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List: kde-core-devel
Subject: Re: Review Request 114219: Do not encode QString to QByteArray and cast it
From: Martin_Gräßlin <mgraesslin () kde ! org>
Date: 2013-11-30 8:48:52
Message-ID: 20131130084852.20506.17665 () vidsolbach ! de
[Download RAW message or body]
> On Nov. 30, 2013, 1:45 a.m., Thomas Lübking wrote:
> > kcontrol/krdb/krdb.cpp, line 102
> > <http://git.reviewboard.kde.org/r/114219/diff/1/?file=221836#file221836line102>
> >
> > QFile::encodeName() seems equal to QString::toLocal8Bit(), ::decodeName() to ::fromLocal8Bit()
> >
> > I don't think one can just drop one of them and whether transcoding is required probably depends on \
> > what is done to the string interim.
> > If at all "KToolInvocation::klauncher()->setLaunchEnv()" would perform a second decode, so it probaly \
> > depends on what that does.
> > Was "locale charmap" determined by the reporter in the bug?
> >
> > ---
> >
> > Secret world domination plan:
> > ------------------------------
> > #1: classified
> > #2: classified
> > #3: force ASCII as global standard
> > #4: classified
> > #5: classified
> > #6: classified
> > #7: classified
> > #8: classified
> > #9: classified
> > #a: classified
>
> Yichao Yu wrote:
> encodeName/toLocal8Bit is used to encode a unicode string to a c-string/byte-array representation and \
> decodeName/fromLocal8Bit does the reverse.
> The proper decoding is already done in QFile::decodeName above and the QString already has the right \
> unicode string in it.
> Basically, QString is not a wrapper of arbitrary c-string/byte-array, rather a wrapper of a unicode \
> string so whatever done to a QString before or after should assume it is a valid unicode string and is \
> independent of what encoding (utf8 in the case of dbus) is needed afterward.
> Encode to a byte array and cast it back can only cause wrong encoding in the second conversion and will \
> not affect what is done in setLaunchEnv.
>
> Yichao Yu wrote:
> Or in another word QString has no encoding (well, by which I mean the internal encoding is trasparent \
> to the user), only byte array and c-string has encoding.
>
> Thomas Lübking wrote:
> QString(QByteArray) according to the API doc actually differs between Qt4 & 5 (fromAscii -> fromUtf8) \
> but an encoding should not happen nevertheless because:
> 282 void KLauncher::setLaunchEnv(const QString &name, const QString &value)
> 283 {
> 284 #ifndef USE_KPROCESS_FOR_KIOSLAVES
> 285 klauncher_header request_header;
> 286 QByteArray requestData;
> 287 requestData.append(name.toLocal8Bit()).append('\0').append(value.toLocal8Bit()).append('\0');
>
> Also QString(QByteArray) is obvisouly problematic by itself for the apparent 4/5 "incompatibility".
>
> Yichao Yu wrote:
> I guess you can also put it in this this way (setLaunchEnv have toLocal8Bit inside) although I still \
> think the simplest way is to remember QString -- encode --> QByteArray, QByteArray -- decode --> \
> QString and always to the necessary explicit conversion.
> That's why I hate hate hate this constructor. (and I've already fixed 3-4 bugs in KDE due to this \
> constructor.) It might actually be helpful to compile KDE with it commented out and replace everything \
> with explicit conversion.....
>
> Yichao Yu wrote:
> I guess you can also put it in this this way (setLaunchEnv have toLocal8Bit inside) although I still \
> think the simplest way is to remember QString -- encode --> QByteArray, QByteArray -- decode --> \
> QString and always to the necessary explicit conversion.
> That's why I hate hate hate this constructor. (and I've already fixed 3-4 bugs in KDE due to this \
> constructor.) It might actually be helpful to compile KDE with it commented out and replace everything \
> with explicit conversion.....
>
> Yichao Yu wrote:
> I guess you can also put it in this this way (setLaunchEnv have toLocal8Bit inside) although I still \
> think the simplest way is to remember QString -- encode --> QByteArray, QByteArray -- decode --> \
> QString and always to the necessary explicit conversion.
> That's why I hate hate hate this constructor. (and I've already fixed 3-4 bugs in KDE due to this \
> constructor.) It might actually be helpful to compile KDE with it commented out and replace everything \
> with explicit conversion.....
