gstreamer/gst/gsturi.c

/* GStreamer
 * Copyright (C) 1999,2000 Erik Walthinsen <omega@cse.ogi.edu>
 *                    2000 Wim Taymans <wtay@chello.be>
 * Copyright (C) 2011 Tim-Philipp Müller <tim centricular net>
 *
 * gsturi.c: register URI handlers
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library 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
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 */

/**
 * SECTION:gsturihandler
 * @short_description: Interface to ease URI handling in plugins.
 *
 * The URIHandler is an interface that is implemented by Source and Sink
 * #GstElement to simplify then handling of URI.
 *
 * An application can use the following functions to quickly get an element
 * that handles the given URI for reading or writing
 * (gst_element_make_from_uri()).
 *
 * Source and Sink plugins should implement this interface when possible.
 */

#ifdef HAVE_CONFIG_H
#  include "config.h"
#endif

#include "gst_private.h"
#include "gst.h"
#include "gsturi.h"
#include "gstinfo.h"
#include "gstregistry.h"

#include "gst-i18n-lib.h"

#include <string.h>

GST_DEBUG_CATEGORY_STATIC (gst_uri_handler_debug);
#define GST_CAT_DEFAULT gst_uri_handler_debug

GType
gst_uri_handler_get_type (void)
{
  static volatile gsize urihandler_type = 0;

  if (g_once_init_enter (&urihandler_type)) {
    GType _type;
    static const GTypeInfo urihandler_info = {
      sizeof (GstURIHandlerInterface),
      NULL,
      NULL,
      NULL,
      NULL,
      NULL,
      0,
      0,
      NULL,
      NULL
    };

    _type = g_type_register_static (G_TYPE_INTERFACE,
        "GstURIHandler", &urihandler_info, 0);

    GST_DEBUG_CATEGORY_INIT (gst_uri_handler_debug, "GST_URI", GST_DEBUG_BOLD,
        "handling of URIs");
    g_once_init_leave (&urihandler_type, _type);
  }
  return urihandler_type;
}

GQuark
gst_uri_error_quark (void)
{
  return g_quark_from_static_string ("gst-uri-error-quark");
}

static const guchar acceptable[96] = {  /* X0   X1   X2   X3   X4   X5   X6   X7   X8   X9   XA   XB   XC   XD   XE   XF */
  0x00, 0x3F, 0x20, 0x20, 0x20, 0x00, 0x2C, 0x3F, 0x3F, 0x3F, 0x3F, 0x22, 0x20, 0x3F, 0x3F, 0x1C,       /* 2X  !"#$%&'()*+,-./   */
  0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x38, 0x20, 0x20, 0x2C, 0x20, 0x2C,       /* 3X 0123456789:;<=>?   */
  0x30, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F,       /* 4X @ABCDEFGHIJKLMNO   */
  0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x20, 0x20, 0x20, 0x20, 0x3F,       /* 5X PQRSTUVWXYZ[\]^_   */
  0x20, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F,       /* 6X `abcdefghijklmno   */
  0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x3F, 0x20, 0x20, 0x20, 0x3F, 0x20        /* 7X pqrstuvwxyz{|}~DEL */
};

typedef enum
{
  UNSAFE_ALL = 0x1,             /* Escape all unsafe characters   */
  UNSAFE_ALLOW_PLUS = 0x2,      /* Allows '+'  */
  UNSAFE_PATH = 0x4,            /* Allows '/' and '?' and '&' and '='  */
  UNSAFE_DOS_PATH = 0x8,        /* Allows '/' and '?' and '&' and '=' and ':' */
  UNSAFE_HOST = 0x10,           /* Allows '/' and ':' and '@' */
  UNSAFE_SLASHES = 0x20         /* Allows all characters except for '/' and '%' */
} UnsafeCharacterSet;

#define HEX_ESCAPE '%'

