url.c

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/* Resolve "." and ".." elements of PATH by destructively modifying
   PATH and return non-zero if PATH has been modified, zero otherwise.

   The algorithm is in spirit similar to the one described in rfc1808,
   although implemented differently, in one pass.  To recap, path
   elements containing only "." are removed, and ".." is taken to mean
   "back up one element".  Single leading and trailing slashes are
   preserved.

   For example, "a/b/c/./../d/.." will yield "a/b/".  More exhaustive
   test examples are provided below.  If you change anything in this
   function, run test_path_simplify to make sure you haven't broken a
   test case.  */

static int
path_simplify (char *path)
{
  char *h = path;		/* hare */
  char *t = path;		/* tortoise */
  char *beg = path;		/* boundary for backing the tortoise */
  char *end = path + strlen (path);

  while (h < end)
    {
      /* Hare should be at the beginning of a path element. */

      if (h[0] == '.' && (h[1] == '/' || h[1] == '\0'))
	{
	  /* Ignore "./". */
	  h += 2;
	}
      else if (h[0] == '.' && h[1] == '.' && (h[2] == '/' || h[2] == '\0'))
	{
	  /* Handle "../" by retreating the tortoise by one path
	     element -- but not past beggining.  */
	  if (t > beg)
	    {
	      /* Move backwards until T hits the beginning of the
		 previous path element or the beginning of path. */
	      for (--t; t > beg && t[-1] != '/'; t--)
		;
	    }
	  else
	    {
	      /* If we're at the beginning, copy the "../" literally
		 move the beginning so a later ".." doesn't remove
		 it.  */
	      beg = t + 3;
	      goto regular;
	    }
	  h += 3;
	}
      else
	{
	regular:
	  /* A regular path element.  If H hasn't advanced past T,
	     simply skip to the next path element.  Otherwise, copy
	     the path element until the next slash.  */
	  if (t == h)
	    {
	      /* Skip the path element, including the slash.  */
	      while (h < end && *h != '/')
		t++, h++;
	      if (h < end)
		t++, h++;
	    }
	  else
	    {
	      /* Copy the path element, including the final slash.  */
	      while (h < end && *h != '/')
		*t++ = *h++;
	      if (h < end)
		*t++ = *h++;
	    }
	}
    }

  if (t != h)
    *t = '\0';

  return t != h;
}

/* Return the length of URL's path.  Path is considered to be
   terminated by one of '?', ';', '#', or by the end of the
   string.  */

static int
path_length (const char *url)
{
  const char *q = strpbrk_or_eos (url, "?;#");
  return q - url;
}

/* Find the last occurrence of character C in the range [b, e), or
   NULL, if none are present.  We might want to use memrchr (a GNU
   extension) under GNU libc.  */

static const char *
find_last_char (const char *b, const char *e, char c)
{
  for (; e > b; e--)
    if (*e == c)
      return e;
  return NULL;
}

/* Merge BASE with LINK and return the resulting URI.

   Either of the URIs may be absolute or relative, complete with the
   host name, or path only.  This tries to reasonably handle all
   foreseeable cases.  It only employs minimal URL parsing, without
   knowledge of the specifics of schemes.

   I briefly considered making this function call path_simplify after
   the merging process, as rfc1738 seems to suggest.  This is a bad
   idea for several reasons: 1) it complexifies the code, and 2)
   url_parse has to simplify path anyway, so it's wasteful to boot.  */

char *
uri_merge (const char *base, const char *link)
{
  int linklength;
  const char *end;
  char *merge;

  if (url_has_scheme (link))
    return xstrdup (link);

  /* We may not examine BASE past END. */
  end = base + path_length (base);
  linklength = strlen (link);

  if (!*link)
    {
      /* Empty LINK points back to BASE, query string and all. */
      return xstrdup (base);
    }
  else if (*link == '?')
    {
      /* LINK points to the same location, but changes the query
	 string.  Examples: */
      /* uri_merge("path",         "?new") -> "path?new"     */
      /* uri_merge("path?foo",     "?new") -> "path?new"     */
      /* uri_merge("path?foo#bar", "?new") -> "path?new"     */
      /* uri_merge("path#foo",     "?new") -> "path?new"     */
      int baselength = end - base;
      merge = xmalloc (baselength + linklength + 1);
      memcpy (merge, base, baselength);
      memcpy (merge + baselength, link, linklength);
      merge[baselength + linklength] = '\0';
    }
  else if (*link == '#')
    {
      /* uri_merge("path",         "#new") -> "path#new"     */
      /* uri_merge("path#foo",     "#new") -> "path#new"     */
      /* uri_merge("path?foo",     "#new") -> "path?foo#new" */
      /* uri_merge("path?foo#bar", "#new") -> "path?foo#new" */
      int baselength;
      const char *end1 = strchr (base, '#');
      if (!end1)
	end1 = base + strlen (base);
      baselength = end1 - base;
      merge = xmalloc (baselength + linklength + 1);
      memcpy (merge, base, baselength);
      memcpy (merge + baselength, link, linklength);
      merge[baselength + linklength] = '\0';
    }
  else if (*link == '/' && *(link + 1) == '/')
    {
      /* LINK begins with "//" and so is a net path: we need to
	 replace everything after (and including) the double slash
	 with LINK. */

