added support for lwip

2025-07-08 08:01:04 +03:00 · 2015-02-15 16:35:01 -06:00
parent 86eb8f94ef
commit 0c07499e54
106 changed files with 41425 additions and 0 deletions
--- a/lwip/core/udp.c
+++ b/lwip/core/udp.c
@ -0,0 +1,665 @@
+/**
+ * @file
+ * User Datagram Protocol module
+ *
+ */
+/*
+ * 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.
+ *
+ */
+
+#include <string.h>
+
+#include "lwip/opt.h"
+
+#include "lwip/def.h"
+#include "lwip/memp.h"
+#include "lwip/inet.h"
+#include "lwip/ip_addr.h"
+#include "lwip/netif.h"
+#include "lwip/udp.h"
+#include "lwip/icmp.h"
+
+#include "lwip/stats.h"
+
+#include "arch/perf.h"
+#include "lwip/snmp.h"
+
+/* The list of UDP PCBs */
+#if LWIP_UDP
+/* exported in udp.h (was static) */
+struct udp_pcb *udp_pcbs = NULL;
+
+static struct udp_pcb *pcb_cache = NULL;
+
+void
+udp_init(void)
+{
+  udp_pcbs = pcb_cache = NULL;
+}
+
+/**
+ * Process an incoming UDP datagram.
+ *
+ * Given an incoming UDP datagram (as a chain of pbufs) this function
+ * finds a corresponding UDP PCB and
+ *
+ * @param pbuf pbuf to be demultiplexed to a UDP PCB.
+ * @param netif network interface on which the datagram was received.
+ *
+ */
+void
+udp_input(struct pbuf *p, struct netif *inp)
+{
+  struct udp_hdr *udphdr;
+  struct udp_pcb *pcb;
+  struct udp_pcb *uncon_pcb;
+  struct ip_hdr *iphdr;
+  u16_t src, dest;
+  u8_t local_match;
+
+  PERF_START;
+
+  UDP_STATS_INC(udp.recv);
+
+  iphdr = p->payload;
+
+  if (p->tot_len < (IPH_HL(iphdr) * 4 + UDP_HLEN)) {
+    /* drop short packets */
+//    LWIP_DEBUGF(UDP_DEBUG,
+//                ("udp_input: short UDP datagram (%"U16_F" bytes) discarded\n", p->tot_len));
+
+    LWIP_DEBUGF(UDP_DEBUG,
+                ("udp_input: short UDP datagram (%u bytes) discarded\n", p->tot_len));
+
+    UDP_STATS_INC(udp.lenerr);
+    UDP_STATS_INC(udp.drop);
+    snmp_inc_udpinerrors();
+    pbuf_free(p);
+    goto end;
+  }
+
+  pbuf_header(p, -((s16_t)(IPH_HL(iphdr) * 4)));
+
+  udphdr = (struct udp_hdr *)p->payload;
+
+  LWIP_DEBUGF(UDP_DEBUG, ("udp_input: received datagram of length %"U16_F"\n", p->tot_len));
+
+  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(&iphdr->dest), ip4_addr2(&iphdr->dest),
+               ip4_addr3(&iphdr->dest), ip4_addr4(&iphdr->dest), ntohs(udphdr->dest),
+               ip4_addr1(&iphdr->src), ip4_addr2(&iphdr->src),
+               ip4_addr3(&iphdr->src), ip4_addr4(&iphdr->src), ntohs(udphdr->src)));
+
+  local_match = 0;
+  uncon_pcb = NULL;
+  /* Iterate through the UDP pcb list for a matching pcb */
+  for (pcb = udp_pcbs; pcb != NULL; pcb = pcb->next) {
+    /* 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(&pcb->local_ip), ip4_addr2(&pcb->local_ip),
+                 ip4_addr3(&pcb->local_ip), ip4_addr4(&pcb->local_ip), pcb->local_port,
+                 ip4_addr1(&pcb->remote_ip), ip4_addr2(&pcb->remote_ip),
+                 ip4_addr3(&pcb->remote_ip), ip4_addr4(&pcb->remote_ip), pcb->remote_port));
+
+    /* compare PCB local addr+port to UDP destination addr+port */
+    if ((pcb->local_port == dest) &&
+        (ip_addr_isany(&pcb->local_ip) ||
+         ip_addr_cmp(&(pcb->local_ip), &(iphdr->dest)) || 
+         ip_addr_isbroadcast(&(iphdr->dest), inp))) {
+      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), &(iphdr->src)))) {
+      /* the first fully matching PCB */
+      break;
+    }
