matlab.net.http.io.MultipartFormProvider class

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

ContentProvider to send multipart/form-data messages

Description

Use this provider to send a multipart form to the server. A multipart form is a message containing a series of parts, where each part has a "control name" and its data. The data can be any of the types allowed for RequestMessage.Body.Data or another ContentProvider.

Some servers require multiple parts under the same name to be in a nested multipart/mixed part. To send nested parts, wrap the parts in a MultipartProvider. For example, to send a message as described at the very end of chapter 17 of the HTML 4.01 specification for form data:

fps = FileProvider(["file1.txt","file2.gif"]); % get array of providers
mp = MultipartProvider(fps);
formProvider = MultipartFormProvider("submit-name","Larry","files",mp);
req = RequestMessage('put',[],formProvider);
req.send(uri);

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

Creation

Description

provider = MultipartFormProvider(Name,Part) creates "multipart/form-data" content specified by one or more name-part pair arguments. Part is form-data containing a Name and its contents. The Part arguments can be any of the types supported by MultipartProvider, including other ContentProvider objects.

If a Part is an array, it is equivalent to repeating the Name,Part for each element of the array. For example, the statement:

MultipartFormProvider("name",FileProvider(["file1" "file2"]))

is equivalent to:

MultipartFormProvider("name",FileProvider("file1"),"name",FileProvider("file2"));

Properties

Public Properties

Names — Part names

string

Part names, specified as a string.

Attributes:

GetAccess	public
SetAccess	public

Parts — Message body parts

cell array

Parts of the message body, specified as a cell array of one or more of these values:

ContentProvider object	The MultipartProvider delegates creation of the part to the specified provider (called the delegate), invoking its complete method to obtain header information about the part and its getData method to obtain the data. The delegate's Header property is used for the header of the part. Any subclass of ContentProvider can be specified here. Normally, the delegate does not specify the content length nor implement the expectedContentLength method, since the end of a part is designated by a boundary string rather than a header field. If that method is implemented to return a nonempty value, then the value is used only to enforce the length of the content, not to create a Content-Length field.
RequestMessage object	The MultipartProvider sends the Header and Body of the RequestMessage as the part. If the Body's Payload property is set, then that is used for the raw payload. Otherwise the Body's Data property is converted based on its type or the Content-Type field in the Header, as described for MessageBody.Data. This option is useful if you have data to send and want to take advantage of the default processing of that data that MATLAB® normally does when sending a RequestMessage. It allows you to specify custom header fields in the request to be used as the part's Header and control how the data is converted, without having to write a ContentProvider subclass. The RequestMessage.RequestLine property is ignored.
MessageBody object	The MessageBody is processed the same as if it was in a RequestMessage that had no Content-Type field. This option is useful if default processing of the data based on its type is sufficient, and you do not need to specify any custom header fields for the part. MATLAB inserts a Content-Type field in the part based on the type of the data. See MessageBody.Data for conversion rules.
Array of ContentProvider, RequestMessage, and/or MessageBody objects	This treats each element of the array as a part. Not a cell array.
Handle to getData method	This method must have the signature of ContentProvider.getData. In this case, the part's Content-Type is set to "application/octet-stream", so this option is useful for sending binary data. When using this option, you cannot specify any custom header fields for the part.
Any other type	If the type does not match any of these types and is not a function handle, then it is treated as if it was present in the Data property of a MessageBody. See the description for MessageBody types.

Attributes:

GetAccess	public
SetAccess	public
Dependent	true

Header — Header fields of message or part

matlab.net.http.HeaderField.empty (default) | matlab.net.http.HeaderField

Header fields of the message or part, specified as a vector of one or more matlab.net.http.HeaderField objects.

This property is only used by subclass authors. MATLAB sets this property before calling the provider's complete method. For non-multipart messages, MATLAB initializes this property to the contents of Request.Header, minus any matlab.net.http.field.GenericFields or empty-valued fields. The ContentProvider uses this property to add header fields that describe the data to be sent, or to add parameters to header fields already in the message. In a delegate for a MultipartProvider, MATLAB initializes this property to header fields that the delegating provider intends to insert for the part. Delegates can modify or change these fields.

Upon return from the provider's complete method, if this not a multipart message, then MATLAB reads this property and merges its contents into the header of Request. Fields in this Header with Names that do not already appear in Request.Header are added to the end of Request.Header. If a field in this Header has a Name that is the same as one in Request.Header, and both have nonempty Values, then:

• If the one in Request.Header is a GenericField, then ignore the one in Header.

• If the one in Request.Header is not a GenericField, then replace it with the one in Header.

If one or both of these has an empty Value, then the field is removed from Request.Header and it is not added as part of normal message completion.

If this is a delegate of a MultipartProvider, then the entire contents of this Header is used as the header of the part. Multipart delegates must not assume that Request.Header contains any fields pertaining to their own Header. A provider can determine whether it is a multipart delegate by checking whether MyDelegator is a MultipartProvider, though this test is unlikely to be needed.

