// Copyright (C) 2023 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only

/*!
    \page qml-qtqml-xmlhttprequest.html
    \title The XMLHttpRequest JavaScript Object
    \inqmlmodule QtQml
    \brief Object for sending requests to a server.

    The \c XMLHttpRequest object allows scripts to perform HTTP client functionality,
    such as submitting form data or loading data asynchronously from a server.

    The \c XMLHttpRequest API is a partial implementation of the
    \l {https://www.w3.org/TR/2014/WD-XMLHttpRequest-20140130/}{W3C XHR Level 1 standard}
    with the following exception:
    \list
    \li It does not enforce the same origin policy.
    \endlist

    \section1 Sending requests

    Use the following steps to send a request using the \c XMLHttpRequest API:
    \list 1
    \li Create a \c XMLHttpRequest object.
    \li Assign a callback function to the \l {function XMLHttpRequest::onreadystatechange}{onreadystatechange} signal handler.
    \li Call \l {void XMLHttpRequest::open(method, url, async)}{open()} with the appropriate HTTP method and URL to request.
    \li Call \l {void XMLHttpRequest::send(data)}{send()}
    \endlist

    The callback function handles the HTTP response for a request.
    It's a good practice to check if the \l{enumeration XMLHttpRequest::readyState}{readyState} is \c DONE in the handler,
    before you use one of the following methods to read the response:
    \list
    \li \l {var XMLHttpRequest::response}{response}
    \li \l {string XMLHttpRequest::responseText}{responseText}
    \li \l {var XMLHttpRequest::responseXML}{responseXML}
    \endlist

    The following example demonstrates how to send a request and read the response:

    \snippet qml/XHRForm.qml 0

    The earlier snippet connects the button's clicked signal to an external \c sendRequest function.
    A resource URL is passed as the first argument, and a callback function to handle UI updates is passed as the second.
    The \c sendRequest function, which exists in an external \c request.js file, can be implemented like this:

    \snippet qml/xmlhttprequest.js 0

    The earlier snippet follows the four simple steps mentioned at the beginning.
    It instantiates the \c XMLHttpRequest object first, and assigns a callback function to handle the response.
    It also calls \l {void XMLHttpRequest::open(method, url, async)}{open()} with an HTTP method and URL, before it sends the request to the server.
    Notice that the second argument to \c sendRequest is called at the end of \l {function XMLHttpRequest::onreadystatechange}{onreadystatechange},
    in order to handle UI updates based on the HTTP response.

    Set the \c QML_XHR_DUMP environment variable to \c 1 if you want to debug a request.
    This will log the following information:
    \list
    \li Method type (GET or POST), URL, and body of sent requests.
    \li URL and body of responses received.
    \li Network error, if any.
    \endlist

    \section1 Accessing local files

    By default, you cannot use the \c XMLHttpRequest object to read files from your local file system.
    If you wish to use this feature to access local files, you can set the following environment variables to \c 1.
    \list
    \li QML_XHR_ALLOW_FILE_READ
    \li QML_XHR_ALLOW_FILE_WRITE
    \endlist
    \warning Use this feature only if you know that the application runs trusted QML and JavaScript code.

    \section1 responseXML document

    The \c responseXML XML DOM tree currently supported by QML is a reduced subset of
    the \l {http://www.w3.org/TR/DOM-Level-3-Core/}{DOM Level 3 Core} API supported in a web browser.
    The following objects and properties are supported by the QML implementation:

    \table
    \header
    \li \b {Node}
    \li \b {Document}
    \li \b {Element}
    \li \b {Attr}
    \li \b {CharacterData}
    \li \b {Text}

    \row
    \li
    \list
    \li nodeName
    \li nodeValue
    \li nodeType
    \li parentNode
    \li childNodes
    \li firstChild
    \li lastChild
    \li previousSibling
    \li nextSibling
    \li attributes
    \endlist

    \li
    \list
    \li xmlVersion
    \li xmlEncoding
    \li xmlStandalone
    \li documentElement
    \endlist

    \li
    \list
    \li tagName
    \endlist

    \li
    \list
    \li name
    \li value
    \li ownerElement
    \endlist

    \li
    \list
    \li data
    \li length
    \endlist

    \li
    \list
    \li isElementContentWhitespace
    \li wholeText
    \endlist

    \endtable

    \section1 void XMLHttpRequest::abort()

    Cancels the current request.

    It changes the \l {enumeration XMLHttpRequest::readyState}{readyState} property to be \c XMLHttpRequest.UNSENT and emits the \c readystatechange signal.

    \section1 string XMLHttpRequest::getAllResponseHeaders()

    Returns a \c String of headers received from the last response.

    The following is an example response header:
    \code
    content-encoding: gzip
    content-type: text/html; charset=UTF-8
    date: Mon, 06 Feb 2023 09:00:08 GMT
    expires: Mon, 13 Feb 2023 09:00:08 GMT
    last-modified: Thu, 17 Oct 2019 07:18:26 GMT
    \endcode

    \sa {string XMLHttpRequest::getResponseHeader(headerName)}{getResponseHeader()}

    \section1 string XMLHttpRequest::getResponseHeader(headerName)

    Returns either the \a headerName value from the last response, or an empty \c String, if the \a headerName is missing.

