hello-uri.c

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/*
     This file is part of GNUnet.
     Copyright (C) 2022, 2026 GNUnet e.V.
 
     GNUnet is free software: you can redistribute it and/or modify it
     under the terms of the GNU Affero General Public License as published
     by the Free Software Foundation, either version 3 of the License,
     or (at your option) any later version.
 
     GNUnet is distributed in the hope that it will be useful, but
     WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     Affero General Public License for more details.
 
     You should have received a copy of the GNU Affero General Public License
     along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
     SPDX-License-Identifier: AGPL3.0-or-later
 */
 
#include "gnunet_time_lib.h"
#include "platform.h"
#include "gnunet_util_lib.h"
#include "gnunet_signatures.h"
#include "gnunet_hello_uri_lib.h"
#include "gnunet_protocols.h"
 
 
GNUNET_NETWORK_STRUCT_BEGIN
 
struct PilsHelloSignaturePurpose
{
  struct GNUNET_CRYPTO_SignaturePurpose purpose;
 
  struct GNUNET_TIME_AbsoluteNBO expiration_time;
 
  struct GNUNET_HashCode h_addrs;
 
};
 
struct HelloUriMessage
{
  struct GNUNET_MessageHeader header;
 
  uint16_t reserved GNUNET_PACKED;
 
  uint16_t url_counter GNUNET_PACKED;
 
  /* followed by a 'block' */
};
 
 
struct BlockHeader
{
  struct GNUNET_PeerIdentity pid;
 
  struct GNUNET_CRYPTO_EddsaSignature sig;
 
  struct GNUNET_TIME_AbsoluteNBO expiration_time;
 
};
 
 
struct DhtHelloMessage
{
  struct GNUNET_MessageHeader header;
 
  uint16_t reserved GNUNET_PACKED;
 
  uint16_t url_counter GNUNET_PACKED;
 
  struct GNUNET_CRYPTO_EddsaSignature sig;
 
  struct GNUNET_TIME_AbsoluteNBO expiration_time;
 
  /* followed by the serialized addresses of the 'block' */
};
 
 
GNUNET_NETWORK_STRUCT_END
 
 
struct Address
{
  struct Address *next;
 
  struct Address *prev;
 
  const char *uri;
 
  size_t uri_len;
};
 
 
struct GNUNET_HELLO_Builder
{
  struct Address *a_head;
 
  struct Address *a_tail;
 
  unsigned int a_length;
 
};
 
struct AddressUriMergeResult
{
  struct GNUNET_HELLO_Builder *builder;
 
  const char *address_uri;
 
  unsigned int found;
 
  unsigned int merged;
};
 
struct GNUNET_HELLO_Parser
{
  struct GNUNET_PeerIdentity pid;
 
  struct Address *a_head;
 
  struct Address *a_tail;
 
  unsigned int a_length;
 
  struct GNUNET_CRYPTO_EddsaSignature sig;
 
  struct GNUNET_TIME_Absolute et;
};
 
 
static void
hash_addresses (const struct Address *addr_start,
                struct GNUNET_HashCode *hash)
{
  struct GNUNET_HashContext *hc;
 
  hc = GNUNET_CRYPTO_hash_context_start ();
 
#if HELLO_DETERMINISTIC_PID_DERIVATION
  for (const struct Address *a = addr_start;
       NULL != a;
       a = a->next)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Hashing over %.*s\n",
                (int) a->uri_len,
                a->uri);
    GNUNET_CRYPTO_hash_context_read (hc,
                                     a->uri,
                                     a->uri_len);
  }
#endif
  GNUNET_CRYPTO_hash_context_finish (hc,
                                     hash);
 
}
 
 
static enum GNUNET_GenericReturnValue
verify_hello (const struct GNUNET_HELLO_Parser *parser,
              struct GNUNET_TIME_Absolute et,
              const struct GNUNET_CRYPTO_EddsaSignature *sig)
{
  struct PilsHelloSignaturePurpose hsp = {
    .purpose.size = htonl (sizeof (hsp)),
    .purpose.purpose = htonl (GNUNET_SIGNATURE_PURPOSE_HELLO),
    .expiration_time = GNUNET_TIME_absolute_hton (et)
  };
 
  hash_addresses (parser->a_head,
                  &hsp.h_addrs);
  if (GNUNET_OK !=
      GNUNET_CRYPTO_eddsa_verify (GNUNET_SIGNATURE_PURPOSE_HELLO,
                                  &hsp,
                                  sig,
                                  &parser->pid.public_key))
  {
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "HELLO signature invalid, rejecting.\n");
    return GNUNET_SYSERR;
  }
  if (GNUNET_TIME_absolute_is_past (et))
    return GNUNET_NO;
  return GNUNET_OK;
}
 
