public_html for local file exchange

I was thinking of finding a way to easily exchange files on my android mobile phone to my computer. My computer is already set up with a full LAMP stack and I had setup a public_html folder for testing of local files. This simply needed extending to offer a php file upload script, and a php file listing script (for selecting a file to download). However, things are never that simple....

Create the public_html configuration an allow php to run

Setup public_html
1. This provides a user with the ability to access files placed in a ~USER directory through a web browser. In the following, replace USER with your user name.
2. Open up a terminal and do the following:
  1. ~$ mkdir -p ~/public_html
  2. ~$ sudo a2enmod userdir
  3. ~$ chmod -R 755 ~/public_html
  4. ~$ sudo systemctl restart apache2
3. If you now place an html file (e.g. index.html) in the public_html folder you can view it in your web browser with the following url:
  1. localhost/~USER/index.html
Allow php to run in your public_html folder by editing your php.conf file ( I am running on php 7.4 therefore php7.4.conf)
1. ~$ sudo nano /etc/apache2/mods-enabled/php7.4.conf
2. Follow the instructions and comment everything between the IfModule tags so that it looks like this:
  # Running PHP scripts in user directories is disabled by default
  #
  # To re-enable PHP in user directories comment the following lines
  # (from <IfModule ...> to </IfModule>.) Do NOT set it to On as it
  # prevents .htaccess files from disabling it.
  #<IfModule mod_userdir.c>
  # <Directory /home/*/public_html>
  # php_admin_flag engine Off
  # </Directory>
  #</IfModule>
3. Then save the file.
4. Restart apache2 again to set the configuration
  1. ~$ sudo systemctl restart apache2
5. php will now work in your ~/public_html directory

Set up the php files and directories

cd into ~public_html and create two directories, one to receive uploaded files, and one to provide files for download
1. ~$ cd ~/public_html
2. ~$ mkdir -p phup
3. ~$ mkdir -p phdn
Create the upload.php file to be able to send files from your device to your computer:
1. ~$ nano upload.php
2. Add the following:
  <?php
  // Simple PHP script to save a file.
  $dir = "phup/";
  $fileName = $_REQUEST['fname'];
  $data = file_get_contents('php://input');
  $store = file_put_contents($dir.$fileName, $data);
  if ($store !== false ) {
  echo "File $fileName saved to server, $store bytes\n";
  } else {
  echo "Error: file $fileName not saved\n";
  }
  ?>
3. Save the file.
4. You would use a url something like this to upload a file
  1. 192.168.1.78/~USER/upload.php?fname=myfile.txt and POST the file
  2. where the IP address is the local IP address of your computer
Create the get file list php:
1. ~$ nano getdirs.php
2. Add the following:
  <?php
  // Simple PHP script to list directories.
  $a = json_encode(array_slice(scandir("phup/"),2));
  $b = json_encode(array_slice(scandir("phdn/"),2));
  echo "[".$a.",".$b."]";
  ?>
3. Here you get a list of the files in both directories and return a stringified JSON list
4. Save the file
5. You would use a url something like this to call the getdirs.php script:
  1. 192.168.1.78/~USER/getdirs.php

Create the App

I built my app using App Inventor and set it up to run on Android 11 devices

I won't go into detail here, because the app I wrote is quite complicated, due to the need to fetch files from all sorts of different directories on the device. Suffice to say, I used three web components, one to upload, one to fetch the directory listings, and one to download files. Upload and Download procedures were for one file at a time.

Currently it works, but I am waiting to see what limitations are applied to file location access when App Inventor targets API 30 ....