+  }
+  /* 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, &iphdr->dest)) {
+    LWIP_DEBUGF(UDP_DEBUG | DBG_TRACE, ("udp_input: calculating checksum\n"));
+#ifdef IPv6
+    if (iphdr->nexthdr == IP_PROTO_UDPLITE) {
+#else
+    if (IPH_PROTO(iphdr) == IP_PROTO_UDPLITE) {
+#endif /* IPv4 */
+      /* Do the UDP Lite checksum */
+#if CHECKSUM_CHECK_UDP
+      if (inet_chksum_pseudo(p, (struct ip_addr *)&(iphdr->src),
+                             (struct ip_addr *)&(iphdr->dest),
+                             IP_PROTO_UDPLITE, ntohs(udphdr->len)) != 0) {
+        LWIP_DEBUGF(UDP_DEBUG | 2,
+                    ("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
+    } else {
+#if CHECKSUM_CHECK_UDP
+      if (udphdr->chksum != 0) {
+        if (inet_chksum_pseudo(p, (struct ip_addr *)&(iphdr->src),
+                               (struct ip_addr *)&(iphdr->dest),
+                               IP_PROTO_UDP, p->tot_len) != 0) {
+          LWIP_DEBUGF(UDP_DEBUG | 2,
+                      ("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
+    }
+    pbuf_header(p, -UDP_HLEN);
+    if (pcb != NULL) {
+      snmp_inc_udpindatagrams();
+      /* callback */
+      if (pcb->recv != NULL)
+        pcb->recv(pcb->recv_arg, pcb, p, &(iphdr->src), src);
+    } else {
+      LWIP_DEBUGF(UDP_DEBUG | DBG_TRACE, ("udp_input: not for us.\n"));
+
+      /* No match was found, send ICMP destination port unreachable unless
+         destination address was broadcast/multicast. */
+
+      if (!ip_addr_isbroadcast(&iphdr->dest, inp) &&
+          !ip_addr_ismulticast(&iphdr->dest)) {
+
+        /* restore pbuf pointer */
+        p->payload = iphdr;
+        icmp_dest_unreach(p, ICMP_DUR_PORT);
+      }
+      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");
+}
+
+/**
+ * Send data to a specified address using UDP.
+ *
+ * @param pcb UDP PCB used to send the data.
+ * @param pbuf chain of pbuf's to be sent.
+ * @param dst_ip Destination IP address.
+ * @param dst_port Destination UDP port.
+ *
+ * If the PCB already has a remote address association, it will
+ * be restored after the data is sent.
+ * 
+ * @return lwIP error code.
+ * - ERR_OK. Successful. No error occured.
+ * - ERR_MEM. Out of memory.
+ * - ERR_RTE. Could not find route to destination address.
+ *
+ * @see udp_disconnect() udp_send()
+ */
+err_t
+udp_sendto(struct udp_pcb *pcb, struct pbuf *p,
+  struct ip_addr *dst_ip, u16_t dst_port)
+{
+  err_t err;
+  /* temporary space for current PCB remote address */
+  struct ip_addr pcb_remote_ip;
+  u16_t pcb_remote_port;
+  /* remember current remote peer address of PCB */
+  pcb_remote_ip.addr = pcb->remote_ip.addr;
+  pcb_remote_port = pcb->remote_port;
+  /* copy packet destination address to PCB remote peer address */
+  pcb->remote_ip.addr = dst_ip->addr;
+  pcb->remote_port = dst_port;
+  /* send to the packet destination address */
+  err = udp_send(pcb, p);
+  /* restore PCB remote peer address */
+  pcb->remote_ip.addr = pcb_remote_ip.addr;
+  pcb->remote_port = pcb_remote_port;
+  return err;
+}
+
+/**
+ * Send data using UDP.
+ *
+ * @param pcb UDP PCB used to send the data.
+ * @param pbuf chain of pbuf's to be sent.
+ *
+ * @return lwIP error code.
+ * - ERR_OK. Successful. No error occured.
+ * - ERR_MEM. Out of memory.
+ * - ERR_RTE. Could not find route to destination address.
