File upload hook - how to integrate existing file manipulation code into Drupal

Question

I want to create a waveform image for every mp3 file I upload in a Drupal 7 website (as admin), and store it as a png for display in the frontend. I can use this script in order to do that.

I want to know what is the Drupal way of integrating that script, specifically:

• I guess that functionality will go into a module; where should I hook? file upload (there will be more than one file types to upload, and I would just want to work on the mp3)?
• how should I save the resulting waveform picture (where in the filesystem and how would I attach it as a field to my custom node type)?

As I'm new to Drupal (but experienced with PHP), I would appreciate a detailed response, but if you know of a module that already does that - I couldn't find it - that would be the shortest answer possible. :)

Thank you!

Answer 1

BetaRide gave you some good links and generic suggestions already, here's some code to help you get a quicker start:

function mymodule_node_presave($node) {
  //drupal_set_message('<pre>'.var_export($node, TRUE).'</pre>');
  if (!isset($node->field_pic['und'][0]) && isset($node->field_file['und'][0]['fid'])) {
    $result = db_query("SELECT filename, uri, filemime FROM {file_managed} WHERE fid = :fid",
    array(':fid' => $node->field_file['und'][0]['fid']));
    $record = $result->fetchObject(); 
    if ($record->filemime == 'audio/mpeg' && pathinfo($record->filename, PATHINFO_EXTENSION) == 'mp3') {
      // TODO - create the picture, save in the temporary files folder and return the filename.
      $filename = 'created_image.png';
      $image = file_get_contents('sites/default/files/tmp/'.$filename);
      // public://pics/ -> sites/default/files/pics
      $file = file_save_data($image, 'public://pics/'.$filename, FILE_EXISTS_RENAME);
      drupal_unlink('sites/default/files/tmp/'.$filename);
      $node->field_pic['und'][0] = (array) $file;
    }
  }
}

This script should work when you have created a content type with 'field_file' and 'field_pic' that both allow 1 entry. First one should accept at least mp3 files and the second png images your linked script will create. The function/hook gets called before saving a node. If there is no image present in the image field and a mp3 file is present in the other you should use the script to create the image and return it's filename. After that a copy of the file from 'sites/default/files/tmp/' gets created into 'sites/default/files/pics' (possible name conflicts are taken care of). Then the temporary file gets deleted and the image info attached to the node. As you might have guessed 'sites/default/files' and it's subfolders should be used to store public files on Drupal sites. You should also make sure 'field_pic' file directory (set up via the GUI) matches with the one used in the code.

Answer 2

1. Create a content type with a file field to upload the mp3 file.
2. Create a custom module and implement hook_node_presave. There you can do whatever you want with your node before it gets saved.
3. For the file handling have a look at File interface.