App Engine 1.8.8 has just been released, and the PHP runtime has some great updates:

• The Socket API is now available for billing-enabled Applications.
• PHP String has been added as a key type in the Admin Console Memcache viewer.
• Added CloudStorageTools::getPublicUrl() method for constructing URLs for Google Cloud Storage objects.
• Opening GCS objects in text mode is now supported.
  • https://code.google.com/p/googleappengine/issues/detail?id=10177
• A false error is now returned if stream_cast is called on a GCS stream.
  • https://code.google.com/p/googleappengine/issues/detail?id=10202