+ *
+ * @see udp_disconnect() udp_sendto()
+ */
+err_t
+udp_send(struct udp_pcb *pcb, struct pbuf *p)
+{
+  struct udp_hdr *udphdr;
+  struct netif *netif;
+  struct ip_addr *src_ip;
+  err_t err;
+  struct pbuf *q; /* q will be sent down the stack */
+
+  LWIP_DEBUGF(UDP_DEBUG | DBG_TRACE | 3, ("udp_send\n"));
+
+  /* if the PCB is not yet bound to a port, bind it here */
+  if (pcb->local_port == 0) {
+    LWIP_DEBUGF(UDP_DEBUG | DBG_TRACE | 2, ("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 | DBG_TRACE | 2, ("udp_send: forced port bind failed\n"));
+      return err;
+    }
+  }
+  /* find the outgoing network interface for this packet */
+  netif = ip_route(&(pcb->remote_ip));
+  /* no outgoing network interface could be found? */
+  if (netif == NULL) {
+    LWIP_DEBUGF(UDP_DEBUG | 1, ("udp_send: No route to 0x%"X32_F"\n", pcb->remote_ip.addr));
+    UDP_STATS_INC(udp.rterr);
+    return ERR_RTE;
+  }
+
+  /* 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 seperate 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 | DBG_TRACE | 2, ("udp_send: could not allocate header\n"));
+      return ERR_MEM;
+    }
+    /* chain header q in front of given pbuf p */
+    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));
+    /* adding a header within p succeeded */
+  } else {
+    /* first pbuf q equals given pbuf */
+    q = p;
+    LWIP_DEBUGF(UDP_DEBUG, ("udp_send: added header in given pbuf %p\n", (void *)p));
+  }
+  /* q now represents the packet to be sent */
+  udphdr = q->payload;
+  udphdr->src = htons(pcb->local_port);
+  udphdr->dest = htons(pcb->remote_port);
+  /* in UDP, 0 checksum means 'no checksum' */
+  udphdr->chksum = 0x0000; 
+
+  /* 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 {
+    /* 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));
+
+  /* UDP Lite protocol? */
+  if (pcb->flags & UDP_FLAGS_UDPLITE) {
+    LWIP_DEBUGF(UDP_DEBUG, ("udp_send: UDP LITE packet length %"U16_F"\n", q->tot_len));
+    /* set UDP message length in UDP header */
+    udphdr->len = htons(pcb->chksum_len);
+    /* calculate checksum */
+#if CHECKSUM_GEN_UDP
+    udphdr->chksum = inet_chksum_pseudo(q, src_ip, &(pcb->remote_ip),
+                                        IP_PROTO_UDP, pcb->chksum_len);
+    /* chksum zero must become 0xffff, as zero means 'no checksum' */
+    if (udphdr->chksum == 0x0000)
+      udphdr->chksum = 0xffff;
+#else
+    udphdr->chksum = 0x0000;
+#endif
+    /* output to IP */
+    LWIP_DEBUGF(UDP_DEBUG, ("udp_send: ip_output_if (,,,,IP_PROTO_UDPLITE,)\n"));
+    err = ip_output_if(q, src_ip, &pcb->remote_ip, pcb->ttl, pcb->tos, IP_PROTO_UDPLITE, netif);    
+  } else {      /* 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) {
+      udphdr->chksum = inet_chksum_pseudo(q, src_ip, &pcb->remote_ip, IP_PROTO_UDP, q->tot_len);
+      /* chksum zero must become 0xffff, as zero means 'no checksum' */
+      if (udphdr->chksum == 0x0000) udphdr->chksum = 0xffff;
+    }
+#else
+    udphdr->chksum = 0x0000;
+#endif
+    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 */
+    err = ip_output_if(q, src_ip, &pcb->remote_ip, pcb->ttl, pcb->tos, IP_PROTO_UDP, netif);    
+  }
+  /* TODO: must this be increased even if error occured? */
+  snmp_inc_udpoutdatagrams();
+
+  /* did we chain a seperate 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;
+}
+
+/**
+ * Bind an UDP PCB.
+ *
+ * @param pcb UDP PCB to be bound with a local address ipaddr and port.
+ * @param ipaddr local IP address to bind with. Use IP_ADDR_ANY to
+ * bind to all local interfaces.
+ * @param port local UDP port to bind with.
+ *
+ * @return lwIP error code.
+ * - ERR_OK. Successful. No error occured.
+ * - ERR_USE. The specified ipaddr and port are already bound to by
+ * another UDP PCB.
