no includes on top level please

[oweals/gnunet.git] / src / fs / fs_download.c

/*
     This file is part of GNUnet.
     (C) 2001-2011 Christian Grothoff (and other contributing authors)

     GNUnet is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published
     by the Free Software Foundation; either version 3, 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
     General Public License for more details.

     You should have received a copy of the GNU General Public License
     along with GNUnet; see the file COPYING.  If not, write to the
     Free Software Foundation, Inc., 59 Temple Place - Suite 330,
     Boston, MA 02111-1307, USA.
*/
/**
 * @file fs/fs_download.c
 * @brief download methods
 * @author Christian Grothoff
 *
 * TODO:
 * - different priority for scheduling probe downloads?
 */
#include "platform.h"
#include "gnunet_constants.h"
#include "gnunet_fs_service.h"
#include "fs.h"
#include "fs_tree.h"

#define DEBUG_DOWNLOAD GNUNET_NO

/**
 * Determine if the given download (options and meta data) should cause
 * use to try to do a recursive download.
 */
static int
is_recursive_download (struct GNUNET_FS_DownloadContext *dc)
{
  return  (0 != (dc->options & GNUNET_FS_DOWNLOAD_OPTION_RECURSIVE)) &&
    ( (GNUNET_YES == GNUNET_FS_meta_data_test_for_directory (dc->meta)) ||
      ( (dc->meta == NULL) &&
        ( (NULL == dc->filename) ||            
          ( (strlen (dc->filename) >= strlen (GNUNET_FS_DIRECTORY_EXT)) &&
            (NULL !=
             strstr (dc->filename + strlen(dc->filename) - strlen(GNUNET_FS_DIRECTORY_EXT),
                     GNUNET_FS_DIRECTORY_EXT)) ) ) ) );              
}


/**
 * We're storing the IBLOCKS after the DBLOCKS on disk (so that we
 * only have to truncate the file once we're done).
 *
 * Given the offset of a block (with respect to the DBLOCKS) and its
 * depth, return the offset where we would store this block in the
 * file.
 * 
 * @param fsize overall file size
 * @param off offset of the block in the file
 * @param depth depth of the block in the tree, 0 for DBLOCK
 * @return off for DBLOCKS (depth == treedepth),
 *         otherwise an offset past the end
 *         of the file that does not overlap
 *         with the range for any other block
 */
static uint64_t
compute_disk_offset (uint64_t fsize,
                     uint64_t off,
                     unsigned int depth)
{
  unsigned int i;
  uint64_t lsize; /* what is the size of all IBlocks for depth "i"? */
  uint64_t loff; /* where do IBlocks for depth "i" start? */
  unsigned int ioff; /* which IBlock corresponds to "off" at depth "i"? */
  
  if (depth == 0)
    return off;
  /* first IBlocks start at the end of file, rounded up
     to full DBLOCK_SIZE */
  loff = ((fsize + DBLOCK_SIZE - 1) / DBLOCK_SIZE) * DBLOCK_SIZE;
  lsize = ( (fsize + DBLOCK_SIZE - 1) / DBLOCK_SIZE) * sizeof (struct ContentHashKey);
  GNUNET_assert (0 == (off % DBLOCK_SIZE));
  ioff = (off / DBLOCK_SIZE);
  for (i=1;i<depth;i++)
    {
      loff += lsize;
      lsize = (lsize + CHK_PER_INODE - 1) / CHK_PER_INODE;
      GNUNET_assert (lsize > 0);
      GNUNET_assert (0 == (ioff % CHK_PER_INODE));
      ioff /= CHK_PER_INODE;
    }
  return loff + ioff * sizeof (struct ContentHashKey);
}


/**
 * Given a block at the given offset and depth, calculate the offset
 * for the CHK at the given index.
 *
 * @param offset the offset of the first
 *        DBLOCK in the subtree of the 
 *        identified IBLOCK
 * @param depth the depth of the IBLOCK in the tree, 0 for DBLOCK
 * @param k which CHK in the IBLOCK are we 
 *        talking about
 * @return offset if k=0, otherwise an appropriately
 *         larger value (i.e., if depth = 1,
 *         the returned value should be offset+k*DBLOCK_SIZE)
 */
static uint64_t
compute_dblock_offset (uint64_t offset,
                       unsigned int depth,
                       unsigned int k)
{
  unsigned int i;
  uint64_t lsize; /* what is the size of the sum of all DBlocks 
                     that a CHK at depth i corresponds to? */

  if (depth == 0)
    return offset;
  lsize = DBLOCK_SIZE;
  for (i=1;i<depth;i++)
    lsize *= CHK_PER_INODE;
  return offset + k * lsize;
}


/**
 * Fill in all of the generic fields for a download event and call the
 * callback.
 *
 * @param pi structure to fill in
 * @param dc overall download context
 */
void
GNUNET_FS_download_make_status_ (struct GNUNET_FS_ProgressInfo *pi,
                                 struct GNUNET_FS_DownloadContext *dc)
{
  pi->value.download.dc = dc;
  pi->value.download.cctx
    = dc->client_info;
  pi->value.download.pctx
    = (dc->parent == NULL) ? NULL : dc->parent->client_info;
  pi->value.download.sctx
    = (dc->search == NULL) ? NULL : dc->search->client_info;
  pi->value.download.uri 
    = dc->uri;
  pi->value.download.filename
    = dc->filename;
  pi->value.download.size
    = dc->length;
  pi->value.download.duration
    = GNUNET_TIME_absolute_get_duration (dc->start_time);
  pi->value.download.completed
    = dc->completed;
  pi->value.download.anonymity
    = dc->anonymity;
  pi->value.download.eta
    = GNUNET_TIME_calculate_eta (dc->start_time,
                                 dc->completed,
                                 dc->length);
  pi->value.download.is_active = (dc->client == NULL) ? GNUNET_NO : GNUNET_YES;
  if (0 == (dc->options & GNUNET_FS_DOWNLOAD_IS_PROBE))
    dc->client_info = dc->h->upcb (dc->h->upcb_cls,
                                   pi);
  else
    dc->client_info = GNUNET_FS_search_probe_progress_ (NULL,
                                                        pi);
}


/**
 * We're ready to transmit a search request to the
 * file-sharing service.  Do it.  If there is 
 * more than one request pending, try to send 
 * multiple or request another transmission.
 *
 * @param cls closure
 * @param size number of bytes available in buf
 * @param buf where the callee should write the message
 * @return number of bytes written to buf
 */
static size_t
transmit_download_request (void *cls,
                           size_t size, 
                           void *buf);


/**
 * Closure for iterator processing results.
 */
struct ProcessResultClosure
{
  
  /**
   * Hash of data.
   */
  GNUNET_HashCode query;

  /**
   * Data found in P2P network.
   */ 
  const void *data;

  /**
   * Our download context.
   */
  struct GNUNET_FS_DownloadContext *dc;
                
  /**
   * Number of bytes in data.
   */
  size_t size;

  /**
   * Type of data.
   */
  enum GNUNET_BLOCK_Type type;

  /**
   * Flag to indicate if this block should be stored on disk.
   */
  int do_store;
  
};


/**
 * Iterator over entries in the pending requests in the 'active' map for the
 * reply that we just got.
 *
 * @param cls closure (our 'struct ProcessResultClosure')
 * @param key query for the given value / request
 * @param value value in the hash map (a 'struct DownloadRequest')
 * @return GNUNET_YES (we should continue to iterate); unless serious error
 */
static int
process_result_with_request (void *cls,
                             const GNUNET_HashCode * key,
                             void *value);


/**
 * We've found a matching block without downloading it.
 * Encrypt it and pass it to our "receive" function as
 * if we had received it from the network.
 * 
 * @param dc download in question
 * @param chk request this relates to
 * @param dr request details
 * @param block plaintext data matching request
 * @param len number of bytes in block
 * @param do_store should we still store the block on disk?
 * @return GNUNET_OK on success
 */
static int
encrypt_existing_match (struct GNUNET_FS_DownloadContext *dc,
                        const struct ContentHashKey *chk,
                        struct DownloadRequest *dr,
                        const char * block,                    
                        size_t len,
                        int do_store)
{
  struct ProcessResultClosure prc;
  char enc[len];
  struct GNUNET_CRYPTO_AesSessionKey sk;
  struct GNUNET_CRYPTO_AesInitializationVector iv;
  GNUNET_HashCode query;
  
  GNUNET_CRYPTO_hash_to_aes_key (&chk->key, &sk, &iv);
  if (-1 == GNUNET_CRYPTO_aes_encrypt (block, len,
                                       &sk,
                                       &iv,
                                       enc))
    {
      GNUNET_break (0);
      return GNUNET_SYSERR;
    }
  GNUNET_CRYPTO_hash (enc, len, &query);
  if (0 != memcmp (&query,
                   &chk->query,
                   sizeof (GNUNET_HashCode)))
    {
      GNUNET_break_op (0);
      return GNUNET_SYSERR;
    }
#if DEBUG_DOWNLOAD
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Matching block for `%s' at offset %llu already present, no need for download!\n",
              dc->filename,
              (unsigned long long) dr->offset);
#endif
  /* already got it! */
  prc.dc = dc;
  prc.data = enc;
  prc.size = len;
  prc.type = (0 == dr->depth) 
    ? GNUNET_BLOCK_TYPE_FS_DBLOCK 
    : GNUNET_BLOCK_TYPE_FS_IBLOCK;
  prc.query = chk->query;
  prc.do_store = do_store;
  process_result_with_request (&prc,
                               &chk->key,
                               dr);
  return GNUNET_OK;
}


/**
 * We've lost our connection with the FS service.
 * Re-establish it and re-transmit all of our
 * pending requests.
 *
 * @param dc download context that is having trouble
 */
static void
try_reconnect (struct GNUNET_FS_DownloadContext *dc);


/**
 * We found an entry in a directory.  Check if the respective child
 * already exists and if not create the respective child download.
 *
 * @param cls the parent download
 * @param filename name of the file in the directory
 * @param uri URI of the file (CHK or LOC)
 * @param meta meta data of the file
 * @param length number of bytes in data
 * @param data contents of the file (or NULL if they were not inlined)
 */
static void 
trigger_recursive_download (void *cls,
                            const char *filename,
                            const struct GNUNET_FS_Uri *uri,
                            const struct GNUNET_CONTAINER_MetaData *meta,
                            size_t length,
                            const void *data);


