res.c

Wget很好的处理了http和ftp的下载,很值得学习的经典代码

             ... non-matching record ...

             User-Agent: *
             ... matching record, but will be pruned later ...

             We have to respect `User-Agent' at the beginning of each
             new record simply because we don't know if we're going to
             encounter "Wget" among the agents or not.  Hence,
             match_user_agent is called when record_count != 0.

             But if record_count is 0, we have to keep calling it
             until it matches, and if that happens, we must not call
             it any more, until the next record.  Hence the other part
             of the condition.  */
          if (record_count != 0 || user_agent_applies == false)
            match_user_agent (value_b, value_e - value_b,
                              &user_agent_applies, &user_agent_exact);
          if (user_agent_exact)
            found_exact = true;
          record_count = 0;
        }
      else if (FIELD_IS ("allow"))
        {
          if (user_agent_applies)
            {
              add_path (specs, value_b, value_e, true, user_agent_exact);
            }
          ++record_count;
        }
      else if (FIELD_IS ("disallow"))
        {
          if (user_agent_applies)
            {
              bool allowed = false;
              if (value_b == value_e)
                /* Empty "disallow" line means everything is *allowed*!  */
                allowed = true;
              add_path (specs, value_b, value_e, allowed, user_agent_exact);
            }
          ++record_count;
        }
      else
        {
          DEBUGP (("Ignoring unknown field at line %d", line_count));
          goto next;
        }

    next:
      p = lineend_real;
      ++line_count;
    }

  if (found_exact)
    {
      /* We've encountered an exactly matching user-agent.  Throw out
         all the stuff with user-agent: *.  */
      prune_non_exact (specs);
    }
  else if (specs->size > specs->count)
    {
      /* add_path normally over-allocates specs->paths.  Reallocate it
         to the correct size in order to conserve some memory.  */
      specs->paths = xrealloc (specs->paths,
                               specs->count * sizeof (struct path_info));
      specs->size = specs->count;
    }

  return specs;
}

/* The same like res_parse, but first map the FILENAME into memory,
   and then parse it.  */

struct robot_specs *
res_parse_from_file (const char *filename)
{
  struct robot_specs *specs;
  struct file_memory *fm = read_file (filename);
  if (!fm)
    {
      logprintf (LOG_NOTQUIET, _("Cannot open %s: %s"),
                 filename, strerror (errno));
      return NULL;
    }
  specs = res_parse (fm->content, fm->length);
  read_file_free (fm);
  return specs;
}

static void
free_specs (struct robot_specs *specs)
{
  int i;
  for (i = 0; i < specs->count; i++)
    xfree (specs->paths[i].path);
  xfree_null (specs->paths);
  xfree (specs);
}

/* Matching of a path according to the specs. */

/* If C is '%' and (ptr[1], ptr[2]) form a hexadecimal number, and if
   that number is not a numerical representation of '/', decode C and
   advance the pointer.  */

#define DECODE_MAYBE(c, ptr) do {                               \
  if (c == '%' && ISXDIGIT (ptr[1]) && ISXDIGIT (ptr[2]))       \
    {                                                           \
      char decoded = X2DIGITS_TO_NUM (ptr[1], ptr[2]);          \
      if (decoded != '/')                                       \
        {                                                       \
          c = decoded;                                          \
          ptr += 2;                                             \
        }                                                       \
    }                                                           \
} while (0)

/* The inner matching engine: return true if RECORD_PATH matches
   URL_PATH.  The rules for matching are described at
   <http://www.robotstxt.org/wc/norobots-rfc.txt>, section 3.2.2.  */

static bool
matches (const char *record_path, const char *url_path)
{
  const char *rp = record_path;
  const char *up = url_path;

  for (; ; ++rp, ++up)
    {
      char rc = *rp;
      char uc = *up;
      if (!rc)
        return true;
      if (!uc)
        return false;
      DECODE_MAYBE(rc, rp);
      DECODE_MAYBE(uc, up);
      if (rc != uc)
        return false;
    }
}