 
static struct GNUNET_HELLO_Parser *
parser_new (const struct GNUNET_PeerIdentity *pid)
{
  struct GNUNET_HELLO_Parser *p;
 
  p = GNUNET_new (struct GNUNET_HELLO_Parser);
  p->pid = *pid;
  return p;
}
 
 
struct GNUNET_HELLO_Builder *
GNUNET_HELLO_builder_new ()
{
  struct GNUNET_HELLO_Builder *builder;
 
  builder = GNUNET_new (struct GNUNET_HELLO_Builder);
  return builder;
}
 
 
const struct GNUNET_PeerIdentity *
GNUNET_HELLO_parser_get_id (const struct GNUNET_HELLO_Parser *parser)
{
  return &parser->pid;
}
 
 
struct GNUNET_HELLO_Builder *
GNUNET_HELLO_builder_from_parser (const struct GNUNET_HELLO_Parser *p,
                                  struct GNUNET_PeerIdentity *pid)
{
  struct GNUNET_HELLO_Builder *builder;
  struct Address *a;
 
  builder = GNUNET_HELLO_builder_new ();
  if (NULL != pid)
    *pid = p->pid;
  /* check for duplicates */
  for (a = p->a_head;
       NULL != a;
       a = a->next)
    GNUNET_HELLO_builder_add_address (builder, a->uri);
  return builder;
}
 
 
void
GNUNET_HELLO_parser_free (struct GNUNET_HELLO_Parser *parser)
{
  struct Address *a;
 
  while (NULL != (a = parser->a_head))
  {
    GNUNET_CONTAINER_DLL_remove (parser->a_head,
                                 parser->a_tail,
                                 a);
    parser->a_length--;
    GNUNET_free (a);
  }
  GNUNET_assert (0 == parser->a_length);
  GNUNET_free (parser);
}
 
 
void
GNUNET_HELLO_builder_free (struct GNUNET_HELLO_Builder *builder)
{
  struct Address *a;
 
  while (NULL != (a = builder->a_head))
  {
    GNUNET_CONTAINER_DLL_remove (builder->a_head,
                                 builder->a_tail,
                                 a);
    builder->a_length--;
    GNUNET_free (a);
  }
  GNUNET_assert (0 == builder->a_length);
  GNUNET_free (builder);
}
 
 
struct GNUNET_HELLO_Parser *
GNUNET_HELLO_parser_from_msg (const struct GNUNET_MessageHeader *msg,
                              const struct GNUNET_PeerIdentity *pid)
{
  return GNUNET_HELLO_parser_from_msg_ (msg,
                                        pid,
                                        GNUNET_NO);
}
 
 
struct GNUNET_HELLO_Parser *
GNUNET_HELLO_parser_from_msg_ (const struct GNUNET_MessageHeader *msg,
                               const struct GNUNET_PeerIdentity *pid,
                               int noverify)
{
  uint16_t size;
 
  /* Callers routinely pass the value of a PEERSTORE record straight in,
     and a zero-length record has a NULL value.  Failing that the same way
     as any other unusable input beats dereferencing it. */
  if (NULL == msg)
  {
    GNUNET_break (0);
    return NULL;
  }
  size = ntohs (msg->size);
  switch (ntohs (msg->type))
  {
  case GNUNET_MESSAGE_TYPE_HELLO_URI:
    {
      const struct HelloUriMessage *h;
 
      if (sizeof (struct HelloUriMessage) > size)
      {
        GNUNET_break_op (0);
        return NULL;
      }
 
      h = (const struct HelloUriMessage *) msg;
      size -= sizeof (*h);
      return GNUNET_HELLO_parser_from_block_ (&h[1],
                                              size,
                                              noverify);
    }
  case GNUNET_MESSAGE_TYPE_DHT_P2P_HELLO:
    {
      struct GNUNET_TIME_Absolute block_expiration;
      struct GNUNET_HELLO_Parser *p;
      size_t block_size;
      void *block;
 
      if (sizeof (struct DhtHelloMessage) > size)
      {
        GNUNET_break_op (0);
        return NULL;
      }
 
      if (GNUNET_SYSERR == GNUNET_HELLO_dht_msg_to_block (
            msg,
            pid,
            &block,
            &block_size,
            &block_expiration))
      {
        GNUNET_break_op (0);
        return NULL;
      }
 
