connect method
Connects to server and returns core information about the task, for example, file size.
Implementation
@override
Future<StateHead> connect(Uri url) async {
logger?.info('worker: Sending head request...');
var headResp = await _conn.head(url);
_logResponse(headResp);
// Fetch content size.
var contentLength = headResp.headers['content-length'];
var size = int.tryParse(contentLength ?? '') ?? -1;
return StateHead(url, url, size);
}