descriptor.c

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	for (i = 0; i < config->bNumInterfaces; i++) {
		int len;
		unsigned char *begin;

		/* Skip over the rest of the Class Specific or Vendor */
		/*  Specific descriptors */
		begin = buffer;
		while (size >= DESC_HEADER_LENGTH) {
			usbi_parse_descriptor(buffer, "bb", &header, 0);

			if ((header.bLength > size) ||
					(header.bLength < DESC_HEADER_LENGTH)) {
				usbi_err(ctx, "invalid descriptor length of %d",
					header.bLength);
				r = LIBUSB_ERROR_IO;
				goto err;
			}

			/* If we find another "proper" descriptor then we're done */
			if ((header.bDescriptorType == LIBUSB_DT_ENDPOINT) ||
					(header.bDescriptorType == LIBUSB_DT_INTERFACE) ||
					(header.bDescriptorType == LIBUSB_DT_CONFIG) ||
					(header.bDescriptorType == LIBUSB_DT_DEVICE))
				break;

			usbi_dbg("skipping descriptor 0x%x\n", header.bDescriptorType);
			buffer += header.bLength;
			size -= header.bLength;
		}

		/* Copy any unknown descriptors into a storage area for */
		/*  drivers to later parse */
		len = (int)(buffer - begin);
		if (len) {
			/* FIXME: We should realloc and append here */
			if (!config->extra_length) {
				config->extra = malloc(len);
				if (!config->extra) {
					r = LIBUSB_ERROR_NO_MEM;
					goto err;
				}

				memcpy((unsigned char *) config->extra, begin, len);
				config->extra_length = len;
			}
		}

		r = parse_interface(ctx, interface + i, buffer, size, host_endian);
		if (r < 0)
			goto err;

		buffer += r;
		size -= r;
	}

	return size;

err:
	clear_configuration(config);
	return r;
}

/** \ingroup desc
 * Get the USB device descriptor for a given device.
 *
 * This is a non-blocking function; the device descriptor is cached in memory.
 *
 * \param dev the device
 * \param desc output location for the descriptor data
 * \returns 0 on success or a LIBUSB_ERROR code on failure
 */
API_EXPORTED int libusb_get_device_descriptor(libusb_device *dev,
	struct libusb_device_descriptor *desc)
{
	unsigned char raw_desc[DEVICE_DESC_LENGTH];
	int host_endian = 0;
	int r;

	usbi_dbg("");
	r = usbi_backend->get_device_descriptor(dev, raw_desc, &host_endian);
	if (r < 0)
		return r;

	memcpy((unsigned char *) desc, raw_desc, sizeof(raw_desc));
	if (host_endian) {
		desc->bcdUSB = libusb_cpu_to_le16(desc->bcdUSB);
		desc->idVendor = libusb_cpu_to_le16(desc->idVendor);
		desc->idProduct = libusb_cpu_to_le16(desc->idProduct);
		desc->bcdDevice = libusb_cpu_to_le16(desc->bcdDevice);
	}
	return 0;
}

/** \ingroup desc
 * Get the USB configuration descriptor for the currently active configuration.
 * This is a non-blocking function which does not involve any requests being
 * sent to the device.
 *
 * \param dev a device
 * \param config output location for the USB configuration descriptor. Only
 * valid if 0 was returned. Must be freed with libusb_free_config_descriptor()
 * after use.
 * \returns 0 on success
 * \returns LIBUSB_ERROR_NOT_FOUND if the device is in unconfigured state
 * \returns another LIBUSB_ERROR code on error
 * \see libusb_get_config_descriptor
 */
API_EXPORTED int libusb_get_active_config_descriptor(libusb_device *dev,
	struct libusb_config_descriptor **config)
{
	struct libusb_config_descriptor *_config = malloc(sizeof(*_config));
	unsigned char tmp[8];
	unsigned char *buf = NULL;
	int host_endian = 0;
	int r;

	usbi_dbg("");
	if (!_config)
		return LIBUSB_ERROR_NO_MEM;

	r = usbi_backend->get_active_config_descriptor(dev, tmp, sizeof(tmp),
		&host_endian);
	if (r < 0)
		goto err;

	usbi_parse_descriptor(tmp, "bbw", _config, host_endian);
	buf = malloc(_config->wTotalLength);
	if (!buf) {
		r = LIBUSB_ERROR_NO_MEM;
		goto err;
	}

	r = usbi_backend->get_active_config_descriptor(dev, buf,
		_config->wTotalLength, &host_endian);
	if (r < 0)
		goto err;

	r = parse_configuration(dev->ctx, _config, buf, host_endian);
	if (r < 0) {
		usbi_err(dev->ctx, "parse_configuration failed with error %d", r);
		goto err;
	} else if (r > 0) {
		usbi_warn(dev->ctx, "descriptor data still left");
	}

	*config = _config;
	return 0;

err:
	free(_config);
	if (buf)
		free(buf);
	return r;
}

/** \ingroup desc
 * Get a USB configuration descriptor based on its index.
 * This is a non-blocking function which does not involve any requests being
 * sent to the device.
 *
 * \param dev a device
 * \param config_index the index of the configuration you wish to retrieve
 * \param config output location for the USB configuration descriptor. Only
 * valid if 0 was returned. Must be freed with libusb_free_config_descriptor()
 * after use.
 * \returns 0 on success
 * \returns LIBUSB_ERROR_NOT_FOUND if the configuration does not exist
 * \returns another LIBUSB_ERROR code on error
 * \see libusb_get_active_config_descriptor()
 * \see libusb_get_config_descriptor_by_value()
 */
API_EXPORTED int libusb_get_config_descriptor(libusb_device *dev,
	uint8_t config_index, struct libusb_config_descriptor **config)
{
	struct libusb_config_descriptor *_config;
	unsigned char tmp[8];
	unsigned char *buf = NULL;
	int host_endian = 0;
	int r;

	usbi_dbg("index %d", config_index);
	if (config_index >= dev->num_configurations)
		return LIBUSB_ERROR_NOT_FOUND;

