Upload/Download a file in a Matlab Web App

Hi everyone,

I have built a GUI with App Designer and complied it to a ctf file. One feature of the GUI is to select, read txt and create a txt file. Here an error occurs.

First clicking the right button, the web app opens a nice window where you can either drop the file or select it. The file is locally on the user's PC.

But after selecting the file, it shows the following error message:

Error occurred during upload/download for: example.txt

No permissions

Error using matlab.ui.control.internal.model.mixin.MultilineTextComponent/set.Text (line 49)

The Matlab Web App Server runs on linux machine and I gave all users write/read permissions to the folder (/local/MathWorks/webapps/R2020a/) containing the app.

But somehow that didn't change anything.

What do I have to do so that the App has the permission to upload/download files?

Thanks in advance

Christian

[J. Alex Lee]

are you first creating a file locally on the web app server before you attempt to serve it to the web client?

if so, are you using absolute paths to specify? if relative path, the web app might not be running where you think it is.

[Christian Idzik]

No I didn't use a local file.

I am using [filen,pathn] = uigetfile('*.txt', 'Please select your txt file');

The aim is that the user of the web app can upload a file which then is checked and used for some calculations.

The questions is if the Web App Server has no permission to download it from the user's Pc or the Web App Server is not allowed to write/read files in a specific folder.

[J. Alex Lee]

Ok so you're confirming that you get error upon only reading the remote file, not on creating it.

I think uigetfile does have to copy the file into some local folder, but I would have thought whatever location that is would r/w-able by default (e.g., the web app server session folder)...wish the error message gives you what folder it was attempting to use that generated the permissions error!

[Christian Idzik]

Yes, I would have thought so too. Unfortunately, the specific folder is not in the error message.

Anyway, thanks!

[J. Alex Lee]

yea, sorry i was no help...i've had some luck in the past trying to diagnose web server working path by outputting various paths when i encountered local write permission issues...but never encountered a problem with the result of uigetfile() itself (on a windows web server though).

My main learning was that the runtime directory is not the directory where the ctf file resides (whereas I believe for stand-alone executables, the working directory is wherever the .exe lives), and so trying to work with relative paths with deployed code is generally confusing.

is it possible the web app is using a system temporary directory like /tmp, that for some reason you have set to r-- or something?

[Christian Idzik]

no problem. ;)

The Matlab Web App Server runs on a linux server(opensuse)

that is a good idea, the question is where the system temorary directory is, I will do some try and error.