libmtp关于MTP协议的实现

于 2022-01-17 16:29:35 发布
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本文链接：https://blog.youkuaiyun.com/bme314/article/details/122534441
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我这里采用了1.1.7的libmtp。但其实计算机上实现这个协议的服务还有很多，而且还不一样。但理论上原理一样。

发送文件的流程

继续上一篇的逻辑。我在example里发现发送文件的协议逻辑。

int sendfile_function(char * from_path, char *to_path)
{
  filesize = sb.st_size;
  filename = basename(from_path);
  parent_id = parse_path (to_path,files,folders);
 
  LIBMTP_file_t *genfile;
  genfile = LIBMTP_new_file_t();
  genfile->filesize = filesize;
  genfile->filename = strdup(filename);
  genfile->filetype = find_filetype (filename);
  genfile->parent_id = parent_id;
  genfile->storage_id = 0;

  printf("Sending file...\n");
  ret = LIBMTP_Send_File_From_File(device, from_path, genfile, progress, NULL);


int LIBMTP_Send_File_From_File(LIBMTP_mtpdevice_t *device,
			       char const * const path, LIBMTP_file_t * const filedata,
			       LIBMTP_progressfunc_t const callback,
			       void const * const data)
{
  int fd;
  int ret;

  if ( (fd = open(path, O_RDONLY)) == -1) {

    add_error_to_errorstack(device, LIBMTP_ERROR_GENERAL, "LIBMTP_Send_File_From_File(): Could not open source file.");
    return -1;
  }
  ret = LIBMTP_Send_File_From_File_Descriptor(device, fd, filedata, callback, data);


int LIBMTP_Send_File_From_File_Descriptor(LIBMTP_mtpdevice_t *device,
			 int const fd, LIBMTP_file_t * const filedata,
                         LIBMTP_progressfunc_t const callback,
			 void const * const data)
{
  uint16_t ret;
  PTPParams *params = (PTPParams *) device->params;
  PTP_USB *ptp_usb = (PTP_USB*) device->usbinfo;
  LIBMTP_file_t *newfilemeta;
  int oldtimeout;
  int timeout;

  if (send_file_object_info(device, filedata))  //发送文件信息
  {
    // no need to output an error since send_file_object_info will already have done so
    return -1;
  }

  // Callbacks
  ptp_usb->callback_active = 1;
  // The callback will deactivate itself after this amount of data has been sent
  // One BULK header for the request, one for the data phase. No parameters to the request.
  ptp_usb->current_transfer_total = filedata->filesize+PTP_USB_BULK_HDR_LEN*2;
  ptp_usb->current_transfer_complete = 0;
  ptp_usb->current_transfer_callback = callback;
  ptp_usb->current_transfer_callback_data = data;

  /*
   * We might need to increase the timeout here, files can be pretty
   * large. Take the default timeout and add the calculated time for
   * this transfer
   */
  get_usb_device_timeout(ptp_usb, &oldtimeout);
  timeout = oldtimeout +
    (ptp_usb->current_transfer_total / guess_usb_speed(ptp_usb)) * 1000;
  set_usb_device_timeout(ptp_usb, timeout);

  ret = ptp_sendobject_fromfd(params, fd, filedata->filesize);   //发送文件

  ptp_usb->callback_active = 0;
  ptp_usb->current_transfer_callback = NULL;
  ptp_usb->current_transfer_callback_data = NULL;
  set_usb_device_timeout(ptp_usb, oldtimeout);

  if (ret == PTP_ERROR_CANCEL) {
    add_error_to_errorstack(device, LIBMTP_ERROR_CANCELLED, "LIBMTP_Send_File_From_File_Descriptor(): Cancelled transfer.");
    return -1;
  }
  if (ret != PTP_RC_OK) {
    add_ptp_error_to_errorstack(device, ret, "LIBMTP_Send_File_From_File_Descriptor(): "
				"Could not send object.");
    return -1;
  }

  add_object_to_cache(device, filedata->item_id);

  /*
   * Get the device-assigned parent_id from the cache.
   * The operation that adds it to the cache will
   * look it up from the device, so we get the new
   * parent_id from the cache.
   */
  newfilemeta = LIBMTP_Get_Filemetadata(device, filedata->item_id);
  if (newfilemeta != NULL) {
    filedata->parent_id = newfilemeta->parent_id;
    filedata->storage_id = newfilemeta->storage_id;
    LIBMTP_destroy_file_t(newfilemeta);
  } else {
    add_error_to_errorstack(device, LIBMTP_ERROR_GENERAL,
			    "LIBMTP_Send_File_From_File_Descriptor(): "
			    "Could not retrieve updated metadata.");
    return -1;
  }