      p = GNUNET_HELLO_parser_from_block_ (block,
                                           block_size,
                                           noverify);
      GNUNET_free (block);
      return p;
    }
  default:
    GNUNET_break_op (0);
    return NULL;
  }
}
 
 
static enum GNUNET_GenericReturnValue
check_address (const char *address)
{
  const char *e;
 
  if (NULL == (e = strstr (address,
                           "://")))
  {
    GNUNET_break_op (0);
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                "Invalid address `%s'\n",
                address);
    return GNUNET_SYSERR;
  }
  if (e == address)
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  for (const char *p = address; p != e; p++)
    if ( (! isalpha ((unsigned char) *p)) &&
         ('+' != *p) )
    {
      GNUNET_break_op (0);
      return GNUNET_SYSERR;
    }
  return GNUNET_OK;
}
 
 
int
static
cmp_address (void*cls, struct Address *a, struct Address *b)
{
  return strcmp (a->uri, b->uri);
}
 
 
static enum GNUNET_GenericReturnValue
parser_add_address (struct GNUNET_HELLO_Parser *parser,
                    const char *address)
{
  struct Address *a;
  enum GNUNET_GenericReturnValue ret;
  size_t alen = strlen (address) + 1;
 
  ret = check_address (address);
  if (GNUNET_OK != ret)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Failed to add address to builder\n");
    return ret;
  }
  /* check for duplicates */
  for (a = parser->a_head;
       NULL != a;
       a = a->next)
    if (0 == strcmp (address,
                     a->uri))
      return GNUNET_NO;
  a = GNUNET_malloc (sizeof (struct Address) + alen);
  a->uri_len = alen;
  memcpy (&a[1],
          address,
          alen);
  a->uri = (const char *) &a[1];
  GNUNET_CONTAINER_DLL_insert_sorted (struct Address,
                                      cmp_address,
                                      NULL,
                                      parser->a_head,
                                      parser->a_tail,
                                      a);
  parser->a_length++;
  return GNUNET_OK;
}
 
 
struct GNUNET_HELLO_Parser *
GNUNET_HELLO_parser_from_block (const void *block,
                                size_t block_size)
{
  return GNUNET_HELLO_parser_from_block_ (block,
                                          block_size,
                                          GNUNET_NO);
}
 
 
struct GNUNET_HELLO_Parser *
GNUNET_HELLO_parser_from_block_ (const void *block,
                                 size_t block_size,
                                 int noverify)
{
  const struct BlockHeader *bh = block;
  struct GNUNET_HELLO_Parser *p;
 
  if (block_size < sizeof (*bh))
  {
    GNUNET_break_op (0);
    return NULL;
  }
  p = parser_new (&bh->pid);
  block += sizeof (*bh);
  block_size -= sizeof (*bh);
  while (block_size > 0)
  {
    const void *end = memchr (block,
                              '\0',
                              block_size);
 
    if (NULL == end)
    {
      GNUNET_break_op (0);
      GNUNET_HELLO_parser_free (p);
      return NULL;
    }
    if (GNUNET_OK !=
        parser_add_address (p,
                            block))
    {
      GNUNET_break_op (0);
      GNUNET_HELLO_parser_free (p);
      return NULL;
    }
    end++;
    block_size -= (end - block);
    block = end;
  }
  {
    struct GNUNET_TIME_Absolute et;
    et = GNUNET_TIME_absolute_ntoh (bh->expiration_time);
    if (GNUNET_YES != noverify)
    {
      enum GNUNET_GenericReturnValue ret;
      ret = verify_hello (p,
                          et,
                          &bh->sig);
      GNUNET_break_op (GNUNET_SYSERR != ret);
      if (GNUNET_OK != ret)
      {
        GNUNET_HELLO_parser_free (p);
        return NULL;
      }
    }
    p->et = et;
    p->sig = bh->sig;
  }
  return p;
}
 