/* Iterate through all paths in SPECS.  For the first one that
   matches, return its allow/reject status.  If none matches,
   retrieval is by default allowed.  */

bool
res_match_path (const struct robot_specs *specs, const char *path)
{
  int i;
  if (!specs)
    return true;
  for (i = 0; i < specs->count; i++)
    if (matches (specs->paths[i].path, path))
      {
        bool allowedp = specs->paths[i].allowedp;
        DEBUGP (("%s path %s because of rule `%s'.\n",
                 allowedp ? "Allowing" : "Rejecting",
                 path, specs->paths[i].path));
        return allowedp;
      }
  return true;
}

/* Registering the specs. */

static struct hash_table *registered_specs;

/* Stolen from cookies.c. */
#define SET_HOSTPORT(host, port, result) do {           \
  int HP_len = strlen (host);                           \
  result = alloca (HP_len + 1 + numdigit (port) + 1);   \
  memcpy (result, host, HP_len);                        \
  result[HP_len] = ':';                                 \
  number_to_string (result + HP_len + 1, port);         \
} while (0)

/* Register RES specs that below to server on HOST:PORT.  They will
   later be retrievable using res_get_specs.  */

void
res_register_specs (const char *host, int port, struct robot_specs *specs)
{
  struct robot_specs *old;
  char *hp, *hp_old;
  SET_HOSTPORT (host, port, hp);

  if (!registered_specs)
    registered_specs = make_nocase_string_hash_table (0);

  if (hash_table_get_pair (registered_specs, hp, &hp_old, &old))
    {
      if (old)
        free_specs (old);
      hash_table_put (registered_specs, hp_old, specs);
    }
  else
    {
      hash_table_put (registered_specs, xstrdup (hp), specs);
    }
}

/* Get the specs that belong to HOST:PORT. */

struct robot_specs *
res_get_specs (const char *host, int port)
{
  char *hp;
  SET_HOSTPORT (host, port, hp);
  if (!registered_specs)
    return NULL;
  return hash_table_get (registered_specs, hp);
}

/* Loading the robots file.  */

#define RES_SPECS_LOCATION "/robots.txt"

/* Retrieve the robots.txt from the server root of the server that
   serves URL.  The file will be named according to the currently
   active rules, and the file name will be returned in *file.

   Return true if robots were retrieved OK, false otherwise.  */

bool
res_retrieve_file (const char *url, char **file)
{
  uerr_t err;
  char *robots_url = uri_merge (url, RES_SPECS_LOCATION);
  int saved_ts_val = opt.timestamping;
  int saved_sp_val = opt.spider;

  logputs (LOG_VERBOSE, _("Loading robots.txt; please ignore errors.\n"));
  *file = NULL;
  opt.timestamping = false;
  opt.spider       = false;
  err = retrieve_url (robots_url, file, NULL, NULL, NULL, false);
  opt.timestamping = saved_ts_val;
  opt.spider       = saved_sp_val;  
  xfree (robots_url);

  if (err != RETROK && *file != NULL)
    {
      /* If the file is not retrieved correctly, but retrieve_url
         allocated the file name, deallocate is here so that the
         caller doesn't have to worry about it.  */
      xfree (*file);
      *file = NULL;
    }
  return err == RETROK;
}

bool
is_robots_txt_url (const char *url)
{
  char *robots_url = uri_merge (url, RES_SPECS_LOCATION);
  bool ret = are_urls_equal (url, robots_url);

  xfree (robots_url);
  
  return ret;
}

void
res_cleanup (void)
{
  if (registered_specs)
    {
      hash_table_iterator iter;
      for (hash_table_iterate (registered_specs, &iter);
           hash_table_iter_next (&iter);
           )
        {
          xfree (iter.key);
          free_specs (iter.value);
        }
      hash_table_destroy (registered_specs);
      registered_specs = NULL;
    }
}

#ifdef TESTING

const char *
test_is_robots_txt_url()
{
  int i;
  struct {
    char *url;
    bool expected_result;
  } test_array[] = {
    { "http://www.yoyodyne.com/robots.txt", true },
    { "http://www.yoyodyne.com/somepath/", false },
    { "http://www.yoyodyne.com/somepath/robots.txt", false },
  };
  
  for (i = 0; i < sizeof(test_array)/sizeof(test_array[0]); ++i) 
    {
      mu_assert ("test_is_robots_txt_url: wrong result", 
                 is_robots_txt_url (test_array[i].url) == test_array[i].expected_result);
    }

  return NULL;
}

#endif /* TESTING */

/*
 * vim: et ts=2 sw=2
 */