Google Data File Stream

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A file with the.TS file extension is a Video Transport Stream file used to store MPEG-2-compressed video data. They're often seen on DVDs in a sequence of multiple.TS files. Free up space on your phone. Faster way to clean up, find, and share files.

  • With Drive for desktop, you stream your Drive files directly from the cloud to your Mac or PC, freeing up disk space and network bandwidth. Because Drive files are stored in the cloud, any changes.
  • A link for downloading the content of the file in a browser. This is only available for files with binary content in Google Drive. WebViewLink: string: A link for opening the file in a relevant Google editor or viewer in a browser. IconLink: string: A static, unauthenticated link to the file's icon. ThumbnailLink: string.
C++ provides the following classes to perform output and input of characters to/from files:
  • ofstream: Stream class to write on files
  • ifstream: Stream class to read from files
  • fstream: Stream class to both read and write from/to files.

These classes are derived directly or indirectly from the classes istream and ostream. We have already used objects whose types were these classes: cin is an object of class istream and cout is an object of class ostreamCached. Therefore, we have already been using classes that are related to our file streams. And in fact, we can use our file streams the same way we are already used to use cin and cout, with the only difference that we have to associate these streams with physical files. Let's see an example:
This code creates a file called example.txt and inserts a sentence into it in the same way we are used to do with Google Data File Streamcout, but using the file stream myfile instead.
But let's go step by step:

Open a file

The first operation generally performed on an object of one of these classes is to associate it to a real file. This procedure is known as to open a file. An open file is represented within a program by a stream (i.e., an object of one of these classes; in the previous example, this was myfile) and any input or output operation performed on this stream object will be applied to the physical file associated to it.
In order to open a file with a stream object we use its member function open:
open (filename, mode);

Where filename is a string representing the name of the file to be opened, and mode is an optional parameter with a combination of the following flags:
ios::inOpen for input operations.
ios::outOpen for output operations.
ios::binaryOpen in binary mode.
ios::ateSet the initial position at the end of the file.
If this flag is not set, the initial position is the beginning of the file.
ios::appAll output operations are performed at the end of the file, appending the content to the current content of the file.
ios::truncIf the file is opened for output operations and it already existed, its previous content is deleted and replaced by the new one.

All these flags can be combined using the bitwise operator OR (). For example, if we want to open the file example.bin in binary mode to add data we could do it by the following call to member function open:

Each of the open member functions of classes ofstream, ifstream and fstream

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has a default mode that is used if the file is opened without a second argument:
classdefault mode parameter
ofstreamios::out
ifstreamios::in
fstreamios::in ios::out

For ifstream and ofstream classes, ios::in and ios::out are automatically and respectively assumed, even if a mode that does not include them is passed as second argument to the openFile member function (the flags are combined).
For fstream, the default value is only applied if the function is called without specifying any value for the mode parameter. If the function is called with any value in that parameter the default mode is overridden, not combined.
File streams opened in binary mode perform input and output operations independently of any format considerations. Non-binary files are known as text files, and some translations may occur due to formatting of some special characters (like newline and carriage return characters).
Since the first task that is performed on a file stream is generally to open a file, these three classes include a constructor that automatically calls the open member function and has the exact same parameters as this member. Therefore, we could also have declared the previous myfile object and conduct the same opening operation in our previous example by writing:
Combining object construction and stream opening in a single statement. Both forms to open a file are valid and equivalent.
To check if a file stream was successful opening a file, you can do it by calling to member is_open. This member function returns a bool value of true in the case that indeed the stream object is associated with an open file, or false otherwise:


Closing a file

When we are finished with our input and output operations on a file we shall close it so that the operating system is notified and its resources become available again. For that, we call the stream's member function close. This member function takes flushes the associated buffers and closes the file:
Once this member function is called, the stream object can be re-used to open another file, and the file is available again to be opened by other processes.
In case that an object is destroyed while still associated with an open file, the destructor automatically calls the member function close.

Text files

Text file streams are those where the ios::binary flag is not included in their opening mode. These files are designed to store text and thus all values that are input or output from/to them can suffer some formatting transformations, which do not necessarily correspond to their literal binary value.
Writing operations on text files are performed in the same way we operated with cout:

Reading from a file can also be performed in the same way that we did with cin:
This last example reads a text file and prints out its content on the screen. We have created a while loop that reads the file line by line, using getline. The value returned by getline is a reference to the stream object itself, which when evaluated as a boolean expression (as in this while-loop) is true if the stream is ready for more operations, and false if either the end of the file has been reached or if some other error occurred.

