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matlab.net.http.io.FileConsumer class

Package: matlab.net.http.io
Superclasses: matlab.net.http.io.ContentConsumer

Consumer for files in HTTP messages

Description

The FileConsumer class provides a convenient way to download a file from a web service, or to save data received from the web in a file. You can specify the name of the file, or let MATLAB® determine the name from information sent by the server or file named in the URI.

The matlab.net.http.io.FileConsumer class is a handle class.

Creation

Description

consumer = FileConsumer(filename,permission,machineformat,encoding) constructs a FileConsumer that creates or overwrites a file with the payload of the response from the server. The parameters have the same meaning as those of the fopen function, and all are optional.

consumer = FileConsumer(FID) sets the FileIdentifier property to FID and writes to that file. FID must be the identifier of a file you opened for writing. MATLAB writes to the file at the current position indicator, so if you open an existing file using 'a+' permission, for example, MATLAB appends to the file. When transfer is completed, MATLAB leaves the position indicator at the end of the file and does not close the file.

Input Arguments

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File or folder name, including full path and optional extension, specified as a character vector or a string scalar. To determine the name of the file that MATLAB creates, see the Filename property.

If filename specifies a file in an existing folder, then MATLAB:

  • Opens the file using fopen(filename,permission,...).

  • If permission is not specified, then opens the file using fopen(filename,'w+').

  • If filename does not include an extension, then MATLAB adds one based on the Content-Type and/or Content-Disposition header field in the received message or the extension of the file name in the URI of the request, if any.

If filename specifies an existing, writable folder, then MATLAB creates a file in the folder with a name derived from the Content-Disposition header field in the response or from the URI, possibly adding an extension based on Content-Type if that name does not contain one.

If filename is missing or empty, then MATLAB creates a file in the current folder. This is equivalent to filename = '.'. The current folder is the folder at the time this FileConsumer was created, not the time this consumer is used in a send request.

Example: 'myTextFile.txt'

Data Types: char | string

File access type, specified as a string. If permission is specified, it must allow write access. The default value is 'w+', which opens or creates a file for reading and writing and discards existing contents, if any.

permission can be any value allowed by the fopen function. The following additional values of permission are supported:

'u+', 'u'

Same as 'w' and 'w+', but if the file exists, then a file is created with a unique name derived from the filename argument. The name of the new file has a hyphen and a sequence number appended to the part of its name excluding the extension.

For example, if filename is 'MyFile.txt' but the file exists, then MATLAB creates the file MyFile-1.txt. The Filename property contains the new file's full path name.

'T'

When appended to a permission, behaves similarly to text mode 't' but uses text mode only if the Content-Type of the data indicates it is character-based. This includes any type specifying a charset parameter or types MATLAB knows to be character-based, such as "application/json".

In all cases, for 'w' and 'w+' permissions (or if permission is not specified), MATLAB does not overwrite an existing file unless the file name is exactly equal to filename.

Example: 'a''w+T'

Data Types: char | string

Order for reading or writing bytes or bits, specified as any value allowed by the fopen function.

Data Types: char | string

Character encoding, specified as any value allowed by the fopen function.

Data Types: char | string

Properties

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Public Properties

Identifier of the file (FID) being written, specified as double. If the consumer was constructed with an FID argument, then this property is the identifier. Data is written to the current file position indicator associated with this identifier, so subclasses should be careful not to change the position accidentally when using this identifier. At the conclusion of the transfer, the file remains open and the position remains at the end of the file.

If the constructor was called with a filename argument, or with no arguments, then this property is the read-only file identifier for that file. This allows subclasses to read the file during transfer without disturbing the position indicator used for writing. At the conclusion of the transfer, this identifier is closed.