MATLAB reads this property only on return from calling the provider's complete method. Changes to this array are ignored once MATLAB calls start.

Class authors should be aware that their subclasses might have added fields to this Header (in their complete method) before calling complete in their superclass. It is best to preserve such fields and not to add fields with the same names. However, adding a parameter to a field is permissible. For example, a superclass can add a charset parameter to an existing Content-Type field that does not already have one.

Attributes:

GetAccess	public
SetAccess	public

ForceChunked — Indicate whether to force chunked transfer coding

false (default) | true

Indicate whether to force chunked transfer coding, specified as boolean. This property is of interest only to subclass authors, and is applicable only to providers that are not multipart delegates. Subclasses set ForceChunked to control whether contents should be sent using chunked transfer coding. If false (default), MATLAB decides whether to send the contents chunked, based on whether it knows the content length at the time the message is ready to be sent:

• If MATLAB knows the content length (which is the case if the message contains a Content-Length field, or if this provider's expectedContentLength method returned a number), then MATLAB decides whether to send it chunked or not.

• If MATLAB does not know the content length (no Content-Length field in the header and expectedContentLength returned empty), then MATLAB always sends the message chunked.

If ForceChunked is true, then MATLAB sends the message chunked regardless of whether it knows the content length, unless the known length is smaller than the chunk size. If this property is true, then the message must not contain a Content-Length field, because HTTP does not allow a chunked message to have a Content-Length field. However, you can still return a nonzero value in the expectedContentLength method if you want MATLAB to verify that you are returning the expected length of data.

When MATLAB chooses to send the message chunked, the size of each chunk is equal to the length of data returned by getData.

MATLAB reads this value after calling the complete method, before calling start. It does not set this field.

Attributes:

GetAccess	public
SetAccess	public

Request — Request message to send

matlab.net.http.RequestMessage

Request message to send, specified as a matlab.net.http.RequestMessage object.

This property is used only by subclass authors. The RequestMessage.send and RequestMessage.complete methods set this property to the RequestMessage in whose Body this provider has been placed, before calling any other methods in this provider, and before adding any additional header fields or validating the message. The provider can examine this message to see what was contained in the original request.

Delegates see the same value for this property as the delegator. ContentProviders should be aware that, if they are delegates, they are not necessarily providing the entire body of the request message, so they should not assume that header fields in this Request are pertinent to the data they are providing. Usually, delegates should ignore header fields in this request relevant to the data, such as Content-Type.

If the provider wishes to add any header fields to this message, or to modify existing ones, it should do so in its complete method by adding those fields to the Header property. The caller of complete (RequestMessage or a delegating provider) determines what to do with those fields. RequestMessage.send and RequestMessage.complete always copy these fields to the Header of the RequestMessage. A delegating provider can copy the fields to its own Header property or insert them into the message (as in the case of MultipartProvider). For more information, see the Header property.

This property is read-only.

Attributes:

GetAccess	public
SetAccess	matlab.net.http.RequestMessage

Protected Properties

Subtype — Provider subtype

"mixed" (default) | string

Provider subtype, specified as a string. The default value "mixed" adds a Content-Type header set to "multipart/mixed" to the message, plus appropriate parameters. Subclasses can alter this value in the constructor or the complete method. This value appears in the Content-Type after "multipart/".

Attributes:

GetAccess	protected
SetAccess	protected

CurrentDelegate — ContentProvider to which this provider is delegating

matlab.net.http.io.ContentProvider | empty

ContentProvider to which this provider is delegating, specified as a matlab.net.http.io.ContentProvider object. This property is set in the calling provider (the delegator) by the delegateTo method to indicate the current delegated provider. If there is no current delegation, then the value is empty.

The complete methods set this property to empty.

Attributes:

GetAccess	protected
SetAccess	protected

MyDelegator — ContentProvider that delegated to this provider

matlab.net.http.io.ContentProvider.empty (default) | matlab.net.http.io.ContentProvider

ContentProvider that delegated to this provider, specified as a matlab.net.http.io.ContentProvider object.

If a ContentProvider delegates responsibility for sending all or a portion of the message data to another provider, then this property identifies the delegating provider to the delegate. For example, a MultipartProvider delegates parts of the message to other providers, so it inserts a handle to itself in each delegate. Otherwise, MyDelegator is empty. The delegateTo method sets this property in the delegate.

Attributes:

GetAccess	protected
SetAccess	protected

Methods

Public Methods

getData

Next buffer of data to send in multipart HTTP request message

Specialized Operators and Functions

These methods specialize standard MATLAB operators and functions and inherited methods for objects in this class.

string	Provider information as string
show	Display provider information

Protected Methods

complete	Complete HTTP header for MultipartProvider
preferredBufferSize	Preferred buffer size for ContentProvider
expectedContentLength	Content length of ContentProvider
start	Start data transfer from MultipartProvider
restartable	Indicate whether ImageProvider is restartable
reusable	Indicate whether ImageProvider is reusable
delegateTo	Delegate to another provider

More About

Class Hierarchy

Introduced in R2018a