      /* uri_merge("foo", "//new/bar")            -> "//new/bar"      */
      /* uri_merge("//old/foo", "//new/bar")      -> "//new/bar"      */
      /* uri_merge("http://old/foo", "//new/bar") -> "http://new/bar" */

      int span;
      const char *slash;
      const char *start_insert;

      /* Look for first slash. */
      slash = memchr (base, '/', end - base);
      /* If found slash and it is a double slash, then replace
	 from this point, else default to replacing from the
	 beginning.  */
      if (slash && *(slash + 1) == '/')
	start_insert = slash;
      else
	start_insert = base;

      span = start_insert - base;
      merge = (char *)xmalloc (span + linklength + 1);
      if (span)
	memcpy (merge, base, span);
      memcpy (merge + span, link, linklength);
      merge[span + linklength] = '\0';
    }
  else if (*link == '/')
    {
      /* LINK is an absolute path: we need to replace everything
	 after (and including) the FIRST slash with LINK.

	 So, if BASE is "http://host/whatever/foo/bar", and LINK is
	 "/qux/xyzzy", our result should be
	 "http://host/qux/xyzzy".  */
      int span;
      const char *slash;
      const char *start_insert = NULL; /* for gcc to shut up. */
      const char *pos = base;
      int seen_slash_slash = 0;
      /* We're looking for the first slash, but want to ignore
	 double slash. */
    again:
      slash = memchr (pos, '/', end - pos);
      if (slash && !seen_slash_slash)
	if (*(slash + 1) == '/')
	  {
	    pos = slash + 2;
	    seen_slash_slash = 1;
	    goto again;
	  }

      /* At this point, SLASH is the location of the first / after
	 "//", or the first slash altogether.  START_INSERT is the
	 pointer to the location where LINK will be inserted.  When
	 examining the last two examples, keep in mind that LINK
	 begins with '/'. */

      if (!slash && !seen_slash_slash)
	/* example: "foo" */
	/*           ^    */
	start_insert = base;
      else if (!slash && seen_slash_slash)
	/* example: "http://foo" */
	/*                     ^ */
	start_insert = end;
      else if (slash && !seen_slash_slash)
	/* example: "foo/bar" */
	/*           ^        */
	start_insert = base;
      else if (slash && seen_slash_slash)
	/* example: "http://something/" */
	/*                           ^  */
	start_insert = slash;

      span = start_insert - base;
      merge = (char *)xmalloc (span + linklength + 1);
      if (span)
	memcpy (merge, base, span);
      memcpy (merge + span, link, linklength);
      merge[span + linklength] = '\0';
    }
  else
    {
      /* LINK is a relative URL: we need to replace everything
	 after last slash (possibly empty) with LINK.

	 So, if BASE is "whatever/foo/bar", and LINK is "qux/xyzzy",
	 our result should be "whatever/foo/qux/xyzzy".  */
      int need_explicit_slash = 0;
      int span;
      const char *start_insert;
      const char *last_slash = find_last_char (base, end, '/');
      if (!last_slash)
	{
	  /* No slash found at all.  Replace what we have with LINK. */
	  start_insert = base;
	}
      else if (last_slash && last_slash >= base + 2
	       && last_slash[-2] == ':' && last_slash[-1] == '/')
	{
	  /* example: http://host"  */
	  /*                      ^ */
	  start_insert = end + 1;
	  need_explicit_slash = 1;
	}
      else
	{
	  /* example: "whatever/foo/bar" */
	  /*                        ^    */
	  start_insert = last_slash + 1;
	}

      span = start_insert - base;
      merge = (char *)xmalloc (span + linklength + 1);
      if (span)
	memcpy (merge, base, span);
      if (need_explicit_slash)
	merge[span - 1] = '/';
      memcpy (merge + span, link, linklength);
      merge[span + linklength] = '\0';
    }

  return merge;
}

#define APPEND(p, s) do {			\
  int len = strlen (s);				\
  memcpy (p, s, len);				\
  p += len;					\
} while (0)

/* Use this instead of password when the actual password is supposed
   to be hidden.  We intentionally use a generic string without giving
   away the number of characters in the password, like previous
   versions did.  */
#define HIDDEN_PASSWORD "*password*"

/* Recreate the URL string from the data in URL.

