Convert QUrl with percent encoding into string

Question

I use a URL entered by the user as text to initialize a QUrl object. Later I want to convert the QUrl back into a string for displaying it and to check it using regular expr

Answer 1

You can use QUrlQuery::toString(QUrl::FullyEncoded) or QUrl::fromPercentEncoding() for this converting.

Answer 2

I am not sure why toDisplayString(QUrl::FullyDecoded) does not work.

After trying several versions I have found that copy.query(QUrl::FullyDecoded) does decode the query part. The Documentation has an example with the the following code does return the decoded URL:

QUrl url("http://test.com/query?q=%2B%2Be%3Axyz%2Fen");
url.setQuery(url.query(QUrl::FullyDecoded), QUrl::DecodedMode);
qDebug() << url.toString();

To solve the problem this way is not optimal because the query part is copied without need.

Answer 3

Conclusion

I've done some research, the conclusion so far is: absurd.

QUrl::fromPercentEncoding() is the way to go and what OP has done in the UPDATE section should've been the accepted answer to the question in title.

I think Qt's document of QUrl::toDisplayString is a little bit misleading :

"Returns a human-displayable string representation of the URL. The output can be customized by passing flags with options. The option RemovePassword is always enabled, since passwords should never be shown back to users."

Actually it doesn't claim any decoding ability, the document here is unclear about it's behavior. But at least the password part is true. I've found some clues on Gitorious:

"Add QUrl::toDisplayString(), which is toString() without password. And fix documentation of toString() which said this was the method to use for displaying to humans, while this has never been true."

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Test Code

In order to discern the decoding ability of different functions. The following code has been tested on Qt 5.2.1 (not tested on Qt 5.3 yet!)

QString target(/*path*/);

QUrl url_path(target);
qDebug() << "[Original String]:" << target;
qDebug() << "--------------------------------------------------------------------";
qDebug() << "(QUrl::toEncoded)          :" << url_path.toEncoded(QUrl::FullyEncoded);
qDebug() << "(QUrl::url)                :" << url_path.url();
qDebug() << "(QUrl::toString)           :" << url_path.toString(); 
qDebug() << "(QUrl::toDisplayString)    :" << url_path.toDisplayString(QUrl::FullyDecoded);
qDebug() << "(QUrl::fromPercentEncoding):" << url_path.fromPercentEncoding(target.toUtf8());

• Return QByteArray: QUrl::toEncoded
• Return QString: QUrl::url, QUrl::toString, QUrl::toDisplayString, QUrl::fromPercentEncoding

P.S. QUrl::url is just synonym for QUrl::toString.

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Output

[Case 1]: When target path = "%_%" (test the functionality of encoding):

[Original String]: "%_%" 
-------------------------------------------------------------------- 
(QUrl::toEncoded)          : "%25_%25" 
(QUrl::url)                : "%25_%25" 
(QUrl::toString)           : "%25_%25" 
(QUrl::toDisplayString)    : "%25_%25" 
(QUrl::fromPercentEncoding): "%_%" 

[Case 2]: When target path = "Meow !" (test the functionality of encoding):

[Original String]: "Meow !" 
-------------------------------------------------------------------- 
(QUrl::toEncoded)          : "Meow%20!" 
(QUrl::url)                : "Meow !" 
(QUrl::toString)           : "Meow !" 
(QUrl::toDisplayString)    : "Meow%20!" // "Meow !" when using QUrl::PrettyDecoded mode
(QUrl::fromPercentEncoding): "Meow !" 

[Case 3]: When target path = "Meow|!" (test the functionality of encoding):

[Original String]: "Meow|!" 
-------------------------------------------------------------------- 
(QUrl::toEncoded)          : "Meow%7C!" 
(QUrl::url)                : "Meow%7C!" 
(QUrl::toString)           : "Meow%7C!" 
(QUrl::toDisplayString)    : "Meow|!" // "Meow%7C!" when using QUrl::PrettyDecoded mode
(QUrl::fromPercentEncoding): "Meow|!" 

[Case 4]: When target path = "http://test.com/query?q=++e:xyz/en" (none % encoded):

[Original String]: "http://test.com/query?q=++e:xyz/en" 
-------------------------------------------------------------------- 
(QUrl::toEncoded)          : "http://test.com/query?q=++e:xyz/en" 
(QUrl::url)                : "http://test.com/query?q=++e:xyz/en" 
(QUrl::toString)           : "http://test.com/query?q=++e:xyz/en" 
(QUrl::toDisplayString)    : "http://test.com/query?q=++e:xyz/en" 
(QUrl::fromPercentEncoding): "http://test.com/query?q=++e:xyz/en" 

[Case 5]: When target path = "http://test.com/query?q=%2B%2Be%3Axyz%2Fen" (% encoded):

[Original String]: "http://test.com/query?q=%2B%2Be%3Axyz%2Fen" 
-------------------------------------------------------------------- 
(QUrl::toEncoded)          : "http://test.com/query?q=%2B%2Be%3Axyz%2Fen" 
(QUrl::url)                : "http://test.com/query?q=%2B%2Be%3Axyz%2Fen" 
(QUrl::toString)           : "http://test.com/query?q=%2B%2Be%3Axyz%2Fen" 
(QUrl::toDisplayString)    : "http://test.com/query?q=%2B%2Be%3Axyz%2Fen" 
(QUrl::fromPercentEncoding): "http://test.com/query?q=++e:xyz/en" 

P.S. I also encounter the bug that Ilya mentioned in comments: Percent Encoding doesn't seem to be working for '+' in QUrl

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Summary

The result of QUrl::toDisplayString is ambiguous. As the document says, the QUrl::FullyDecoded mode must be used with care. No matter what type of URL you got, encode them by QUrl::toEncode and display them with QUrl::fromPercentEncoding when necessary.

As for the malfunction of percent-encoded URLs in QWebView mentioned in OP, more details are needed to debug it. Different function and different mode used could be the reason.

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Helpful Resources

1. RFC 3986 (which QUrl conforms)
2. Encode table
3. Source of qurl.cpp on Gitorious