matlab.net.http.io.GenericConsumer class

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

Consumer for multiple content types in HTTP messages

Description

Use this consumer to handle streaming for multiple content types when you cannot predict in advance which types the server returns.

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

Creation

Description

consumer = GenericConsumer constructs a GenericConsumer using default consumers.

consumer = GenericConsumer(types,consumer) constructs a GenericConsumer to handle the specified types using the corresponding consumer. You can specify several argument pairs in any order as types1,consumer1,...,typesN,consumerN. MATLAB® searches the types in the order they appear and uses the first match. If there are no matches among the specified types, MATLAB uses the default set of consumers, depending on the type.

consumer = GenericConsumer(puthandle) constructs a ContentConsumer that calls the function specified by puthandle for each call to this consumer's putData method.

Input Arguments

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Content types, specified as a string array, character vector, or cell array of character vectors. types specifies content types using the syntax "type/subtype".

The type and subtype components in each element of types are treated as regular expressions, matched against the type/subtype of the ContentTypeField in the response, with the addition that a lone '*' for a type or subtype matches any type or subtype, and all searches are anchored to both the start and end of the string. For example,

Type/Subtype

Matches
text/*Type 'text' and any subtype
*/.*json.*Any type with subtype that contains 'json'
*/.*jsonAny type with subtype that ends with 'json'
*/*Any type or subtype

If the subtype is '*', you can omit the trailing '/*'. text is the same as 'text/*'.

types are searched in order they appear, and the first match is used. If there are no matches among the specified types, a default set of consumers is used, depending on the type, in this order:

Type/Subtype

Default Consumer
multipart/*MultipartConsumer
image/*ImageConsumer
.*/.*json.*JSONConsumer
*/*StringConsumer
*/*BinaryConsumer

While both StringConsumer and BinaryConsumer are used for any type, StringConsumer only accepts types for which it can determine a charset, specified as text/*, any type with a charset attribute, or one of the types MATLAB knows is character-based, such as "application/xml" and "application/javascript". If StringConsumer rejects the type, then BinaryConsumer accepts the type and stores the unconverted payload in Response.Body.Data as a uint8 vector.

When this consumer chooses a matching delegate based on this search criteria, it invokes the delegate's initialize method to see if the delegate accepts the payload. If the method returns false to indicate that the delegate does not accept, then this consumer continues searching the list to find the next matching delegate.

Content consumer, specified as a matlab.net.http.io.ContentConsumer object that can handle one of the specified types, or a handle to a function returning a ContentConsumer that can handle those types.

Handle to a function with the following ContentConsumer.putData syntax:

[length,stop] = putData(data)

where data a uint8 array and length is the length of that array.

Use this syntax to process all input from the server using a single function, when you know the type of data that the server returns. The function does not have access to the ResponseMessage or any information about this consumer.

Properties

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Public Properties

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

putData method of the delegate, specified as a function handle, or specified as [] if CurrentDelegate is set.

This property is set by delegateTo. Subclasses should invoke this function in their putData method to send data to the delegate or to end the delegate's portion of the data by sending uint8.empty:

[len, stop] = obj.PutMethod(data);

At the end of the message, after the above call to any delegate to end the message, subclasses should set PutMethod to empty and invoke the call putData(uint8.empty) in their superclass so that this class knows the message has ended. This putData call will leave PutMethod empty or set it back to the puthandle argument passed to the constructor.

Attributes:

GetAccess

protected

SetAccess

protected

Dependent

true

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