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/**

 * @file

 * DNS - host name to IP address resolver.

 *

 */

/**

 * This file implements a DNS host name to IP address resolver.

 * Port to lwIP from uIP

 * by Jim Pettinato April 2007

 * uIP version Copyright (c) 2002-2003, Adam Dunkels.

 * 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.

 *

 *

 * DNS.C

 *

 * The lwIP DNS resolver functions are used to lookup a host name and

 * map it to a numerical IP address. It maintains a list of resolved

 * hostnames that can be queried with the dns_lookup() function.

 * New hostnames can be resolved using the dns_query() function.

 *

 * The lwIP version of the resolver also adds a non-blocking version of

 * gethostbyname() that will work with a raw API application. This function

 * checks for an IP address string first and converts it if it is valid.

 * gethostbyname() then does a dns_lookup() to see if the name is

 * already in the table. If so, the IP is returned. If not, a query is

 * issued and the function returns with a ERR_INPROGRESS status. The app

 * using the dns client must then go into a waiting state.

 *

 * Once a hostname has been resolved (or found to be non-existent),

 * the resolver code calls a specified callback function (which

 * must be implemented by the module that uses the resolver).

 */

/*-----------------------------------------------------------------------------

 * RFC 1035 - Domain names - implementation and specification

 * RFC 2181 - Clarifications to the DNS Specification

 *----------------------------------------------------------------------------*/

/** @todo: define good default values (rfc compliance) */

/** @todo: improve answer parsing, more checkings... */

/** @todo: check RFC1035 - 7.3. Processing responses */

/*-----------------------------------------------------------------------------

 * Includes

 *----------------------------------------------------------------------------*/

#include "lwip/opt.h"

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

#include "lwip/udp.h"

#include "lwip/mem.h"

#include "lwip/dns.h"

#include <string.h>

/** DNS server IP address */

#ifndef DNS_SERVER_ADDRESS

#define DNS_SERVER_ADDRESS        inet_addr("208.67.222.222") /* resolver1.opendns.com */

#endif

/** DNS server port address */

#ifndef DNS_SERVER_PORT

#define DNS_SERVER_PORT           53

#endif

/** DNS maximum number of retries when asking for a name, before "timeout". */

#ifndef DNS_MAX_RETRIES

#define DNS_MAX_RETRIES           4

#endif

/** DNS resource record max. TTL (one week as default) */

#ifndef DNS_MAX_TTL

#define DNS_MAX_TTL               604800

#endif

/* DNS protocol flags */

#define DNS_FLAG1_RESPONSE        0x80

#define DNS_FLAG1_OPCODE_STATUS   0x10

#define DNS_FLAG1_OPCODE_INVERSE  0x08

#define DNS_FLAG1_OPCODE_STANDARD 0x00

#define DNS_FLAG1_AUTHORATIVE     0x04

#define DNS_FLAG1_TRUNC           0x02

#define DNS_FLAG1_RD              0x01

#define DNS_FLAG2_RA              0x80

#define DNS_FLAG2_ERR_MASK        0x0f

#define DNS_FLAG2_ERR_NONE        0x00

#define DNS_FLAG2_ERR_NAME        0x03

/* DNS protocol states */

#define DNS_STATE_UNUSED          0

#define DNS_STATE_NEW             1

#define DNS_STATE_ASKING          2

#define DNS_STATE_DONE            3

#ifdef PACK_STRUCT_USE_INCLUDES

#  include "arch/bpstruct.h"

#endif

PACK_STRUCT_BEGIN

#if (defined(__MWERKS__)  || defined(__CWCC__))

        #pragma options align= packed

#endif

/** DNS message header */

struct dns_hdr {

  u16_t id;

  u8_t flags1;

  u8_t flags2;

  u16_t numquestions;

  u16_t numanswers;

  u16_t numauthrr;

  u16_t numextrarr;

} PACK_STRUCT_STRUCT;