Checking state flags

The following member functions exist to check for specific states of a stream (all of them return a bool value):
bad()
Returns true if a reading or writing operation fails. For example, in the case that we try to write to a file that is not open for writing or if the device where we try to write has no space left.
fail()
Returns true in the same cases as bad(), but also in the case that a format error happens, like when an alphabetical character is extracted when we are trying to read an integer number.
eof()
Returns true if a file open for reading has reached the end.
good()
It is the most generic state flag: it returns false in the same cases in which calling any of the previous functions would return true. Note that good and bad are not exact opposites (good checks more state flags at once).

The member function clear() can be used to reset the state flags.

get and put stream positioning

All i/o streams objects keep internally -at least- one internal position:
ifstream, like istream, keeps an internal get position with the location of the element to be read in the next input operation.
ofstream, like ostream, keeps an internal put position with the location where the next element has to be written.
Finally, fstream, keeps both, the get and the put position, like iostream.
These internal stream positions point to the locations within the stream where the next reading or writing operation is performed. These positions can be observed and modified using the following member functions:

tellg() and tellp()

These two member functions with no parameters return a value of the member type streampos, which is a type representing the current get position (in the case of tellg) or the put position (in the case of tellp).

seekg() and seekp()

These functions allow to change the location of the get and put positions. Both functions are overloaded with two different prototypes. The first form is:
seekg ( position );
seekp ( position );

Using this prototype, the stream pointer is changed to the absolute position position (counting from the beginning of the file). The type for this parameter is streampos, which is the same type as returned by functions

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tellg and tellp.
The other form for these functions is:
seekg ( offset, direction );
seekp ( offset, direction );

Using this prototype, the get or put position is set to an offset value relative to some specific point determined by the parameter direction. offset is of type streamoff. And direction is of type seekdir, which is an enumerated type that determines the point from where offset is counted from, and that can take any of the following values:
ios::begoffset counted from the beginning of the stream
ios::curoffset counted from the current position
ios::endoffset counted from the end of the stream

The following example uses the member functions we have just seen to obtain the size of a file:

FileNotice the type we have used for variables

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begin and end:
streampos is a specific type used for buffer and file positioning and is the type returned by file.tellg(). Values of this type can safely be subtracted from other values of the same type, and can also be converted to an integer type large enough to contain the size of the file.
These stream positioning functions use two particular types: streampos and streamoff. These types are also defined as member types of the stream class:
TypeMember typeDescription
streamposios::pos_typeDefined as fpos<mbstate_t>.
It can be converted to/from streamoff and can be added or subtracted values of these types.
streamoffios::off_typeIt is an alias of one of the fundamental integral types (such as int or long long).

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Each of the member types above is an alias of its non-member equivalent (they are the exact same type). It does not matter which one is used. The member types are more generic, because they are the same on all stream objects (even on streams using exotic types of characters), but the non-member types are widely used in existing code for historical reasons.

Binary files

For binary files, reading and writing data with the extraction and insertion operators (<< and >>) and functions like getline is not efficient, since we do not need to format any data and data is likely not formatted in lines.
File streams include two member functions specifically designed to read and write binary data sequentially: write and read. The first one (write) is a member function of ostream (inherited by ofstream). And read is a member function of istream (inherited by ifstream). Objects of class fstream have both. Their prototypes are:
write ( memory_block, size );
read ( memory_block, size );

Where memory_block is of type char* (pointer to char), and represents the address of an array of bytes where the read data elements are stored or from where the data elements to be written are taken. The size parameter is an integer value that specifies the number of characters to be read or written from/to the memory block.

In this example, the entire file is read and stored in a memory block. Let's examine how this is done:
First, the file is open with the ios::ate flag, which means that the get pointer will be positioned at the end of the file. This way, when we call to member tellg(), we will directly obtain the size of the file.
Once we have obtained the size of the file, we request the allocation of a memory block large enough to hold the entire file:
Right after that, we proceed to set the get position at the beginning of the file (remember that we opened the file with this pointer at the end), then we read the entire file, and finally close it:

At this point we could operate with the data obtained from the file. But our program simply announces that the content of the file is in memory and then finishes.

