Qt FTP Solution

Kats

Hey!

I'm a new user to the Qt platform and only vaguely understand the power it provides, but I'm using it for a project in-house that I really just need a simple solution/tutorial/walkthrough of how to accomplish.

As I understand and have read other articles, Qt 5 removed built-in FTP functionality. Another post mentioned something about QNetwork handling this, but I'm entirely unclear how this is supposed to work? What classes do I use? How do I implement those classes? What are the functions I should be looking up? Are there any decently commented tutorials that show me how a normal Qt user would set this up? (The code examples on the site are not well documented at all. Just throwing raw, nearly-uncommented code at you and expecting you to just intrinsically understand what's going on.)

As I said before, I've never used the Qt library before, but I can't imagine that it's really so complicated that I can't just include QNetwork and create a class to handle everything with a few lines of code.

? Offline

Hi, welcome to the forum. The simple solution is to use https://github.com/qt/qtftp.

TioRoy

You can check the docs too:

http://doc.qt.io/qt-5/qtnetwork-programming.html

Or search some examples like this:

QString filename="Data.txt";
QFile file( filename );
file.open(QIODevice::ReadWrite);
file.write("HELLO") ;

QUrl urlup("ftp://127.0.0.1/file.txt");
urlup.setPassword("123");
urlup.setUserName("user");
urlup.setPort(21);
QNetworkAccessManager *nam = new QNetworkAccessManager;
QNetworkRequest requp(urlup);
nam->put(requp,&file);
file.close();

Kats

@TioRoy Wow. That is probably the simplest and cleanest looking example that I've seen for something like this in a long time. Thank you so much. I hate for it to seem like I'm just asking other people to do the work for me, but I really have no clue how this library works and it's absolutely massive. If I weren't working on an actual project for my workplace, I'd be more inclined to really sit down and learn it more, but I more or less just really need something working with the time crunch I've been on lately.

I'll try it out and let you know if I have any more questions.

Kats

I'm actually running into a really weird issue. QNetworkAccessManager has no ability to use a mkdir command of any kind on the FTP server according this this post?

I have to hunt for, download, figure out how to install and link to a third-party addon library for QFtp compatibility in Qt5 to utilize a function that was readily available in the previous version? Did the Qt developers really make the worst mistake of any library and blatantly remove functionality from future versions with no replacement or is this post just misleading and there actually is a mkdir or similar command available to QNetworkAccessManager or any other Qt5 standard class?

VRonin

@Kats said in Qt FTP Solution:

Did the Qt developers really [...] remove functionality from future versions with no replacement

Yes and this is not the only instance. The point is that a migration in technology forced the change. I also do not advise to go back to QtFtp module as it's unsupported.

In reality, while we got used (and is convenient) to have everything we need packed from Qt, it's quite natural to have libraries that specifically focus on one task rather than a catch all as the Qt framework is.

For networking* my advice is to set Qt aside and use a well established, actively maintained library that focus on the task you want to achieve. My suggestion here is libcurl as its popularity is unmatched in my opinion

P.S.
The example posted above is leaking memory like a bandit

*over FTP, FTPS, Gopher, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, POP3, POP3S, RTMP, RTSP, SCP, SFTP, SMB, SMTP, SMTPS, Telnet and TFTP

mrjj

Hi
If you go libcurl route, maybe this will help
~~https://github.com/grynko/curlite~~

Please see next post.

VRonin

@mrjj https://github.com/jpbarrette/curlpp is more mature but I still didn't manage to get a reliable and robust build on Windows (MSVC2013), great on other platforms though

Kats

Well, I managed to get the QFtp working regardless. I have no ambition not to use it simply due to the time constraints on my project. I'm 100% sure there are better, more robust solutions out there, but I simply don't have the time to hunt and search through all of them. I'm already using the Qt Library, it's just easier to keep with the theme since QFtp objects are so easy to work with and they have the level of control that I need.

Before Qt, I'd messed with FtpLib, Lib Ftp and LibCurl and couldn't get any of them to compile properly. It became 2 or 3 days of an absolute nightmare with zero results, so I just went with a trusted option that actually works: Qt.

Side Note: Thank you guys so much. This community is so much more pleasant to work with than StackOverflow. You're actually informative!

VRonin

@Kats said in Qt FTP Solution:

Before Qt, I'd messed with [..] LibCurl and couldn't get any of them to compile properly

example commands to build and install libcurl on Windows MSVC 2013 32bit
assuming you have openssl in C:\openssl and zlib in C:\zlibBuild this will place the result in C:\libcurl

pushd C:\
CALL "C:/Program Files (x86)/Microsoft Visual Studio 12.0/VC/vcvarsall.bat"
popd
echo on
mkdir deps
xcopy C:\openssl\* deps\ /S /Y
xcopy C:\zlibBuild\* deps\ /S /Y
cd winbuild
nmake /f Makefile.vc mode=dll WITH_DEVEL=../deps WITH_SSL=dll WITH_ZLIB=dll VC=12 DEBUG=yes 
nmake /f Makefile.vc mode=dll WITH_DEVEL=../deps WITH_SSL=dll WITH_ZLIB=dll VC=12 DEBUG=no
cd ..\
if not exist "C:\libcurl" mkdir "C:\libcurl"
if not exist "C:\libcurl\include" mkdir "C:\libcurl\include"
xcopy include\* C:\libcurl\include /S /Y
xcopy builds\libcurl-vc12-x86-debug-dll-ssl-dll-zlib-dll-ipv6-sspi\* C:\libcurl\ /S /Y
xcopy builds\libcurl-vc12-x86-release-dll-ssl-dll-zlib-dll-ipv6-sspi\* C:\libcurl\ /S /Y

Kats

Okay, I'm running into an extremely large problem, now.

I had QFtp working where it would connect to the server perfectly fine, but when I come back into the office today and pull up the build, it DOES NOT CONNECT. When I use it, it doesn't even pretend like it's trying to connect.

I've been using a threaded loop to monitor QFtp's state and it always stays at 3. I have a slot setup to catch any changes, but it never does. The Ftp server also never sees the attempted connection either.

I have no idea what's going on because apparently this is a problem that nobody in the history of Qt has ever had before.

mrjj

@Kats
Hi
If you restart whole pc, will it then connect again?
Also make sure firewall or scanner is not blocking it.

Kats

I can connect to the server through every other FTP service on my computer (all browsers and FileZilla connect instantly).

QFtp is the only service that does not connect. It's exhibiting the exact same behavior as if I'm attempting to connect to the wrong address, but this is simply not possible because the address I'm connecting to (192.168.1.26) is available to all local devices. I'm using the exact same address and credentials as on everything else but is acting like the ftp server doesn't exist.

VRonin

My money is on firewall blocking it

Kats

It was not a firewall. It's because QFtp objects apparently can't be instantiated from inside of a thread. They can only be created inside the main thread of the program, regardless of their scope. Fixing that solved my issue and I've since completed what I was working on.

Kats

Hey, again, I can't thank you guys enough for you input on helping me troubleshoot this project, but it's helped both show me a newfound appreciation (and possibly future dependency) for Qt as well as streamline my current production environment, which is really helpful!

So thanks so much, even if my frustration peaked through every now and again.