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82 lines
3.3 KiB
Plaintext
82 lines
3.3 KiB
Plaintext
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// Copyright (C) 2020 The Qt Company Ltd.
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// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
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/*!
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\example http
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\examplecategory {Networking}
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\meta tags {http,network,https,proxy}
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\title HTTP Client
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\ingroup examples-network
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\brief Demonstrates a simple HTTP client.
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This example demonstrates how a simple HTTP client can fetch files
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from remote hosts.
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\image http-example.webp
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The main work of this example is done in the HttpWindow class.
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Thus we will focus on that.
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\snippet http/httpwindow.cpp qnam-download
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Using QNetworkAccessManager, we begin the download of a resource as
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pointed to by the \c url. If you are unfamiliar with it or the function used,
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QNetworkAccessManager::get(), or simply want to look into it in more detail,
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take a look at its documentation and the documentation for
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QNetworkReply and QNetworkRequest.
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\snippet http/httpwindow.cpp connecting-reply-to-slots
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Above, we connect some of the reply's signals to slots in the class.
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These slots will take care of both incoming data and finalizing the
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download/handling errors.
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\snippet http/httpwindow.cpp networkreply-readyread-1
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As for handling the incoming data, since we don't know the maximum
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download size of any potential input and we don't want to exhaust
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the memory of any computer which might run the example program, we
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handle incoming data in QNetworkReply::readyRead() instead of in
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QNetworkReply::finished().
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\snippet http/httpwindow.cpp networkreply-readyread-2
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Then we write the data to file as it arrives. It is less convenient,
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but the application will consume less memory at its peak!
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\snippet http/httpwindow.cpp sslerrors-1
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With the QNetworkReply::sslErrors() signal we can also handle errors that may
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occur during the TLS handshake when connecting to secure websites (i.e. HTTPS).
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\snippet http/httpwindow.cpp sslerrors-2
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In this example, we show a dialog to the user so that they can choose whether
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or not to ignore the errors.
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\snippet http/httpwindow.cpp networkreply-error-handling-1
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\snippet http/httpwindow.cpp networkreply-error-handling-2
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If an error occurs then QNetworkReply will emit the
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QNetworkReply::errorOccurred() signal, followed by the
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QNetworkReply::finished() signal. In this example, we only connect to the
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latter. We handle any potential error(s) in the respective slot by deleting
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the file we were writing to, and display the error with our status label.
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\snippet http/httpwindow.cpp qnam-auth-required-1
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If you connect to a website that uses
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\l{https://developer.mozilla.org/en-US/docs/Web/HTTP/Authentication}{HTTP authentication},
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assuming you didn't supply the credentials that should be used ahead of time,
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you can handle missing credentials when the website requests it. With QNetworkAccessManager,
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we do this in a slot connected to the signal
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QNetworkAccessManager::authenticationRequired(). We make this connection once,
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in the constructor.
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\snippet http/httpwindow.cpp qnam-auth-required-2
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In this example, we show a dialog where the user can either insert a
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username and password, or cancel. Canceling causes the request to fail.
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*/
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