Buffers and Synchronization

When we operate with file streams, these are associated to an internal buffer object of type streambufStream. This buffer object may represent a memory block that acts as an intermediary between the stream and the physical file. For example, with an ofstream, each time the member function put (which writes a single character) is called, the character may be inserted in this intermediate buffer instead of being written directly to the physical file with which the stream is associated.
The operating system may also define other layers of buffering for reading and writing to files.
When the buffer is flushed, all the data contained in it is written to the physical medium (if it is an output stream). This process is called synchronization and takes place under any of the following circumstances:
  • When the file is closed: before closing a file, all buffers that have not yet been flushed are synchronized and all pending data is written or read to the physical medium.
  • When the buffer is full: Buffers have a certain size. When the buffer is full it is automatically synchronized.
  • Explicitly, with manipulators: When certain manipulators are used on streams, an explicit synchronization takes place. These manipulators are: flush and endl.
  • Explicitly, with member function sync(): Calling the stream's member function sync() causes an immediate synchronization. This function returns an int value equal to -1 if the stream has no associated buffer or in case of failure. Otherwise (if the stream buffer was successfully synchronized) it returns 0.
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The Drive API allows you to upload file data when you create or update aFile. For information on how to create ametadata-only File, refer to Create files.

There are three types of uploads you can perform:

  • Simple upload (uploadType=media). Use this upload type to quickly transfera small media file (5 MB or less) without supplying metadata. To perform asimple upload, refer to Perform a simple upload.

  • Multipart upload (uploadType=multipart). Use this upload type to quicklytransfer a small file (5 MB or less) and metadata that describes the file, in asingle request. To perform a multipart upload, refer toPerform a multipart upload.

  • Resumable upload (uploadType=resumable). Use this upload type for largefiles (greater than 5 MB) and when there's a high chance of networkinterruption, such as when creating a file from a mobile app. Resumable uploadsare also a good choice for most applications because they also work for smallfiles at a minimal cost of one additional HTTP request per upload. To perform aresumable upload, refer to Perform a resumable upload.

The Google API client libraries implement at least one of the types of uploads.Refer to the client library documentation for additional details on how to useeach of the types.

Note: In the Drive API documentation, media refers to all available files withMIME types supported for upload to Google Drive. For a list of supported MIMEtypes, refer toGoogle Workspace and Drive MIME types.Note: Users can upload any file type to Drive using the Drive UI and Drive attempts to detect and automatically set the MIME type. Ifthe MIME type can't be detected, the MIME type is set toapplication/octet-stream.

Perform a simple upload

To perform a simple upload, use thefiles.create method with uploadType=media.

The following shows how to perform a simple upload:

HTTP

  1. Create a POST request to the method's /upload URI with the queryparameter of uploadType=media:

    POST https://www.googleapis.com/upload/drive/v3/files?uploadType=media

  2. Add the file's data to the request body.

  3. Add these HTTP headers:

    • Content-Type. Set to the MIME media type of the object being uploaded.
    • Content-Length. Set to the number of bytes you upload. This header isnot required if you use chunked transfer encoding.
  4. Send the request. If the request succeeds, the server returns theHTTP 200 OK status code along with the file's metadata.

Note: To update an existing file, use PUT.

When you perform a simple upload, basic metadata is created and some attributesare inferred from the file, such as the MIME type or modifiedTime. Youcan use a simple upload in cases where you have small files and file metadataisn't important.

Perform a multipart upload

A multipart upload request allows you to send metadata along with the datato upload. Use this option if the data you send is small enough to uploadagain, in its entirety, if the connection fails.

To perform a multipart upload,use the files.create method withuploadType=multipart.The following shows how to perform a multipart upload:

Java

Python

Node.js

HTTP

  1. Create a POST request to the method's /upload URI with the queryparameter of uploadType=multipart:

    POST https://www.googleapis.com/upload/drive/v3/files?uploadType=multipart

  2. Create the body of the request. Format the body according to themultipart/related content type [RFC 2387], which contains two parts:

    • Metadata. The metadata must come first and must have a Content-Typeheader set to application/json;charset=UTF-8. Add the file's metadatain JSON format.
    • Media. The media must come second and must have a Content-Type headerof any MIME type. Add the file's data to the media part.

    Identify each part with a boundary string, preceded by two hyphens. Inaddition, add two hyphens after the final boundary string.

  3. Add these top-level HTTP headers:

    • Content-Type. Set to multipart/related and include the boundarystring you're using to identify the different parts of the request. Forexample: Content-Type: multipart/related; boundary=foo_bar_baz
    • Content-Length. Set to the total number of bytes in the request body.
  4. Send the request.

To create or update the metadata portion only, without the associated data,send a POST or PUT request to the standard resource endpoint:https://www.googleapis.com/drive/v3/files If the request succeeds,the server returns the HTTP 200 OK status code along with the file'smetadata.

Note: To update an existing file, use PUT.

When creating files, files should specify a file extension in thefile's name field. For example, when creating a photo JPEG file, you mightspecify something like 'name': 'photo.jpg' in the metadata. Subsequent callsto files.get return the read-onlyfileExtension property containing the extension originally specified in thename field.

