ReceiveString Returns Only the Immediately Available Data

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Demonstrates that Socket.ReceiveString returns only the text immediately available and not the entire response. The example connects to chilkatsoft.com over TLS and requests big_helloWorld.txt, a large text file of roughly 74,000 lines. A single ReceiveString call returns just the first portion of the response, and the example reports how many characters were received compared with the total size given by the response Content-Length header.

import 'package:chilkat/chilkat.dart';

void main() {
  final socket = CkSocket();

  // Connect to chilkatsoft.com over TLS.
  final bTls = true;
  final maxWaitMs = 5000;
  try {
    socket.connect('chilkatsoft.com', 443, bTls, maxWaitMs);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  socket.stringCharset = 'utf-8';

  // Send an HTTP GET request for big_helloWorld.txt, a large text file of roughly 74,000 lines of
  // "Hello World!".  This uses a minimal HTTP request only to exercise ReceiveString against a public
  // server -- for real HTTP work, use the Chilkat Http, Rest, or HttpCurl classes instead.
  final httpReq = 'GET /big_helloWorld.txt HTTP/1.1\r\nHost: chilkatsoft.com\r\nConnection: close\r\n\r\n';
  try {
    socket.sendString(httpReq);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Call ReceiveString a single time.  It returns only the text that is immediately available --
  // typically just the first network packet -- and does NOT wait for the entire response to arrive.
  final String responseText;
  try {
    responseText = socket.receiveString();
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Load the received text into a StringBuilder so its length can be measured and the Content-Length
  // header extracted.  The Content-Length header gives the total size, in bytes, of the response body.
  final sb = CkStringBuilder();
  sb.append(responseText);
  final String contentLength;
  try {
    contentLength = sb.getBetween('Content-Length: ', '\r\n');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Compare what this single ReceiveString returned against the full size of the expected response.
  // The received amount is only a small fraction of the total.
  print('Characters received so far (headers + partial body): ${sb.length}');
  print('Expected response body size (Content-Length): $contentLength bytes');

  // A single ReceiveString call returns whatever is currently available, so it cannot indicate whether
  // the full response has arrived.  This makes it difficult to know when a response is complete: the
  // application must either know how many bytes to expect (for example from a Content-Length header or
  // an application-defined length prefix) and keep receiving until that many bytes are collected, or
  // keep receiving until the peer closes the connection.
}