/**
 * We're done downloading a directory.  Open the file and
 * trigger all of the (remaining) child downloads.
 *
 * @param dc context of download that just completed
 */
static void
full_recursive_download (struct GNUNET_FS_DownloadContext *dc)
{
  size_t size;
  uint64_t size64;
  void *data;
  struct GNUNET_DISK_FileHandle *h;
  struct GNUNET_DISK_MapHandle *m;
  
  size64 = GNUNET_FS_uri_chk_get_file_size (dc->uri);
  size = (size_t) size64;
  if (size64 != (uint64_t) size)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                  _("Recursive downloads of directories larger than 4 GB are not supported on 32-bit systems\n"));
      return;
    }
  if (dc->filename != NULL)
    {
      h = GNUNET_DISK_file_open (dc->filename,
                                 GNUNET_DISK_OPEN_READ,
                                 GNUNET_DISK_PERM_NONE);
    }
  else
    {
      GNUNET_assert (dc->temp_filename != NULL);
      h = GNUNET_DISK_file_open (dc->temp_filename,
                                 GNUNET_DISK_OPEN_READ,
                                 GNUNET_DISK_PERM_NONE);
    }
  if (h == NULL)
    return; /* oops */
  data = GNUNET_DISK_file_map (h, &m, GNUNET_DISK_MAP_TYPE_READ, size);
  if (data == NULL)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                  _("Directory too large for system address space\n"));
    }
  else
    {
      GNUNET_FS_directory_list_contents (size,
                                         data,
                                         0,
                                         &trigger_recursive_download,
                                         dc);         
      GNUNET_DISK_file_unmap (m);
    }
  GNUNET_DISK_file_close (h);
  if (dc->filename == NULL)
    {
      if (0 != UNLINK (dc->temp_filename))
        GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_WARNING,
                                  "unlink",
                                  dc->temp_filename);
      GNUNET_free (dc->temp_filename);
      dc->temp_filename = NULL;
    }
}


/**
 * Check if all child-downloads have completed (or trigger them if
 * necessary) and once we're completely done, signal completion (and
 * possibly recurse to parent).  This function MUST be called when the
 * download of a file itself is done or when the download of a file is
 * done and then later a direct child download has completed (and
 * hence this download may complete itself).
 *
 * @param dc download to check for completion of children
 */
static void
check_completed (struct GNUNET_FS_DownloadContext *dc)
{
  struct GNUNET_FS_ProgressInfo pi;
  struct GNUNET_FS_DownloadContext *pos;

  /* first, check if we need to download children */
  if ( (dc->child_head == NULL) &&
       (is_recursive_download (dc)) )
    full_recursive_download (dc);  
  /* then, check if children are done already */
  pos = dc->child_head;
  while (pos != NULL)
    {
      if ( (pos->emsg == NULL) &&
           (pos->completed < pos->length) )
        return; /* not done yet */
      if ( (pos->child_head != NULL) &&
           (pos->has_finished != GNUNET_YES) )
        return; /* not transitively done yet */
      pos = pos->next;
    }
  /* All of our children are done, so mark this download done */
  dc->has_finished = GNUNET_YES;
  if (dc->job_queue != NULL)
    {
      GNUNET_FS_dequeue_ (dc->job_queue);
      dc->job_queue = NULL;
    }
  GNUNET_FS_download_sync_ (dc);

  /* signal completion */
  pi.status = GNUNET_FS_STATUS_DOWNLOAD_COMPLETED;
  GNUNET_FS_download_make_status_ (&pi, dc);

  /* let parent know */
  if (dc->parent != NULL)
    check_completed (dc->parent);  
}


/**
 * We got a block of plaintext data (from the meta data).
 * Try it for upward reconstruction of the data.  On success,
 * the top-level block will move to state BRS_DOWNLOAD_UP.
 *
 * @param dc context for the download
 * @param dr download request to match against
 * @param data plaintext data, starting from the beginning of the file
 * @param data_len number of bytes in data
 */ 
static void
try_match_block (struct GNUNET_FS_DownloadContext *dc,
                 struct DownloadRequest *dr,
                 const char *data,
                 size_t data_len)
{
  struct GNUNET_FS_ProgressInfo pi;
  unsigned int i;
  char enc[DBLOCK_SIZE];
  struct ContentHashKey chks[CHK_PER_INODE];
  struct ContentHashKey in_chk;
  struct GNUNET_CRYPTO_AesSessionKey sk;
  struct GNUNET_CRYPTO_AesInitializationVector iv;
  size_t dlen;
  struct DownloadRequest *drc;
  struct GNUNET_DISK_FileHandle *fh;
  int complete;
  const char *fn;
  const char *odata;
  size_t odata_len;
  
  odata = data;
  odata_len = data_len;
  if (BRS_DOWNLOAD_UP == dr->state)
    return;
  if (dr->depth > 0)
    {
      complete = GNUNET_YES;
      for (i=0;i<dr->num_children;i++)
        {
          drc = dr->children[i];
          try_match_block (dc,
                           drc,
                           data, data_len);
          if (drc->state != BRS_RECONSTRUCT_META_UP)
            complete = GNUNET_NO;
          else
            chks[i] = drc->chk;
        }
      if (GNUNET_YES != complete)
        return;
      data = (const char*) chks;
      dlen = dr->num_children * sizeof (struct ContentHashKey);
    }
  else
    {
      if (dr->offset > data_len) 
        return; /* oops */
      dlen = GNUNET_MIN (data_len - dr->offset,
                         DBLOCK_SIZE);
    }
  GNUNET_CRYPTO_hash (&data[dr->offset],
                      dlen,
                      &in_chk.key);
  GNUNET_CRYPTO_hash_to_aes_key (&in_chk.key, &sk, &iv);
  if (-1 == GNUNET_CRYPTO_aes_encrypt (&data[dr->offset], dlen,
                                       &sk,
                                       &iv,
                                       enc))
    {
      GNUNET_break (0);
      return;
    }
  GNUNET_CRYPTO_hash (enc, dlen, &in_chk.query);
  switch (dr->state)
    {
    case BRS_INIT:
      dr->chk = in_chk;
      dr->state = BRS_RECONSTRUCT_META_UP;
      break;
    case BRS_CHK_SET:
      if (0 != memcmp (&in_chk,
                       &dr->chk,
                       sizeof (struct ContentHashKey)))
        {
          /* other peer provided bogus meta data */
          GNUNET_break_op (0);
          break;
        }
      /* write block to disk */
      fn = dc->filename != NULL 
        ? dc->filename 
        : dc->temp_filename;
      fh = GNUNET_DISK_file_open (fn,
                                  GNUNET_DISK_OPEN_READWRITE | 
                                  GNUNET_DISK_OPEN_CREATE | 
                                  GNUNET_DISK_OPEN_TRUNCATE,
                                  GNUNET_DISK_PERM_USER_READ |
                                  GNUNET_DISK_PERM_USER_WRITE |
                                  GNUNET_DISK_PERM_GROUP_READ |
                                  GNUNET_DISK_PERM_OTHER_READ);     
      if (fh == NULL)
        {
          GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_ERROR,
                                    "open",
                                    fn);
          GNUNET_asprintf (&dc->emsg,
                           _("Failed to open file `%s' for writing"),
                           fn);
          GNUNET_DISK_file_close (fh);
          dr->state = BRS_ERROR;
          pi.status = GNUNET_FS_STATUS_DOWNLOAD_ERROR;
          pi.value.download.specifics.error.message = dc->emsg;
          GNUNET_FS_download_make_status_ (&pi, dc); 
          return;
        }
      if (data_len != 
          GNUNET_DISK_file_write (fh,
                                  odata,
                                  odata_len))
        {
          GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_ERROR,
                                    "write",
                                    fn);              
          GNUNET_asprintf (&dc->emsg,
                           _("Failed to open file `%s' for writing"),
                           fn);
          GNUNET_DISK_file_close (fh);
          dr->state = BRS_ERROR;
          pi.status = GNUNET_FS_STATUS_DOWNLOAD_ERROR;
          pi.value.download.specifics.error.message = dc->emsg;
          GNUNET_FS_download_make_status_ (&pi, dc);      
          return;
        }
      GNUNET_DISK_file_close (fh);
      /* signal success */      
      dr->state = BRS_DOWNLOAD_UP;
      dc->completed = dc->length;
      GNUNET_FS_download_sync_ (dc);
      pi.status = GNUNET_FS_STATUS_DOWNLOAD_PROGRESS;
      pi.value.download.specifics.progress.data = data;
      pi.value.download.specifics.progress.offset = 0;
      pi.value.download.specifics.progress.data_len = dlen;
      pi.value.download.specifics.progress.depth = 0;
      GNUNET_FS_download_make_status_ (&pi, dc);
      if (0 != truncate (dc->filename,
                         GNUNET_ntohll (dc->uri->data.chk.file_length)))
        GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_WARNING,
                                  "truncate",
                                  dc->filename);
      check_completed (dc);      
      break;
    default:
      /* how did we get here? */
      GNUNET_break (0);
      break;
    }
}


/**
 * Type of a function that libextractor calls for each
 * meta data item found.  If we find full data meta data,
 * call 'try_match_block' on it.
 *
 * @param cls our 'struct GNUNET_FS_DownloadContext*'
 * @param plugin_name name of the plugin that produced this value;
 *        special values can be used (i.e. '&lt;zlib&gt;' for zlib being
 *        used in the main libextractor library and yielding
 *        meta data).
 * @param type libextractor-type describing the meta data
 * @param format basic format information about data 
 * @param data_mime_type mime-type of data (not of the original file);
 *        can be NULL (if mime-type is not known)
 * @param data actual meta-data found
 * @param data_len number of bytes in data
 * @return 0 to continue extracting, 1 to abort
 */ 
static int
match_full_data (void *cls,
                 const char *plugin_name,
                 enum EXTRACTOR_MetaType type,
                 enum EXTRACTOR_MetaFormat format,
                 const char *data_mime_type,
                 const char *data,
                 size_t data_len)
{
  struct GNUNET_FS_DownloadContext *dc = cls;

  if (type != EXTRACTOR_METATYPE_GNUNET_FULL_DATA) 
    return 0;
#if DEBUG_DOWNLOAD
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Found %u bytes of FD!\n",
              (unsigned int) data_len);
#endif
  if (GNUNET_FS_uri_chk_get_file_size (dc->uri) != data_len)
    {
      GNUNET_break_op (0);
      return 1; /* bogus meta data */
    }
  try_match_block (dc,
                   dc->top_request,
                   data,
                   data_len);
  return 1;
}


