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);      /* UDP */  } else {    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_tudp_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;  /* 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_tudp_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;}voidudp_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;}voidudp_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() */voidudp_remove(struct udp_pcb *pcb){  struct udp_pcb *pcb2;  /* 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_DEBUGvoidudp_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 */