>
> Yichao Yu wrote:
> ahh.... sth wrong with my network.... sorry for the duplicated post...
I just had a look at the history of the specific line of code and tracked it back to "This commit was \
manufactured by cvs2svn" (238ffd07).
The original line was:
QCString value = QFile::encodeName(list.join(":"));
doing several porting conversions via at one step QByteArray to finally QString. Given that it used to be \
a QByteArray the ::encodeName seems reasonable, but since it's QString I think that it's save to drop it.
- Martin
-----------------------------------------------------------
This is an automatically generated e-mail. To reply, visit:
http://git.reviewboard.kde.org/r/114219/#review44857
-----------------------------------------------------------
On Nov. 30, 2013, 5:38 a.m., Yichao Yu wrote:
>
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> http://git.reviewboard.kde.org/r/114219/
> -----------------------------------------------------------
>
> (Updated Nov. 30, 2013, 5:38 a.m.)
>
>
> Review request for kde-workspace, David Faure, Martin Gräßlin, and Hugo Pereira Da Costa.
>
>
> Bugs: 327919
> http://bugs.kde.org/show_bug.cgi?id=327919
>
>
> Repository: kde-workspace
>
>
> Description
> -------
>
> list.join already returns a QString and there is no need to encode it and cast back to QString \
> again....
> P.S. for a patch that applies to both KDE4 and KF5(master for kde-workspace, frameworks for kdelibs?) \
> How should I submit review request? Should I add both in branch or submit two review request? (But \
> often the patch cannot apply directly due to context or file path changes).
>
> Diffs
> -----
>
> kcontrol/krdb/krdb.cpp 92d84e9
>
> Diff: http://git.reviewboard.kde.org/r/114219/diff/
>
>
> Testing
> -------
>
> Compiles.
> Fixes the problem here.
>
>
> Thanks,
>
> Yichao Yu
>
>
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This is an automatically generated e-mail. To reply, visit:
<a href="http://git.reviewboard.kde.org/r/114219/">http://git.reviewboard.kde.org/r/114219/</a>
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<blockquote style="margin-left: 1em; border-left: 2px solid #d0d0d0; padding-left: 10px;">
<p style="margin-top: 0;">On November 30th, 2013, 1:45 a.m. CET, <b>Thomas Lübking</b> wrote:</p>
<blockquote style="margin-left: 1em; border-left: 2px solid #d0d0d0; padding-left: 10px;">
<table width="100%" border="0" bgcolor="white" style="border: 1px solid #C0C0C0; border-collapse: \
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<tr>
<th colspan="4" bgcolor="#F0F0F0" style="border-bottom: 1px solid #C0C0C0; font-size: 9pt; padding: \
4px 8px; text-align: left;"> <a \
href="http://git.reviewboard.kde.org/r/114219/diff/1/?file=221836#file221836line102" style="color: black; \
font-weight: bold; text-decoration: underline;">kcontrol/krdb/krdb.cpp</a> <span style="font-weight: \
normal;">
(Diff revision 1)
</span>
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</thead>
<tbody style="background-color: #e4d9cb; padding: 4px 8px; text-align: center;">
<tr>
<td colspan="4"><pre style="font-size: 8pt; line-height: 140%; margin: 0; ">static void \
applyGtkStyles(bool active, int version)</pre></td>
</tr>
</tbody>
<tbody>
<tr>
<th bgcolor="#e9eaa8" style="border-right: 1px solid #C0C0C0;" align="right"><font \
size="2">102</font></th> <td bgcolor="#fdfebc" width="50%"><pre style="font-size: 8pt; line-height: \
140%; margin: 0; "> <span class="n">QString</span> <span class="n">value</span> <span \
class="o">=</span> <span class="n"><span class="hl">QFile</span></span><span class="o"><span \
class="hl">::</span></span><span class="n"><span class="hl">encodeName</span></span><span class="p"><span \
class="hl">(</span></span><span class="n">list</span><span class="p">.</span><span \
class="n">join</span><span class="p">(</span><span class="s">":"</span><span class="p">)<span \
class="hl">)</span>;</span></pre></td> <th bgcolor="#e9eaa8" style="border-left: 1px solid #C0C0C0; \
border-right: 1px solid #C0C0C0;" align="right"><font size="2">102</font></th> <td bgcolor="#fdfebc" \
width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> <span class="n">QString</span> \
<span class="n">value</span> <span class="o">=</span> <span class="n">list</span><span \
class="p">.</span><span class="n">join</span><span class="p">(</span><span \
class="s">":"</span><span class="p">);</span></pre></td> </tr>
</tbody>
</table>
<pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: \
-o-pre-wrap; word-wrap: break-word;">QFile::encodeName() seems equal to QString::toLocal8Bit(), \
::decodeName() to ::fromLocal8Bit()
I don't think one can just drop one of them and whether transcoding is required probably depends on \
what is done to the string interim.