/*  Escape undesirable characters using %
 *  -------------------------------------
 *
 * This function takes a pointer to a string in which
 * some characters may be unacceptable unescaped.
 * It returns a string which has these characters
 * represented by a '%' character followed by two hex digits.
 *
 * This routine returns a g_malloced string.
 */

static const gchar hex[16] = "0123456789ABCDEF";

static gchar *
escape_string_internal (const gchar * string, UnsafeCharacterSet mask)
{
#define ACCEPTABLE_CHAR(a) ((a)>=32 && (a)<128 && (acceptable[(a)-32] & use_mask))

  const gchar *p;
  gchar *q;
  gchar *result;
  guchar c;
  gint unacceptable;
  UnsafeCharacterSet use_mask;

  g_return_val_if_fail (mask == UNSAFE_ALL
      || mask == UNSAFE_ALLOW_PLUS
      || mask == UNSAFE_PATH
      || mask == UNSAFE_DOS_PATH
      || mask == UNSAFE_HOST || mask == UNSAFE_SLASHES, NULL);

  if (string == NULL) {
    return NULL;
  }

  unacceptable = 0;
  use_mask = mask;
  for (p = string; *p != '\0'; p++) {
    c = *p;
    if (!ACCEPTABLE_CHAR (c)) {
      unacceptable++;
    }
    if ((use_mask == UNSAFE_HOST) && (unacceptable || (c == '/'))) {
      /* when escaping a host, if we hit something that needs to be escaped, or we finally
       * hit a path separator, revert to path mode (the host segment of the url is over).
       */
      use_mask = UNSAFE_PATH;
    }
  }

  result = g_malloc (p - string + unacceptable * 2 + 1);

  use_mask = mask;
  for (q = result, p = string; *p != '\0'; p++) {
    c = *p;

    if (!ACCEPTABLE_CHAR (c)) {
      *q++ = HEX_ESCAPE;        /* means hex coming */
      *q++ = hex[c >> 4];
      *q++ = hex[c & 15];
    } else {
      *q++ = c;
    }
    if ((use_mask == UNSAFE_HOST) && (!ACCEPTABLE_CHAR (c) || (c == '/'))) {
      use_mask = UNSAFE_PATH;
    }
  }

  *q = '\0';

  return result;
}

/* escape_string:
 * @string: string to be escaped
 *
 * Escapes @string, replacing any and all special characters
 * with equivalent escape sequences.
 *
 * Return value: a newly allocated string equivalent to @string
 * but with all special characters escaped
 **/
static gchar *
escape_string (const gchar * string)
{
  return escape_string_internal (string, UNSAFE_ALL);
}

static int
hex_to_int (gchar c)
{
  return c >= '0' && c <= '9' ? c - '0'
      : c >= 'A' && c <= 'F' ? c - 'A' + 10
      : c >= 'a' && c <= 'f' ? c - 'a' + 10 : -1;
}

static int
unescape_character (const char *scanner)
{
  int first_digit;
  int second_digit;

  first_digit = hex_to_int (*scanner++);
  if (first_digit < 0) {
    return -1;
  }

  second_digit = hex_to_int (*scanner);
  if (second_digit < 0) {
    return -1;
  }

  return (first_digit << 4) | second_digit;
}

/* unescape_string:
 * @escaped_string: an escaped URI, path, or other string
 * @illegal_characters: a string containing a sequence of characters
 * considered "illegal", '\0' is automatically in this list.
 *
 * Decodes escaped characters (i.e. PERCENTxx sequences) in @escaped_string.
 * Characters are encoded in PERCENTxy form, where xy is the ASCII hex code
 * for character 16x+y.
 *
 * Return value: a newly allocated string with the unescaped equivalents,
 * or %NULL if @escaped_string contained one of the characters
 * in @illegal_characters.
 **/
static char *
unescape_string (const gchar * escaped_string, const gchar * illegal_characters)
{
  const gchar *in;
  gchar *out, *result;
  gint character;

  if (escaped_string == NULL) {
    return NULL;
  }

  result = g_malloc (strlen (escaped_string) + 1);

  out = result;
  for (in = escaped_string; *in != '\0'; in++) {
    character = *in;
    if (*in == HEX_ESCAPE) {
      character = unescape_character (in + 1);