Perform a resumable upload

A resumable upload allows you to resume an upload operation after acommunication failure interrupts the flow of data. Because you don'thave to restart large file uploads from the start, resumable uploads can alsoreduce your bandwidth usage if there is a network failure.

Resumable uploads are useful when your file sizes mightvary greatly or when there is a fixed time limit for requests (mobile OSbackground tasks and certain AppEngine requests). You might also use resumableuploads for situations where you want to show an upload progress bar.

A resumable upload consists of three high-level steps:

  1. Send the initial request and retrieve the resumable session URI.
  2. Upload the data and monitor upload state.
  3. (optional) If upload is disturbed, resume the upload.

Send the initial request

To initiate aresumable upload, use the files.createmethod with uploadType=resumable.

HTTP

  1. Create a POST request to the method's /upload URI with the queryparameter of uploadType=resumable:

    POST https://www.googleapis.com/upload/drive/v3/files?uploadType=resumable

    If the initiation request succeeds, the response includes a 200 OKHTTP status code. In addition, it includes a Location header that specifiesthe resumable session URI:

    You should save the resumable session URI so you can upload the file data andquery the upload status. A resumable session URI expires after one week.

    Note: To update an existing file, use PUT.
  2. If you have metadata for the file, add the metadata to the request body inJSON format. Otherwise, leave the request body empty.

  3. Add these HTTP headers:

    • X-Upload-Content-Type. Optional. Set to the MIME type of the filedata, which is transferred in subsequent requests. If the MIME type of thedata is not specified in metadata or through this header, the object isserved as application/octet-stream.
    • X-Upload-Content-Length. Optional. Set to the number of bytes of filedata, which is transferred in subsequent requests.
    • Content-Type. Required if you have metadata for the file. Set toapplication/json;charset=UTF-8.
    • Content-Length. Required unless you use chunked transfer encoding. Setto the number of bytes in the body of this initial request.
  4. Send the request. If the session initiation request succeeds, the responseincludes a 200 OK HTTP status code. In addition, the response includes aLocation header that specifies the resumable session URI. Use the resumablesession URI to upload the file data and query the upload status. A resumablesession URI expires after one week.

  5. Copy and save the resumable session URL.

  6. Continue to Uploading content

Upload the content

There are two ways to upload a file with a resumable session:

  • Upload content in a single request. Use this approach when the file can be uploaded in one request,if there is no fixed time limit for any single request, or you don't need to display an upload progress indicator.This approach is usually best because it requires fewer requests and results in better performance.
  • Upload the content in multiple chunks. Use this approach if you need toreduce the amount of data transferred in any single request. You might need toreduce data transferred when there is a fixed time limit for individualrequests, as can be the case for certain classes of Google App Engine requests.This approach is also useful if you need to provide a customizedindicator to show the upload progress.

HTTP - single request

  1. Create a PUT request to the resumable session URI.
  2. Add the file's data to the request body.
  3. Add a Content-Length HTTP header, set to the number of bytes in the file.
  4. Send the request. If the upload request is interrupted, or if you receive a5xx response, follow the procedure in Resume an interrupted upload.

HTTP - multiple requests

  1. Create a PUT request to the resumable session URI.

  2. Add the chunk's data to the request body. Create chunks in multiples of256 KB (256 x 1024 bytes) in size, except for the final chunk that completesthe upload. Keep the chunk size as large as possible so that the upload isefficient.

  3. Add these HTTP headers:

    • Content-Length. Set to the number of bytes in the current chunk.
    • Content-Range. Set to show which bytes in the file you upload. Forexample, Content-Range: bytes 0-524287/2000000 shows that you upload thefirst 524,288 bytes (256 x 1024 x 2) in a 2,000,000 byte file.
  4. Send the request, and process the response. If the upload request isinterrupted, or if you receive a 5xx response, follow the procedure inResume an interrupted upload.

  5. Repeat steps 1 through 4 for each chunk that remains in the file. Use theRange header in the response to determine where to start the next chunk. Donot assume that the server received all bytes sent in the previous request.

When the entire file upload is complete, you receive a 200 OK or201 Created response, along with any metadata associated with the resource.

Resume an interrupted upload

If an upload request is terminated before a response, or if youreceive a 503 Service Unavailable response, then you need to resume theinterrupted upload.

HTTP

  1. To request the upload status, create an empty PUT request to theresumable session URI.

  2. Add a Content-Range header to indicate that the current position in thefile is unknown. For example, set the Content-Range to */2000000 if yourtotal file length is 2,000,000 bytes. If you don't know the full size of thefile, set the Content-Range to */*.