If at all "KToolInvocation::klauncher()->setLaunchEnv()" would perform a second decode, so \
it probaly depends on what that does.
Was "locale charmap" determined by the reporter in the bug?
---
Secret world domination plan:
------------------------------
#1: classified
#2: classified
#3: force ASCII as global standard
#4: classified
#5: classified
#6: classified
#7: classified
#8: classified
#9: classified
#a: classified</pre>
</blockquote>
<p>On November 30th, 2013, 2:14 a.m. CET, <b>Yichao Yu</b> wrote:</p>
<blockquote style="margin-left: 1em; border-left: 2px solid #d0d0d0; padding-left: 10px;">
<pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: \
-o-pre-wrap; word-wrap: break-word;">encodeName/toLocal8Bit is used to encode a unicode string to a \
c-string/byte-array representation and decodeName/fromLocal8Bit does the reverse.
The proper decoding is already done in QFile::decodeName above and the QString already has the right \
unicode string in it.
Basically, QString is not a wrapper of arbitrary c-string/byte-array, rather a wrapper of a unicode \
string so whatever done to a QString before or after should assume it is a valid unicode string and is \
independent of what encoding (utf8 in the case of dbus) is needed afterward.
Encode to a byte array and cast it back can only cause wrong encoding in the second conversion and will \
not affect what is done in setLaunchEnv. </pre>
</blockquote>
<p>On November 30th, 2013, 2:20 a.m. CET, <b>Yichao Yu</b> wrote:</p>
<blockquote style="margin-left: 1em; border-left: 2px solid #d0d0d0; padding-left: 10px;">
<pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: \
-o-pre-wrap; word-wrap: break-word;">Or in another word QString has no encoding (well, by which I mean \
the internal encoding is trasparent to the user), only byte array and c-string has encoding. </pre>
</blockquote>
<p>On November 30th, 2013, 2:53 a.m. CET, <b>Thomas Lübking</b> wrote:</p>
<blockquote style="margin-left: 1em; border-left: 2px solid #d0d0d0; padding-left: 10px;">
<pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: \
-o-pre-wrap; word-wrap: break-word;">QString(QByteArray) according to the API doc actually differs \
between Qt4 & 5 (fromAscii -> fromUtf8) but an encoding should not happen nevertheless because:
282 void KLauncher::setLaunchEnv(const QString &name, const QString &value)
283 {
284 #ifndef USE_KPROCESS_FOR_KIOSLAVES
285 klauncher_header request_header;
286 QByteArray requestData;
287 requestData.append(name.toLocal8Bit()).append('\0').append(value.toLocal8Bit()).append('\0');
Also QString(QByteArray) is obvisouly problematic by itself for the apparent 4/5 \
"incompatibility".</pre> </blockquote>
<p>On November 30th, 2013, 3:13 a.m. CET, <b>Yichao Yu</b> wrote:</p>
<blockquote style="margin-left: 1em; border-left: 2px solid #d0d0d0; padding-left: 10px;">
<pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: \
-o-pre-wrap; word-wrap: break-word;">I guess you can also put it in this this way (setLaunchEnv have \
toLocal8Bit inside) although I still think the simplest way is to remember QString -- encode --> \
QByteArray, QByteArray -- decode --> QString and always to the necessary explicit conversion.
That's why I hate hate hate this constructor. (and I've already fixed 3-4 bugs in KDE due to this \
constructor.) It might actually be helpful to compile KDE with it commented out and replace everything \
with explicit conversion..... </pre>
</blockquote>
<p>On November 30th, 2013, 3:13 a.m. CET, <b>Yichao Yu</b> wrote:</p>
<blockquote style="margin-left: 1em; border-left: 2px solid #d0d0d0; padding-left: 10px;">
<pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: \
-o-pre-wrap; word-wrap: break-word;">I guess you can also put it in this this way (setLaunchEnv have \
toLocal8Bit inside) although I still think the simplest way is to remember QString -- encode --> \
QByteArray, QByteArray -- decode --> QString and always to the necessary explicit conversion.