Attributes:

GetAccess

public

SetAccess

private

Full path name of the file being written, specified as a string. If the consumer was constructed with an FID argument, then this property is the name of the file. Otherwise, this value might not be set until MATLAB has begun writing to the file during receipt of a response message, since the file name cannot necessarily be determined until all headers have been received. Use this property to determine the file that was written. Filename is also stored in the Response.Body.Data property.

Attributes:

GetAccess

public

SetAccess

private

Suggested buffer size, specified as uint64. MATLAB sets AllocationLength to the anticipated size of buffers of data passed to putData. The actual size might be smaller or larger. To improve performance, the consumer can use this value to preallocate space to handle the data.

MATLAB sets this property before calling the start method for the convenience of subclasses.

Attributes:

GetAccess

public

SetAccess

public

Expected length of the payload, specified as uint64. The property normally is the Value property of the matlab.net.http.field.ContentLengthField in the Header property.

If ContentLength is empty, then the length is not known. The payload ends when putData(uint8.empty) is called.

MATLAB sets this property before calling initialize, for the convenience of subclasses that might benefit from knowing the length of the data.

If this ContentConsumer is a delegate of a top-level consumer, then the value of ContentLength might be different from the ContentLength value of the top-level consumer.

Example: numel(someData) where someData is type uint8

Attributes:

GetAccess

public

SetAccess

public

Media type of payload, specified as a matlab.net.http.MediaType object. The property normally is the Value property of the matlab.net.http.field.ContentTypeField in the Header property. If the ContentType property is empty, then the ContentTypeField is empty or nonexistent.

MATLAB sets this property before calling initialize for the convenience of subclasses that might want to examine the MediaType. Subclasses can set this property if they determine from the data that it is of a different MediaType.

At the end of the transfer, MATLAB copies this value into the Response.Body.ContentType property.

Example: 'application/octet-stream'

Attributes:

GetAccess

public

SetAccess

public

Header of the payload currently being processed, specified as a matlab.net.http.HeaderField object.

Consumers use this header to determine how to process the payload that is being sent to them. For a top-level consumer, this value is the same as Response.Header. For a delegate, the value might be different. For example, in a multipart message processed by a MultipartConsumer, it is the header of the part that this delegate is processing. The delegate can still examine Response.Header for headers of the original message.

MATLAB sets this property before calling initialize, for the convenience of subclasses.

Attributes:

GetAccess

public

SetAccess

public

The completed RequestMessage that was sent, specified as a matlab.net.http.RequestMessage object. This is the final RequestMessage after all redirections, which is the completedrequest return value from the send method.

MATLAB sets this property before calling initialize, for the convenience of subclasses.

Attributes:

GetAccess

public

SetAccess

public

The ResponseMessage being processed, specified as a matlab.net.http.ResponseMessage object.

MATLAB sets the Response property before calling initialize. The value is the ResponseMessage after headers have been received but before receiving any payload. At the start of the response message processing (or the start of a part for multipart messages), the ResponseMesssage.Body property is a MessageBody object with empty Data and Payload properties. To store received data, consumers can modify the Response and MessageBody.Data properties during data transfer. Usually, consumers that process and then store data set Response.Body.Data to their processed payload, though this is not required. At the completion of the transfer, MATLAB returns this Response to the caller of send. Consumers should not modify other Response properties, such as Header or StatusLine, as those changes are returned to the caller of send.

The Response.Body.Payload property is empty during the transfer and consumers should not attempt to modify it. If the HTTPOptions.SavePayload property is set, then MATLAB sets Payload to the received payload at the end of the transfer of the message or the part (after the call to putData(uint8.empty)) or when an exception occurs.

If an exception occurs in the consumer during message processing, then MATLAB throws an HTTPException object. The History property contains this Response value.

If the consumer is a delegate that is processing part of a multipart message, then Response.Header contains the header of the whole message, and the Payload and Data properties of Response.Body are cleared before invoking the ContentConsumer for each part. At the conclusion of each part, a new ResponseMessage is added to the end of the array of ResponseMessage objects in the original response's Body.Data containing the Header from this object and the Body from this property. The next delegate sees a fresh Response with an empty MessageBody, not the previous delegate's MessageBody.