PACK_STRUCT_END

#ifdef PACK_STRUCT_USE_INCLUDES

#  include "arch/epstruct.h"

#endif

#ifdef PACK_STRUCT_USE_INCLUDES

#  include "arch/bpstruct.h"

#endif

PACK_STRUCT_BEGIN

#if (defined(__MWERKS__)  || defined(__CWCC__))

        #pragma options align= packed

#endif

/** DNS query message structure */

struct dns_query {

  /* DNS query record starts with either a domain name or a pointer

     to a name already present somewhere in the packet. */

  u16_t type;

  u16_t class;

} PACK_STRUCT_STRUCT;

PACK_STRUCT_END

#ifdef PACK_STRUCT_USE_INCLUDES

#  include "arch/epstruct.h"

#endif

#ifdef PACK_STRUCT_USE_INCLUDES

#  include "arch/bpstruct.h"

#endif

PACK_STRUCT_BEGIN

#if (defined(__MWERKS__)  || defined(__CWCC__))

        #pragma options align= packed

#endif

/** DNS answer message structure */

struct dns_answer {

  /* DNS answer record starts with either a domain name or a pointer

     to a name already present somewhere in the packet. */

  u16_t type;

  u16_t class;

  u32_t ttl;

  u16_t len;

} PACK_STRUCT_STRUCT;

PACK_STRUCT_END

#ifdef PACK_STRUCT_USE_INCLUDES

#  include "arch/epstruct.h"

#endif

/** DNS table entry */

struct dns_table_entry {

  u8_t  state;

  u8_t  numdns;

  u8_t  tmr;

  u8_t  retries;

  u8_t  seqno;

  u8_t  err;

  u32_t ttl;

  char name[DNS_MAX_NAME_LENGTH];

  struct ip_addr ipaddr;

  /* pointer to callback on DNS query done */

  dns_found_callback found;

  void *arg;

};

/* forward declarations */

static void dns_recv(void *s, struct udp_pcb *pcb, struct pbuf *p, struct ip_addr *addr, u16_t port);

static void dns_check_entries(void);

/*-----------------------------------------------------------------------------

 * Globales

 *----------------------------------------------------------------------------*/

/* DNS variables */

static struct udp_pcb        *dns_pcb;

static u8_t                   dns_seqno;

static struct dns_table_entry dns_table[DNS_TABLE_SIZE];

static struct ip_addr         dns_servers[DNS_MAX_SERVERS];

#if (DNS_USES_STATIC_BUF == 1)

static u8_t                   dns_payload[DNS_MSG_SIZE];

#endif /* (DNS_USES_STATIC_BUF == 1) */

/**

 * Initialize the resolver: set up the UDP pcb and configure the default server

 * (DNS_SERVER_ADDRESS).

 */

void

dns_init()

{

  struct ip_addr dnsserver;

  /* initialize default DNS server address */

  dnsserver.addr = DNS_SERVER_ADDRESS;

  LWIP_DEBUGF(DNS_DEBUG, ("dns_init: initializing\n"));

  /* if dns client not yet initialized... */

  if (dns_pcb == NULL) {

    dns_pcb = udp_new();

    if (dns_pcb != NULL) {

      /* initialize DNS table not needed (initialized to zero since it is a

       * global variable) */

      LWIP_ASSERT("For implicit initialization to work, DNS_STATE_UNUSED needs to be 0",

        DNS_STATE_UNUSED == 0);

      /* initialize DNS client */

      udp_bind(dns_pcb, IP_ADDR_ANY, 0);

      udp_recv(dns_pcb, dns_recv, NULL);

      /* initialize default DNS primary server */

      dns_setserver(0, &dnsserver);

    }

  }

}

/**

 * Initialize one of the DNS servers.

