Access Files on MATLAB Web App Server

MATLAB^® Web App Server™ allows you to deploy and share MATLAB web apps through a web browser interface. When working with these web apps, users often need to access, manipulate, and exchange files between the server and client machines. You can package files along with a web app, read and write to files on the server, and download files to a local client.

For information on setting up a MATLAB Web App Server instance, see Set Up MATLAB Web App Server.

Package Files in Web App

Files included in the web app archive at compile time are embedded in the CTF and added to the path when the web app runs. Files are located at the deployable archive root ctfroot in a cache folder on the server. These files should be treated as read-only.

To specify paths to packaged files in your web app code, locate the file using the which function or specify the file location relative to ctfroot. Use isdeployed to toggle between local and deployed paths.

For more information on including files at compile time, see Include and Access Files in Packaged Applications (MATLAB Compiler).

Include MEX Files, DLLs, or Shared Libraries

When you compile MATLAB functions containing MEX files, ensure that the dependency analysis process can find them. In particular, note that:

Since the dependency analysis function cannot examine MEX files, DLLs, or shared libraries to determine their dependencies, explicitly include all executable files these files require.
If you have any doubts that a MATLAB function called by a MEX file, DLL, or shared library can be found during dependency analysis, then manually include that function.
Not all functions are compatible with the compiler. Check the file mccExcludedFiles.log after your build completes. This file lists all functions called from your application that you cannot deploy.

Write to File During Web App Session

During a running web app session, files read from or written to the current working directory write to the session folder, which is a local folder on the server that is created for each running session of a web app and given a unique ID for each session. The session folder is automatically added to the path for a running app session and acts as the current working directory. Folders are not shared between sessions, files in a session folder are not available in other app sessions, and each folder is automatically deleted when the session ends. You can use the session folder in workflows involving uigetfile and uiputfile to pass data between the server and client machines.

Server File Storage Locations

You can read/write to a specific file location on the server by using a hardcoded path in your MATLAB code. The path must point to a location that exists in the server storage, and paths must be specific to the file system on the server machine. Changes made to files in static locations on the server are shared across all app sessions.

In order for your web apps to interact with local files or directories that are not along the app search path (i.e. outside of the app/session caches), the worker account that runs the apps service must have the necessary permissions to read and write to these locations. By default, worker accounts do not have read/write permissions to most locations on the server machine. You must explicitly grant the worker account read/write permissions to these files or folders on the server machine using a command-line tool such as chmod or by editing permissions in Windows^® Explorer. For cloud deployments, you must remotely connect to the server instance to set file permissions. For more information on the service accounts, see Set Up MATLAB Web App Server.

Shared or Network Locations

You can read and write to a database or network location from a web app. The database or network location must be accessible from MATLAB Web App Server. Changes made to shared locations persist across all app sessions. The MATLAB Web App Server secrets management capabilities can be useful in ensuring security with this type of workflow. For details, see Handle Sensitive Information in Deployed Applications.

The worker account must have read and write access to the shared location. For network locations, this often requires that the worker uses a network or domain account, as you typically cannot grant local accounts access to non-local file locations.

Note

Some additional setup steps, toolboxes, or drivers may be necessary to deploy web apps that access databases. For example, to deploy a web app that uses the MySQL native interface, you must first install the MySQL/C++ Connector file on the server machine, as shown in Deploy MySQL Native Interface Database Application with MATLAB Compiler (Database Toolbox).

Download Files From Web App

To save files to a client machine from a web app, use uiputfile to get the path to the download location. You can use this path as the destination in write functions such as save and exportgraphics to download files to the client machine.

For example, save the graph displayed on the app component app.UIAxes as a PNG file.

% Get the path to the download location 
[f, p] = uiputfile('*.png');
% Save the plot to the specified path
exportgraphics(app.UIAxes,fullfile(p,f));

Files downloaded from a web app are always placed in the download location specified by the client browser. The user can specify a file name in the uiputfile dialogue box, but the destination folder can only be changed from their browser settings. While uiputfile and uigetfile are supported for passing files to/from web apps, the uigetdir function is not supported for use with web apps. For more information, see Web App Limitations and Unsupported Functionality.