      /* Check for an illegal character. We consider '\0' illegal here. */
      if (character <= 0
          || (illegal_characters != NULL
              && strchr (illegal_characters, (char) character) != NULL)) {
        g_free (result);
        return NULL;
      }
      in += 2;
    }
    *out++ = (char) character;
  }

  *out = '\0';
  g_assert ((gsize) (out - result) <= strlen (escaped_string));
  return result;

}


static void
gst_uri_protocol_check_internal (const gchar * uri, gchar ** endptr)
{
  gchar *check = (gchar *) uri;

  g_assert (uri != NULL);
  g_assert (endptr != NULL);

  if (g_ascii_isalpha (*check)) {
    check++;
    while (g_ascii_isalnum (*check) || *check == '+'
        || *check == '-' || *check == '.')
      check++;
  }

  *endptr = check;
}

/**
 * gst_uri_protocol_is_valid:
 * @protocol: A string
 *
 * Tests if the given string is a valid protocol identifier. Protocols
 * must consist of alphanumeric characters, '+', '-' and '.' and must
 * start with a alphabetic character. See RFC 3986 Section 3.1.
 *
 * Returns: %TRUE if the string is a valid protocol identifier, %FALSE otherwise.
 */
gboolean
gst_uri_protocol_is_valid (const gchar * protocol)
{
  gchar *endptr;

  g_return_val_if_fail (protocol != NULL, FALSE);

  gst_uri_protocol_check_internal (protocol, &endptr);

  return *endptr == '\0' && ((gsize) (endptr - protocol)) >= 2;
}

/**
 * gst_uri_is_valid:
 * @uri: A URI string
 *
 * Tests if the given string is a valid URI identifier. URIs start with a valid
 * scheme followed by ":" and maybe a string identifying the location.
 *
 * Returns: %TRUE if the string is a valid URI
 */
gboolean
gst_uri_is_valid (const gchar * uri)
{
  gchar *endptr;

  g_return_val_if_fail (uri != NULL, FALSE);

  gst_uri_protocol_check_internal (uri, &endptr);

  return *endptr == ':' && ((gsize) (endptr - uri)) >= 2;
}

/**
 * gst_uri_get_protocol:
 * @uri: A URI string
 *
 * Extracts the protocol out of a given valid URI. The returned string must be
 * freed using g_free().
 *
 * Returns: The protocol for this URI.
 */
gchar *
gst_uri_get_protocol (const gchar * uri)
{
  gchar *colon;

  g_return_val_if_fail (uri != NULL, NULL);
  g_return_val_if_fail (gst_uri_is_valid (uri), NULL);

  colon = strstr (uri, ":");

  return g_ascii_strdown (uri, colon - uri);
}

/**
 * gst_uri_has_protocol:
 * @uri: a URI string
 * @protocol: a protocol string (e.g. "http")
 *
 * Checks if the protocol of a given valid URI matches @protocol.
 *
 * Returns: %TRUE if the protocol matches.
 */
gboolean
gst_uri_has_protocol (const gchar * uri, const gchar * protocol)
{
  gchar *colon;

  g_return_val_if_fail (uri != NULL, FALSE);
  g_return_val_if_fail (protocol != NULL, FALSE);
  g_return_val_if_fail (gst_uri_is_valid (uri), FALSE);

  colon = strstr (uri, ":");

  if (colon == NULL)
    return FALSE;

  return (g_ascii_strncasecmp (uri, protocol, (gsize) (colon - uri)) == 0);
}

/**
 * gst_uri_get_location:
 * @uri: A URI string
 *
 * Extracts the location out of a given valid URI, ie. the protocol and "://"
 * are stripped from the URI, which means that the location returned includes
 * the hostname if one is specified. The returned string must be freed using
 * g_free().
 *
 * Free-function: g_free
 *
 * Returns: (transfer full): the location for this URI. Returns %NULL if the
 *     URI isn't valid. If the URI does not contain a location, an empty
 *     string is returned.
 */
gchar *
gst_uri_get_location (const gchar * uri)
{
  const gchar *colon;
  gchar *unescaped = NULL;

  g_return_val_if_fail (uri != NULL, NULL);
  g_return_val_if_fail (gst_uri_is_valid (uri), NULL);

  colon = strstr (uri, "://");
  if (!colon)
    return NULL;

  unescaped = unescape_string (colon + 3, "/");