 
struct GNUNET_TIME_Absolute
GNUNET_HELLO_get_expiration_time_from_msg (const struct
                                           GNUNET_MessageHeader *msg)
{
  struct GNUNET_TIME_Absolute et;
  if (GNUNET_MESSAGE_TYPE_HELLO_URI == ntohs (msg->type))
  {
    const struct HelloUriMessage *h = (const struct HelloUriMessage *) msg;
    const struct BlockHeader *bh = (const struct BlockHeader *) &h[1];
    if (ntohs (msg->size) <
        sizeof (struct HelloUriMessage) + sizeof (struct BlockHeader))
    {
      GNUNET_break_op (0);
      return GNUNET_TIME_UNIT_ZERO_ABS;
    }
    if (ntohs (msg->size) ==
        sizeof (struct HelloUriMessage) + sizeof (struct BlockHeader))
    {
      /* Well-formed, but carries no address: nothing worth keeping.  This is
         what our own HELLO looks like before a communicator has reported an
         address, so it is not a protocol violation. */
      return GNUNET_TIME_UNIT_ZERO_ABS;
    }
 
    et = GNUNET_TIME_absolute_ntoh (bh->expiration_time);
    return et;
  }
  else if (GNUNET_MESSAGE_TYPE_DHT_P2P_HELLO == ntohs (msg->type))
  {
    const struct DhtHelloMessage *dht_hello
      = (const struct DhtHelloMessage *) msg;
    if (ntohs (msg->size) < sizeof (struct DhtHelloMessage))
    {
      GNUNET_break_op (0);
      return GNUNET_TIME_UNIT_ZERO_ABS;
    }
 
    et = GNUNET_TIME_absolute_ntoh (dht_hello->expiration_time);
    return et;
  }
  else
    GNUNET_break_op (0);
  return GNUNET_TIME_UNIT_ZERO_ABS;
}
 
 
enum GNUNET_GenericReturnValue
GNUNET_HELLO_builder_add_address (struct GNUNET_HELLO_Builder *builder,
                                  const char *address)
{
  struct Address *a;
  enum GNUNET_GenericReturnValue ret;
  size_t alen = strlen (address) + 1;
 
  ret = check_address (address);
  if (GNUNET_OK != ret)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Failed to add address to builder\n");
    return ret;
  }
  /* check for duplicates */
  for (a = builder->a_head;
       NULL != a;
       a = a->next)
    if (0 == strcmp (address,
                     a->uri))
      return GNUNET_NO;
  a = GNUNET_malloc (sizeof (struct Address) + alen);
  a->uri_len = alen;
  memcpy (&a[1],
          address,
          alen);
  a->uri = (const char *) &a[1];
  GNUNET_CONTAINER_DLL_insert_sorted (struct Address,
                                      cmp_address,
                                      NULL,
                                      builder->a_head,
                                      builder->a_tail,
                                      a);
  builder->a_length++;
  return GNUNET_OK;
}
 
 
struct GNUNET_HELLO_Parser *
GNUNET_HELLO_parser_from_url (const char *url)
{
  const char *q;
  const char *s1;
  const char *s2;
  struct GNUNET_PeerIdentity pid;
  struct GNUNET_TIME_Absolute et;
  size_t len;
  struct GNUNET_HELLO_Parser *p;
  struct GNUNET_CRYPTO_EddsaSignature sig;
 
  if (0 != strncasecmp (url,
                        "gnunet://hello/",
                        strlen ("gnunet://hello/")))
    return NULL;
  url += strlen ("gnunet://hello/");
  s1 = strchr (url, '/');
  if (NULL == s1)
  {
    GNUNET_break_op (0);
    return NULL;
  }
  s2 = strchr (s1 + 1, '/');
  if (NULL == s2)
  {
    GNUNET_break_op (0);
    return NULL;
  }
  q = strchr (url, '?');
  if (NULL == q)
    q = url + strlen (url);
  if (GNUNET_OK !=
      GNUNET_STRINGS_string_to_data (url,
                                     s1 - url,
                                     &pid,
                                     sizeof(pid)))
  {
    GNUNET_break_op (0);
    return NULL;
  }
  if (GNUNET_OK !=
      GNUNET_STRINGS_string_to_data (s1 + 1,
                                     s2 - (s1 + 1),
                                     &sig,
                                     sizeof(sig)))
  {
    GNUNET_break_op (0);
    return NULL;
  }
  {
    uint64_t sec;
    char dummy = '?';
 
    if ( (0 == sscanf (s2 + 1,
                       "%" PRIu64 "%c",
                       &sec,
                       &dummy)) ||
         ('?' != dummy) )
    {
      GNUNET_break_op (0);
      return NULL;
    }
    et.abs_value_us = sec;
  }
 
  p = parser_new (&pid);
  p->et = et;
  p->sig = sig;
  len = strlen (q);
  while (len > 0)
  {
    const char *eq;
    const char *amp;
    char *addr = NULL;
    char *uri;
 
