Make images submitted via a Google Form publicly viewable.

google-forms-public-images.js

/**
 * Make images submitted via a Google Form publicly viewable.
 *
 * Updated version at https://gist.github.com/bef1b29628be234978f6d286f4e719ba
 *
 * INSTRUCTIONS
 *
 * 1. Open the response spreadsheet.
 * 2. Open the script editor (Tools -> Script Editor), paste the content of this
 *    file inside the editor, and save (Ctrl+S or Cmd+S).
 * 3. Take note of the names of all the form questions/spreadsheet columns containing
 *    image URLs, and insert them into the IMAGE_COLUMNS variable, below.
 * 4. Click on the clock icon in the script editor and set the following trigger:
 *     Run: onFormSubmit
 *     Events: From spreadsheet - On form submit.
 * 5. After you save, you'll be asked to give permissions; do it.
 * 6. Submit a form response containing one or more uploaded images.
 *
 * If everything goes fine, the uploaded images will be publicly viewable. You can test
 * this by opening each image URL in the spreadsheet in an incognito window; if you see
 * it, it worked.
 *
 * TROUBLESHOOTING
 * If the code does not work or does not fire, please:
 * - 1) set the DEBUG variable below to true.
 * - 2) Submit a form response.
 * - 3) Open the script editor and open both the error log (View -> Stackdriver Error
 *      Reporting) and the basic log (View -> Log).
 *
 * Here's a list of common errors and their fixes:
 *
 *  - "You do not have permission to call getFileById" in the error log: This means that
 *    the script could not access the image because it was not authorized by Google Drive.
 *    To authorize the script, delete the trigger (Edit -> Current project's triggers)
 *    and add it back.
 */


/**
 * CHANGE HERE
 */

/* Names of the form fields containing image URLs */
var IMAGE_COLUMNS = [
  'Image'
];

/* Whether to print log messages using Logger.log() */
var DEBUG = false;


/**
 * DO NOT TOUCH FROM HERE ON
 */

/**
 * Process the image URL in a from submission.
 *
 * Attach to the "On form submit" trigger.
 */
function onFormSubmit( e ) {

  /* Debug */
  DEBUG && Logger.log( "Named Values");
  DEBUG && Logger.log( e.namedValues );
  DEBUG && Logger.log( "Range Values");
  DEBUG && Logger.log( e.range.getValues() );

  /* Function that will set permissions for each image */
  var callback = processImage;
  var callbackArgs = [
    DriveApp.Access.ANYONE_WITH_LINK,
    DriveApp.Permission.VIEW
  ];

  /* Process each image in turn */
  for (var i = 0; i < IMAGE_COLUMNS.length; i++) {
    var imageColumn = IMAGE_COLUMNS[i];

    /* Return if image has not been submitted or if the field is not present */
    if ( Object.keys( e.namedValues ).indexOf( imageColumn ) === -1 ) {
      Logger.log( "WARNING: Form does not have field named ' " + imageColumn + "', will skip" );
      continue;
    }
    else if ( ! e.namedValues[ imageColumn ][0] ) {
      Logger.log( "WARNING: Field ' " + imageColumn + "' is empty, will skip" );
      continue;
    }

    /* Process the image URL */
    processField( e.range, imageColumn, callback, callbackArgs );
  }

}


/**
 * Apply a function to a cell within a row.
 *
 * The cell is found by means of its column header; its content is overwritten
 * by the value returned by the callback function.
 *
 * GOOGLE FORM
 * If applied to a Google Form submission via the trigger 'onFormSubmit', then
 * set rowRange = e.range. Note however that this function only replaces what is
 * shown in the spreadsheet: the response stored in the form won't be changed.
 * 
 * @arg {rowRange} rowRange - Range containing the row containing the cell to be
 * modified. If the range contains multiple rows, only the first row will be considered.
 * @arg {string} header - Header of the column with the cell to process.
 * @arg {function} callback - Function that will be applied to the cell; its return value
 * will overwrite the cell's content. Its arguments are the original cell value (passed
 * automatically) and the values in callbackArgs.
 * @arg {array} callbackArgs - Arguments to the callback function, given as an array.
 * The old cell value will
 * @return {mixed} - The new value for the cell; return undefined if the header is not
 * found or if there's a mismatch between the sheet headers and the number of values in
 * the first row of the range, or if the callback is not a valid function.
 */
function processField( rowRange, cellHeader, callback, callbackArgs ) {

  /* Get sheet headers */
  var sheet = rowRange.getSheet();
  var sheetHeaders = sheet.getRange( 1, 1, 1, sheet.getLastColumn() ).getValues()[0];

  /* Find position in headers of the cell column */
  var cellColumnIndex = sheetHeaders.indexOf( cellHeader );

  /* Debug */
  DEBUG && Logger.log( "processField: Sheet has the following headers:" );
  DEBUG && Logger.log( "processField: " + sheetHeaders );
  DEBUG && Logger.log( "processField: Cell column '" + cellHeader + "' found at index " + cellColumnIndex );
  
  if ( cellColumnIndex === -1 ) {
    return undefined;
  }

  /* Get range values */
  var values = rowRange.getValues()[0];

  if ( values.length <= cellColumnIndex ) {
    Logger.log( "processField: Field probably has too few fields, skipping." );
    return undefined;
  }