/**
 * Set the state of the given download request to
 * BRS_DOWNLOAD_UP and propagate it up the tree.
 *
 * @param dr download request that is done
 */
static void
propagate_up (struct DownloadRequest *dr)
{
  unsigned int i;

  do
    {
      dr->state = BRS_DOWNLOAD_UP;
      dr = dr->parent;
      if (dr == NULL)
        break;
      for (i=0;i<dr->num_children;i++)
        if (dr->children[i]->state != BRS_DOWNLOAD_UP)
          break;
    }
  while (i == dr->num_children);
}


/**
 * Try top-down reconstruction.  Before, the given request node
 * must have the state BRS_CHK_SET.  Afterwards, more nodes may
 * have that state or advanced to BRS_DOWNLOAD_DOWN or even
 * BRS_DOWNLOAD_UP.  It is also possible to get BRS_ERROR on the
 * top level.
 *
 * @param dc overall download this block belongs to
 * @param dr block to reconstruct
 */
static void
try_top_down_reconstruction (struct GNUNET_FS_DownloadContext *dc,
                             struct DownloadRequest *dr)
{
  uint64_t off;
  char block[DBLOCK_SIZE];
  GNUNET_HashCode key;
  uint64_t total;
  size_t len;
  unsigned int i;
  unsigned int chk_off;
  struct DownloadRequest *drc;
  uint64_t child_block_size;
  const struct ContentHashKey *chks;
  int up_done;
  
  GNUNET_assert (dc->rfh != NULL);
  GNUNET_assert (dr->state == BRS_CHK_SET);
  total = GNUNET_FS_uri_chk_get_file_size (dc->uri);
  GNUNET_assert (dr->depth < dc->treedepth);
  len = GNUNET_FS_tree_calculate_block_size (total,
                                             dr->offset,
                                             dr->depth);
  GNUNET_assert (len <= DBLOCK_SIZE);
  off = compute_disk_offset (total,
                             dr->offset,
                             dr->depth);
  if (dc->old_file_size < off + len) 
    return; /* failure */
  if (off  != 
      GNUNET_DISK_file_seek (dc->rfh,
                             off,
                             GNUNET_DISK_SEEK_SET) ) 
    {
      GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_WARNING,
                                "seek",
                                dc->filename);
      return; /* failure */
    }
  if (len != 
      GNUNET_DISK_file_read (dc->rfh,
                             block,
                             len)) 
    {
      GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_WARNING,
                                "read",
                                dc->filename);
      return; /* failure */
    }
  GNUNET_CRYPTO_hash (block, len, &key);
  if (0 != memcmp (&key,
                   &dr->chk.key,
                   sizeof (GNUNET_HashCode)))
    return; /* mismatch */
  if (GNUNET_OK !=
      encrypt_existing_match (dc,
                              &dr->chk,
                              dr,
                              block,
                              len,
                              GNUNET_NO))
    {
      /* hash matches but encrypted block does not, really bad */
      dr->state = BRS_ERROR;
      /* propagate up */
      while (dr->parent != NULL)
        {
          dr = dr->parent;
          dr->state = BRS_ERROR;
        }
      return;
    }
  /* block matches */
  dr->state = BRS_DOWNLOAD_DOWN;

  /* set CHKs for children */
  up_done = GNUNET_YES;
  chks = (const struct ContentHashKey*) block;
  for (i=0;i<dr->num_children;i++)
    {
      drc = dr->children[i];
      GNUNET_assert (drc->offset >= dr->offset);
      child_block_size = GNUNET_FS_tree_compute_tree_size (drc->depth);
      GNUNET_assert (0 == (drc->offset - dr->offset) % child_block_size);
      chk_off = (drc->offset - dr->offset) / child_block_size;
      GNUNET_assert (drc->state == BRS_INIT);
      drc->state = BRS_CHK_SET;
      drc->chk = chks[chk_off];
      try_top_down_reconstruction (dc, drc);
      if (drc->state != BRS_DOWNLOAD_UP)
        up_done = GNUNET_NO; /* children not all done */
    } 
  if (up_done == GNUNET_YES)
    propagate_up (dr); /* children all done (or no children...) */
}


/**
 * Schedule the download of the specified block in the tree.
 *
 * @param dc overall download this block belongs to
 * @param dr request to schedule
 */
static void
schedule_block_download (struct GNUNET_FS_DownloadContext *dc,
                         struct DownloadRequest *dr)
{
  unsigned int i;

  switch (dr->state)
    {
    case BRS_INIT:
      GNUNET_assert (0);
      break;
    case BRS_RECONSTRUCT_DOWN:
      GNUNET_assert (0);
      break;
    case BRS_RECONSTRUCT_META_UP:
      GNUNET_assert (0);
      break;
    case BRS_RECONSTRUCT_UP:
      GNUNET_assert (0);
      break;
    case BRS_CHK_SET:
      /* normal case, start download */
      break;
    case BRS_DOWNLOAD_DOWN:
      for (i=0;i<dr->num_children;i++)
        schedule_block_download (dc, dr->children[i]);
      return;
    case BRS_DOWNLOAD_UP:
      /* We're done! */
      return;
    case BRS_ERROR:
      GNUNET_break (0);
      return;
    }
#if DEBUG_DOWNLOAD
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Scheduling download at offset %llu and depth %u for `%s'\n",
              (unsigned long long) dr->offset,
              dr->depth,
              GNUNET_h2s (&dr->chk.query));
#endif
  GNUNET_assert (GNUNET_NO ==
                 GNUNET_CONTAINER_multihashmap_contains_value (dc->active,
                                                               &dr->chk.query,
                                                               dr));
  GNUNET_CONTAINER_multihashmap_put (dc->active,
                                     &dr->chk.query,
                                     dr,
                                     GNUNET_CONTAINER_MULTIHASHMAPOPTION_MULTIPLE);
  if (dc->client == NULL)
    return; /* download not active */
  GNUNET_CONTAINER_DLL_insert (dc->pending_head,
                               dc->pending_tail,
                               dr);
  dr->is_pending = GNUNET_YES;
  if (NULL == dc->th)
    dc->th = GNUNET_CLIENT_notify_transmit_ready (dc->client,
                                                  sizeof (struct SearchMessage),
                                                  GNUNET_CONSTANTS_SERVICE_TIMEOUT,
                                                  GNUNET_NO,
                                                  &transmit_download_request,
                                                  dc);
}


#define GNUNET_FS_URI_CHK_PREFIX GNUNET_FS_URI_PREFIX GNUNET_FS_URI_CHK_INFIX

/**
 * We found an entry in a directory.  Check if the respective child
 * already exists and if not create the respective child download.
 *
 * @param cls the parent download
 * @param filename name of the file in the directory
 * @param uri URI of the file (CHK or LOC)
 * @param meta meta data of the file
 * @param length number of bytes in data
 * @param data contents of the file (or NULL if they were not inlined)
 */
static void 
trigger_recursive_download (void *cls,
                            const char *filename,
                            const struct GNUNET_FS_Uri *uri,
                            const struct GNUNET_CONTAINER_MetaData *meta,
                            size_t length,
                            const void *data)
{
  struct GNUNET_FS_DownloadContext *dc = cls;  
  struct GNUNET_FS_DownloadContext *cpos;
  char *temp_name;
  char *fn;
  char *us;
  char *ext;
  char *dn;
  char *pos;
  char *full_name;
  char *sfn;

  if (NULL == uri)
    return; /* entry for the directory itself */
  cpos = dc->child_head;
  while (cpos != NULL)
    {
      if ( (GNUNET_FS_uri_test_equal (uri,
                                      cpos->uri)) ||
           ( (filename != NULL) &&
             (0 == strcmp (cpos->filename,
                           filename)) ) )
        break;  
      cpos = cpos->next;
    }
  if (cpos != NULL)
    return; /* already exists */
  fn = NULL;
  if (NULL == filename)
    {
      fn = GNUNET_FS_meta_data_suggest_filename (meta);
      if (fn == NULL)
        {
          us = GNUNET_FS_uri_to_string (uri);
          fn = GNUNET_strdup (&us [strlen (GNUNET_FS_URI_CHK_PREFIX)]);
          GNUNET_free (us);
        }
      else if (fn[0] == '.')
        {
          ext = fn;
          us = GNUNET_FS_uri_to_string (uri);
          GNUNET_asprintf (&fn,
                           "%s%s",
                           &us[strlen (GNUNET_FS_URI_CHK_PREFIX)], ext);
          GNUNET_free (ext);
          GNUNET_free (us);
        }
      /* change '\' to '/' (this should have happened
       during insertion, but malicious peers may
       not have done this) */
      while (NULL != (pos = strstr (fn, "\\")))
        *pos = '/';
      /* remove '../' everywhere (again, well-behaved
         peers don't do this, but don't trust that
         we did not get something nasty) */
      while (NULL != (pos = strstr (fn, "../")))
        {
          pos[0] = '_';
          pos[1] = '_';
          pos[2] = '_';
        }
      filename = fn;
    }
  if (dc->filename == NULL)
    {
      full_name = NULL;
    }
  else
    {
      dn = GNUNET_strdup (dc->filename);
      GNUNET_break ( (strlen (dn) >= strlen (GNUNET_FS_DIRECTORY_EXT)) &&
                     (NULL !=
                      strstr (dn + strlen(dn) - strlen(GNUNET_FS_DIRECTORY_EXT),
                              GNUNET_FS_DIRECTORY_EXT)) );
      sfn = GNUNET_strdup (filename);
      while ( (strlen (sfn) > 0) &&
              (filename[strlen(sfn)-1] == '/') )
        sfn[strlen(sfn)-1] = '\0';
      if ( (strlen (dn) >= strlen (GNUNET_FS_DIRECTORY_EXT)) &&
           (NULL !=
            strstr (dn + strlen(dn) - strlen(GNUNET_FS_DIRECTORY_EXT),
                    GNUNET_FS_DIRECTORY_EXT)) )      
        dn[strlen(dn) - strlen (GNUNET_FS_DIRECTORY_EXT)] = '\0';      
      if ( (GNUNET_YES == GNUNET_FS_meta_data_test_for_directory (meta)) &&
           ( (strlen (filename) < strlen (GNUNET_FS_DIRECTORY_EXT)) ||
             (NULL ==
              strstr (filename + strlen(filename) - strlen(GNUNET_FS_DIRECTORY_EXT),
                      GNUNET_FS_DIRECTORY_EXT)) ) )
        {
          GNUNET_asprintf (&full_name,
                           "%s%s%s%s",
                           dn,
                           DIR_SEPARATOR_STR,
                           sfn,
                           GNUNET_FS_DIRECTORY_EXT);
        }
      else
        {
          GNUNET_asprintf (&full_name,
                           "%s%s%s",
                           dn,
                           DIR_SEPARATOR_STR,
                           sfn);
        }
      GNUNET_free (dn);
    }
  if ( (full_name != NULL) &&
       (GNUNET_OK !=
        GNUNET_DISK_directory_create_for_file (full_name)) )
    {
      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                  _("Failed to create directory for recursive download of `%s'\n"),
                  full_name);
      GNUNET_free (full_name);
      GNUNET_free_non_null (fn);
      return;
    }