  /* On Windows an URI might look like file:///c:/foo/bar.txt or
   * file:///c|/foo/bar.txt (some Netscape versions) and we want to
   * return c:/foo/bar.txt as location rather than /c:/foo/bar.txt.
   * Can't use g_filename_from_uri() here because it will only handle the
   * file:// protocol */
#ifdef G_OS_WIN32
  if (unescaped != NULL && unescaped[0] == '/' &&
      g_ascii_isalpha (unescaped[1]) &&
      (unescaped[2] == ':' || unescaped[2] == '|')) {
    unescaped[2] = ':';
    memmove (unescaped, unescaped + 1, strlen (unescaped + 1) + 1);
  }
#endif

  GST_LOG ("extracted location '%s' from URI '%s'", GST_STR_NULL (unescaped),
      uri);
  return unescaped;
}

/**
 * gst_uri_construct:
 * @protocol: Protocol for URI
 * @location: (transfer none): Location for URI
 *
 * Constructs a URI for a given valid protocol and location.
 *
 * Free-function: g_free
 *
 * Returns: (transfer full): a new string for this URI. Returns %NULL if the
 *     given URI protocol is not valid, or the given location is %NULL.
 */
gchar *
gst_uri_construct (const gchar * protocol, const gchar * location)
{
  char *escaped, *proto_lowercase;
  char *retval;

  g_return_val_if_fail (gst_uri_protocol_is_valid (protocol), NULL);
  g_return_val_if_fail (location != NULL, NULL);

  proto_lowercase = g_ascii_strdown (protocol, -1);
  escaped = escape_string (location);
  retval = g_strdup_printf ("%s://%s", proto_lowercase, escaped);
  g_free (escaped);
  g_free (proto_lowercase);

  return retval;
}

typedef struct
{
  GstURIType type;
  const gchar *protocol;
}
SearchEntry;

static gboolean
search_by_entry (GstPluginFeature * feature, gpointer search_entry)
{
  const gchar *const *protocols;
  GstElementFactory *factory;
  SearchEntry *entry = (SearchEntry *) search_entry;

  if (!GST_IS_ELEMENT_FACTORY (feature))
    return FALSE;
  factory = GST_ELEMENT_FACTORY_CAST (feature);

  if (factory->uri_type != entry->type)
    return FALSE;

  protocols = gst_element_factory_get_uri_protocols (factory);

  if (protocols == NULL) {
    g_warning ("Factory '%s' implements GstUriHandler interface but returned "
        "no supported protocols!", gst_plugin_feature_get_name (feature));
    return FALSE;
  }

  while (*protocols != NULL) {
    if (g_ascii_strcasecmp (*protocols, entry->protocol) == 0)
      return TRUE;
    protocols++;
  }
  return FALSE;
}

static gint
sort_by_rank (GstPluginFeature * first, GstPluginFeature * second)
{
  return gst_plugin_feature_get_rank (second) -
      gst_plugin_feature_get_rank (first);
}

static GList *
get_element_factories_from_uri_protocol (const GstURIType type,
    const gchar * protocol)
{
  GList *possibilities;
  SearchEntry entry;

  g_return_val_if_fail (protocol, NULL);

  entry.type = type;
  entry.protocol = protocol;
  possibilities = gst_registry_feature_filter (gst_registry_get (),
      search_by_entry, FALSE, &entry);

  return possibilities;
}

/**
 * gst_uri_protocol_is_supported:
 * @type: Whether to check for a source or a sink
 * @protocol: Protocol that should be checked for (e.g. "http" or "smb")
 *
 * Checks if an element exists that supports the given URI protocol. Note
 * that a positive return value does not imply that a subsequent call to
 * gst_element_make_from_uri() is guaranteed to work.
 *
 * Returns: %TRUE
*/
gboolean
gst_uri_protocol_is_supported (const GstURIType type, const gchar * protocol)
{
  GList *possibilities;

  g_return_val_if_fail (protocol, FALSE);

  possibilities = get_element_factories_from_uri_protocol (type, protocol);

  if (possibilities) {
    g_list_free (possibilities);
    return TRUE;
  } else
    return FALSE;
}

