Re: [Interest] QNetwork classes for submitting google forms

[Jason H]

> Sent: Monday, June 14, 2021 at 1:42 PM
> From: "Jason H" <jh...@gmx.com>
> To: "Scott Bloom" <sc...@towel42.com>
> Cc: "Thiago Macieira" <thiago.macie...@intel.com>, "interest@qt-project.org" 
> <interest@qt-project.org>
> Subject: Re: [Interest] QNetwork classes for submitting google forms
>
> 
> 
> > Sent: Monday, June 14, 2021 at 1:12 PM
> > From: "Scott Bloom" <sc...@towel42.com>
> > To: "Thiago Macieira" <thiago.macie...@intel.com>, 
> > "interest@qt-project.org" <interest@qt-project.org>
> > Subject: Re: [Interest] QNetwork classes for submitting google forms
> >
> > This has come up a couple times for me through the years (essentially make 
> > a network request and don’t return until the request has finished).
> > 
> > Is there an example anywhere of the "Thiago" (proper.. 😊 ) way to code 
> > this?  I see this issue in a similar vane to using QThread, when the 
> > Trolls/Nokia/TQP (I forget who originally wrote it) wrote up a small but 
> > very effective white paper on the proper method of using Qthread, it 
> > clarified a ton of questions for many people.
> > 
> 
> 
> You'd probably get feedback that QThread is "too heavy" and for i/o bound 
> processes one async event loop is enough. (I've been on the rx end of that)
> 
> I think my highest of levels approach is correct:
> https://lists.qt-project.org/pipermail/interest/attachments/20210602/9366d8ea/attachment-0001.html
>  (apologies for the HTML, but my mailer responds by what ever I am replying 
> to.)
> 
> The one caveat to my code, is if you don't need synchronous requests 
> (regrettably, this part of my app requires them) then you can ignore the 
> QEventloop stuff, that is leave lines that references `loop` it out, and 
> you'll have a fully async inline lambda.
> 
> You however are asking for a synchronous and this I think is the best way. 
> Feel free to assault the code, (Thiago and others.) I would like Qt to adopt 
> some kind of this pattern.

I cleaned this up a bit:

What to request : http://1270.0.1:4321/file?f=1234 (GET)
What to do: { /* save file */ } or { /* handle error */ }
  
Invocation:
       remoteCloud->synchronousPostFile("http://1270.0.1:4321/file?f=1234";      
                                       
           [=] (QNetworkReply* reply, QString filename) {
               if (reply->error() == QNetworkReply::NoError) {
                  { /* save file */ }
               } else {
                  { /* handle error */ }
               }
            } // end of lambda
       ); // end of call


void RemoteCloud::synchronousGetFile(const QString& endpoint, 
std::function<void (QNetworkReply *, const QString &)> lambda) {
    QEventLoop loop; 
    QNetworkReply * reply = remoteCloud->get(endpoint);
    QObject::connect(reply, &QNetworkReply::finished, &loop, 
&QEventLoop::quit); 
    QObject::connect(reply, &QNetworkReply::finished, reply, [=]{
        lambda(reply);
        reply->deleteLater(); 
    });
    loop.exec(); // wait for finished before returning
}


void RemoteCloud::getFile(const QString& endpoint, std::function<void 
(QNetworkReply *, const QString &)> lambda) {
    QNetworkReply * reply = remoteCloud->get(endpoint);
    QObject::connect(reply, &QNetworkReply::finished, reply, [=]{
        lambda(reply);
        reply->deleteLater(); // always cleanup after the lambda ran
    });
}
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