  temp_name = NULL;
#if DEBUG_DOWNLOAD
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Triggering recursive download of size %llu with %u bytes MD\n",
              (unsigned long long) GNUNET_FS_uri_chk_get_file_size (uri),
              (unsigned int) GNUNET_CONTAINER_meta_data_get_serialized_size (meta));
#endif
  GNUNET_FS_download_start (dc->h,
                            uri,
                            meta,
                            full_name, temp_name,
                            0,
                            GNUNET_FS_uri_chk_get_file_size (uri),
                            dc->anonymity,
                            dc->options,
                            NULL,
                            dc);
  GNUNET_free_non_null (full_name);
  GNUNET_free_non_null (temp_name);
  GNUNET_free_non_null (fn);
}


/**
 * (recursively) free download request structure
 *
 * @param dr request to free
 */
void
GNUNET_FS_free_download_request_ (struct DownloadRequest *dr)
{
  unsigned int i;

  if (dr == NULL)
    return;
  for (i=0;i<dr->num_children;i++)
    GNUNET_FS_free_download_request_ (dr->children[i]);
  GNUNET_free_non_null (dr->children);
  GNUNET_free (dr);
}


/**
 * Iterator over entries in the pending requests in the 'active' map for the
 * reply that we just got.
 *
 * @param cls closure (our 'struct ProcessResultClosure')
 * @param key query for the given value / request
 * @param value value in the hash map (a 'struct DownloadRequest')
 * @return GNUNET_YES (we should continue to iterate); unless serious error
 */
static int
process_result_with_request (void *cls,
                             const GNUNET_HashCode *key,
                             void *value)
{
  struct ProcessResultClosure *prc = cls;
  struct DownloadRequest *dr = value;
  struct GNUNET_FS_DownloadContext *dc = prc->dc;
  struct DownloadRequest *drc;
  struct GNUNET_DISK_FileHandle *fh = NULL;
  struct GNUNET_CRYPTO_AesSessionKey skey;
  struct GNUNET_CRYPTO_AesInitializationVector iv;
  char pt[prc->size];
  struct GNUNET_FS_ProgressInfo pi;
  uint64_t off;
  size_t bs;
  size_t app;
  int i;
  struct ContentHashKey *chk;

#if DEBUG_DOWNLOAD
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received block `%s' matching pending request at depth %u and offset %llu/%llu\n",
              GNUNET_h2s (key),
              dr->depth,
              (unsigned long long) dr->offset,
              (unsigned long long) GNUNET_ntohll (dc->uri->data.chk.file_length));
              
#endif
  bs = GNUNET_FS_tree_calculate_block_size (GNUNET_ntohll (dc->uri->data.chk.file_length),
                                            dr->offset,
                                            dr->depth);
  if (prc->size != bs)
    {
      GNUNET_asprintf (&dc->emsg,
                       _("Internal error or bogus download URI (expected %u bytes at depth %u and offset %llu/%llu, got %u bytes)\n"),
                       bs,
                       dr->depth,
                       (unsigned long long) dr->offset,
                       (unsigned long long) GNUNET_ntohll (dc->uri->data.chk.file_length),
                       prc->size);
      GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                  "%s", 
                  dc->emsg);
      while (dr->parent != NULL)
        {
          dr->state = BRS_ERROR;
          dr = dr->parent;
        }
      dr->state = BRS_ERROR;
      goto signal_error;
    }

  (void) GNUNET_CONTAINER_multihashmap_remove (dc->active,
                                               &prc->query,
                                               dr);
  if (GNUNET_YES == dr->is_pending)
    {
      GNUNET_CONTAINER_DLL_remove (dc->pending_head,
                                   dc->pending_tail,
                                   dr);
      dr->is_pending = GNUNET_NO;
    }


  GNUNET_CRYPTO_hash_to_aes_key (&dr->chk.key, &skey, &iv);
  if (-1 == GNUNET_CRYPTO_aes_decrypt (prc->data,
                                       prc->size,
                                       &skey,
                                       &iv,
                                       pt))
    {
      GNUNET_break (0);
      dc->emsg = GNUNET_strdup (_("internal error decrypting content"));
      goto signal_error;
    }
  off = compute_disk_offset (GNUNET_ntohll (dc->uri->data.chk.file_length),
                             dr->offset,
                             dr->depth);
  /* save to disk */
  if ( ( GNUNET_YES == prc->do_store) &&
       ( (dc->filename != NULL) ||
         (is_recursive_download (dc)) ) &&
       ( (dr->depth == dc->treedepth) ||
         (0 == (dc->options & GNUNET_FS_DOWNLOAD_NO_TEMPORARIES)) ) )
    {
      fh = GNUNET_DISK_file_open (dc->filename != NULL 
                                  ? dc->filename 
                                  : dc->temp_filename, 
                                  GNUNET_DISK_OPEN_READWRITE | 
                                  GNUNET_DISK_OPEN_CREATE,
                                  GNUNET_DISK_PERM_USER_READ |
                                  GNUNET_DISK_PERM_USER_WRITE |
                                  GNUNET_DISK_PERM_GROUP_READ |
                                  GNUNET_DISK_PERM_OTHER_READ);    
      if (NULL == fh)
        {
          GNUNET_asprintf (&dc->emsg,
                           _("Download failed: could not open file `%s': %s\n"),
                           dc->filename,
                           STRERROR (errno));
          goto signal_error;
        }      
#if DEBUG_DOWNLOAD
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Saving decrypted block to disk at offset %llu\n",
                  (unsigned long long) off);
#endif
      if ( (off  != 
            GNUNET_DISK_file_seek (fh,
                                   off,
                                   GNUNET_DISK_SEEK_SET) ) )
        {
          GNUNET_asprintf (&dc->emsg,
                           _("Failed to seek to offset %llu in file `%s': %s\n"),
                           (unsigned long long) off,
                           dc->filename,
                           STRERROR (errno));
          goto signal_error;
        }
      if (prc->size !=
          GNUNET_DISK_file_write (fh,
                                  pt,
                                  prc->size))
        {
          GNUNET_asprintf (&dc->emsg,
                           _("Failed to write block of %u bytes at offset %llu in file `%s': %s\n"),
                           (unsigned int) prc->size,
                           (unsigned long long) off,
                           dc->filename,
                           STRERROR (errno));
          goto signal_error;
        }
      GNUNET_break (GNUNET_OK == GNUNET_DISK_file_close (fh));
      fh = NULL;
    }

  if (dr->depth == 0) 
    {
      /* DBLOCK, update progress and try recursion if applicable */
      app = prc->size;
      if (dr->offset < dc->offset)
        {
          /* starting offset begins in the middle of pt,
             do not count first bytes as progress */
          GNUNET_assert (app > (dc->offset - dr->offset));
          app -= (dc->offset - dr->offset);       
        }
      if (dr->offset + prc->size > dc->offset + dc->length)
        {
          /* end of block is after relevant range,
             do not count last bytes as progress */
          GNUNET_assert (app > (dr->offset + prc->size) - (dc->offset + dc->length));
          app -= (dr->offset + prc->size) - (dc->offset + dc->length);
        }
      dc->completed += app;

      /* do recursive download if option is set and either meta data
         says it is a directory or if no meta data is given AND filename 
         ends in '.gnd' (top-level case) */
      if (is_recursive_download (dc))
        GNUNET_FS_directory_list_contents (prc->size,
                                           pt,
                                           off,
                                           &trigger_recursive_download,
                                           dc);         
            
    }
  dr->state = BRS_DOWNLOAD_DOWN;
  pi.status = GNUNET_FS_STATUS_DOWNLOAD_PROGRESS;
  pi.value.download.specifics.progress.data = pt;
  pi.value.download.specifics.progress.offset = dr->offset;
  pi.value.download.specifics.progress.data_len = prc->size;
  pi.value.download.specifics.progress.depth = dr->depth;
  GNUNET_FS_download_make_status_ (&pi, dc);
  GNUNET_assert (dc->completed <= dc->length);
  if (dr->depth == 0) 
    propagate_up (dr);

  if (dc->completed == dc->length)
    {
      /* download completed, signal */
#if DEBUG_DOWNLOAD
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Download completed, truncating file to desired length %llu\n",
                  (unsigned long long) GNUNET_ntohll (dc->uri->data.chk.file_length));
#endif
      /* truncate file to size (since we store IBlocks at the end) */
      if (dc->filename != NULL)
        {
          if (0 != truncate (dc->filename,
                             GNUNET_ntohll (dc->uri->data.chk.file_length)))
            GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_WARNING,
                                      "truncate",
                                      dc->filename);
        }
      GNUNET_assert (dr->depth == 0);
      check_completed (dc);
    }
  if (dr->depth == 0) 
    {
      /* bottom of the tree, no child downloads possible, just sync */
      GNUNET_FS_download_sync_ (dc);
      return GNUNET_YES;
    }