 *

 * @param numdns the index of the DNS server to set must be < DNS_MAX_SERVERS

 * @param dnsserver IP address of the DNS server to set

 */

void

dns_setserver(u8_t numdns, struct ip_addr *dnsserver)

{

  if ((numdns < DNS_MAX_SERVERS) && (dns_pcb != NULL) &&

      (dnsserver != NULL) && (dnsserver->addr !=0 )) {

    dns_servers[numdns] = (*dnsserver);

  }

}

/**

 * Obtain one of the currently configured DNS server.

 *

 * @param numdns the index of the DNS server

 * @return IP address of the indexed DNS server or "ip_addr_any" if the DNS

 *         server has not been configured.

 */

struct ip_addr

dns_getserver(u8_t numdns)

{

  if (numdns < DNS_MAX_SERVERS) {

    return dns_servers[numdns];

  } else {

    return *IP_ADDR_ANY;

  }

}

/**

 * The DNS resolver client timer - handle retries and timeouts and should

 * be called every DNS_TMR_INTERVAL milliseconds (every second by default).

 */

void

dns_tmr(void)

{

  if (dns_pcb != NULL) {

    LWIP_DEBUGF(DNS_DEBUG, ("dns_tmr: dns_check_entries\n"));

    dns_check_entries();

  }

}

/**

 * Look up a hostname in the array of known hostnames.

 *

 * @note This function only looks in the internal array of known

 * hostnames, it does not send out a query for the hostname if none

 * was found. The function dns_enqueue() can be used to send a query

 * for a hostname.

 *

 * @param name the hostname to look up

 * @return the hostname's IP address, as u32_t (instead of struct ip_addr to

 *         better check for failure: != 0) or 0 if the hostname was not found

 *         in the cached dns_table.

 */

static u32_t

dns_lookup(const char *name)

{

  u8_t i;

  /* Walk through name list, return entry if found. If not, return NULL. */

  for (i = 0; i < DNS_TABLE_SIZE; ++i) {

    if ((dns_table[i].state == DNS_STATE_DONE) &&

        (strcmp(name, dns_table[i].name) == 0)) {

      LWIP_DEBUGF(DNS_DEBUG, ("dns_lookup: \"%s\": found = ", name));

      ip_addr_debug_print(DNS_DEBUG, &(dns_table[i].ipaddr));

      LWIP_DEBUGF(DNS_DEBUG, ("\n"));

      return dns_table[i].ipaddr.addr;

    }

  }

  return 0;

}

#if DNS_DOES_NAME_CHECK

/**

 * Compare the "dotted" name "query" with the encoded name "response"

 * to make sure an answer from the DNS server matches the current dns_table

 * entry (otherwise, answers might arrive late for hostname not on the list

 * any more).

 *

 * @param query hostname (not encoded) from the dns_table

 * @param response encoded hostname in the DNS response

 * @return 0: names equal; 1: names differ

 */

static u8_t

dns_compare_name(unsigned char *query, unsigned char *response)

{

  unsigned char n;

  do {

    n = *response++;

    /** @see RFC 1035 - 4.1.4. Message compression */

    if ((n & 0xc0) == 0xc0) {

      /* Compressed name */

      break;

    } else {

      /* Not compressed name */

      while (n > 0) {

        if ((*query) != (*response)) {

          return 1;

        }

        ++response;

        ++query;

        --n;

      };

      ++query;

    }

  } while (*response != 0);

  return 0;

}

#endif /* DNS_DOES_NAME_CHECK */

/**

 * Walk through a compact encoded DNS name and return the end of the name.

 *

 * @param query encoded DNS name in the DNS server response

 * @return end of the name

 */

static unsigned char *

dns_parse_name(unsigned char *query)

{

  unsigned char n;

  do {

    n = *query++;

    /** @see RFC 1035 - 4.1.4. Message compression */

    if ((n & 0xc0) == 0xc0) {

      /* Compressed name */

      break;

    } else {

      /* Not compressed name */

      while (n > 0) {

        ++query;

        --n;

      };

    }

  } while (*query != 0);

  return query + 1;

}

/**

 * Send a DNS query packet.