+ *
+ * @see udp_disconnect()
+ */
+err_t
+udp_bind(struct udp_pcb *pcb, struct ip_addr *ipaddr, u16_t port)
+{
+  struct udp_pcb *ipcb;
+  u8_t rebind;
+
+  LWIP_DEBUGF(UDP_DEBUG | DBG_TRACE | 3, ("udp_bind(ipaddr = "));
+  ip_addr_debug_print(UDP_DEBUG, ipaddr);
+  LWIP_DEBUGF(UDP_DEBUG | DBG_TRACE | 3, (", 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;
+    }
+
+    /* this code does not allow upper layer to share a UDP port for
+       listening to broadcast or multicast traffic (See SO_REUSE_ADDR and
+       SO_REUSE_PORT under *BSD). TODO: See where it fits instead, OR
+       combine with implementation of UDP PCB flags. Leon Woestenberg. */
+#ifdef LWIP_UDP_TODO
+    /* port matches that of PCB in list? */
+    else
+      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;
+      }
+#endif
+  }
+
+  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++;
+        ipcb = udp_pcbs;
+      } else
+        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 | DBG_TRACE | DBG_STATE,
+              ("udp_bind: bound to %"U16_F".%"U16_F".%"U16_F".%"U16_F", port %"U16_F"\n",
+               (u16_t)(ntohl(pcb->local_ip.addr) >> 24 & 0xff),
+               (u16_t)(ntohl(pcb->local_ip.addr) >> 16 & 0xff),
+               (u16_t)(ntohl(pcb->local_ip.addr) >> 8 & 0xff),
+               (u16_t)(ntohl(pcb->local_ip.addr) & 0xff), pcb->local_port));
+  return ERR_OK;
+}
+/**
+ * Connect an UDP PCB.
+ *
+ * This will associate the UDP PCB with the remote address.
+ *
+ * @param pcb UDP PCB to be connected with remote address ipaddr and port.
+ * @param ipaddr remote IP address to connect with.
+ * @param port remote UDP port to connect with.
+ *
+ * @return lwIP error code
+ *
+ * @see udp_disconnect()
+ */
+err_t
+udp_connect(struct udp_pcb *pcb, struct ip_addr *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;
+/** TODO: this functionality belongs in upper layers */
+#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;
+    }
+    /** TODO: this will bind the udp pcb locally, to the interface which
+        is used to route output packets to the remote address. However, we
+        might want to accept incoming packets on any interface! */
+    pcb->local_ip = netif->ip_addr;
+  } else if (ip_addr_isany(&pcb->remote_ip)) {
+    pcb->local_ip.addr = 0;
+  }
+#endif
+  LWIP_DEBUGF(UDP_DEBUG | DBG_TRACE | DBG_STATE,
+              ("udp_connect: connected to %"U16_F".%"U16_F".%"U16_F".%"U16_F",port %"U16_F"\n",
+               (u16_t)(ntohl(pcb->remote_ip.addr) >> 24 & 0xff),
+               (u16_t)(ntohl(pcb->remote_ip.addr) >> 16 & 0xff),
+               (u16_t)(ntohl(pcb->remote_ip.addr) >> 8 & 0xff),
+               (u16_t)(ntohl(pcb->remote_ip.addr) & 0xff), pcb->remote_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(&pcb->remote_ip, IP_ADDR_ANY);
+  pcb->remote_port = 0;
+  /* mark PCB as unconnected */
+  pcb->flags &= ~UDP_FLAGS_CONNECTED;
+}
+
+void
+udp_recv(struct udp_pcb *pcb,
+         void (* recv)(void *arg, struct udp_pcb *upcb, struct pbuf *p,
+                       struct ip_addr *addr, u16_t port),
+         void *recv_arg)
+{
+  /* remember recv() callback and user data */
+  pcb->recv = recv;
+  pcb->recv_arg = recv_arg;
+}
+
+/**
+ * Remove an UDP PCB.
+ *
+ * @param pcb UDP PCB to be removed. The PCB is removed from the list of
+ * UDP PCB's and the data structure is freed from memory.
+ *
+ * @see udp_new()
+ */
+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);
+}
+
+/**
+ * Create a UDP PCB.
+ *
+ * @return The UDP PCB which was created. NULL if the PCB data structure
+ * could not be allocated.
+ *
+ * @see udp_remove()
+ */
+struct udp_pcb *
+udp_new(void)
+{
+  struct udp_pcb *pcb;
+  pcb = memp_malloc(MEMP_UDP_PCB);
+  /* could allocate UDP PCB? */
+  if (pcb != NULL) {
+    /* 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 */