#if DEBUG_DOWNLOAD
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Triggering downloads of children (this block was at depth %u and offset %llu)\n",
              dr->depth,
              (unsigned long long) dr->offset);
#endif
  GNUNET_assert (0 == (prc->size % sizeof(struct ContentHashKey)));
  chk = (struct ContentHashKey*) pt;
  for (i=(prc->size / sizeof(struct ContentHashKey))-1;i>=0;i--)
    {
      off = compute_dblock_offset (dr->offset,
                                   dr->depth,
                                   i);
      drc = dr->children[i];
      switch (drc->state)
        {
        case BRS_INIT:
          drc->chk = chk[i];
          drc->state = BRS_CHK_SET;
          schedule_block_download (dc, drc);
          break;
        case BRS_RECONSTRUCT_DOWN:
          GNUNET_assert (0);
          break;
        case BRS_RECONSTRUCT_META_UP:
          GNUNET_assert (0);
          break;
        case BRS_RECONSTRUCT_UP:
          GNUNET_assert (0);
          break;
        case BRS_CHK_SET:
          GNUNET_assert (0);
          break;
        case BRS_DOWNLOAD_DOWN:
          GNUNET_assert (0);
          break;
        case BRS_DOWNLOAD_UP:
          GNUNET_assert (0);
          break;
        case BRS_ERROR:
          GNUNET_assert (0);
          break;
        default:
          GNUNET_assert (0);
          break;
        }
    }
  GNUNET_FS_download_sync_ (dc);
  return GNUNET_YES;

 signal_error:
  if (fh != NULL)
    GNUNET_DISK_file_close (fh);
  pi.status = GNUNET_FS_STATUS_DOWNLOAD_ERROR;
  pi.value.download.specifics.error.message = dc->emsg;
  GNUNET_FS_download_make_status_ (&pi, dc);
  /* abort all pending requests */
  if (NULL != dc->th)
    {
      GNUNET_CLIENT_notify_transmit_ready_cancel (dc->th);
      dc->th = NULL;
    }
  GNUNET_CLIENT_disconnect (dc->client, GNUNET_NO);
  dc->client = NULL;
  GNUNET_FS_free_download_request_ (dc->top_request);
  dc->top_request = NULL;
  GNUNET_CONTAINER_multihashmap_destroy (dc->active);
  dc->active = NULL;
  dc->pending_head = NULL;
  dc->pending_tail = NULL;
  GNUNET_FS_download_sync_ (dc);
  return GNUNET_NO;
}


/**
 * Process a download result.
 *
 * @param dc our download context
 * @param type type of the result
 * @param data the (encrypted) response
 * @param size size of data
 */
static void
process_result (struct GNUNET_FS_DownloadContext *dc,
                enum GNUNET_BLOCK_Type type,
                const void *data,
                size_t size)
{
  struct ProcessResultClosure prc;

  prc.dc = dc;
  prc.data = data;
  prc.size = size;
  prc.type = type;
  prc.do_store = GNUNET_YES;
  GNUNET_CRYPTO_hash (data, size, &prc.query);
#if DEBUG_DOWNLOAD
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received result for query `%s' from `%s'-service\n",
              GNUNET_h2s (&prc.query),
              "FS");
#endif
  GNUNET_CONTAINER_multihashmap_get_multiple (dc->active,
                                              &prc.query,
                                              &process_result_with_request,
                                              &prc);
}


/**
 * Type of a function to call when we receive a message
 * from the service.
 *
 * @param cls closure
 * @param msg message received, NULL on timeout or fatal error
 */
static void 
receive_results (void *cls,
                 const struct GNUNET_MessageHeader * msg)
{
  struct GNUNET_FS_DownloadContext *dc = cls;
  const struct PutMessage *cm;
  uint16_t msize;

  if ( (NULL == msg) ||
       (ntohs (msg->type) != GNUNET_MESSAGE_TYPE_FS_PUT) ||
       (sizeof (struct PutMessage) > ntohs(msg->size)) )
    {
      GNUNET_break (msg == NULL);       
      try_reconnect (dc);
      return;
    }
  msize = ntohs(msg->size);
  cm = (const struct PutMessage*) msg;
  process_result (dc, 
                  ntohl (cm->type),
                  &cm[1],
                  msize - sizeof (struct PutMessage));
  if (dc->client == NULL)
    return; /* fatal error */
  /* continue receiving */
  GNUNET_CLIENT_receive (dc->client,
                         &receive_results,
                         dc,
                         GNUNET_TIME_UNIT_FOREVER_REL);
}



/**
 * We're ready to transmit a search request to the
 * file-sharing service.  Do it.  If there is 
 * more than one request pending, try to send 
 * multiple or request another transmission.
 *
 * @param cls closure
 * @param size number of bytes available in buf
 * @param buf where the callee should write the message
 * @return number of bytes written to buf
 */
static size_t
transmit_download_request (void *cls,
                           size_t size, 
                           void *buf)
{
  struct GNUNET_FS_DownloadContext *dc = cls;
  size_t msize;
  struct SearchMessage *sm;
  struct DownloadRequest *dr;

  dc->th = NULL;
  if (NULL == buf)
    {
#if DEBUG_DOWNLOAD
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Transmitting download request failed, trying to reconnect\n");
#endif
      try_reconnect (dc);
      return 0;
    }
  GNUNET_assert (size >= sizeof (struct SearchMessage));
  msize = 0;
  sm = buf;
  while ( (NULL != (dr = dc->pending_head)) &&
          (size >= msize + sizeof (struct SearchMessage)) )
    {
#if DEBUG_DOWNLOAD
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Transmitting download request for `%s' to `%s'-service\n",
                  GNUNET_h2s (&dr->chk.query),
                  "FS");
#endif
      memset (sm, 0, sizeof (struct SearchMessage));
      sm->header.size = htons (sizeof (struct SearchMessage));
      sm->header.type = htons (GNUNET_MESSAGE_TYPE_FS_START_SEARCH);
      if (0 != (dc->options & GNUNET_FS_DOWNLOAD_OPTION_LOOPBACK_ONLY))
        sm->options = htonl (1);
      else
        sm->options = htonl (0);      
      if (dr->depth == 0)
        sm->type = htonl (GNUNET_BLOCK_TYPE_FS_DBLOCK);
      else
        sm->type = htonl (GNUNET_BLOCK_TYPE_FS_IBLOCK);
      sm->anonymity_level = htonl (dc->anonymity);
      sm->target = dc->target.hashPubKey;
      sm->query = dr->chk.query;
      GNUNET_CONTAINER_DLL_remove (dc->pending_head,
                                   dc->pending_tail,
                                   dr);
      dr->is_pending = GNUNET_NO;
      msize += sizeof (struct SearchMessage);
      sm++;
    }
  if (dc->pending_head != NULL)
    {
      dc->th = GNUNET_CLIENT_notify_transmit_ready (dc->client,
                                                    sizeof (struct SearchMessage),
                                                    GNUNET_CONSTANTS_SERVICE_TIMEOUT,
                                                    GNUNET_NO,
                                                    &transmit_download_request,
                                                    dc); 
      GNUNET_assert (dc->th != NULL);
    }
  return msize;
}


/**
 * Reconnect to the FS service and transmit our queries NOW.
 *
 * @param cls our download context
 * @param tc unused
 */
static void
do_reconnect (void *cls,
              const struct GNUNET_SCHEDULER_TaskContext *tc)
{
  struct GNUNET_FS_DownloadContext *dc = cls;
  struct GNUNET_CLIENT_Connection *client;
  
  dc->task = GNUNET_SCHEDULER_NO_TASK;
  client = GNUNET_CLIENT_connect ("fs",
                                  dc->h->cfg);
  if (NULL == client)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                  "Connecting to `%s'-service failed, will try again.\n",
                  "FS");
      try_reconnect (dc);
      return;
    }
  dc->client = client;
  if (dc->pending_head != NULL)
    {
      dc->th = GNUNET_CLIENT_notify_transmit_ready (client,
                                                    sizeof (struct SearchMessage),
                                                    GNUNET_CONSTANTS_SERVICE_TIMEOUT,
                                                    GNUNET_NO,
                                                    &transmit_download_request,
                                                    dc);
      GNUNET_assert (dc->th != NULL);
    }
  GNUNET_CLIENT_receive (client,
                         &receive_results,
                         dc,
                         GNUNET_TIME_UNIT_FOREVER_REL);
}


/**
 * Add entries to the pending list.
 *
 * @param cls our download context
 * @param key unused
 * @param entry entry of type "struct DownloadRequest"
 * @return GNUNET_OK
 */
static int
retry_entry (void *cls,
             const GNUNET_HashCode *key,
             void *entry)
{
  struct GNUNET_FS_DownloadContext *dc = cls;
  struct DownloadRequest *dr = entry;

  dr->next = NULL;
  dr->prev = NULL;
  GNUNET_CONTAINER_DLL_insert (dc->pending_head,
                               dc->pending_tail,
                               dr);
  dr->is_pending = GNUNET_YES;
  return GNUNET_OK;
}


/**
 * We've lost our connection with the FS service.
 * Re-establish it and re-transmit all of our
 * pending requests.
 *
 * @param dc download context that is having trouble
 */
static void
try_reconnect (struct GNUNET_FS_DownloadContext *dc)
{
  
  if (NULL != dc->client)
    {
#if DEBUG_DOWNLOAD
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Moving all requests back to pending list\n");
#endif
      if (NULL != dc->th)
        {
          GNUNET_CLIENT_notify_transmit_ready_cancel (dc->th);
          dc->th = NULL;
        }
      /* full reset of the pending list */
      dc->pending_head = NULL;
      dc->pending_tail = NULL;
      GNUNET_CONTAINER_multihashmap_iterate (dc->active,
                                             &retry_entry,
                                             dc);
      GNUNET_CLIENT_disconnect (dc->client, GNUNET_NO);
      dc->client = NULL;
    }
#if DEBUG_DOWNLOAD
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Will try to reconnect in 1s\n");
#endif
  dc->task
    = GNUNET_SCHEDULER_add_delayed (GNUNET_TIME_UNIT_SECONDS,
                                    &do_reconnect,
                                    dc);
}


/**
 * We're allowed to ask the FS service for our blocks.  Start the download.
 *
 * @param cls the 'struct GNUNET_FS_DownloadContext'
 * @param client handle to use for communcation with FS (we must destroy it!)
 */
static void
activate_fs_download (void *cls,
                      struct GNUNET_CLIENT_Connection *client)
{
  struct GNUNET_FS_DownloadContext *dc = cls;
  struct GNUNET_FS_ProgressInfo pi;

