transmission/libtransmission/magnet.c

/*
 * This file Copyright (C) Mnemosyne LLC
 *
 * This file is licensed by the GPL version 2. Works owned by the
 * Transmission project are granted a special exemption to clause 2 (b)
 * so that the bulk of its code can remain under the MIT license.
 * This exemption does not extend to derived works not owned by
 * the Transmission project.
 *
 * $Id$
 */

#include <assert.h>
#include <string.h> /* strchr () */
#include <stdio.h> /* sscanf () */

#include "transmission.h"
#include "bencode.h"
#include "magnet.h"
#include "utils.h"
#include "web.h"

/***
****
***/

/* this base32 code converted from code by Robert Kaye and Gordon Mohr
 * and is public domain. see http://bitzi.com/publicdomain for more info */

static const int base32Lookup[] =
{
  0xFF,0xFF,0x1A,0x1B,0x1C,0x1D,0x1E,0x1F, /* '0', '1', '2', '3', '4', '5', '6', '7' */
  0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF, /* '8', '9', ':', ';', '<', '=', '>', '?' */
  0xFF,0x00,0x01,0x02,0x03,0x04,0x05,0x06, /* '@', 'A', 'B', 'C', 'D', 'E', 'F', 'G' */
  0x07,0x08,0x09,0x0A,0x0B,0x0C,0x0D,0x0E, /* 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O' */
  0x0F,0x10,0x11,0x12,0x13,0x14,0x15,0x16, /* 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W' */
  0x17,0x18,0x19,0xFF,0xFF,0xFF,0xFF,0xFF, /* 'X', 'Y', 'Z', '[', '\', ']', '^', '_' */
  0xFF,0x00,0x01,0x02,0x03,0x04,0x05,0x06, /* '`', 'a', 'b', 'c', 'd', 'e', 'f', 'g' */
  0x07,0x08,0x09,0x0A,0x0B,0x0C,0x0D,0x0E, /* 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o' */
  0x0F,0x10,0x11,0x12,0x13,0x14,0x15,0x16, /* 'p', 'q', 'r', 's', 't', 'u', 'v', 'w' */
  0x17,0x18,0x19,0xFF,0xFF,0xFF,0xFF,0xFF  /* 'x', 'y', 'z', '{', '|', '}', '~', 'DEL' */
};

static const int base32LookupLen = sizeof (base32Lookup) / sizeof (base32Lookup[0]);

static void
base32_to_sha1 (uint8_t * out, const char * in, const int inlen)
{
  const int outlen = 20;
  int i, index, offset;

  memset (out, 0, 20);

  assert (inlen == 32);

  for (i=0, index=0, offset=0; i<inlen; ++i)
    {
      int digit;
      int lookup = in[i] - '0';

      /* Skip chars outside the lookup table */
      if (lookup<0 || lookup>=base32LookupLen)
        continue;

      /* If this digit is not in the table, ignore it */
      digit = base32Lookup[lookup];
      if (digit == 0xFF)
        continue;

      if (index <= 3)
        {
          index = (index + 5) % 8;
          if (index == 0)
            {
              out[offset] |= digit;
              offset++;
              if (offset >= outlen)
                break;
            }
          else
            {
              out[offset] |= digit << (8 - index);
            }
        }
      else
        {
          index = (index + 5) % 8;
          out[offset] |= (digit >> index);
          offset++;

          if (offset >= outlen)
            break;
          out[offset] |= digit << (8 - index);
        }
    }
}