  3. Send the request.

  4. Process the response:

    • A 200 OK or 201 Created response indicates that the upload wascompleted, and no further action is necessary.
    • A 308 Resume Incomplete response indicates that you need to continueto upload the file.
    • A 404 Not Found response indicates the upload session has expired andthe upload needs to be restarted from the start.
  5. If you received a 308 Resume Incomplete response, process the response'sRange header, to determine which bytes the server has received. If theresponse doesn't have a Range header, no bytes have been received.For example, a Range header of bytes=0-42 indicates that the first43 bytes of the file have been received and that the next chunk to uploadwould start with byte 43.

  6. Now that you know where to resume the upload, continue to upload the filebeginning with the next byte. Include aContent-Range header to indicate which portion of the file you send. Forexample, Content-Range: bytes 43-1999999/2000000 indicates that yousend bytes 43 through 1,999,999.

Handle media upload errors

When you upload media, follow these best practices to handle errors:

  • For 5xx errors, resume or retry uploads that fail due to connectioninterruptions. For further information on handling 5xx errors, refer toResolve errors
  • For 403 rate limit errors, retry the upload. For further information onhandling 403 rate limit errors, refer toResolve a 403 error: Rate limit exceeded
  • For any 4xx errors (including 403) during a resumable upload, restart theupload. These errors indicate the upload session has expired and must berestarted by requesting a new session URI. Upload sessions alsoexpire after 1 week of inactivity.

Import to Google Docs types

When you create a file in Google Drive, you might want to convert the fileinto a Google Workspace file type, such as a GoogleDoc or Sheet. For example, maybe youwant to convert a document from your favorite word processor into a Google Docto take advantage of Google Doc's features.

To convert a file to a specific Google Workspacefile type, specify the Google Workspace mimeTypewhen creating the file.The following shows how to convert a CSV file to aGoogle Workspace sheet:

To see if a conversion is available, check theAbout resource's importFormats arrayprior to creating the file. Supported conversions are available dynamicallyin this array. Some common import formats are:

FromTo
Microsoft Word, OpenDocument Text, HTML, RTF, plain textGoogle Docs
Microsoft Excel, OpenDocument Spreadsheet, CSV, TSV, plain textGoogle Sheets
Microsoft Powerpoint, OpenDocument PresentationGoogle Slides
JPEG, PNG, GIF, BMP, PDFGoogle Docs (embeds the image in a Doc)
plain text (special MIME type), JSONGoogle Apps Script

When you upload and convert media during an update request to a Google Doc,Sheet, or Slide, the full contents of the document are replaced.

When you convert an image to a Google doc, Drive uses Optical CharacterRecognition (OCR) to convert the image to text. You can improve the quality ofthe OCR algorithm by specifying theapplicable BCP 47 languagecode in the ocrLanguageparameter. The extracted text appears in the Google Docs documentalongside the embedded image.

Use a pregenerated ID to upload files

The Drive API allows you to retrieve a list of pregenerated file IDsused to upload and create resources. Upload and file creationrequests can use these pregenerated IDs. Set the id fieldin the file metadata.

To create pregenerated IDs, call file.generateIdswith the number of IDs to create.

You can safely retry uploads with pregenerated IDs in the case of anindeterminate server error or timeout. If the file was successfullycreated, subsequent retries return a HTTP 409 error, they do notcreate duplicate files.

Note: Pregenerated IDs are not supported for native Google Documentcreation, or uploads where conversion to native Google Document format is requested.

Define indexable text for unknown file types

Users can use the Drive UI to search for document content. You can also use thefile.list and the fullText field to searchfor content from your app. For further information on searching for files, referto Search for files and folders

Note: Indexable text is indexed as HTML. If you save the indexable text string<section attribute='value1'>Here's some text</section>, then 'Here's sometext' is indexed, but 'value1' is not.

To allow content searches, Drive automatically indexes document contents when itrecognizes the file type. Recognized file types include text documents, PDFs,images with text, and other common types. If your app saves files that Drivedoesn't recognize, you should include text in the contentHints.indexableTextfield of the file. When specifying indexableText, keep in mind:

  • Ensure you capture key terms and concepts that you expect a user to searchfor.
  • The size limit for contentHints.indexableText is 128KiB.
  • You do not need to order the text in order of importance; the indexerdetermines importance.
  • Indexable text should be updated by your application with each save.
  • Ensure any indexableText actually appears in the contents or metadata ofthe file. Don't try to force a file to appear in search results by includingterms that don't appear in the contents or metadata. Users don't like toperform searches that result in files containing irrelevant content.