#if DEBUG_DOWNLOAD
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Download activated\n");
#endif
  GNUNET_assert (NULL != client);
  GNUNET_assert (dc->client == NULL);
  GNUNET_assert (dc->th == NULL);
  dc->client = client;
  GNUNET_CLIENT_receive (client,
                         &receive_results,
                         dc,
                         GNUNET_TIME_UNIT_FOREVER_REL);
  pi.status = GNUNET_FS_STATUS_DOWNLOAD_ACTIVE;
  GNUNET_FS_download_make_status_ (&pi, dc);
  GNUNET_assert (dc->pending_head == NULL);
  GNUNET_assert (dc->pending_tail == NULL);
  GNUNET_CONTAINER_multihashmap_iterate (dc->active,
                                         &retry_entry,
                                         dc);
#if DEBUG_DOWNLOAD
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Asking for transmission to FS service\n");
#endif
  if (dc->pending_head != NULL)
    {
      dc->th = GNUNET_CLIENT_notify_transmit_ready (dc->client,
                                                    sizeof (struct SearchMessage),
                                                    GNUNET_CONSTANTS_SERVICE_TIMEOUT,
                                                    GNUNET_NO,
                                                    &transmit_download_request,
                                                    dc);    
      GNUNET_assert (dc->th != NULL);
    }
}


/**
 * We must stop to ask the FS service for our blocks.  Pause the download.
 *
 * @param cls the 'struct GNUNET_FS_DownloadContext'
 */
static void
deactivate_fs_download (void *cls)
{
  struct GNUNET_FS_DownloadContext *dc = cls;
  struct GNUNET_FS_ProgressInfo pi;

#if DEBUG_DOWNLOAD
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Download deactivated\n");
#endif  
  if (NULL != dc->th)
    {
      GNUNET_CLIENT_notify_transmit_ready_cancel (dc->th);
      dc->th = NULL;
    }
  if (NULL != dc->client)
    {
      GNUNET_CLIENT_disconnect (dc->client, GNUNET_NO);
      dc->client = NULL;
    }
  dc->pending_head = NULL;
  dc->pending_tail = NULL;
  pi.status = GNUNET_FS_STATUS_DOWNLOAD_INACTIVE;
  GNUNET_FS_download_make_status_ (&pi, dc);
}


/**
 * (recursively) Create a download request structure.
 *
 * @param parent parent of the current entry
 * @param depth depth of the current entry, 0 are the DBLOCKs,
 *              top level block is 'dc->treedepth - 1'
 * @param dr_offset offset in the original file this block maps to
 *              (as in, offset of the first byte of the first DBLOCK 
 *               in the subtree rooted in the returned download request tree)
 * @param file_start_offset desired starting offset for the download
 *             in the original file; requesting tree should not contain
 *             DBLOCKs prior to the file_start_offset
 * @param desired_length desired number of bytes the user wanted to access
 *        (from file_start_offset).  Resulting tree should not contain
 *        DBLOCKs after file_start_offset + file_length.
 * @return download request tree for the given range of DBLOCKs at
 *         the specified depth
 */
static struct DownloadRequest *
create_download_request (struct DownloadRequest *parent,
                         unsigned int depth,
                         uint64_t dr_offset,
                         uint64_t file_start_offset,
                         uint64_t desired_length)
{
  struct DownloadRequest *dr;
  unsigned int i;
  unsigned int head_skip;
  uint64_t child_block_size;
  
  dr = GNUNET_malloc (sizeof (struct DownloadRequest));
  dr->parent = parent;
  dr->depth = depth;
  dr->offset = dr_offset;
  if (depth > 0)
    {
      child_block_size = GNUNET_FS_tree_compute_tree_size (depth - 1);
      
      /* calculate how many blocks at this level are not interesting
         from the start (rounded down), either because of the requested
         file offset or because this IBlock is further along */
      if (dr_offset < file_start_offset)
        head_skip = file_start_offset / child_block_size;       
      else
        head_skip = dr_offset / child_block_size;       

      /* calculate index of last block at this level that is interesting (rounded up) */
      dr->num_children = file_start_offset + desired_length / child_block_size;
      if (dr->num_children * child_block_size < file_start_offset + desired_length)
        dr->num_children++; /* round up */

      /* now we can get the total number of children for this block */
      dr->num_children -= head_skip;
      if (dr->num_children > CHK_PER_INODE)
        dr->num_children = CHK_PER_INODE; /* cap at max */

      /* why else would we have gotten here to begin with? (that'd be a bad logic error) */
      GNUNET_assert (dr->num_children > 0); 

      dr->children = GNUNET_malloc (dr->num_children * 
                                    sizeof (struct DownloadRequest *));
      for (i=0;i<dr->num_children;i++)
        dr->children[i] = create_download_request (dr,
                                                   depth - 1,
                                                   dr_offset + i * child_block_size,
                                                   file_start_offset,
                                                   desired_length);      
    }
  return dr;
}


/**
 * Continuation after a possible attempt to reconstruct
 * the current IBlock from the existing file.
 *
 * @param cls the 'struct ReconstructContext'
 * @param tc scheduler context
 */
static void
reconstruct_cont (void *cls,
                  const struct GNUNET_SCHEDULER_TaskContext *tc)
{
  struct GNUNET_FS_DownloadContext *dc = cls;

  /* clean up state from tree encoder */
  if (dc->te != NULL)
    {
      GNUNET_FS_tree_encoder_finish (dc->te, NULL, NULL);
      dc->te = NULL;
    }
  if (dc->task != GNUNET_SCHEDULER_NO_TASK)
    {
      GNUNET_SCHEDULER_cancel (dc->task);
      dc->task = GNUNET_SCHEDULER_NO_TASK;
    }
  if (dc->rfh != NULL)
    {
      GNUNET_break (GNUNET_OK == GNUNET_DISK_file_close (dc->rfh));
      dc->rfh = NULL;
    }
  /* start "normal" download */
  schedule_block_download (dc, 
                           dc->top_request);
}


/**
 * Task requesting the next block from the tree encoder.
 *
 * @param cls the 'struct GNUJNET_FS_DownloadContext' we're processing
 * @param tc task context
 */
static void
get_next_block (void *cls,
                const struct GNUNET_SCHEDULER_TaskContext *tc)
{
  struct GNUNET_FS_DownloadContext *dc = cls;

  dc->task = GNUNET_SCHEDULER_NO_TASK;
  GNUNET_FS_tree_encoder_next (dc->te);
}



/**
 * Function called asking for the current (encoded)
 * block to be processed.  After processing the
 * client should either call "GNUNET_FS_tree_encode_next"
 * or (on error) "GNUNET_FS_tree_encode_finish".
 *
 * This function checks if the content on disk matches
 * the expected content based on the URI.
 * 
 * @param cls closure
 * @param chk content hash key for the block
 * @param offset offset of the block
 * @param depth depth of the block, 0 for DBLOCK
 * @param type type of the block (IBLOCK or DBLOCK)
 * @param block the (encrypted) block
 * @param block_size size of block (in bytes)
 */
static void 
reconstruct_cb (void *cls,
                const struct ContentHashKey *chk,
                uint64_t offset,
                unsigned int depth,
                enum GNUNET_BLOCK_Type type,
                const void *block,
                uint16_t block_size)
{
  struct GNUNET_FS_DownloadContext *dc = cls;
  struct GNUNET_FS_ProgressInfo pi;
  struct DownloadRequest *dr;
  uint64_t blen;
  unsigned int chld;

  /* find corresponding request entry */
  dr = dc->top_request;
  while (dr->depth > depth)
    {
      blen = GNUNET_FS_tree_compute_tree_size (dr->depth);
      chld = (offset - dr->offset) / blen;
      GNUNET_assert (chld < dr->num_children);
      dr = dr->children[chld];
    }
  switch (dr->state)
    {
    case BRS_INIT:
      break;
    case BRS_RECONSTRUCT_DOWN:
      break;
    case BRS_RECONSTRUCT_META_UP:
      break;
    case BRS_RECONSTRUCT_UP:
      break;
    case BRS_CHK_SET:
      if (0 == memcmp (chk,
                       &dr->chk,
                       sizeof (struct ContentHashKey)))
        {
          /* block matches, hence tree below matches; 
             this request is done! */
          dr->state = BRS_DOWNLOAD_UP;
          /* calculate how many bytes of payload this block
             corresponds to */
          blen = GNUNET_FS_tree_compute_tree_size (dr->depth);
          /* how many of those bytes are in the requested range? */
          blen = GNUNET_MIN (blen,
                             dc->length + dc->offset - dr->offset);
          /* signal progress */
          dc->completed += blen;
          pi.status = GNUNET_FS_STATUS_DOWNLOAD_PROGRESS;
          pi.value.download.specifics.progress.data = NULL;
          pi.value.download.specifics.progress.offset = offset;
          pi.value.download.specifics.progress.data_len = 0;
          pi.value.download.specifics.progress.depth = 0;
          GNUNET_FS_download_make_status_ (&pi, dc);             
        }
      else
        {
        }
      break; 
    case BRS_DOWNLOAD_DOWN:
      break; 
    case BRS_DOWNLOAD_UP:
      break;
    case BRS_ERROR:
      break;
    default:
      GNUNET_assert (0);
      break;
    }
  if ( (dr == dc->top_request) &&
       (dr->state == BRS_DOWNLOAD_UP) )
    {
      check_completed (dc);
      return;
    }
  dc->task = GNUNET_SCHEDULER_add_now (&get_next_block,
                                       dc);
}


/**
 * Function called by the tree encoder to obtain a block of plaintext
 * data (for the lowest level of the tree).
 *
 * @param cls our 'struct ReconstructContext'
 * @param offset identifies which block to get
 * @param max (maximum) number of bytes to get; returning
 *        fewer will also cause errors
 * @param buf where to copy the plaintext buffer
 * @param emsg location to store an error message (on error)
 * @return number of bytes copied to buf, 0 on error
 */
static size_t
fh_reader (void *cls,
           uint64_t offset,
           size_t max, 
           void *buf,
           char **emsg)
{
  struct GNUNET_FS_DownloadContext *dc = cls;
  struct GNUNET_DISK_FileHandle *fh = dc->rfh;
  ssize_t ret;

  *emsg = NULL;
  if (offset !=
      GNUNET_DISK_file_seek (fh,
                             offset,
                             GNUNET_DISK_SEEK_SET))
    {
      *emsg = GNUNET_strdup (strerror (errno));
      return 0;
    }
  ret = GNUNET_DISK_file_read (fh, buf, max);
  if (ret < 0)
    {
      *emsg = GNUNET_strdup (strerror (errno));
      return 0;
    }
  return ret;
}