/**
 * gst_element_make_from_uri:
 * @type: Whether to create a source or a sink
 * @uri: URI to create an element for
 * @elementname: (allow-none): Name of created element, can be %NULL.
 * @error: (allow-none): address where to store error information, or %NULL.
 *
 * Creates an element for handling the given URI.
 *
 * Returns: (transfer floating): a new element or %NULL if none could be created
 */
GstElement *
gst_element_make_from_uri (const GstURIType type, const gchar * uri,
    const gchar * elementname, GError ** error)
{
  GList *possibilities, *walk;
  gchar *protocol;
  GstElement *ret = NULL;

  g_return_val_if_fail (gst_is_initialized (), NULL);
  g_return_val_if_fail (GST_URI_TYPE_IS_VALID (type), NULL);
  g_return_val_if_fail (gst_uri_is_valid (uri), NULL);
  g_return_val_if_fail (error == NULL || *error == NULL, NULL);

  GST_DEBUG ("type:%d, uri:%s, elementname:%s", type, uri, elementname);

  protocol = gst_uri_get_protocol (uri);
  possibilities = get_element_factories_from_uri_protocol (type, protocol);

  if (!possibilities) {
    GST_DEBUG ("No %s for URI '%s'", type == GST_URI_SINK ? "sink" : "source",
        uri);
    /* The error message isn't great, but we don't expect applications to
     * show that error to users, but call the missing plugins functions */
    g_set_error (error, GST_URI_ERROR, GST_URI_ERROR_UNSUPPORTED_PROTOCOL,
        _("No URI handler for the %s protocol found"), protocol);
    g_free (protocol);
    return NULL;
  }
  g_free (protocol);

  possibilities = g_list_sort (possibilities, (GCompareFunc) sort_by_rank);
  walk = possibilities;
  while (walk) {
    GstElementFactory *factory = walk->data;
    GError *uri_err = NULL;

    ret = gst_element_factory_create (factory, elementname);
    if (ret != NULL) {
      GstURIHandler *handler = GST_URI_HANDLER (ret);

      if (gst_uri_handler_set_uri (handler, uri, &uri_err))
        break;

      GST_WARNING ("%s didn't accept URI '%s': %s", GST_OBJECT_NAME (ret), uri,
          uri_err->message);

      if (error != NULL && *error == NULL)
        g_propagate_error (error, uri_err);
      else
        g_error_free (uri_err);

      gst_object_unref (ret);
      ret = NULL;
    }
    walk = walk->next;
  }
  gst_plugin_feature_list_free (possibilities);

  GST_LOG_OBJECT (ret, "created %s for URL '%s'",
      type == GST_URI_SINK ? "sink" : "source", uri);

  /* if the first handler didn't work, but we found another one that works */
  if (ret != NULL)
    g_clear_error (error);

  return ret;
}

/**
 * gst_uri_handler_get_uri_type:
 * @handler: A #GstURIHandler.
 *
 * Gets the type of the given URI handler
 *
 * Returns: the #GstURIType of the URI handler.
 * Returns #GST_URI_UNKNOWN if the @handler isn't implemented correctly.
 */
guint
gst_uri_handler_get_uri_type (GstURIHandler * handler)
{
  GstURIHandlerInterface *iface;
  guint ret;

  g_return_val_if_fail (GST_IS_URI_HANDLER (handler), GST_URI_UNKNOWN);

  iface = GST_URI_HANDLER_GET_INTERFACE (handler);
  g_return_val_if_fail (iface != NULL, GST_URI_UNKNOWN);
  g_return_val_if_fail (iface->get_type != NULL, GST_URI_UNKNOWN);