  return 0;
}

再往下send_file_object_info就是发送的具体协议了。

    /*
     * MTP enhanched does it this way (from a sniff):
     * -> PTP_OC_MTP_SendObjectPropList (0x9808):
     *    20 00 00 00 01 00 08 98 1B 00 00 00 01 00 01 00
     *    FF FF FF FF 00 30 00 00 00 00 00 00 12 5E 00 00
     *    Length: 0x00000020
     *    Type:   0x0001 PTP_USB_CONTAINER_COMMAND
     *    Code:   0x9808
     *    Transaction ID: 0x0000001B
     *    Param1: 0x00010001 <- store
     *    Param2: 0xffffffff <- parent handle (-1 ?)
     *    Param3: 0x00003000 <- file type PTP_OFC_Undefined - we don't know about PDF files
     *    Param4: 0x00000000 <- file length MSB (-0x0c header len)
     *    Param5: 0x00005e12 <- file length LSB (-0x0c header len)
     *
     * -> PTP_OC_MTP_SendObjectPropList (0x9808):
     *    46 00 00 00 02 00 08 98 1B 00 00 00 03 00 00 00
     *    00 00 00 00 07 DC FF FF 0D 4B 00 53 00 30 00 36 - dc07 = file name
     *    00 30 00 33 00 30 00 36 00 2E 00 70 00 64 00 66
     *    00 00 00 00 00 00 00 03 DC 04 00 00 00 00 00 00 - dc03 = protection status
     *    00 4F DC 02 00 01                               - dc4f = non consumable
     *    Length: 0x00000046
     *    Type:   0x0002 PTP_USB_CONTAINER_DATA
     *    Code:   0x9808
     *    Transaction ID: 0x0000001B
     *    Metadata....
     *    0x00000003 <- Number of metadata items
     *    0x00000000 <- Object handle, set to 0x00000000 since it is unknown!
     *    0xdc07     <- metadata type: file name
     *    0xffff     <- metadata type: string
     *    0x0d       <- number of (uint16_t) characters
     *    4b 53 30 36 30 33 30 36 2e 50 64 66 00 "KS060306.pdf", null terminated
     *    0x00000000 <- Object handle, set to 0x00000000 since it is unknown!
     *    0xdc03     <- metadata type: protection status
     *    0x0004     <- metadata type: uint16_t
     *    0x0000     <- not protected
     *    0x00000000 <- Object handle, set to 0x00000000 since it is unknown!
     *    0xdc4f     <- non consumable
     *    0x0002     <- metadata type: uint8_t
     *    0x01       <- non-consumable (this device cannot display PDF)
     *
     * <- Read 0x18 bytes back
     *    18 00 00 00 03 00 01 20 1B 00 00 00 01 00 01 00
     *    00 00 00 00 01 40 00 00
     *    Length: 0x000000018
     *    Type:   0x0003 PTP_USB_CONTAINER_RESPONSE
     *    Code:   0x2001 PTP_OK
     *    Transaction ID: 0x0000001B
     *    Param1: 0x00010001 <- store
     *    Param2: 0x00000000 <- parent handle
     *    Param3: 0x00004001 <- new file/object ID
     *
     * -> PTP_OC_SendObject (0x100d)
     *    0C 00 00 00 01 00 0D 10 1C 00 00 00
     * -> ... all the bytes ...
     * <- Read 0x0c bytes back
     *    0C 00 00 00 03 00 01 20 1C 00 00 00
     *    ... Then update metadata one-by one, actually (instead of sending it first!) ...
     */


/**
 * ptp_sendobjectinfo:
 * params:	PTPParams*
 *		uint32_t* store		- destination StorageID on Responder
 *		uint32_t* parenthandle 	- Parent ObjectHandle on responder
 * 		uint32_t* handle	- see Return values
 *		PTPObjectInfo* objectinfo- ObjectInfo that is to be sent
 * 
 * Sends ObjectInfo of file that is to be sent via SendFileObject.
 *
 * Return values: Some PTP_RC_* code.
 * Upon success : uint32_t* store	- Responder StorageID in which
 *					  object will be stored
 *		  uint32_t* parenthandle- Responder Parent ObjectHandle
 *					  in which the object will be stored
 *		  uint32_t* handle	- Responder's reserved ObjectHandle
 *					  for the incoming object
 **/
uint16_t
ptp_sendobjectinfo (PTPParams* params, uint32_t* store, 
			uint32_t* parenthandle, uint32_t* handle,
			PTPObjectInfo* objectinfo)
{
	uint16_t ret;
	PTPContainer ptp;
	unsigned char* oidata=NULL;
	uint32_t size;