 *

 * @param numdns index of the DNS server in the dns_servers table

 * @param name hostname to query

 * @param id index of the hostname in dns_table, used as transaction ID in the

 *        DNS query packet

 * @return ERR_OK if packet is sent; an err_t indicating the problem otherwise

 */

static err_t

dns_send(u8_t numdns, const char* name, u8_t id)

{

  err_t err;

  struct dns_hdr *hdr;

  struct dns_query qry;

  struct pbuf *p;

  char *query, *nptr;

  const char *pHostname;

  u8_t n;

  LWIP_DEBUGF(DNS_DEBUG, ("dns_send: dns_servers[%"U16_F"] \"%s\": request\n",

              (u16_t)(numdns), name));

  LWIP_ASSERT("dns server out of array", numdns < DNS_MAX_SERVERS);

  LWIP_ASSERT("dns server has no IP address set", dns_servers[numdns].addr != 0);

  /* if here, we have either a new query or a retry on a previous query to process */

  p = pbuf_alloc(PBUF_TRANSPORT, sizeof(struct dns_hdr) + DNS_MAX_NAME_LENGTH +

                 sizeof(struct dns_query), PBUF_RAM);

  if (p != NULL) {

    LWIP_ASSERT("pbuf must be in one piece", p->next == NULL);

    /* fill dns header */

    hdr = (struct dns_hdr*)p->payload;

    memset(hdr, 0, sizeof(struct dns_hdr));

    hdr->id = htons(id);

    hdr->flags1 = DNS_FLAG1_RD;

    hdr->numquestions = htons(1);

    query = (char*)hdr + sizeof(struct dns_hdr);

    pHostname = name;

    --pHostname;

    /* convert hostname into suitable query format. */

    do {

      ++pHostname;

      nptr = query;

      ++query;

      for(n = 0; *pHostname != '.' && *pHostname != 0; ++pHostname) {

        *query = *pHostname;

        ++query;

        ++n;

      }

      *nptr = n;

    } while(*pHostname != 0);

    *query++='\0';

    /* fill dns query */

    qry.type  = htons(DNS_RRTYPE_A);

    qry.class = htons(DNS_RRCLASS_IN);

    MEMCPY( query, &qry, sizeof(struct dns_query));

    /* resize pbuf to the exact dns query */

    pbuf_realloc(p, (query + sizeof(struct dns_query)) - ((char*)(p->payload)));

    /* connect to the server for faster receiving */

    udp_connect(dns_pcb, &dns_servers[numdns], DNS_SERVER_PORT);

    /* send dns packet */

    err = udp_sendto(dns_pcb, p, &dns_servers[numdns], DNS_SERVER_PORT);

    /* free pbuf */

    pbuf_free(p);

  } else {

    err = ERR_MEM;

  }

  return err;

}

/**

 * dns_check_entry() - see if pEntry has not yet been queried and, if so, sends out a query.

 * Check an entry in the dns_table:

 * - send out query for new entries

 * - retry old pending entries on timeout (also with different servers)

 * - remove completed entries from the table if their TTL has expired

 *

 * @param i index of the dns_table entry to check

 */

static void

dns_check_entry(u8_t i)

{

  struct dns_table_entry *pEntry = &dns_table[i];

  LWIP_ASSERT("array index out of bounds", i < DNS_TABLE_SIZE);

  switch(pEntry->state) {

    case DNS_STATE_NEW: {

      /* initialize new entry */

      pEntry->state   = DNS_STATE_ASKING;

      pEntry->numdns  = 0;

      pEntry->tmr     = 1;

      pEntry->retries = 0;

      /* send DNS packet for this entry */

      dns_send(pEntry->numdns, pEntry->name, i);

      break;

