dataprotocol.c

GStreamer是一个开源的多媒体框架库。利用它

  g_return_val_if_fail (length, FALSE);
  g_return_val_if_fail (header, FALSE);
  g_return_val_if_fail (payload, FALSE);

  /* first construct payload, since we need the length */
  switch (GST_EVENT_TYPE (event)) {
    case GST_EVENT_UNKNOWN:
      GST_WARNING ("Unknown event, ignoring");
      return FALSE;
    case GST_EVENT_EOS:
    case GST_EVENT_FLUSH_START:
    case GST_EVENT_FLUSH_STOP:
    case GST_EVENT_NEWSEGMENT:
      pl_length = 0;
      *payload = NULL;
      break;
    case GST_EVENT_SEEK:
    {
      gdouble rate;
      GstFormat format;
      GstSeekFlags flags;
      GstSeekType cur_type, stop_type;
      gint64 cur, stop;

      gst_event_parse_seek ((GstEvent *) event, &rate, &format, &flags,
          &cur_type, &cur, &stop_type, &stop);

      pl_length = 4 + 4 + 4 + 8 + 4 + 8;
      *payload = g_malloc0 (pl_length);
      /* FIXME write rate */
      GST_WRITE_UINT32_BE (*payload, (guint32) format);
      GST_WRITE_UINT32_BE (*payload + 4, (guint32) flags);
      GST_WRITE_UINT32_BE (*payload + 8, (guint32) cur_type);
      GST_WRITE_UINT64_BE (*payload + 12, (guint64) cur);
      GST_WRITE_UINT32_BE (*payload + 20, (guint32) stop_type);
      GST_WRITE_UINT64_BE (*payload + 24, (guint64) stop);
      break;
    }
    case GST_EVENT_QOS:
    case GST_EVENT_NAVIGATION:
    case GST_EVENT_TAG:
      GST_WARNING ("Unhandled event type %d, ignoring", GST_EVENT_TYPE (event));
      return FALSE;
    default:
      GST_WARNING ("Unknown event type %d, ignoring", GST_EVENT_TYPE (event));
      return FALSE;
  }

  /* now we can create and fill the header */
  h = g_malloc0 (GST_DP_HEADER_LENGTH);
  *length = GST_DP_HEADER_LENGTH;

  /* version, flags, type */
  GST_DP_INIT_HEADER (h, GST_DP_VERSION_0_2, flags,
      GST_DP_PAYLOAD_EVENT_NONE + GST_EVENT_TYPE (event));

  /* length */
  GST_WRITE_UINT32_BE (h + 6, (guint32) pl_length);
  /* timestamp */
  GST_WRITE_UINT64_BE (h + 10, GST_EVENT_TIMESTAMP (event));

  GST_DP_SET_CRC (h, flags, *payload, pl_length);

  GST_LOG ("created header from event:");
  gst_dp_dump_byte_array (h, GST_DP_HEADER_LENGTH);

  *header = h;
  return TRUE;
}
#endif

static gboolean
gst_dp_packet_from_event_1_0 (const GstEvent * event, GstDPHeaderFlag flags,
    guint * length, guint8 ** header, guint8 ** payload)
{
  guint8 *h;
  guint32 pl_length;            /* length of payload */
  guchar *string = NULL;

  g_return_val_if_fail (GST_IS_EVENT (event), FALSE);
  g_return_val_if_fail (length, FALSE);
  g_return_val_if_fail (header, FALSE);
  g_return_val_if_fail (payload, FALSE);

  *length = GST_DP_HEADER_LENGTH;
  h = g_malloc0 (GST_DP_HEADER_LENGTH);

  if (event->structure) {
    string = (guchar *) gst_structure_to_string (event->structure);
    GST_LOG ("event %p has structure, string %s", event, string);
    pl_length = strlen ((gchar *) string) + 1;  /* include trailing 0 */
  } else {
    GST_LOG ("event %p has no structure", event);
    pl_length = 0;
  }

  /* version, flags, type */
  GST_DP_INIT_HEADER (h, GST_DP_VERSION_1_0, flags,
      GST_DP_PAYLOAD_EVENT_NONE + GST_EVENT_TYPE (event));