	PTP_CNT_INIT(ptp);
	ptp.Code=PTP_OC_SendObjectInfo;
	ptp.Param1=*store;
	ptp.Param2=*parenthandle;
	ptp.Nparam=2;
	
	size=ptp_pack_OI(params, objectinfo, &oidata);
	ret = ptp_transaction(params, &ptp, PTP_DP_SENDDATA, size, &oidata, NULL); 
	free(oidata);
	*store=ptp.Param1;
	*parenthandle=ptp.Param2;
	*handle=ptp.Param3; 
	return ret;
}

/* Transaction data phase description */
#define PTP_DP_NODATA		0x0000	/* no data phase */
#define PTP_DP_SENDDATA		0x0001	/* sending data */
#define PTP_DP_GETDATA		0x0002	/* receiving data */
#define PTP_DP_DATA_MASK	0x00ff	/* data phase mask */


/**
 * ptp_sendobject_fromfd:
 * params:	PTPParams*
 *		fd                      - File descriptor to read() object from
 *              uint64_t size           - File/object size
 *
 * Sends object from file descriptor by consecutive reads from this
 * descriptor.
 *
 * Return values: Some PTP_RC_* code.
 **/
uint16_t
ptp_sendobject_fromfd (PTPParams* params, int fd, uint64_t size)
{
	PTPContainer	ptp;
	PTPDataHandler	handler;
	uint16_t	ret;

	ptp_init_fd_handler (&handler, fd);
	PTP_CNT_INIT(ptp);
	ptp.Code=PTP_OC_SendObject;
	ptp.Nparam=0;
	ret = ptp_transaction_new(params, &ptp, PTP_DP_SENDDATA, size, &handler);
	ptp_exit_fd_handler (&handler);
	return ret;
}

读取文件

进行下对比

int LIBMTP_Get_File_To_File_Descriptor(LIBMTP_mtpdevice_t *device,
					uint32_t const id,
					int const fd,
					LIBMTP_progressfunc_t const callback,
					void const * const data)
{
  uint16_t ret;
  PTPParams *params = (PTPParams *) device->params;
  PTP_USB *ptp_usb = (PTP_USB*) device->usbinfo;
  PTPObject *ob;

  ret = ptp_object_want (params, id, PTPOBJECT_OBJECTINFO_LOADED, &ob);
  if (ret != PTP_RC_OK) {
    add_error_to_errorstack(device, LIBMTP_ERROR_GENERAL, "LIBMTP_Get_File_To_File_Descriptor(): Could not get object info.");
    return -1;
  }
  if (ob->oi.ObjectFormat == PTP_OFC_Association) {
    add_error_to_errorstack(device, LIBMTP_ERROR_GENERAL, "LIBMTP_Get_File_To_File_Descriptor(): Bad object format.");
    return -1;
  }

  // Callbacks
  ptp_usb->callback_active = 1;
  ptp_usb->current_transfer_total = ob->oi.ObjectCompressedSize+
    PTP_USB_BULK_HDR_LEN+sizeof(uint32_t); // Request length, one parameter
  ptp_usb->current_transfer_complete = 0;
  ptp_usb->current_transfer_callback = callback;
  ptp_usb->current_transfer_callback_data = data;

  ret = ptp_getobject_tofd(params, id, fd);

  ptp_usb->callback_active = 0;
  ptp_usb->current_transfer_callback = NULL;
  ptp_usb->current_transfer_callback_data = NULL;

ptp_object_want (PTPParams *params, uint32_t handle, unsigned int want, PTPObject **retob) {
	uint16_t	ret;
	PTPObject	*ob;
	/*Camera 		*camera = ((PTPData *)params->data)->camera;*/

	/* If GetObjectInfo is broken, force GetPropList */
	if (params->device_flags & DEVICE_FLAG_PROPLIST_OVERRIDES_OI)
		want |= PTPOBJECT_MTPPROPLIST_LOADED;

	*retob = NULL;
	if (!handle) {
		ptp_debug (params, "ptp_object_want: querying handle 0?\n");
		return PTP_RC_GeneralError;
	}
	ret = ptp_object_find_or_insert (params, handle, &ob);
	if (ret != PTP_RC_OK)
		return PTP_RC_GeneralError;
	*retob = ob;
	/* Do we have all of it already? */
	if ((ob->flags & want) == want)
		return PTP_RC_OK;

#define X (PTPOBJECT_OBJECTINFO_LOADED|PTPOBJECT_STORAGEID_LOADED|PTPOBJECT_PARENTOBJECT_LOADED)
	if ((want & X) && ((ob->flags & X) != X)) {
		uint32_t	saveparent = 0;
		