  ret = iface->get_type (G_OBJECT_TYPE (handler));
  g_return_val_if_fail (GST_URI_TYPE_IS_VALID (ret), GST_URI_UNKNOWN);

  return ret;
}

/**
 * gst_uri_handler_get_protocols:
 * @handler: A #GstURIHandler.
 *
 * Gets the list of protocols supported by @handler. This list may not be
 * modified.
 *
 * Returns: (transfer none) (element-type utf8): the supported protocols.
 *     Returns %NULL if the @handler isn't implemented properly, or the @handler
 *     doesn't support any protocols.
 */
const gchar *const *
gst_uri_handler_get_protocols (GstURIHandler * handler)
{
  GstURIHandlerInterface *iface;
  const gchar *const *ret;

  g_return_val_if_fail (GST_IS_URI_HANDLER (handler), NULL);

  iface = GST_URI_HANDLER_GET_INTERFACE (handler);
  g_return_val_if_fail (iface != NULL, NULL);
  g_return_val_if_fail (iface->get_protocols != NULL, NULL);

  ret = iface->get_protocols (G_OBJECT_TYPE (handler));
  g_return_val_if_fail (ret != NULL, NULL);

  return ret;
}

/**
 * gst_uri_handler_get_uri:
 * @handler: A #GstURIHandler
 *
 * Gets the currently handled URI.
 *
 * Returns: (transfer full): the URI currently handled by the @handler.
 *   Returns %NULL if there are no URI currently handled. The
 *   returned string must be freed with g_free() when no longer needed.
 */
gchar *
gst_uri_handler_get_uri (GstURIHandler * handler)
{
  GstURIHandlerInterface *iface;
  gchar *ret;

  g_return_val_if_fail (GST_IS_URI_HANDLER (handler), NULL);

  iface = GST_URI_HANDLER_GET_INTERFACE (handler);
  g_return_val_if_fail (iface != NULL, NULL);
  g_return_val_if_fail (iface->get_uri != NULL, NULL);
  ret = iface->get_uri (handler);
  if (ret != NULL)
    g_return_val_if_fail (gst_uri_is_valid (ret), NULL);

  return ret;
}

/**
 * gst_uri_handler_set_uri:
 * @handler: A #GstURIHandler
 * @uri: URI to set
 * @error: (allow-none): address where to store a #GError in case of
 *    an error, or %NULL
 *
 * Tries to set the URI of the given handler.
 *
 * Returns: %TRUE if the URI was set successfully, else %FALSE.
 */
gboolean
gst_uri_handler_set_uri (GstURIHandler * handler, const gchar * uri,
    GError ** error)
{
  GstURIHandlerInterface *iface;
  gboolean ret;
  gchar *new_uri, *protocol, *location, *colon;

  g_return_val_if_fail (GST_IS_URI_HANDLER (handler), FALSE);
  g_return_val_if_fail (gst_uri_is_valid (uri), FALSE);
  g_return_val_if_fail (error == NULL || *error == NULL, FALSE);

  iface = GST_URI_HANDLER_GET_INTERFACE (handler);
  g_return_val_if_fail (iface != NULL, FALSE);
  g_return_val_if_fail (iface->set_uri != NULL, FALSE);

  protocol = gst_uri_get_protocol (uri);

  if (iface->get_protocols) {
    const gchar *const *protocols;
    const gchar *const *p;
    gboolean found_protocol = FALSE;

    protocols = iface->get_protocols (G_OBJECT_TYPE (handler));
    if (protocols != NULL) {
      for (p = protocols; *p != NULL; ++p) {
        if (g_ascii_strcasecmp (protocol, *p) == 0) {
          found_protocol = TRUE;
          break;
        }
      }

      if (!found_protocol) {
        g_set_error (error, GST_URI_ERROR, GST_URI_ERROR_UNSUPPORTED_PROTOCOL,
            _("URI scheme '%s' not supported"), protocol);
        g_free (protocol);
        return FALSE;
      }
    }
  }

  colon = strstr (uri, ":");
  location = g_strdup (colon);

  new_uri = g_strdup_printf ("%s%s", protocol, location);

  ret = iface->set_uri (handler, uri, error);

  g_free (new_uri);
  g_free (location);
  g_free (protocol);

  return ret;
}

static gchar *
gst_file_utils_canonicalise_path (const gchar * path)
{
  gchar **parts, **p, *clean_path;