  /* length */
  GST_WRITE_UINT32_BE (h + 6, pl_length);
  /* timestamp */
  GST_WRITE_UINT64_BE (h + 10, GST_EVENT_TIMESTAMP (event));

  GST_DP_SET_CRC (h, flags, *payload, pl_length);

  GST_LOG ("created header from event:");
  gst_dp_dump_byte_array (h, GST_DP_HEADER_LENGTH);
  *header = h;
  *payload = string;
  return TRUE;
}

/*** DEPACKETIZING FUNCTIONS ***/

/**
 * gst_dp_buffer_from_header:
 * @header_length: the length of the packet header
 * @header: the byte array of the packet header
 *
 * Creates a newly allocated #GstBuffer from the given header.
 * The buffer data needs to be copied into it before validating.
 *
 * Use this function if you want to pre-allocate a buffer based on the
 * packet header to read the packet payload in to.
 *
 * This function does not check the header passed to it, use
 * gst_dp_validate_header() first if the header data is unchecked.
 *
 * Returns: A #GstBuffer if the buffer was successfully created, or NULL.
 */
GstBuffer *
gst_dp_buffer_from_header (guint header_length, const guint8 * header)
{
  GstBuffer *buffer;

  g_return_val_if_fail (header != NULL, NULL);
  g_return_val_if_fail (header_length >= GST_DP_HEADER_LENGTH, NULL);
  g_return_val_if_fail (GST_DP_HEADER_PAYLOAD_TYPE (header) ==
      GST_DP_PAYLOAD_BUFFER, NULL);

  buffer =
      gst_buffer_new_and_alloc ((guint) GST_DP_HEADER_PAYLOAD_LENGTH (header));

  GST_BUFFER_TIMESTAMP (buffer) = GST_DP_HEADER_TIMESTAMP (header);
  GST_BUFFER_DURATION (buffer) = GST_DP_HEADER_DURATION (header);
  GST_BUFFER_OFFSET (buffer) = GST_DP_HEADER_OFFSET (header);
  GST_BUFFER_OFFSET_END (buffer) = GST_DP_HEADER_OFFSET_END (header);
  GST_BUFFER_FLAGS (buffer) = GST_DP_HEADER_BUFFER_FLAGS (header);

  return buffer;
}

/**
 * gst_dp_caps_from_packet:
 * @header_length: the length of the packet header
 * @header: the byte array of the packet header
 * @payload: the byte array of the packet payload
 *
 * Creates a newly allocated #GstCaps from the given packet.
 *
 * This function does not check the arguments passed to it, use
 * gst_dp_validate_packet() first if the header and payload data are
 * unchecked.
 *
 * Returns: A #GstCaps containing the caps represented in the packet,
 *          or NULL if the packet could not be converted.
 */
GstCaps *
gst_dp_caps_from_packet (guint header_length, const guint8 * header,
    const guint8 * payload)
{
  GstCaps *caps;
  gchar *string;

  g_return_val_if_fail (header, NULL);
  g_return_val_if_fail (header_length >= GST_DP_HEADER_LENGTH, NULL);
  g_return_val_if_fail (GST_DP_HEADER_PAYLOAD_TYPE (header) ==
      GST_DP_PAYLOAD_CAPS, NULL);
  g_return_val_if_fail (payload, NULL);

  /* 0 sized payload length will work create NULL string */
  string = g_strndup ((gchar *) payload, GST_DP_HEADER_PAYLOAD_LENGTH (header));
  caps = gst_caps_from_string (string);
  g_free (string);

  return caps;
}

static GstEvent *
gst_dp_event_from_packet_0_2 (guint header_length, const guint8 * header,
    const guint8 * payload)
{
  GstEvent *event = NULL;
  GstEventType type;

  type = GST_DP_HEADER_PAYLOAD_TYPE (header) - GST_DP_PAYLOAD_EVENT_NONE;
  switch (type) {
    case GST_EVENT_UNKNOWN:
      GST_WARNING ("Unknown event, ignoring");
      return FALSE;
    case GST_EVENT_EOS:
    case GST_EVENT_FLUSH_START:
    case GST_EVENT_FLUSH_STOP:
    case GST_EVENT_NEWSEGMENT:
      event = gst_event_new_custom (type, NULL);
      GST_EVENT_TIMESTAMP (event) = GST_DP_HEADER_TIMESTAMP (header);
      break;
    case GST_EVENT_SEEK:
    {
      gdouble rate;
      GstFormat format;
      GstSeekFlags flags;
      GstSeekType cur_type, stop_type;
      gint64 cur, stop;

      g_return_val_if_fail (payload != NULL, NULL);

