Incompatibility with CKEditor causes infinite recursion

I'm not certain what changed between 7.x-1.6 and 7.x-1.8 that caused this error, as the older plugin worked fine. This turned into a wild-goose chase of a sort, till I realized that the fault (maybe?) lies with the CKEditor plugin. The issue is:

    echo file_create_url($content['field_file']);

Results in an out of memory error coming from token.tokens.inc:895. So I put in "breakpoint" to perform a debug backtrace before the offending block.

  // Break on >75MB memory usage
  if (memory_get_usage(true) > 75 * 1048576) {
    ob_end_clean();
    echo '<pre>&#039;;&#10;    debug_print_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS);&#10;    echo &#039;</pre>';
    die;
  }

And you can pretty clearly find the infinite recursion with that output. I sorted this so that order of execution goes from top to bottom, rather than the default debug_print_backtrace() output.

file_create_url() called at [sites/all/modules/ckeditor/ckeditor.module:605]
DrupalStorageStreamWrapper->getExternalUrl() called at [includes/all.inc:404]
Storage->serveURL() called at [sites/all/modules/storage_api/core_bridge/storage_core_bridge.module:701]
Storage->access() called at [sites/all/modules/storage_api/storage.inc:383]
module_invoke() called at [sites/all/modules/storage_api/storage.inc:142]
call_user_func_array() called at [includes/all.inc:866]
storage_core_bridge_storage_access()
file_download_access() called at [sites/all/modules/storage_api/core_bridge/storage_core_bridge.module:437]
file_download_headers() called at [includes/all.inc:2070]
ckeditor_file_download() called at [includes/all.inc:2035]
file_create_url() called at [sites/all/modules/ckeditor/ckeditor.module:605]

The problem is, when checking if the URI is accessible storage_core_bridge_storage_access() invokes file_download_access(), which goes to modules implementing a hook. CKEditor then picks it up and calls file_create_url() once more—and bingo, infinite recursion!

My fix, temporarily, is to patch the ckeditor_file_download() hook to only download public/private/http/https URLs.

function ckeditor_file_download($uri) {
  if (in_array(parse_url($uri, PHP_URL_SCHEME), array('public', 'private', 'http', 'https'))
      && ($path = file_create_url($uri)))
  {

However, I'm not 100% certain: is the fault CKEditor's, or Storage? Since I've never had this issue, on multiple sites, till I upgraded the Storage API I'm thinking its a potential issue with Storage. Especially since other modules could make the same mistake and call file_create_url() from within hook_file_download().

At the least, I figured that posting this would probably help someone else.