optional #GCancellable object, %NULL to ignore
a location to place the contents of the file
a location to place the current entity tag for the file, or %NULL if the entity tag is not needed
Return: %TRUE if the @file's contents were successfully loaded. %FALSE if there were errors.
GException on failure.
Loads the content of the file into memory. The data is always zero-terminated, but this is not included in the resultant @length. The returned @content should be freed with g_free() when no longer needed.
If @cancellable is not %NULL, then the operation can be cancelled by triggering the cancellable object from another thread. If the operation was cancelled, the error %G_IO_ERROR_CANCELLED will be returned.