Missing "+" when calling QNetworkAccessManager.post()?

[MorrisLiang]

Here is a strange thing I came cross.When I post something using QNetworkAccessManager:

QByteArray content;
fillContent(content);
qDebug()<<content;
QNetworkAccessManager manager;
manager.post(QNetworkRequest(requestURL),content);

QByteArray content;
fillContent(content);
qDebug()<<content;
QNetworkAccessManager manager;
manager.post(QNetworkRequest(requestURL),content);

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So,I the third line,I can see the output like this:
"signature=LgcuKoofUFtO+LKWPnARcpJyeRo=&signature_ method=HMAC-SHA1"

But when the reply finished,I output the data of reply:

qDebug()<<reply->readAll();

qDebug()<<reply->readAll();

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I get error message from the sever:
"Signature does not match. Expected: LgcuKoofUFtO+LKWPnARcpJyeRo= Got: LgcuKoofUFtO LKWPnARcpJyeRo="
You see,the "+" in the middle of the signature is missing...
It's pretty strange.Does anybody know how to fix it?

BTW,I can't encode the data to percent-encoding(like %20%4Babcde) before calling QNetworkAccessManager.post(),because the sever will assume this is wrong too.