Connection closed before full header was received

[chengqing97]

Issue:

I am getting this error when sending requests to some URLs:

Unhandled exception:
HttpException: Connection closed before full header was received, uri = https://dictionary.cambridge.org/dictionary/english/hello

My environment:

Dart: Dart SDK version: 2.16.1 (stable) on "linux_x64"
OS: Debian 11 bullseye
Kernel: x86_64 Linux 5.10.0-11-amd64

Steps to reproduce:

1. Create a main.dart
2. Inside main.dart:

import 'dart:convert';
import 'dart:io';

void main(List<String> arguments) async {
  final url1 = Uri.parse("https://dictionary.cambridge.org/dictionary/english/hello");
  final url2 = Uri.parse("https://dict.youdao.com/w/hello");

  var client = HttpClient();
  try {
    HttpClientRequest request = await client.getUrl(url1);
    HttpClientResponse response = await request.close();
    final stringData = await response.transform(utf8.decoder).join();
    print(stringData);
  } finally {
    client.close();
  }
}

3. Run the code dart run main.dart

I can make request to url2 just fine. I'm only getting error when making request to url1

[ghost]

Probably a duplicate of flutter/flutter#41573.

[brianquinlan]

It looks like "dictionary.cambridge.org" is doing some sort of user agent sniffing.

If I change the user agent with:

client.userAgent = 'curl/7.77.0';

Then the server produces a valid HTTP response.

[Rishyash]

For those who are getting these crash as fatal crash.
https://medium.com/@rishyash8/flutter-firebase-crash-report-because-of-connection-closed-before-full-header-was-received-7ace6e84bc5d