipcb = ipcb->next) {
    if (pcb == ipcb) {
      /* already on the list, just return */
      return ERR_OK;
    }
  }
  /* PCB not yet on the list, add PCB now */
  pcb->next = udp_pcbs;
  udp_pcbs = pcb;
  return ERR_OK;
}

void
udp_disconnect(struct udp_pcb *pcb)
{
  /* reset remote address association */
  ip_addr_set_any(&pcb->remote_ip);
  pcb->remote_port = 0;
  /* mark PCB as unconnected */
  pcb->flags &= ~UDP_FLAGS_CONNECTED;
}

void
udp_recv(struct udp_pcb *pcb, udp_recv_fn recv, void *recv_arg)
{
  /* remember recv() callback and user data */
  pcb->recv = recv;
  pcb->recv_arg = recv_arg;
}

void
udp_remove(struct udp_pcb *pcb)
{
  struct udp_pcb *pcb2;

  snmp_delete_udpidx_tree(pcb);
  /* pcb to be removed is first in list? */
  if (udp_pcbs == pcb) {
    /* make list start at 2nd pcb */
    udp_pcbs = udp_pcbs->next;
    /* pcb not 1st in list */
  } else {
    for (pcb2 = udp_pcbs; pcb2 != NULL; pcb2 = pcb2->next) {
      /* find pcb in udp_pcbs list */
      if (pcb2->next != NULL && pcb2->next == pcb) {
        /* remove pcb from list */
        pcb2->next = pcb->next;
      }
    }
  }
  memp_free(MEMP_UDP_PCB, pcb);
}

struct udp_pcb *
udp_new(void)
{
  struct udp_pcb *pcb;
  pcb = (struct udp_pcb *)memp_malloc(MEMP_UDP_PCB);
  /* could allocate UDP PCB? */
  if (pcb != NULL) {
    /* UDP Lite: by initializing to all zeroes, chksum_len is set to 0
     * which means checksum is generated over the whole datagram per default
     * (recommended as default by RFC 3828). */
    /* initialize PCB to all zeroes */
    memset(pcb, 0, sizeof(struct udp_pcb));
    pcb->ttl = UDP_TTL;
  }
  return pcb;
}

#if UDP_DEBUG

void
udp_debug_print(struct udp_hdr *udphdr)
{
  LWIP_DEBUGF(UDP_DEBUG, ("UDP header:\n"));
  LWIP_DEBUGF(UDP_DEBUG, ("+-------------------------------+\n"));
  LWIP_DEBUGF(UDP_DEBUG, ("|     %5"U16_F"     |     %5"U16_F"     | (src port, dest port)\n",
                          ntohs(udphdr->src), ntohs(udphdr->dest)));
  LWIP_DEBUGF(UDP_DEBUG, ("+-------------------------------+\n"));
  LWIP_DEBUGF(UDP_DEBUG, ("|     %5"U16_F"     |     0x%04"X16_F"    | (len, chksum)\n",
                          ntohs(udphdr->len), ntohs(udphdr->chksum)));
  LWIP_DEBUGF(UDP_DEBUG, ("+-------------------------------+\n"));
}
#endif /* UDP_DEBUG */

#endif /* LWIP_UDP */