    /* skip ?/& separator */
    len--;
    q++;
    eq = strchr (q, '=');
    if ( (eq == q) ||
         (NULL == eq) )
    {
      GNUNET_break_op (0);
      GNUNET_HELLO_parser_free (p);
      return NULL;
    }
    amp = strchr (eq, '&');
    if (NULL == amp)
      amp = &q[len];
    GNUNET_STRINGS_urldecode (eq + 1,
                              amp - (eq + 1),
                              &addr);
    if ( (NULL == addr) ||
         (0 == strlen (addr)) )
    {
      GNUNET_free (addr);
      GNUNET_break_op (0);
      GNUNET_HELLO_parser_free (p);
      return NULL;
    }
    GNUNET_asprintf (&uri,
                     "%.*s://%s",
                     (int) (eq - q),
                     q,
                     addr);
    GNUNET_free (addr);
    if (GNUNET_OK !=
        parser_add_address (p,
                            uri))
    {
      GNUNET_break_op (0);
      GNUNET_free (uri);
      GNUNET_HELLO_parser_free (p);
      return NULL;
    }
    GNUNET_free (uri);
    /* move to next URL */
    len -= (amp - q);
    q = amp;
  }
 
  {
    enum GNUNET_GenericReturnValue ret;
 
    ret = verify_hello (p,
                        et,
                        &p->sig);
    GNUNET_break_op (GNUNET_SYSERR != ret);
    if (GNUNET_OK != ret)
    {
      GNUNET_HELLO_parser_free (p);
      return NULL;
    }
  }
  return p;
}
 
 
char *
GNUNET_HELLO_parser_to_url (const struct GNUNET_HELLO_Parser *parser)
{
  char *result;
  char *pids;
  char *sigs;
  const char *sep = "?";
 
  pids = GNUNET_STRINGS_data_to_string_alloc (&parser->pid,
                                              sizeof (parser->pid));
  sigs = GNUNET_STRINGS_data_to_string_alloc (&parser->sig,
                                              sizeof (parser->sig));
  GNUNET_asprintf (&result,
                   "gnunet://hello/%s/%s/%" PRIu64,
                   pids,
                   sigs,
                   parser->et.abs_value_us);
  GNUNET_free (sigs);
  GNUNET_free (pids);
  for (struct Address *a = parser->a_head;
       NULL != a;
       a = a->next)
  {
    char *eou_url_encoded;
    char *tmp;
    int pfx_len;
    const char *eou;
 
    eou = strstr (a->uri,
                  "://");
    if (NULL == eou)
    {
      GNUNET_break_op (0);
      GNUNET_free (result);
      return NULL;
    }
    pfx_len = eou - a->uri;
    eou += 3;
    GNUNET_STRINGS_urlencode (a->uri_len - 4 - pfx_len,
                              eou,
                              &eou_url_encoded);
    GNUNET_asprintf (&tmp,
                     "%s%s%.*s=%s",
                     result,
                     sep,
                     pfx_len,
                     a->uri,
                     eou_url_encoded);
    GNUNET_free (eou_url_encoded);
    GNUNET_free (result);
    result = tmp;
    sep = "&";
  }
  return result;
}
 
 
enum GNUNET_GenericReturnValue
GNUNET_HELLO_parser_to_block (const struct GNUNET_HELLO_Parser *parser,
                              void *block,
                              size_t *block_size)
{
  struct BlockHeader bh;
  size_t needed = sizeof (bh);
  char *pos;
 
  for (struct Address *a = parser->a_head;
       NULL != a;
       a = a->next)
  {
    GNUNET_assert (needed + a->uri_len > needed);
    needed += a->uri_len;
  }
  if ( (NULL == block) ||
       (needed > *block_size) )
  {
    *block_size = needed;
    return GNUNET_NO;
  }
  bh.pid = parser->pid;
  bh.sig = parser->sig;
  bh.expiration_time = GNUNET_TIME_absolute_hton (parser->et);
  memcpy (block,
          &bh,
          sizeof (bh));
  pos = block + sizeof (bh);
  for (struct Address *a = parser->a_head;
       NULL != a;
       a = a->next)
  {
    memcpy (pos,
            a->uri,
            a->uri_len);
    pos += a->uri_len;
  }
  *block_size = needed;
  return GNUNET_OK;
}
 
 
struct GNUNET_MQ_Envelope *
GNUNET_HELLO_parser_to_env (const struct GNUNET_HELLO_Parser *parser)
{
  struct GNUNET_MQ_Envelope *env;
  struct HelloUriMessage *msg;
  size_t blen;
 