/**
 * Task that creates the initial (top-level) download
 * request for the file.
 *
 * @param cls the 'struct GNUNET_FS_DownloadContext'
 * @param tc scheduler context
 */
void
GNUNET_FS_download_start_task_ (void *cls,
                                const struct GNUNET_SCHEDULER_TaskContext *tc)
{
  struct GNUNET_FS_DownloadContext *dc = cls;  
  struct GNUNET_FS_ProgressInfo pi;
  struct GNUNET_DISK_FileHandle *fh;

#if DEBUG_DOWNLOAD
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Start task running...\n");
#endif
  dc->task = GNUNET_SCHEDULER_NO_TASK;
  if (dc->length == 0)
    {
      /* no bytes required! */
      if (dc->filename != NULL) 
        {
          fh = GNUNET_DISK_file_open (dc->filename != NULL 
                                      ? dc->filename 
                                      : dc->temp_filename, 
                                      GNUNET_DISK_OPEN_READWRITE |
                                      GNUNET_DISK_OPEN_CREATE |
                                      ( (0 == GNUNET_FS_uri_chk_get_file_size (dc->uri)) 
                                        ? GNUNET_DISK_OPEN_TRUNCATE : 0),
                                      GNUNET_DISK_PERM_USER_READ |
                                      GNUNET_DISK_PERM_USER_WRITE |
                                      GNUNET_DISK_PERM_GROUP_READ |
                                      GNUNET_DISK_PERM_OTHER_READ);
          GNUNET_DISK_file_close (fh);
        }
      GNUNET_FS_download_sync_ (dc);
      check_completed (dc);
      return;
    }
  if (dc->emsg != NULL) 
    return;
  if (dc->top_request == NULL)
    {
      dc->top_request = create_download_request (NULL, dc->treedepth - 1, 0,
                                                 dc->offset, dc->length);
      dc->top_request->state = BRS_CHK_SET;
      dc->top_request->chk = (dc->uri->type == chk) 
        ? dc->uri->data.chk.chk
        : dc->uri->data.loc.fi.chk;
      /* signal start */
      GNUNET_FS_download_sync_ (dc);
      pi.status = GNUNET_FS_STATUS_DOWNLOAD_START;
      pi.value.download.specifics.start.meta = dc->meta;
      GNUNET_FS_download_make_status_ (&pi, dc);
    }
  GNUNET_FS_download_start_downloading_ (dc);
  /* attempt reconstruction from disk */
  if (GNUNET_YES == GNUNET_DISK_file_test (dc->filename))    
    dc->rfh = GNUNET_DISK_file_open (dc->filename,
                                     GNUNET_DISK_OPEN_READ,
                                     GNUNET_DISK_PERM_NONE);    
  if (dc->top_request->state == BRS_CHK_SET)
    {
      if (dc->rfh != NULL)
        {
          /* first, try top-down */
#if DEBUG_DOWNLOAD
          GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                      "Trying top-down reconstruction for `%s'\n",
                      dc->filename);
#endif
          try_top_down_reconstruction (dc, dc->top_request);
          switch (dc->top_request->state)
            {
            case BRS_CHK_SET:
              break; /* normal */
            case BRS_DOWNLOAD_DOWN:
              break; /* normal, some blocks already down */
            case BRS_DOWNLOAD_UP:
              /* already done entirely, party! */
              if (dc->rfh != NULL)
                {
                  /* avoid hanging on to file handle longer than 
                     necessary */
                  GNUNET_DISK_file_close (dc->rfh);
                  dc->rfh = NULL;
                }
              return;      
            case BRS_ERROR:
              GNUNET_asprintf (&dc->emsg,
                               _("Invalid URI"));
              GNUNET_FS_download_sync_ (dc);
              pi.status = GNUNET_FS_STATUS_DOWNLOAD_ERROR;
              pi.value.download.specifics.error.message = dc->emsg;
              GNUNET_FS_download_make_status_ (&pi, dc);
              return;
            default:
              GNUNET_assert (0);
              break;
            }
        }
    }
  /* attempt reconstruction from meta data */
  if ( (GNUNET_FS_uri_chk_get_file_size (dc->uri) <= MAX_INLINE_SIZE) &&
       (NULL != dc->meta) )
    {
#if DEBUG_DOWNLOAD
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Trying to find embedded meta data for download of size %llu with %u bytes MD\n",
                  (unsigned long long) GNUNET_FS_uri_chk_get_file_size (dc->uri),
                  (unsigned int) GNUNET_CONTAINER_meta_data_get_serialized_size (dc->meta));
#endif
      GNUNET_CONTAINER_meta_data_iterate (dc->meta,
                                          &match_full_data,
                                          dc);
      if (dc->top_request->state == BRS_DOWNLOAD_UP)
        {
          if (dc->rfh != NULL)
            {
              /* avoid hanging on to file handle longer than 
                 necessary */
              GNUNET_DISK_file_close (dc->rfh);
              dc->rfh = NULL;
            }
          return; /* finished, status update was already done for us */
        }
    }
  if (dc->rfh != NULL)
    {
      /* finally, try bottom-up */
#if DEBUG_DOWNLOAD
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Trying bottom-up reconstruction of file `%s'\n",
                  dc->filename);
#endif
      dc->te = GNUNET_FS_tree_encoder_create (dc->h,
                                              dc->old_file_size,
                                              dc,
                                              &fh_reader,
                                              &reconstruct_cb,
                                              NULL,
                                              &reconstruct_cont);     
      dc->task = GNUNET_SCHEDULER_add_now (&get_next_block,
                                           dc);
    }
  else
    {
      /* simple, top-level download */
        schedule_block_download (dc, 
                                 dc->top_request);
    }
  if (dc->top_request->state == BRS_DOWNLOAD_UP)
    check_completed (dc);
}


/**
 * Create SUSPEND event for the given download operation
 * and then clean up our state (without stop signal).
 *
 * @param cls the 'struct GNUNET_FS_DownloadContext' to signal for
 */
void
GNUNET_FS_download_signal_suspend_ (void *cls)
{
  struct GNUNET_FS_DownloadContext *dc = cls;
  struct GNUNET_FS_ProgressInfo pi;

  if (dc->top != NULL)
    GNUNET_FS_end_top (dc->h, dc->top);
  while (NULL != dc->child_head)
    GNUNET_FS_download_signal_suspend_ (dc->child_head);  
  if (dc->search != NULL)
    {
      dc->search->download = NULL;
      dc->search = NULL;
    }
  if (dc->job_queue != NULL)
    {
      GNUNET_FS_dequeue_ (dc->job_queue);
      dc->job_queue = NULL;
    }
  if (dc->parent != NULL)
    GNUNET_CONTAINER_DLL_remove (dc->parent->child_head,
                                 dc->parent->child_tail,
                                 dc);  
  if (dc->task != GNUNET_SCHEDULER_NO_TASK)
    {
      GNUNET_SCHEDULER_cancel (dc->task);
      dc->task = GNUNET_SCHEDULER_NO_TASK;
    }
  pi.status = GNUNET_FS_STATUS_DOWNLOAD_SUSPEND;
  GNUNET_FS_download_make_status_ (&pi, dc);
  if (dc->te != NULL)
    {
      GNUNET_FS_tree_encoder_finish (dc->te, NULL, NULL);       
      dc->te = NULL;
    }
  if (dc->rfh != NULL)
    {
      GNUNET_DISK_file_close (dc->rfh);
      dc->rfh = NULL;
    }
  GNUNET_FS_free_download_request_ (dc->top_request);
  if (dc->active != NULL)
    {
      GNUNET_CONTAINER_multihashmap_destroy (dc->active);
      dc->active = NULL;
    }
  GNUNET_free_non_null (dc->filename);
  GNUNET_CONTAINER_meta_data_destroy (dc->meta);
  GNUNET_FS_uri_destroy (dc->uri);
  GNUNET_free_non_null (dc->temp_filename);
  GNUNET_free_non_null (dc->serialization);
  GNUNET_free (dc);
}


/**
 * Download parts of a file.  Note that this will store
 * the blocks at the respective offset in the given file.  Also, the
 * download is still using the blocking of the underlying FS
 * encoding.  As a result, the download may *write* outside of the
 * given boundaries (if offset and length do not match the 32k FS
 * block boundaries). <p>
 *
 * This function should be used to focus a download towards a
 * particular portion of the file (optimization), not to strictly
 * limit the download to exactly those bytes.
 *
 * @param h handle to the file sharing subsystem
 * @param uri the URI of the file (determines what to download); CHK or LOC URI
 * @param meta known metadata for the file (can be NULL)
 * @param filename where to store the file, maybe NULL (then no file is
 *        created on disk and data must be grabbed from the callbacks)
 * @param tempname where to store temporary file data, not used if filename is non-NULL;
 *        can be NULL (in which case we will pick a name if needed); the temporary file
 *        may already exist, in which case we will try to use the data that is there and
 *        if it is not what is desired, will overwrite it
 * @param offset at what offset should we start the download (typically 0)
 * @param length how many bytes should be downloaded starting at offset
 * @param anonymity anonymity level to use for the download
 * @param options various options
 * @param cctx initial value for the client context for this download
 * @param parent parent download to associate this download with (use NULL
 *        for top-level downloads; useful for manually-triggered recursive downloads)
 * @return context that can be used to control this download
 */
struct GNUNET_FS_DownloadContext *
GNUNET_FS_download_start (struct GNUNET_FS_Handle *h,
                          const struct GNUNET_FS_Uri *uri,
                          const struct GNUNET_CONTAINER_MetaData *meta,
                          const char *filename,
                          const char *tempname,
                          uint64_t offset,
                          uint64_t length,
                          uint32_t anonymity,
                          enum GNUNET_FS_DownloadOptions options,
                          void *cctx,
                          struct GNUNET_FS_DownloadContext *parent)
{
  struct GNUNET_FS_DownloadContext *dc;