/***
****
***/

#define MAX_TRACKERS 64
#define MAX_WEBSEEDS 64

tr_magnet_info *
tr_magnetParse (const char * uri)
{
  bool got_checksum = false;
  int trCount = 0;
  int wsCount = 0;
  char * tr[MAX_TRACKERS];
  char * ws[MAX_WEBSEEDS];
  char * displayName = NULL;
  uint8_t sha1[SHA_DIGEST_LENGTH];
  tr_magnet_info * info = NULL;

  if ((uri != NULL) && !memcmp (uri, "magnet:?", 8))
    {
      const char * walk;

      for (walk=uri+8; walk && *walk;)
        {
          const char * key = walk;
          const char * delim = strchr (key, '=');
          const char * val = delim == NULL ? NULL : delim + 1;
          const char * next = strchr (delim == NULL ? key : val, '&');
          int keylen, vallen;

          if (delim != NULL)
            keylen = delim - key;
          else if (next != NULL)
            keylen = next - key;
          else
            keylen = strlen (key);

          if (val == NULL)
            vallen = 0;
          else if (next != NULL)
            vallen = next - val;
          else
            vallen = strlen (val);

          if ((keylen==2) && !memcmp (key, "xt", 2) && val && !memcmp (val, "urn:btih:", 9))
            {
              const char * hash = val + 9;
              const int hashlen = vallen - 9;

              if (hashlen == 40)
                {
                  tr_hex_to_sha1 (sha1, hash);
                  got_checksum = true;
                }
              else if (hashlen == 32)
                {
                  base32_to_sha1 (sha1, hash, hashlen);
                  got_checksum = true;
                }
            }

          if ((vallen > 0) && (keylen==2) && !memcmp (key, "dn", 2))
            displayName = tr_http_unescape (val, vallen);

          if ((vallen > 0) && (trCount < MAX_TRACKERS))
            {
              int i;
              if ((keylen==2) && !memcmp (key, "tr", 2))
                tr[trCount++] = tr_http_unescape (val, vallen);
              else if ((sscanf (key, "tr.%d=", &i) == 1) && (i >= 0)) /* ticket #3341 and #5134 */
                tr[trCount++] = tr_http_unescape (val, vallen);
            }

          if ((vallen > 0) && (keylen==2) && !memcmp (key, "ws", 2) && (wsCount < MAX_WEBSEEDS))
            ws[wsCount++] = tr_http_unescape (val, vallen);

          walk = next != NULL ? next + 1 : NULL;
        }
    }

  if (got_checksum)
    {
      info = tr_new0 (tr_magnet_info, 1);
      info->displayName = displayName;
      info->trackerCount = trCount;
      info->trackers = tr_memdup (tr, sizeof (char*) * trCount);
      info->webseedCount = wsCount;
      info->webseeds = tr_memdup (ws, sizeof (char*) * wsCount);
      memcpy (info->hash, sha1, sizeof (uint8_t) * SHA_DIGEST_LENGTH);
    }

  return info;
}

void
tr_magnetFree (tr_magnet_info * info)
{
  if (info != NULL)
    {
      int i;

      for (i=0; i<info->trackerCount; ++i)
        tr_free (info->trackers[i]);
      tr_free (info->trackers);

      for (i=0; i<info->webseedCount; ++i)
        tr_free (info->webseeds[i]);
      tr_free (info->webseeds);

      tr_free (info->displayName);
      tr_free (info);
    }
}

void
tr_magnetCreateMetainfo (const tr_magnet_info * info, tr_benc * top)
{
  int i;
  tr_benc * d;
  tr_bencInitDict (top, 4);

  /* announce list */
  if (info->trackerCount == 1)
    {
      tr_bencDictAddStr (top, "announce", info->trackers[0]);
    }
  else
    {
      tr_benc * trackers = tr_bencDictAddList (top, "announce-list", info->trackerCount);
      for (i=0; i<info->trackerCount; ++i)
        tr_bencListAddStr (tr_bencListAddList (trackers, 1), info->trackers[i]);
    }

  /* webseeds */
  if (info->webseedCount > 0)
    {
      tr_benc * urls = tr_bencDictAddList (top, "url-list", info->webseedCount);
      for (i=0; i<info->webseedCount; ++i)
        tr_bencListAddStr (urls, info->webseeds[i]);
    }

  /* nonstandard keys */
  d = tr_bencDictAddDict (top, "magnet-info", 2);
  tr_bencDictAddRaw (d, "info_hash", info->hash, 20);
  if (info->displayName != NULL)
    tr_bencDictAddStr (d, "display-name", info->displayName);
}