  if (parser->a_length > UINT16_MAX)
  {
    GNUNET_break_op (0);
    return NULL;
  }
  blen = 0;
  GNUNET_assert (GNUNET_NO ==
                 GNUNET_HELLO_parser_to_block (parser,
                                               NULL,
                                               &blen));
  env = GNUNET_MQ_msg_extra (msg,
                             blen,
                             GNUNET_MESSAGE_TYPE_HELLO_URI);
  msg->url_counter = htons ((uint16_t) parser->a_length);
  GNUNET_assert (GNUNET_OK ==
                 GNUNET_HELLO_parser_to_block (parser,
                                               &msg[1],
                                               &blen));
  return env;
}
 
 
enum GNUNET_GenericReturnValue
GNUNET_HELLO_builder_del_address (struct GNUNET_HELLO_Builder *builder,
                                  const char *address)
{
  struct Address *a;
 
  /* check for duplicates */
  for (a = builder->a_head;
       NULL != a;
       a = a->next)
    if (0 == strcmp (address,
                     a->uri))
      break;
  if (NULL == a)
    return GNUNET_NO;
  GNUNET_CONTAINER_DLL_remove (builder->a_head,
                               builder->a_tail,
                               a);
  builder->a_length--;
  GNUNET_free (a);
  return GNUNET_OK;
}
 
 
void
GNUNET_HELLO_builder_iterate (const struct GNUNET_HELLO_Builder *builder,
                              GNUNET_HELLO_UriCallback uc,
                              void *uc_cls)
{
  struct Address *nxt;
 
  for (struct Address *a = builder->a_head;
       NULL != a;
       a = nxt)
  {
    nxt = a->next;
    uc (uc_cls,
        NULL,
        a->uri);
  }
}
 
 
const struct GNUNET_PeerIdentity*
GNUNET_HELLO_parser_iterate (const struct GNUNET_HELLO_Parser *parser,
                             GNUNET_HELLO_UriCallback uc,
                             void *uc_cls)
{
  struct Address *nxt;
 
  if (NULL == uc)
    return &parser->pid;
  for (struct Address *a = parser->a_head;
       NULL != a;
       a = nxt)
  {
    nxt = a->next;
    uc (uc_cls,
        &parser->pid,
        a->uri);
  }
  return &parser->pid;
}
 
 
enum GNUNET_GenericReturnValue
GNUNET_HELLO_dht_msg_to_block (const struct GNUNET_MessageHeader *hello,
                               const struct GNUNET_PeerIdentity *pid,
                               void **block,
                               size_t *block_size,
                               struct GNUNET_TIME_Absolute *block_expiration)
{
  const struct DhtHelloMessage *msg
    = (const struct DhtHelloMessage *) hello;
  uint16_t len = ntohs (hello->size);
  struct BlockHeader *bh;
  struct GNUNET_HELLO_Parser *b;
  enum GNUNET_GenericReturnValue ret;
 
  if (GNUNET_MESSAGE_TYPE_DHT_P2P_HELLO != ntohs (hello->type))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  if (len < sizeof (*msg))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  len -= sizeof (*msg);
  *block_size = len + sizeof (*bh);
  *block = GNUNET_malloc (*block_size);
  bh = *block;
  bh->pid = *pid;
  bh->sig = msg->sig;
  bh->expiration_time = msg->expiration_time;
  *block_expiration = GNUNET_TIME_absolute_ntoh (msg->expiration_time);
  memcpy (&bh[1],
          &msg[1],
          len);
  b = GNUNET_HELLO_parser_from_block (*block,
                                      *block_size);
  if (NULL == b)
  {
    GNUNET_break_op (0);
    GNUNET_free (*block);
    *block_size = 0;
    return GNUNET_SYSERR;
  }
  ret = verify_hello (b,
                      *block_expiration,
                      &msg->sig);
  GNUNET_HELLO_parser_free (b);
  if (GNUNET_SYSERR == ret)
  {
    GNUNET_free (*block);
    *block_size = 0;
    return GNUNET_SYSERR;
  }
  return ret;
}
 
 
char *
GNUNET_HELLO_address_to_prefix (const char *address)
{
  const char *dash;
 
  dash = strchr (address, '-');
  if (NULL == dash)
    return NULL;
  return GNUNET_strndup (address, dash - address);
}
 