  /* Get current value of cell */
  var cellValue = values[ cellColumnIndex ];
  
  /* Debug */
  DEBUG && Logger.log( "processField: Cell's current value: '" + cellValue + "'" );

  /* Check that the callback is a valid function */
  if ( typeof callback !== 'function' ) {
    Logger.log( 'processField: Callback is not a function' );
    return undefined;
  }

  /* Prepend the cell value to the callback arguments */
  var args = callbackArgs.slice();
  args.unshift( cellValue );

  /* Debug */
  DEBUG && Logger.log( "processField: Callback will be called with following arguments:" );
  DEBUG && Logger.log( "processField: " + args );

  /* Process the cell's content by applying the callback to the old
  cell value. The return value will be inserted in the cell */
  var newCellValue = callback.apply( null, args );
  
  /* Replace the cell's content in the spreadsheet */
  values[ cellColumnIndex ] = newCellValue;
  rowRange.setValues( [ values ] );

  /* Debug */
  DEBUG && Logger.log( "processField: Cell's new value: '" + newCellValue + "'" );

}


/**
 * Process a Google Drive image so that it can be embedded in a Google
 * Document.
 *
 * The functions does the following:
 *
 * - Returns a more share-friendly image URL.
 * - Assigns the image the given access & permission levels.
 * - Proportionally rescale the image to a maximum width (TODO)
 *
 * @arg {string} imageUrl - The image URL in Google Drive.
 * @arg {access} newAccess - The access level to be assigned to the image.
 * Default is DriveApp.Access.ANYONE_WITH_LINK.
 * @arg {permission} newPermissions - The permission level to be assigned to the image.
 * Default is DriveApp.Permission.VIEW.
 * @arg {int} maxPixelWidth - The maximum width for the image. If the image has a
 * width in pixels bigger than number, its width will be scaled down to this number.
 * The height will be scaled down proportionally. Nothing will be done unless a number
 * is given for this argument.
 * @return {string|bool} - The share-ready URL of the image in Google Drive;
 * false for failure.
 */
function processImage( imageUrl, newAccess, newPermissions, maxPixelWidth ) {

  newAccess = ( typeof newAccess !== 'undefined' ) ? newAccess : DriveApp.Access.ANYONE_WITH_LINK;
  newPermissions = ( typeof newPermissions !== 'undefined' ) ? newPermissions : DriveApp.Permission.VIEW;

  // ====================
  // = Change image URL =
  // ====================
  var newImageUrl = imageUrl.replace( 'open?', 'uc?export=view&' );

  /* Debug */
  DEBUG && Logger.log( "Image URL = " + imageUrl );
  DEBUG && Logger.log( "New Image URL = " + newImageUrl );


  // =====================
  // = Assig permissions =
  // =====================
  
  var fileId = getIdFromUrl( newImageUrl );
  
  if ( ! fileId ) {
    Logger.log( "Image is not a Google Drive file, or failed to get its Drive ID" );
    Logger.log( "Image URL: " + newImageUrl );
    return newImageUrl;
  }
  
  /* Debug */
  DEBUG && Logger.log( "Image ID in Google Drive = " + fileId );

  /* Get the Google Drive file */
  var imageDriveFile = DriveApp.getFileById( fileId );

  if ( ! imageDriveFile ) {
    Logger.log( "Could not get Drive file corresponding to ID " + fileId );
    return newImageUrl;
  }

  /* Debug */
  DEBUG && Logger.log( "Retrieved file from Google Drive" );
  DEBUG && Logger.log( "File currently has the following access:" );
  DEBUG && Logger.log( imageDriveFile.getSharingAccess() );
  DEBUG && Logger.log( "File currently has the following permissions:" );
  DEBUG && Logger.log( imageDriveFile.getSharingPermission() );

  /* Change image access & permissions to public view */
  imageDriveFile.setSharing( newAccess, newPermissions );

  /* Debug */
  DEBUG && Logger.log( "Updated file's access & permission in Google Drive" );
  DEBUG && Logger.log( "File now has the following access:" );
  DEBUG && Logger.log( imageDriveFile.getSharingAccess() );
  DEBUG && Logger.log( "File now has the following permissions:" );
  DEBUG && Logger.log( imageDriveFile.getSharingPermission() );

  return newImageUrl;

}


/**
 * Extract ID of Google Drive file from its URL.
 *
 * Works with these types of URLs:
 * - https://drive.google.com/file/d/1JFEQIVH1CsVjMsP4WBAoNY-gaUmDkjCo/view
 * - https://drive.google.com/uc?export=view&id=1IMh0vGytbKQb-mK2TTjgqw7jHKVl00Eq
 *
 * Adjust the regex to add different kinds of URLs.
 *
 * Returns null if the ID could not be parsed from the URL.
 */
function getIdFromUrl(url) {
  var output = null; // initialize output
  var re = /[\/&?](?:d\/|id\=)(.+)\/?/;
  var results = re.exec( url );
  if ( results.hasOwnProperty( '1' ) ) {
    output = results[1];
  }
  return output;
}