      /* FIXME, read rate */
      rate = 1.0;
      format = (GstFormat) GST_READ_UINT32_BE (payload);
      flags = (GstSeekFlags) GST_READ_UINT32_BE (payload + 4);
      cur_type = (GstSeekType) GST_READ_UINT32_BE (payload + 8);
      cur = (gint64) GST_READ_UINT64_BE (payload + 12);
      stop_type = (GstSeekType) GST_READ_UINT32_BE (payload + 20);
      stop = (gint64) GST_READ_UINT64_BE (payload + 24);

      event = gst_event_new_seek (rate, format, flags, cur_type, cur,
          stop_type, stop);
      GST_EVENT_TIMESTAMP (event) = GST_DP_HEADER_TIMESTAMP (header);
      break;
    }
    case GST_EVENT_QOS:
    case GST_EVENT_NAVIGATION:
    case GST_EVENT_TAG:
      GST_WARNING ("Unhandled event type %d, ignoring", type);
      return FALSE;
    default:
      GST_WARNING ("Unknown event type %d, ignoring", type);
      return FALSE;
  }

  return event;
}

static GstEvent *
gst_dp_event_from_packet_1_0 (guint header_length, const guint8 * header,
    const guint8 * payload)
{
  GstEvent *event = NULL;
  GstEventType type;
  gchar *string = NULL;
  GstStructure *s = NULL;

  type = GST_DP_HEADER_PAYLOAD_TYPE (header) - GST_DP_PAYLOAD_EVENT_NONE;
  if (payload) {
    string =
        g_strndup ((gchar *) payload, GST_DP_HEADER_PAYLOAD_LENGTH (header));
    s = gst_structure_from_string (string, NULL);
    g_free (string);
  }
  event = gst_event_new_custom (type, s);
  return event;
}


/**
 * gst_dp_event_from_packet:
 * @header_length: the length of the packet header
 * @header: the byte array of the packet header
 * @payload: the byte array of the packet payload
 *
 * Creates a newly allocated #GstEvent from the given packet.
 *
 * This function does not check the arguments passed to it, use
 * gst_dp_validate_packet() first if the header and payload data are
 * unchecked.
 *
 * Returns: A #GstEvent if the event was successfully created,
 *          or NULL if an event could not be read from the payload.
 */
GstEvent *
gst_dp_event_from_packet (guint header_length, const guint8 * header,
    const guint8 * payload)
{
  guint8 major, minor;

  g_return_val_if_fail (header, NULL);
  g_return_val_if_fail (header_length >= GST_DP_HEADER_LENGTH, NULL);

  major = GST_DP_HEADER_MAJOR_VERSION (header);
  minor = GST_DP_HEADER_MINOR_VERSION (header);

  if (major == 0 && minor == 2)
    return gst_dp_event_from_packet_0_2 (header_length, header, payload);
  else if (major == 1 && minor == 0)
    return gst_dp_event_from_packet_1_0 (header_length, header, payload);
  else {
    GST_ERROR ("Unknown GDP version %d.%d", major, minor);
    return NULL;
  }
}

/**
 * gst_dp_validate_header:
 * @header_length: the length of the packet header
 * @header: the byte array of the packet header
 *
 * Validates the given packet header by checking the CRC checksum.
 *
 * Returns: %TRUE if the CRC matches, or no CRC checksum is present.
 */
gboolean
gst_dp_validate_header (guint header_length, const guint8 * header)
{
  guint16 crc_read, crc_calculated;

  g_return_val_if_fail (header != NULL, FALSE);
  g_return_val_if_fail (header_length >= GST_DP_HEADER_LENGTH, FALSE);

  if (!(GST_DP_HEADER_FLAGS (header) & GST_DP_HEADER_FLAG_CRC_HEADER))
    return TRUE;

  crc_read = GST_DP_HEADER_CRC_HEADER (header);