 
enum GNUNET_GenericReturnValue
GNUNET_HELLO_build_url (const struct GNUNET_HELLO_Builder *builder,
                        const struct GNUNET_PeerIdentity *pid,
                        const struct GNUNET_CRYPTO_EddsaSignature *sig,
                        struct GNUNET_TIME_Absolute expiration,
                        char **result)
{
  char *pids;
  char *sigs;
  const char *sep = "?";
 
  pids = GNUNET_STRINGS_data_to_string_alloc (pid,
                                              sizeof (*pid));
  sigs = GNUNET_STRINGS_data_to_string_alloc (sig,
                                              sizeof (*sig));
  GNUNET_asprintf (result,
                   "gnunet://hello/%s/%s/%" PRIu64,
                   pids,
                   sigs,
                   expiration.abs_value_us);
  GNUNET_free (sigs);
  GNUNET_free (pids);
  for (struct Address *a = builder->a_head;
       NULL != a;
       a = a->next)
  {
    char *eou_url_encoded;
    char *tmp;
    int pfx_len;
    const char *eou;
 
    eou = strstr (a->uri,
                  "://");
    if (NULL == eou)
    {
      GNUNET_break_op (0);
      GNUNET_free (*result);
      return GNUNET_SYSERR;
    }
    pfx_len = eou - a->uri;
    eou += 3;
    GNUNET_STRINGS_urlencode (a->uri_len - 4 - pfx_len,
                              eou,
                              &eou_url_encoded);
    GNUNET_asprintf (&tmp,
                     "%s%s%.*s=%s",
                     *result,
                     sep,
                     pfx_len,
                     a->uri,
                     eou_url_encoded);
    GNUNET_free (eou_url_encoded);
    GNUNET_free (*result);
    *result = tmp;
    sep = "&";
  }
  return GNUNET_OK;
}
 
 
void
GNUNET_HELLO_builder_hash_addresses (const struct GNUNET_HELLO_Builder *builder,
                                     struct GNUNET_HashCode *hash)
{
  hash_addresses (builder->a_head, hash);
}
 
 
struct GNUNET_MQ_Envelope*
GNUNET_HELLO_builder_to_env (
  const struct GNUNET_HELLO_Builder *builder,
  const struct GNUNET_PeerIdentity *pid,
  const struct GNUNET_CRYPTO_EddsaSignature *hello_sig,
  struct GNUNET_TIME_Absolute expiration_time)
{
  struct GNUNET_MQ_Envelope *env;
  struct HelloUriMessage *msg;
  size_t blen;
 
  if (builder->a_length > UINT16_MAX)
  {
    GNUNET_break_op (0);
    return NULL;
  }
  blen = GNUNET_HELLO_get_builder_to_block_size (builder);
  env = GNUNET_MQ_msg_extra (msg,
                             blen,
                             GNUNET_MESSAGE_TYPE_HELLO_URI);
  msg->url_counter = htons ((uint16_t) builder->a_length);
  GNUNET_HELLO_builder_to_block (builder,
                                 pid,
                                 hello_sig,
                                 expiration_time,
                                 (char*) &msg[1]);
  return env;
}
 
 
struct GNUNET_MessageHeader *
GNUNET_HELLO_parser_to_dht_hello_msg (const struct GNUNET_HELLO_Parser *parser)
{
  struct BlockHeader *block;
  struct DhtHelloMessage *msg;
  size_t block_size;
 
 
  block_size = 0;
  GNUNET_assert (GNUNET_NO ==
                 GNUNET_HELLO_parser_to_block (parser,
                                               NULL,
                                               &block_size));
  msg = GNUNET_malloc (sizeof (*msg)
                       + block_size);
  if (GNUNET_OK !=
      GNUNET_HELLO_parser_to_block (parser,
                                    &msg[1],
                                    &block_size))
  {
    GNUNET_free (msg);
    return NULL;
  }
  block = (struct BlockHeader*) &msg[1];
  msg->sig = block->sig;
  msg->expiration_time = block->expiration_time;
  memmove (&msg[1],
           (char*) block + sizeof (*block),
           block_size - sizeof (*block));
  msg->header.type = htons (GNUNET_MESSAGE_TYPE_DHT_P2P_HELLO);
  msg->header.size = htons (sizeof (*msg)
                            + block_size
                            - sizeof (*block));
  msg->url_counter = htons ((uint16_t) parser->a_length);
  return &msg->header;
}
 
 
struct GNUNET_MessageHeader *
GNUNET_HELLO_builder_to_dht_hello_msg (
  const struct GNUNET_HELLO_Builder *builder,
  const struct GNUNET_PeerIdentity *pid,
  const struct GNUNET_CRYPTO_EddsaSignature *hello_sig,
  struct GNUNET_TIME_Absolute expiration_time)
{
  struct BlockHeader *block;
  struct DhtHelloMessage *msg;
  size_t block_size;
 
