QJson doesn't work with QNetworkReply about qjson

[danvratil]

From Qt doc:
"QNetworkReply is a sequential-access QIODevice, which means that once data is read from the object, it no longer kept by the device. It is therefore the application's responsibility to keep this data if it needs to."

You probably read the data somewhere else first, then try to read them again and pass it to QJson parser.

[flavio]

I checked the code. Everything works fine when the QNetworkReply is done.

For example:

void Downloader::replyFinished(QNetworkReply* reply)
{
  QJson::Parser parser;
  bool ok;

  QVariant v = parser.parse(reply, &ok);
  qDebug() << ok;
  qDebug() << v;
}

Works like a charm.

The issue happens with code like this one:

  QNetworkReply* reply = m_manager->get(QNetworkRequest(QUrl(url)));
  QJson::Parser parser;
  bool ok;

  QVariant v = parser.parse(reply, &ok);
  qDebug() << ok;
  qDebug() << v;

In this case ok will be set to true and v will be an empty variant. That happens because the QNetworkReply::atEnd() returns true inside of JsonScanner::yylex.

The only solution to this problem would be to provide a dedicated Parser::parse(QNetworkReply*, bool*) that somehow takes advantage of the readyRead() signal.

Hints/opinions?

[danvratil]

The first approach is the correct one. You have to wait for reply to receive all data before accessing them.

In the second example, you send a GET request, which is AFAIK actually started when the method returns to event loop, so when you immediately pass it to QJson, it calls readAll() and receives an empty string. ok is set to truebecause empty string is valid and is correctly parsed into an empty object.

It's your responsibility to ensure that you pass a ready QIODevice to QJson::Parser.

[flavio]

I totally agree with you. I'm going to close this issue as a INVALID one.

BTW: this issue was filed by a user a long time ago on the old bug tracking system, but I never had time to look into it.