		/* One EOS issue, where getobjecthandles(root) returns obs without root flag. */
		if (ob->flags & PTPOBJECT_PARENTOBJECT_LOADED)
			saveparent = ob->oi.ParentObject;

		ret = ptp_getobjectinfo (params, handle, &ob->oi);
		if (ret != PTP_RC_OK) {
			/* kill it from the internal list ... */
			ptp_remove_object_from_cache(params, handle);
			return ret;
		}

uint16_t
ptp_getobjectinfo (PTPParams* params, uint32_t handle,
			PTPObjectInfo* objectinfo)
{
	uint16_t ret;
	PTPContainer ptp;
	unsigned char* oi=NULL;
	unsigned int len;

	PTP_CNT_INIT(ptp);
	ptp.Code=PTP_OC_GetObjectInfo;//  0x1008
	ptp.Param1=handle;
	ptp.Nparam=1;
	len=0;
	ret=ptp_transaction(params, &ptp, PTP_DP_GETDATA, 0, &oi, &len);  //0x0002
	if (ret == PTP_RC_OK) ptp_unpack_OI(params, oi, objectinfo, len);
	free(oi);
	return ret;
}

三、协议公共 接口

/* Old style transaction, based on memory */
uint16_t
ptp_transaction (PTPParams* params, PTPContainer* ptp, 
		uint16_t flags, uint64_t sendlen,
		unsigned char **data, unsigned int *recvlen
) {
	PTPDataHandler	handler;
	uint16_t	ret;

	switch (flags & PTP_DP_DATA_MASK) {
	case PTP_DP_SENDDATA:
		ret = ptp_init_send_memory_handler (&handler, *data, sendlen);
		if (ret != PTP_RC_OK) return ret;
		break;
	case PTP_DP_GETDATA:
		ret = ptp_init_recv_memory_handler (&handler);
		if (ret != PTP_RC_OK) return ret;
		break;
	default:break;
	}
	ret = ptp_transaction_new (params, ptp, flags, sendlen, &handler);
	switch (flags & PTP_DP_DATA_MASK) {
	case PTP_DP_SENDDATA:
		ptp_exit_send_memory_handler (&handler);
		break;
	case PTP_DP_GETDATA: {
		unsigned long len;
		ptp_exit_recv_memory_handler (&handler, data, &len);
		if (recvlen)
			*recvlen = len;
		break;
	}
	default:break;
	}
	return ret;
}

/* PTP v1.0 operation codes */
#define PTP_OC_Undefined                0x1000
#define PTP_OC_GetDeviceInfo            0x1001
#define PTP_OC_OpenSession              0x1002
#define PTP_OC_CloseSession             0x1003
#define PTP_OC_GetStorageIDs            0x1004
#define PTP_OC_GetStorageInfo           0x1005
#define PTP_OC_GetNumObjects            0x1006
#define PTP_OC_GetObjectHandles         0x1007
#define PTP_OC_GetObjectInfo            0x1008
#define PTP_OC_GetObject                0x1009
#define PTP_OC_GetThumb                 0x100A
#define PTP_OC_DeleteObject             0x100B
#define PTP_OC_SendObjectInfo           0x100C
#define PTP_OC_SendObject               0x100D

这部分操作码和我在手机内核中看到的操作码虽然名称不一样，但功能基本是对应的。

struct _PTPContainer {
	uint16_t Code;
	uint32_t SessionID;
	uint32_t Transaction_ID;
	/* params  may be of any type of size less or equal to uint32_t */
	uint32_t Param1;
	uint32_t Param2;
	uint32_t Param3;
	/* events can only have three parameters */
	uint32_t Param4;
	uint32_t Param5;
	/* the number of meaningfull parameters */
	uint8_t	 Nparam;
};
typedef struct _PTPContainer PTPContainer;

这部分PTPContainer->code就是具体操作码

//文件信息
struct _PTPObjectInfo {
	uint32_t StorageID;
	uint16_t ObjectFormat;
	uint16_t ProtectionStatus;
	/* In the regular objectinfo this is 32bit,
	 * but we keep the general object size here
	 * that also arrives via other methods and so
	 * use 64bit */
	uint64_t ObjectCompressedSize;
	uint16_t ThumbFormat;
	uint32_t ThumbCompressedSize;
	uint32_t ThumbPixWidth;
	uint32_t ThumbPixHeight;
	uint32_t ImagePixWidth;
	uint32_t ImagePixHeight;
	uint32_t ImageBitDepth;
	uint32_t ParentObject;
	uint16_t AssociationType;
	uint32_t AssociationDesc;
	uint32_t SequenceNumber;
	char 	*Filename;
	time_t	CaptureDate;
	time_t	ModificationDate;
	char	*Keywords;
};
typedef struct _PTPObjectInfo PTPObjectInfo;

PTPParams* params属于设备信息

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