	_config = malloc(sizeof(*_config));
	if (!_config)
		return LIBUSB_ERROR_NO_MEM;

	r = usbi_backend->get_config_descriptor(dev, config_index, tmp,
		sizeof(tmp), &host_endian);
	if (r < 0)
		goto err;

	usbi_parse_descriptor(tmp, "bbw", _config, host_endian);
	buf = malloc(_config->wTotalLength);
	if (!buf) {
		r = LIBUSB_ERROR_NO_MEM;
		goto err;
	}

	r = usbi_backend->get_config_descriptor(dev, config_index, buf,
		_config->wTotalLength, &host_endian);
	if (r < 0)
		goto err;

	r = parse_configuration(dev->ctx, _config, buf, host_endian);
	if (r < 0) {
		usbi_err(dev->ctx, "parse_configuration failed with error %d", r);
		goto err;
	} else if (r > 0) {
		usbi_warn(dev->ctx, "descriptor data still left");
	}

	*config = _config;
	return 0;

err:
	free(_config);
	if (buf)
		free(buf);
	return r;
}

/* iterate through all configurations, returning the index of the configuration
 * matching a specific bConfigurationValue in the idx output parameter, or -1
 * if the config was not found.
 * returns 0 or a LIBUSB_ERROR code
 */
int usbi_get_config_index_by_value(struct libusb_device *dev,
	uint8_t bConfigurationValue, int *idx)
{
	int i;

	usbi_dbg("value %d", bConfigurationValue);
	for (i = 0; i < dev->num_configurations; i++) {
		unsigned char tmp[6];
		int host_endian;
		int r = usbi_backend->get_config_descriptor(dev, i, tmp, sizeof(tmp),
			&host_endian);
		if (r < 0)
			return r;
		if (tmp[5] == bConfigurationValue) {
			*idx = i;
			return 0;
		}
	}

	*idx = -1;
	return 0;
}

/** \ingroup desc
 * Get a USB configuration descriptor with a specific bConfigurationValue.
 * This is a non-blocking function which does not involve any requests being
 * sent to the device.
 *
 * \param dev a device
 * \param bConfigurationValue the bConfigurationValue of the configuration you
 * wish to retrieve
 * \param config output location for the USB configuration descriptor. Only
 * valid if 0 was returned. Must be freed with libusb_free_config_descriptor()
 * after use.
 * \returns 0 on success
 * \returns LIBUSB_ERROR_NOT_FOUND if the configuration does not exist
 * \returns another LIBUSB_ERROR code on error
 * \see libusb_get_active_config_descriptor()
 * \see libusb_get_config_descriptor()
 */
API_EXPORTED int libusb_get_config_descriptor_by_value(libusb_device *dev,
	uint8_t bConfigurationValue, struct libusb_config_descriptor **config)
{
	int idx;
	int r = usbi_get_config_index_by_value(dev, bConfigurationValue, &idx);
	if (r < 0)
		return r;
	else if (idx == -1)
		return LIBUSB_ERROR_NOT_FOUND;
	else
		return libusb_get_config_descriptor(dev, idx, config);
}

/** \ingroup desc
 * Free a configuration descriptor obtained from
 * libusb_get_active_config_descriptor() or libusb_get_config_descriptor().
 * It is safe to call this function with a NULL config parameter, in which
 * case the function simply returns.
 *
 * \param config the configuration descriptor to free
 */
API_EXPORTED void libusb_free_config_descriptor(
	struct libusb_config_descriptor *config)
{
	if (!config)
		return;

	clear_configuration(config);
	free(config);
}

/** \ingroup desc
 * Retrieve a string descriptor in C style ASCII.
 *
 * Wrapper around libusb_get_string_descriptor(). Uses the first language 
 * supported by the device.
 *
 * \param dev a device handle
 * \param desc_index the index of the descriptor to retrieve
 * \param data output buffer for ASCII string descriptor
 * \param length size of data buffer
 * \returns number of bytes returned in data, or LIBUSB_ERROR code on failure
 */
API_EXPORTED int libusb_get_string_descriptor_ascii(libusb_device_handle *dev,
	uint8_t desc_index, unsigned char *data, int length)
{
	unsigned char tbuf[255]; /* Some devices choke on size > 255 */
	int r, langid, si, di;

	/* Asking for the zero'th index is special - it returns a string
	 * descriptor that contains all the language IDs supported by the device.
	 * Typically there aren't many - often only one. The language IDs are 16
	 * bit numbers, and they start at the third byte in the descriptor. See
	 * USB 2.0 specification section 9.6.7 for more information. */
	r = libusb_get_string_descriptor(dev, 0, 0, tbuf, sizeof(tbuf));
	if (r < 0)
		return r;

	if (r < 4)
		return LIBUSB_ERROR_IO;

	langid = tbuf[2] | (tbuf[3] << 8);

	r = libusb_get_string_descriptor(dev, desc_index, langid, tbuf,
		sizeof(tbuf));
	if (r < 0)
		return r;

	if (tbuf[1] != LIBUSB_DT_STRING)
		return LIBUSB_ERROR_IO;

	if (tbuf[0] > r)
		return LIBUSB_ERROR_IO;

	for (di = 0, si = 2; si < tbuf[0]; si += 2) {
		if (di >= (length - 1))
			break;

		if (tbuf[si + 1]) /* high byte */
			data[di++] = '?';
		else
			data[di++] = tbuf[si];
	}

	data[di] = 0;
	return di;
}