  /* don't include the last two crc fields for the crc check */
  crc_calculated = gst_dp_crc (header, header_length - 4);
  if (crc_read != crc_calculated)
    goto crc_error;

  GST_LOG ("header crc validation: %02x", crc_read);
  return TRUE;

  /* ERRORS */
crc_error:
  {
    GST_WARNING ("header crc mismatch: read %02x, calculated %02x", crc_read,
        crc_calculated);
    return FALSE;
  }
}

/**
 * gst_dp_validate_payload:
 * @header_length: the length of the packet header
 * @header: the byte array of the packet header
 * @payload: the byte array of the packet payload
 *
 * Validates the given packet payload using the given packet header
 * by checking the CRC checksum.
 *
 * Returns: %TRUE if the CRC matches, or no CRC checksum is present.
 */
gboolean
gst_dp_validate_payload (guint header_length, const guint8 * header,
    const guint8 * payload)
{
  guint16 crc_read, crc_calculated;

  g_return_val_if_fail (header != NULL, FALSE);
  g_return_val_if_fail (header_length >= GST_DP_HEADER_LENGTH, FALSE);

  if (!(GST_DP_HEADER_FLAGS (header) & GST_DP_HEADER_FLAG_CRC_PAYLOAD))
    return TRUE;

  crc_read = GST_DP_HEADER_CRC_PAYLOAD (header);
  crc_calculated = gst_dp_crc (payload, GST_DP_HEADER_PAYLOAD_LENGTH (header));
  if (crc_read != crc_calculated)
    goto crc_error;

  GST_LOG ("payload crc validation: %02x", crc_read);
  return TRUE;

  /* ERRORS */
crc_error:
  {
    GST_WARNING ("payload crc mismatch: read %02x, calculated %02x", crc_read,
        crc_calculated);
    return FALSE;
  }
}

/**
 * gst_dp_validate_packet:
 * @header_length: the length of the packet header
 * @header: the byte array of the packet header
 * @payload: the byte array of the packet payload
 *
 * Validates the given packet by checking version information and checksums.
 *
 * Returns: %TRUE if the packet validates.
 */
gboolean
gst_dp_validate_packet (guint header_length, const guint8 * header,
    const guint8 * payload)
{
  if (!gst_dp_validate_header (header_length, header))
    return FALSE;
  if (!gst_dp_validate_payload (header_length, header, payload))
    return FALSE;

  return TRUE;
}

/**
 * gst_dp_packetizer_new:
 * @version: the #GstDPVersion of the protocol to packetize for.
 *
 * Creates a new packetizer.
 *
 * Returns: a newly allocated #GstDPPacketizer
 */
GstDPPacketizer *
gst_dp_packetizer_new (GstDPVersion version)
{
  GstDPPacketizer *ret;

  ret = g_malloc0 (sizeof (GstDPPacketizer));
  ret->version = version;

  switch (version) {
#ifndef GST_REMOVE_DEPRECATED
    case GST_DP_VERSION_0_2:
      ret->header_from_buffer = gst_dp_header_from_buffer;
      ret->packet_from_caps = gst_dp_packet_from_caps;
      ret->packet_from_event = gst_dp_packet_from_event;
      break;
#endif
    case GST_DP_VERSION_1_0:
      ret->header_from_buffer = gst_dp_header_from_buffer_1_0;
      ret->packet_from_caps = gst_dp_packet_from_caps_1_0;
      ret->packet_from_event = gst_dp_packet_from_event_1_0;
      break;
    default:
      g_free (ret);
      ret = NULL;
      break;
  }

  return ret;
}

/**
 * gst_dp_packetizer_free:
 * @packetizer: the #GstDPPacketizer to free.
 *
 * Free the given packetizer.
 */
void
gst_dp_packetizer_free (GstDPPacketizer * packetizer)
{
  g_free (packetizer);
}