That's why I hate hate hate this constructor. (and I've already fixed 3-4 bugs in KDE due to this \
constructor.) It might actually be helpful to compile KDE with it commented out and replace everything \
with explicit conversion..... </pre>
</blockquote>
<p>On November 30th, 2013, 3:13 a.m. CET, <b>Yichao Yu</b> wrote:</p>
<blockquote style="margin-left: 1em; border-left: 2px solid #d0d0d0; padding-left: 10px;">
<pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: \
-o-pre-wrap; word-wrap: break-word;">I guess you can also put it in this this way (setLaunchEnv have \
toLocal8Bit inside) although I still think the simplest way is to remember QString -- encode --> \
QByteArray, QByteArray -- decode --> QString and always to the necessary explicit conversion.
That's why I hate hate hate this constructor. (and I've already fixed 3-4 bugs in KDE due to this \
constructor.) It might actually be helpful to compile KDE with it commented out and replace everything \
with explicit conversion..... </pre>
</blockquote>
<p>On November 30th, 2013, 3:15 a.m. CET, <b>Yichao Yu</b> wrote:</p>
<blockquote style="margin-left: 1em; border-left: 2px solid #d0d0d0; padding-left: 10px;">
<pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: \
-o-pre-wrap; word-wrap: break-word;">ahh.... sth wrong with my network.... sorry for the duplicated \
post...</pre> </blockquote>
</blockquote>
<pre style="margin-left: 1em; white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; \
white-space: -o-pre-wrap; word-wrap: break-word;">I just had a look at the history of the specific line \
of code and tracked it back to "This commit was manufactured by cvs2svn" (238ffd07).
The original line was:
QCString value = QFile::encodeName(list.join(":"));
doing several porting conversions via at one step QByteArray to finally QString. Given that it used to be \
a QByteArray the ::encodeName seems reasonable, but since it's QString I think that it's save to \
drop it.</pre> <br />
<p>- Martin</p>
<br />
<p>On November 30th, 2013, 5:38 a.m. CET, Yichao Yu wrote:</p>
<table bgcolor="#fefadf" width="100%" cellspacing="0" cellpadding="8" style="background-image: \
url('http://git.reviewboard.kde.org/static/rb/images/review_request_box_top_bg.ab6f3b1072c9.png'); \
background-position: left top; background-repeat: repeat-x; border: 1px black solid;"> <tr>
<td>
<div>Review request for kde-workspace, David Faure, Martin Gräßlin, and Hugo Pereira Da Costa.</div>
<div>By Yichao Yu.</div>
<p style="color: grey;"><i>Updated Nov. 30, 2013, 5:38 a.m.</i></p>
<div style="margin-top: 1.5em;">
<b style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Bugs: </b>
<a href="http://bugs.kde.org/show_bug.cgi?id=327919">327919</a>
</div>
<div style="margin-top: 1.5em;">
<b style="color: #575012; font-size: 10pt;">Repository: </b>
kde-workspace
</div>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Description </h1>
<table width="100%" bgcolor="#ffffff" cellspacing="0" cellpadding="10" style="border: 1px solid \
#b8b5a0"> <tr>
<td>
<pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: \
-pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">list.join already returns a QString and \
there is no need to encode it and cast back to QString again....
P.S. for a patch that applies to both KDE4 and KF5(master for kde-workspace, frameworks for kdelibs?) How \
should I submit review request? Should I add both in branch or submit two review request? (But often the \
patch cannot apply directly due to context or file path changes).</pre> </td>
</tr>
</table>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Testing </h1>
<table width="100%" bgcolor="#ffffff" cellspacing="0" cellpadding="10" style="border: 1px solid #b8b5a0">
<tr>
<td>
<pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: \
-pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">Compiles. Fixes the problem here.
</pre>
</td>
</tr>
</table>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Diffs</b> </h1>
<ul style="margin-left: 3em; padding-left: 0;">
<li>kcontrol/krdb/krdb.cpp <span style="color: grey">(92d84e9)</span></li>
</ul>
<p><a href="http://git.reviewboard.kde.org/r/114219/diff/" style="margin-left: 3em;">View Diff</a></p>
</td>
</tr>
</table>
</div>
</body>
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