function onRead( error, file ) {
			if ( error ) {
				debug( 'Encountered an error when attempting to read file: %s. Error: %s', files[ idx ], error.message );
				return done( error );
			}
			file = insert( file, h );
			writeFile( fpath, file, FOPTS, onWrite );
		}
Callback invoked upon reading a file.

@private
@param {(Error|null)} error - error object
@param {string} file - file contents
@returns {void}