 
  block_size = GNUNET_HELLO_get_builder_to_block_size (builder);
  msg = GNUNET_malloc (sizeof (*msg)
                       + block_size);
  block = (struct BlockHeader*) &msg[1];
  GNUNET_HELLO_builder_to_block (builder,
                                 pid,
                                 hello_sig,
                                 expiration_time,
                                 (char*) &msg[1]);
  msg->sig = block->sig;
  msg->expiration_time = block->expiration_time;
  memmove (&msg[1],
           (char*) block + sizeof (*block),
           block_size - sizeof (*block));
  msg->header.type = htons (GNUNET_MESSAGE_TYPE_DHT_P2P_HELLO);
  msg->header.size = htons (sizeof (*msg)
                            + block_size
                            - sizeof (*block));
  msg->url_counter = htons ((uint16_t) builder->a_length);
  return &msg->header;
}
 
 
void
GNUNET_HELLO_builder_to_block (
  const struct GNUNET_HELLO_Builder *builder,
  const struct GNUNET_PeerIdentity *pid,
  const struct GNUNET_CRYPTO_EddsaSignature *sig,
  struct GNUNET_TIME_Absolute expiration_time,
  char *block)
{
  struct BlockHeader bh = { 0 };
  char *pos;
  struct GNUNET_TIME_Absolute et;
 
  if (NULL != pid)
    bh.pid = *pid;
  if (NULL != sig)
    bh.sig = *sig;
  if (GNUNET_TIME_UNIT_ZERO_ABS.abs_value_us == expiration_time.abs_value_us)
    et = GNUNET_TIME_relative_to_absolute (GNUNET_HELLO_ADDRESS_EXPIRATION);
  else
    et = expiration_time;
  bh.expiration_time = GNUNET_TIME_absolute_hton (et);
  memcpy (block,
          &bh,
          sizeof (bh));
  pos = block + sizeof (bh);
  for (struct Address *a = builder->a_head; NULL != a; a = a->next)
  {
    memcpy (pos,
            a->uri,
            a->uri_len);
    pos += a->uri_len;
  }
}
 
 
enum GNUNET_GenericReturnValue
GNUNET_HELLO_builder_to_url2 (const struct GNUNET_HELLO_Builder *builder,
                              const struct GNUNET_PeerIdentity *pid,
                              const struct GNUNET_CRYPTO_EddsaSignature *sig,
                              struct GNUNET_TIME_Absolute validity,
                              char **result)
{
  return GNUNET_HELLO_build_url (builder,
                                 pid,
                                 sig,
                                 validity,
                                 result);
}
 
 
enum GNUNET_GenericReturnValue
GNUNET_HELLO_builder_to_url (const struct GNUNET_HELLO_Builder *builder,
                             const struct GNUNET_PeerIdentity *pid,
                             const struct GNUNET_CRYPTO_EddsaSignature *sig,
                             char **result)
{
  struct GNUNET_TIME_Absolute et;
 
  et = GNUNET_TIME_relative_to_absolute (GNUNET_HELLO_ADDRESS_EXPIRATION);
 
  return GNUNET_HELLO_builder_to_url2 (builder,
                                       pid,
                                       sig,
                                       et,
                                       result);
}
 
 
size_t
GNUNET_HELLO_get_builder_to_block_size (
  const struct GNUNET_HELLO_Builder *builder)
{
  struct BlockHeader bh;
  size_t needed = sizeof (bh);
 
  for (struct Address *a = builder->a_head;
       NULL != a;
       a = a->next)
  {
    GNUNET_assert (needed + a->uri_len > needed);
    needed += a->uri_len;
  }
  return needed;
}
 
 
enum GNUNET_GenericReturnValue
GNUNET_HELLO_builder_address_list_cmp (const struct GNUNET_HELLO_Builder *
                                       abuilder,
                                       const struct GNUNET_HELLO_Builder *
                                       bbuilder)
{
  bool found = false;
  for (struct Address *a = abuilder->a_head; NULL != a; a = a->next)
  {
    for (struct Address *b = bbuilder->a_head; NULL != b; b = b->next)
    {
      if (0 != strcmp (b->uri, a->uri))
        continue;
      found = true;
      break;
    }
    if (! found)
      return GNUNET_NO;
    found = false;
  }
  return GNUNET_YES;
}