    \sa {string XMLHttpRequest::getAllResponseHeaders()}{getAllResponseHeaders()}

    \section1 void XMLHttpRequest::open(method, url, async)

    Specify the HTTP \a method you want the request to use, as well as the \a url you wish to request.
    You should make sure to always call this function before \l {void XMLHttpRequest::send(data)}{send()}.
    An optional third parameter \a async can be used to decide whether the request should be asynchronous or not.
    The default value is \c true.

    Emits the \c readystatechange signal, which calls the \l {function XMLHttpRequest::onreadystatechange}{onreadystatechange} handler with
    the \l {enumeration XMLHttpRequest::readyState}{readyState} property set to \c XMLHttpRequest.OPENED.

    \section1 void XMLHttpRequest::send(data)

    Sends the request to the server.
    You can use the optional argument \a data to add extra data to the body of the request.
    This can be useful for POST requests, where you typically want the request to contain extra data.

    The \l {enumeration XMLHttpRequest::readyState}{readyState} property is updated once a response has been received from the server,
    and while the response is being processed. It will first be set to \c HEADERS_RECEIVED, then to \c LOADING,
    and finally \c DONE, once the response has been fully processed.
    The \c readystatechange signal is emitted every time \l {enumeration XMLHttpRequest::readyState}{readyState} is updated.

    \section1 void XMLHttpRequest::setRequestHeader(header, value)

    Adds a new header to the next request you wish to send.
    This is a key-value pair, which has the name \a header and the corresponding \a value.

    \section1 void XMLHttpRequest::overrideMimeType(mime)
    \since 6.6

    Forces the \c XMLHttpRequest to interpret the data received in the next HTTP response,
    as if it had the MIME type \a mime, rather than the one provided by the server.

    \section1 function XMLHttpRequest::onreadystatechange

    Choose a callback function you want to get invoked whenever the \l {enumeration XMLHttpRequest::readyState}{readyState} of the \c XMLHttpRequest object changes.

    \sa {enumeration XMLHttpRequest::readyState}{readyState}

    \section1 enumeration XMLHttpRequest::readyState
    \readonly

    Indicates the current state of the \c XMLHttpRequest object.

    The value can be one of the following:
    \value XMLHttpRequest.UNSENT The request is not initialized, which is the state before calling \l {void XMLHttpRequest::open(method, url, async)}{open()}.
    \value XMLHttpRequest.OPENED The request is initialized, meaning \l {void XMLHttpRequest::open(method, url, async)}{open()} was previously called, but no further progress.
    \value XMLHttpRequest.HEADERS_RECEIVED Received a reply from the sever, but the request is not fully processed yet.
    \value XMLHttpRequest.LOADING Downloading data from the server.
    \value XMLHttpRequest.DONE Finished processing the request.

    \sa {function XMLHttpRequest::onreadystatechange}{onreadystatechange}

    \section1 string XMLHttpRequest::responseURL
    \readonly
    \since 6.6

    Returns the url that was used to retrieve the response data, after any redirects have occurred.

    \section1 string XMLHttpRequest::responseText
    \readonly

    Returns a \c String containing the data received from the last response.

    \sa {var XMLHttpRequest::responseXML}{responseXML}

    \section1 var XMLHttpRequest::responseXML
    \readonly

    Returns either a \c Document, or \c null, if the response content cannot be parsed as XML or HTML.
    See the \l {responseXML document}{responseXML document} section for more information.

    \sa {string XMLHttpRequest::responseText}{responseText}

    \section1 var XMLHttpRequest::response
    \readonly

    Returns either a \c String, an \c ArrayBuffer, or a \c Document,
    depending on the \l {string XMLHttpRequest::responseType}{responseType} of the last request.

    \sa {string XMLHttpRequest::responseType}{responseType}, {string XMLHttpRequest::responseText}{responseText}, {var XMLHttpRequest::responseXML}{responseXML}

    \section1 string XMLHttpRequest::responseType

    Returns a \c String describing the content type of the last response received.
    \list
    \li If the response type is "text" or an empty \c String, the response content is a UTF-16 encoded \c String.
    \li If the response type is "arraybuffer", it means that the response content is an \c ArrayBuffer containing binary data.
    \li If the response type is "json", the response content should be a JSON \c Document.
    \li If the response type is "document", it means that the response content is an XML \c Document, which can be safely read with the \l {var XMLHttpRequest::responseXML}{responseXML} property.
    \endlist

    \sa {var XMLHttpRequest::response}{response}

    \section1 int XMLHttpRequest::status
    \readonly

    Returns the status code for the last response received.

    \sa {string XMLHttpRequest::statusText}{statusText}

    \section1 string XMLHttpRequest::statusText
    \readonly

    Returns a \c String that has the status message associated with the status code for the last response received.

    \sa {int XMLHttpRequest::status}{status}
*/