#ifdef G_OS_WIN32
  {
    GST_WARNING ("FIXME: canonicalise win32 path");
    return g_strdup (path);
  }
#endif

  parts = g_strsplit (path, "/", -1);

  p = parts;
  while (*p != NULL) {
    if (strcmp (*p, ".") == 0) {
      /* just move all following parts on top of this, incl. NUL terminator */
      g_free (*p);
      memmove (p, p + 1, (g_strv_length (p + 1) + 1) * sizeof (gchar *));
      /* re-check the new current part again in the next iteration */
      continue;
    } else if (strcmp (*p, "..") == 0 && p > parts) {
      /* just move all following parts on top of the previous part, incl.
       * NUL terminator */
      g_free (*(p - 1));
      g_free (*p);
      memmove (p - 1, p + 1, (g_strv_length (p + 1) + 1) * sizeof (gchar *));
      /* re-check the new current part again in the next iteration */
      --p;
      continue;
    }
    ++p;
  }
  if (*path == '/') {
    guint num_parts;

    num_parts = g_strv_length (parts) + 1;      /* incl. terminator */
    parts = g_renew (gchar *, parts, num_parts + 1);
    memmove (parts + 1, parts, num_parts * sizeof (gchar *));
    parts[0] = g_strdup ("/");
  }

  clean_path = g_build_filenamev (parts);
  g_strfreev (parts);
  return clean_path;
}

static gboolean
file_path_contains_relatives (const gchar * path)
{
  return (strstr (path, "/./") != NULL || strstr (path, "/../") != NULL ||
      strstr (path, G_DIR_SEPARATOR_S "." G_DIR_SEPARATOR_S) != NULL ||
      strstr (path, G_DIR_SEPARATOR_S ".." G_DIR_SEPARATOR_S) != NULL);
}

/**
 * gst_filename_to_uri:
 * @filename: absolute or relative file name path
 * @error: pointer to error, or %NULL
 *
 * Similar to g_filename_to_uri(), but attempts to handle relative file paths
 * as well. Before converting @filename into an URI, it will be prefixed by
 * the current working directory if it is a relative path, and then the path
 * will be canonicalised so that it doesn't contain any './' or '../' segments.
 *
 * On Windows #filename should be in UTF-8 encoding.
 */
gchar *
gst_filename_to_uri (const gchar * filename, GError ** error)
{
  gchar *abs_location = NULL;
  gchar *uri, *abs_clean;

  g_return_val_if_fail (filename != NULL, NULL);
  g_return_val_if_fail (error == NULL || *error == NULL, NULL);

  if (g_path_is_absolute (filename)) {
    if (!file_path_contains_relatives (filename)) {
      uri = g_filename_to_uri (filename, NULL, error);
      goto beach;
    }

    abs_location = g_strdup (filename);
  } else {
    gchar *cwd;

    cwd = g_get_current_dir ();
    abs_location = g_build_filename (cwd, filename, NULL);
    g_free (cwd);

    if (!file_path_contains_relatives (abs_location)) {
      uri = g_filename_to_uri (abs_location, NULL, error);
      goto beach;
    }
  }

  /* path is now absolute, but contains '.' or '..' */
  abs_clean = gst_file_utils_canonicalise_path (abs_location);
  GST_LOG ("'%s' -> '%s' -> '%s'", filename, abs_location, abs_clean);
  uri = g_filename_to_uri (abs_clean, NULL, error);
  g_free (abs_clean);

beach:

  g_free (abs_location);
  GST_DEBUG ("'%s' -> '%s'", filename, uri);
  return uri;
}