  GNUNET_assert (GNUNET_FS_uri_test_chk (uri) ||
                 GNUNET_FS_uri_test_loc (uri) );
                 
  if ( (offset + length < offset) ||
       (offset + length > GNUNET_FS_uri_chk_get_file_size (uri)) )
    {      
      GNUNET_break (0);
      return NULL;
    }
#if DEBUG_DOWNLOAD
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Starting download `%s' of %llu bytes\n",
              filename,
              (unsigned long long) length);
#endif
  dc = GNUNET_malloc (sizeof(struct GNUNET_FS_DownloadContext));
  dc->h = h;
  dc->parent = parent;
  if (parent != NULL)
    {
      GNUNET_CONTAINER_DLL_insert (parent->child_head,
                                   parent->child_tail,
                                   dc);
    }
  dc->uri = GNUNET_FS_uri_dup (uri);
  dc->meta = GNUNET_CONTAINER_meta_data_duplicate (meta);
  dc->client_info = cctx;
  dc->start_time = GNUNET_TIME_absolute_get ();
  if (NULL != filename)
    {
      dc->filename = GNUNET_strdup (filename);
      if (GNUNET_YES == GNUNET_DISK_file_test (filename))
        GNUNET_DISK_file_size (filename,
                               &dc->old_file_size,
                               GNUNET_YES);
    }
  if (GNUNET_FS_uri_test_loc (dc->uri))
    GNUNET_assert (GNUNET_OK ==
                   GNUNET_FS_uri_loc_get_peer_identity (dc->uri,
                                                        &dc->target));
  dc->offset = offset;
  dc->length = length;
  dc->anonymity = anonymity;
  dc->options = options;
  dc->active = GNUNET_CONTAINER_multihashmap_create (1 + 2 * (length / DBLOCK_SIZE));
  dc->treedepth = GNUNET_FS_compute_depth (GNUNET_FS_uri_chk_get_file_size(dc->uri));
  if ( (filename == NULL) &&
       (is_recursive_download (dc) ) )
    {
      if (tempname != NULL)
        dc->temp_filename = GNUNET_strdup (tempname);
      else
        dc->temp_filename = GNUNET_DISK_mktemp ("gnunet-directory-download-tmp");    
    }

#if DEBUG_DOWNLOAD
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Download tree has depth %u\n",
              dc->treedepth);
#endif
  if (parent == NULL)
    {
      dc->top = GNUNET_FS_make_top (dc->h,
                                    &GNUNET_FS_download_signal_suspend_,
                                    dc);
    }
  dc->task = GNUNET_SCHEDULER_add_now (&GNUNET_FS_download_start_task_, 
                                       dc);
  return dc;
}


/**
 * Download parts of a file based on a search result.  The download
 * will be associated with the search result (and the association
 * will be preserved when serializing/deserializing the state).
 * If the search is stopped, the download will not be aborted but
 * be 'promoted' to a stand-alone download.
 *
 * As with the other download function, this will store
 * the blocks at the respective offset in the given file.  Also, the
 * download is still using the blocking of the underlying FS
 * encoding.  As a result, the download may *write* outside of the
 * given boundaries (if offset and length do not match the 32k FS
 * block boundaries). <p>
 *
 * The given range can be used to focus a download towards a
 * particular portion of the file (optimization), not to strictly
 * limit the download to exactly those bytes.
 *
 * @param h handle to the file sharing subsystem
 * @param sr the search result to use for the download (determines uri and
 *        meta data and associations)
 * @param filename where to store the file, maybe NULL (then no file is
 *        created on disk and data must be grabbed from the callbacks)
 * @param tempname where to store temporary file data, not used if filename is non-NULL;
 *        can be NULL (in which case we will pick a name if needed); the temporary file
 *        may already exist, in which case we will try to use the data that is there and
 *        if it is not what is desired, will overwrite it
 * @param offset at what offset should we start the download (typically 0)
 * @param length how many bytes should be downloaded starting at offset
 * @param anonymity anonymity level to use for the download
 * @param options various download options
 * @param cctx initial value for the client context for this download
 * @return context that can be used to control this download
 */
struct GNUNET_FS_DownloadContext *
GNUNET_FS_download_start_from_search (struct GNUNET_FS_Handle *h,
                                      struct GNUNET_FS_SearchResult *sr,
                                      const char *filename,
                                      const char *tempname,
                                      uint64_t offset,
                                      uint64_t length,
                                      uint32_t anonymity,
                                      enum GNUNET_FS_DownloadOptions options,
                                      void *cctx)
{
  struct GNUNET_FS_DownloadContext *dc;

  if ( (sr == NULL) ||
       (sr->download != NULL) )
    {
      GNUNET_break (0);
      return NULL;
    }
  GNUNET_assert (GNUNET_FS_uri_test_chk (sr->uri) ||
                 GNUNET_FS_uri_test_loc (sr->uri) );             
  if ( (offset + length < offset) ||
       (offset + length > sr->uri->data.chk.file_length) )
    {      
      GNUNET_break (0);
      return NULL;
    }
#if DEBUG_DOWNLOAD
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Starting download `%s' of %llu bytes\n",
              filename,
              (unsigned long long) length);
#endif
  dc = GNUNET_malloc (sizeof(struct GNUNET_FS_DownloadContext));
  dc->h = h;
  dc->search = sr;
  sr->download = dc;
  if (sr->probe_ctx != NULL)
    {
      GNUNET_FS_download_stop (sr->probe_ctx, GNUNET_YES);
      sr->probe_ctx = NULL;      
    }
  dc->uri = GNUNET_FS_uri_dup (sr->uri);
  dc->meta = GNUNET_CONTAINER_meta_data_duplicate (sr->meta);
  dc->client_info = cctx;
  dc->start_time = GNUNET_TIME_absolute_get ();
  if (NULL != filename)
    {
      dc->filename = GNUNET_strdup (filename);
      if (GNUNET_YES == GNUNET_DISK_file_test (filename))
        GNUNET_DISK_file_size (filename,
                               &dc->old_file_size,
                               GNUNET_YES);
    }
  if (GNUNET_FS_uri_test_loc (dc->uri))
    GNUNET_assert (GNUNET_OK ==
                   GNUNET_FS_uri_loc_get_peer_identity (dc->uri,
                                                        &dc->target));
  dc->offset = offset;
  dc->length = length;
  dc->anonymity = anonymity;
  dc->options = options;
  dc->active = GNUNET_CONTAINER_multihashmap_create (1 + 2 * (length / DBLOCK_SIZE));
  dc->treedepth = GNUNET_FS_compute_depth (GNUNET_ntohll(dc->uri->data.chk.file_length));
  if ( (filename == NULL) &&
       (is_recursive_download (dc) ) )
    {
      if (tempname != NULL)
        dc->temp_filename = GNUNET_strdup (tempname);
      else
        dc->temp_filename = GNUNET_DISK_mktemp ("gnunet-directory-download-tmp");    
    }

#if DEBUG_DOWNLOAD
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Download tree has depth %u\n",
              dc->treedepth);
#endif
  dc->task = GNUNET_SCHEDULER_add_now (&GNUNET_FS_download_start_task_, 
                                       dc);
  return dc;  
}


/**
 * Start the downloading process (by entering the queue).
 *
 * @param dc our download context
 */
void
GNUNET_FS_download_start_downloading_ (struct GNUNET_FS_DownloadContext *dc)
{
  if (dc->completed == dc->length)
    return;
  GNUNET_assert (dc->job_queue == NULL);
  dc->job_queue = GNUNET_FS_queue_ (dc->h, 
                                    &activate_fs_download,
                                    &deactivate_fs_download,
                                    dc,
                                    (dc->length + DBLOCK_SIZE-1) / DBLOCK_SIZE);
}


/**
 * Stop a download (aborts if download is incomplete).
 *
 * @param dc handle for the download
 * @param do_delete delete files of incomplete downloads
 */
void
GNUNET_FS_download_stop (struct GNUNET_FS_DownloadContext *dc,
                         int do_delete)
{
  struct GNUNET_FS_ProgressInfo pi;
  int have_children;

  if (dc->top != NULL)
    GNUNET_FS_end_top (dc->h, dc->top);


  if (dc->task != GNUNET_SCHEDULER_NO_TASK)
    {
      GNUNET_SCHEDULER_cancel (dc->task);
      dc->task = GNUNET_SCHEDULER_NO_TASK;
    }
  if (dc->search != NULL)
    {
      dc->search->download = NULL;
      dc->search = NULL;
    }
  if (dc->job_queue != NULL)
    {
      GNUNET_FS_dequeue_ (dc->job_queue);
      dc->job_queue = NULL;
    }
  if (dc->te != NULL)
    {
      GNUNET_FS_tree_encoder_finish (dc->te, NULL, NULL);
      dc->te = NULL;
    }
  have_children = (NULL != dc->child_head) ? GNUNET_YES : GNUNET_NO;
  while (NULL != dc->child_head)
    GNUNET_FS_download_stop (dc->child_head, 
                             do_delete);
  if (dc->parent != NULL)
    GNUNET_CONTAINER_DLL_remove (dc->parent->child_head,
                                 dc->parent->child_tail,
                                 dc);  
  if (dc->serialization != NULL)
    GNUNET_FS_remove_sync_file_ (dc->h,
                                 ( (dc->parent != NULL)  || (dc->search != NULL) )
                                 ? GNUNET_FS_SYNC_PATH_CHILD_DOWNLOAD 
                                 : GNUNET_FS_SYNC_PATH_MASTER_DOWNLOAD , 
                                 dc->serialization);
  if ( (GNUNET_YES == have_children) &&
       (dc->parent == NULL) )
    GNUNET_FS_remove_sync_dir_ (dc->h, 
                                (dc->search != NULL) 
                                ? GNUNET_FS_SYNC_PATH_CHILD_DOWNLOAD 
                                : GNUNET_FS_SYNC_PATH_MASTER_DOWNLOAD,
                                dc->serialization);  
  pi.status = GNUNET_FS_STATUS_DOWNLOAD_STOPPED;
  GNUNET_FS_download_make_status_ (&pi, dc);
  GNUNET_FS_free_download_request_ (dc->top_request);
  dc->top_request = NULL;
  if (dc->active != NULL)
    {
      GNUNET_CONTAINER_multihashmap_destroy (dc->active);
      dc->active = NULL;
    }
  if (dc->filename != NULL)
    {
      if ( (dc->completed != dc->length) &&
           (GNUNET_YES == do_delete) )
        {
          if (0 != UNLINK (dc->filename))
            GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_WARNING,
                                      "unlink",
                                      dc->filename);
        }
      GNUNET_free (dc->filename);
    }
  GNUNET_CONTAINER_meta_data_destroy (dc->meta);
  GNUNET_FS_uri_destroy (dc->uri);
  if (NULL != dc->temp_filename)
    {
      if (0 != UNLINK (dc->temp_filename))
        GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_ERROR,
                                  "unlink",
                                  dc->temp_filename);
      GNUNET_free (dc->temp_filename);
    }
  GNUNET_free_non_null (dc->serialization);
  GNUNET_free (dc);
}

/* end of fs_download.c */