   If HIDE is non-zero (as it is when we're calling this on a URL we
   plan to print, but not when calling it to canonicalize a URL for
   use within the program), password will be hidden.  Unsafe
   characters in the URL will be quoted.  */

char *
url_string (const struct url *url, int hide_password)
{
  int size;
  char *result, *p;
  char *quoted_host, *quoted_user = NULL, *quoted_passwd = NULL;

  int scheme_port  = supported_schemes[url->scheme].default_port;
  const char *scheme_str = supported_schemes[url->scheme].leading_string;
  int fplen = full_path_length (url);

  int brackets_around_host;

  assert (scheme_str != NULL);

  /* Make sure the user name and password are quoted. */
  if (url->user)
    {
      quoted_user = url_escape_allow_passthrough (url->user);
      if (url->passwd)
	{
	  if (hide_password)
	    quoted_passwd = HIDDEN_PASSWORD;
	  else
	    quoted_passwd = url_escape_allow_passthrough (url->passwd);
	}
    }

  /* In the unlikely event that the host name contains non-printable
     characters, quote it for displaying to the user.  */
  quoted_host = url_escape_allow_passthrough (url->host);

  /* Undo the quoting of colons that URL escaping performs.  IPv6
     addresses may legally contain colons, and in that case must be
     placed in square brackets.  */
  if (quoted_host != url->host)
    unescape_single_char (quoted_host, ':');
  brackets_around_host = strchr (quoted_host, ':') != NULL;

  size = (strlen (scheme_str)
	  + strlen (quoted_host)
	  + (brackets_around_host ? 2 : 0)
	  + fplen
	  + 1);
  if (url->port != scheme_port)
    size += 1 + numdigit (url->port);
  if (quoted_user)
    {
      size += 1 + strlen (quoted_user);
      if (quoted_passwd)
	size += 1 + strlen (quoted_passwd);
    }

  p = result = xmalloc (size);

  APPEND (p, scheme_str);
  if (quoted_user)
    {
      APPEND (p, quoted_user);
      if (quoted_passwd)
	{
	  *p++ = ':';
	  APPEND (p, quoted_passwd);
	}
      *p++ = '@';
    }

  if (brackets_around_host)
    *p++ = '[';
  APPEND (p, quoted_host);
  if (brackets_around_host)
    *p++ = ']';
  if (url->port != scheme_port)
    {
      *p++ = ':';
      p = number_to_string (p, url->port);
    }

  full_path_write (url, p);
  p += fplen;
  *p++ = '\0';

  assert (p - result == size);

  if (quoted_user && quoted_user != url->user)
    xfree (quoted_user);
  if (quoted_passwd && !hide_password && quoted_passwd != url->passwd)
    xfree (quoted_passwd);
  if (quoted_host != url->host)
    xfree (quoted_host);

  return result;
}

/* Return non-zero if scheme a is similar to scheme b.
 
   Schemes are similar if they are equal.  If SSL is supported, schemes
   are also similar if one is http (SCHEME_HTTP) and the other is https
   (SCHEME_HTTPS).  */
int
schemes_are_similar_p (enum url_scheme a, enum url_scheme b)
{
  if (a == b)
    return 1;
#ifdef HAVE_SSL
  if ((a == SCHEME_HTTP && b == SCHEME_HTTPS)
      || (a == SCHEME_HTTPS && b == SCHEME_HTTP))
    return 1;
#endif
  return 0;
}

#if 0
/* Debugging and testing support for path_simplify. */

/* Debug: run path_simplify on PATH and return the result in a new
   string.  Useful for calling from the debugger.  */
static char *
ps (char *path)
{
  char *copy = xstrdup (path);
  path_simplify (copy);
  return copy;
}

static void
run_test (char *test, char *expected_result, int expected_change)
{
  char *test_copy = xstrdup (test);
  int modified = path_simplify (test_copy);

  if (0 != strcmp (test_copy, expected_result))
    {
      printf ("Failed path_simplify(\"%s\"): expected \"%s\", got \"%s\".\n",
	      test, expected_result, test_copy);
    }
  if (modified != expected_change)
    {
      if (expected_change == 1)
	printf ("Expected modification with path_simplify(\"%s\").\n",
		test);
      else
	printf ("Expected no modification with path_simplify(\"%s\").\n",
		test);
    }
  xfree (test_copy);
}

static void
test_path_simplify (void)
{
  static struct {
    char *test, *result;
    int should_modify;
  } tests[] = {
    { "",			"",		0 },
    { ".",			"",		1 },
    { "./",			"",		1 },
    { "..",			"..",		0 },
    { "../",			"../",		0 },
    { "foo",			"foo",		0 },
    { "foo/bar",		"foo/bar",	0 },
    { "foo///bar",		"foo///bar",	0 },
    { "foo/.",			"foo/",		1 },
    { "foo/./",			"foo/",		1 },
    { "foo./",			"foo./",	0 },
    { "foo/../bar",		"bar",		1 },
    { "foo/../bar/",		"bar/",		1 },
    { "foo/bar/..",		"foo/",		1 },
    { "foo/bar/../x",		"foo/x",	1 },
    { "foo/bar/../x/",		"foo/x/",	1 },
    { "foo/..",			"",		1 },
    { "foo/../..",		"..",		1 },
    { "foo/../../..",		"../..",	1 },
    { "foo/../../bar/../../baz", "../../baz",	1 },
    { "a/b/../../c",		"c",		1 },
    { "./a/../b",		"b",		1 }
  };
  int i;

  for (i = 0; i < countof (tests); i++)
    {
      char *test = tests[i].test;
      char *expected_result = tests[i].result;
      int   expected_change = tests[i].should_modify;
      run_test (test, expected_result, expected_change);
    }
}
#endif