How to create a tunnel for sending a proxy request in Dart?

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To create a tunnel for sending a proxy request in Dart, you can use the dart:io library and HttpClient class to create a tunnel through which the proxy request can be sent.

Here is an example code to create a tunnel:

import 'dart:io';

Future<void> main() async {
  final client = HttpClient();
  // create a tunnel through the proxy server
  final conn = await client.open(
    'CONNECT myserver.com:443 HTTP/1.1\r\n'
    'Host: myserver.com:443\r\n'
    'Proxy-Authorization: Basic BASE64_ENCODED_CREDENTIALS\r\n'
    '\r\n',
    'myproxy.com',
    8080
  );  
  // Use the tunnel to send a request to server
  final request = await HttpClient().getUrl(Uri.parse('https://myserver.com/path'));
  final response = await (await conn).send(request);
  final body = await response.stream.bytesToString();
  print(body);
  // close the connection
  await (await conn).close();
}

In this example, we first create an HttpClient instance and then open a connection using the open method. The open method takes three arguments: the first argument is the CONNECT request to create the tunnel, the second argument is the proxy server domain name or IP address, and the third argument is the proxy server port number.

After the tunnel is established, we can use that connection to send a request to our target server using the HttpClient instance. Here we send a GET request to /path on the https://myserver.com. We then wait for the response and read its body.

Finally, we close the connection by calling the close method on the connection object.