    }

    case DNS_STATE_ASKING: {

      if (--pEntry->tmr == 0) {

        if (++pEntry->retries == DNS_MAX_RETRIES) {

          if ((pEntry->numdns+1<DNS_MAX_SERVERS) && (dns_servers[pEntry->numdns+1].addr!=0)) {

            /* change of server */

            pEntry->numdns++;

            pEntry->tmr     = 1;

            pEntry->retries = 0;

            break;

          } else {

            LWIP_DEBUGF(DNS_DEBUG, ("dns_check_entry: \"%s\": timeout\n", pEntry->name));

            /* call specified callback function if provided */

            if (pEntry->found)

              (*pEntry->found)(pEntry->name, NULL, pEntry->arg);

            /* flush this entry */

            pEntry->state   = DNS_STATE_UNUSED;

            pEntry->found   = NULL;

            break;

          }

        }

        /* wait longer for the next retry */

        pEntry->tmr = pEntry->retries;

        /* send DNS packet for this entry */

        dns_send(pEntry->numdns, pEntry->name, i);

      }

      break;

    }

    case DNS_STATE_DONE: {

      /* if the time to live is nul */

      if (--pEntry->ttl == 0) {

        LWIP_DEBUGF(DNS_DEBUG, ("dns_check_entry: \"%s\": flush\n", pEntry->name));

        /* flush this entry */

        pEntry->state = DNS_STATE_UNUSED;

        pEntry->found = NULL;

      }

      break;

    }

    case DNS_STATE_UNUSED:

      /* nothing to do */

      break;

    default:

      LWIP_ASSERT("unknown dns_table entry state:", 0);

      break;

  }

}

/**

 * Call dns_check_entry for each entry in dns_table - check all entries.

 */

static void

dns_check_entries(void)

{

  u8_t i;

  for (i = 0; i < DNS_TABLE_SIZE; ++i) {

    dns_check_entry(i);

  }

}

/**

 * Receive input function for DNS response packets arriving for the dns UDP pcb.

 *

 * @params see udp.h

 */

static void

dns_recv(void *arg, struct udp_pcb *pcb, struct pbuf *p, struct ip_addr *addr, u16_t port)

{

  u8_t i;

  char *pHostname;

  struct dns_hdr *hdr;

  struct dns_answer ans;

  struct dns_table_entry *pEntry;

  u8_t nquestions, nanswers;

#if (DNS_USES_STATIC_BUF == 0)

  u8_t dns_payload[DNS_MSG_SIZE];

#endif /* (DNS_USES_STATIC_BUF == 0) */

#if (DNS_USES_STATIC_BUF == 2)

  u8_t* dns_payload;

#endif /* (DNS_USES_STATIC_BUF == 2) */

  LWIP_UNUSED_ARG(arg);

  LWIP_UNUSED_ARG(pcb);

  LWIP_UNUSED_ARG(addr);

  LWIP_UNUSED_ARG(port);

  /* is the dns message too big ? */

  if (p->tot_len > DNS_MSG_SIZE) {

    LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: pbuf too big\n"));

    /* free pbuf and return */

    goto memerr1;

  }

  /* is the dns message big enough ? */

  if (p->tot_len < (sizeof(struct dns_hdr) + sizeof(struct dns_query) + sizeof(struct dns_answer))) {

    LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: pbuf too small\n"));

    /* free pbuf and return */

    goto memerr1;

  }

#if (DNS_USES_STATIC_BUF == 2)

  dns_payload = mem_malloc(p->tot_len);

  if (dns_payload == NULL) {

    LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: mem_malloc error\n"));

    /* free pbuf and return */

    goto memerr1;