Attributes:

GetAccess

public

SetAccess

public

Dependent

true

Destination of the request being processed, specified as a matlab.net.URI object. This value is the original destination URI as determined by send. It is not the URI of a proxy or the final URI after redirections.

MATLAB sets this property before calling initialize, for the convenience of subclasses.

Attributes:

GetAccess

public

SetAccess

public

Protected Properties

Function, specified as a function handle, called by the putData method to append additional data. The putData method in this class calls the AppendFcn function to append data it receives in its data argument to existing data in the response message. The function must have the signature:

AppendFcn(consumer,newdata)

where newdata is the data to be appended to the array at consumer.Response.Body.Data. It is the responsibility of this method to update consumer.CurrentLength to reflect the new length of Data. If newdata is empty, which indicates the end of the stream, then the function should update Response.Body.Data to its final value.

The default behavior, if this property is empty, uses an internal function that treats Data as an array of arbitrary values supporting the horzcat function. It efficiently adds newdata by preallocating space, maintaining CurrentLength to be the actual length of data stored. At the end of the message, it truncates Response.Body.Data to CurrentLength.

Subclasses can change this property if horzcat is not appropriate for the append process. For example, when a StringConsumer builds a scalar string, it would add to the string using the plus function instead of horzcat.

Subclasses that do not invoke ContentConsumer.putData to append data, or which are satisfied with horzcat behavior when appending data, can ignore this property.

Example: @customAppend where @customAppend is defined by the consumer

Attributes:

GetAccess

protected

SetAccess

protected

The ContentConsumer to which this consumer is delegating, specified as a matlab.net.http.io.ContentConsumer object. The delegateTo method of the calling consumer (the delegator) sets the CurrentDelegate property. If there is no current delegation, then the value is [].

MATLAB sets CurrentDelegate to [] before calling initialize.

Attributes:

GetAccess

protected

SetAccess

protected

Length of data currently in the Response.Body.Data property, specified as uint64.

This property is used when Response.Body.Data has been preallocated to a size larger than the actual amount of data currently stored, to indicate the length of that stored data. If this property is empty, then it means that all of Response.Body.Data contains the stored data or that a ContentConsumer subclass is disposing of the data in some way other than storing it in Response.Body.Data.

This property is used and set by the putData method in this base class when the AppendFcn property is empty. It is for the benefit of subclasses that call putData and want to examine already-stored data, and/or any implementations of AppendFcn that maintain results in Response.Body.Data.

Subclasses that use putData also can modify this property to reset the position in the buffer where the data is stored. For example, when the default AppendFcn function is used, a subclass that processes all of Response.Body.Data on each call to putData might no longer have a use for the original data, so it can reset the CurrentLength property to 1 so that the next putData call overwrites the buffer with new data. There is no need to clear elements in the buffer past the end of the new data.

Subclasses that do not call putData can use this property to track their own data, or can leave it unset (empty). MATLAB does not place any constraints on the value that can be set here and does not use it for any purpose other than to determine where the default AppendFcn should store the next buffer of data, and where to truncate the data at the end of the message. Set this property to empty before the final call to putData(uint8.empty) to prevent truncation of the data.

MATLAB sets this property to empty before each call to initialize.

Attributes:

GetAccess

protected

SetAccess

protected

The ContentConsumer that delegated to this consumer, specified as a matlab.net.http.io.ContentConsumer object. If this consumer is a delegate that was invoked by another consumer, such as a GenericConsumer or MultipartConsumer, then this is the calling consumer. It is empty in a top-level consumer specified in the call to send.

Delegates can use this property to access properties of their delegators, for example, to determine which consumer delegated to them.

Attributes:

GetAccess

protected

SetAccess

protected

Methods

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More About

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Introduced in R2018a