  }

#endif /* (DNS_USES_STATIC_BUF == 2) */

  /* copy dns payload inside static buffer for processing */

  if (pbuf_copy_partial(p, dns_payload, p->tot_len, 0) == p->tot_len) {

    /* The ID in the DNS header should be our entry into the name table. */

    hdr = (struct dns_hdr*)dns_payload;

    i = htons(hdr->id);

    if (i < DNS_TABLE_SIZE) {

      pEntry = &dns_table[i];

      if(pEntry->state == DNS_STATE_ASKING) {

        /* This entry is now completed. */

        pEntry->state = DNS_STATE_DONE;

        pEntry->err   = hdr->flags2 & DNS_FLAG2_ERR_MASK;

        /* We only care about the question(s) and the answers. The authrr

           and the extrarr are simply discarded. */

        nquestions = htons(hdr->numquestions);

        nanswers   = htons(hdr->numanswers);

        /* Check for error. If so, call callback to inform. */

        if (((hdr->flags1 & DNS_FLAG1_RESPONSE) == 0) || (pEntry->err != 0) || (nquestions != 1)) {

          LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": error in flags\n", pEntry->name));

          /* call callback to indicate error, clean up memory and return */

          goto responseerr;

        }

#if DNS_DOES_NAME_CHECK

        /* Check if the name in the "question" part match with the name in the entry. */

        if (dns_compare_name((unsigned char *)(pEntry->name), (unsigned char *)dns_payload + sizeof(struct dns_hdr)) != 0) {

          LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": response not match to query\n", pEntry->name));

          /* call callback to indicate error, clean up memory and return */

          goto responseerr;

        }

#endif /* DNS_DOES_NAME_CHECK */

        /* Skip the name in the "question" part */

        pHostname = (char *) dns_parse_name((unsigned char *)dns_payload + sizeof(struct dns_hdr)) + sizeof(struct dns_query);

        while(nanswers > 0) {

          /* skip answer resource record's host name */

          pHostname = (char *) dns_parse_name((unsigned char *)pHostname);

          /* Check for IP address type and Internet class. Others are discarded. */

          MEMCPY(&ans, pHostname, sizeof(struct dns_answer));

          if((ntohs(ans.type) == DNS_RRTYPE_A) && (ntohs(ans.class) == DNS_RRCLASS_IN) && (ntohs(ans.len) == sizeof(struct ip_addr)) ) {

            /* read the answer resource record's TTL, and maximize it if needed */

            pEntry->ttl = ntohl(ans.ttl);

            if (pEntry->ttl > DNS_MAX_TTL) {

              pEntry->ttl = DNS_MAX_TTL;

            }

            /* read the IP address after answer resource record's header */

            MEMCPY( &(pEntry->ipaddr), (pHostname+sizeof(struct dns_answer)), sizeof(struct ip_addr));

            LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": response = ", pEntry->name));

            ip_addr_debug_print(DNS_DEBUG, (&(pEntry->ipaddr)));

            LWIP_DEBUGF(DNS_DEBUG, ("\n"));

            /* call specified callback function if provided */

            if (pEntry->found) {

              (*pEntry->found)(pEntry->name, &pEntry->ipaddr, pEntry->arg);

            }

            /* deallocate memory and return */

            goto memerr2;

          } else {

            pHostname = pHostname + sizeof(struct dns_answer) + htons(ans.len);

          }

          --nanswers;

        }

        LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": error in response\n", pEntry->name));

        /* call callback to indicate error, clean up memory and return */

        goto responseerr;

      }

    }

  }

  /* deallocate memory and return */

  goto memerr2;

responseerr:

  /* ERROR: call specified callback function with NULL as name to indicate an error */

  if (pEntry->found) {

    (*pEntry->found)(pEntry->name, NULL, pEntry->arg);

  }

  /* flush this entry */

  pEntry->state = DNS_STATE_UNUSED;

  pEntry->found = NULL;

memerr2:

#if (DNS_USES_STATIC_BUF == 2)

  /* free dns buffer */

  mem_free(dns_payload);

#endif /* (DNS_USES_STATIC_BUF == 2) */

memerr1:

  /* free pbuf */

  pbuf_free(p);

  return;

}