"InvalidResponse: invalid header" error on some websites

[Shnatsel]

On some websites, e.g. http://opentrainer.ru, attohttpc fails with the following error:

InvalidResponse: invalid header

Firefox and curl work fine.

32 websites out of the top million from Feb 3 Tranco list are affected.

Tested using this code. Test tool output from all affected websites: atto-invalid-header.tar.gz

[adamreichold]

The linked site contains a multi-line continuation of a header value

Content-Security-Policy: script-src 'self' 'unsafe-inline' 'unsafe-eval' 
      https://staticxx.facebook.com 
      https://connect.facebook.net/ 
      https://tagmanager.google.com/ 
      https://www.googletagmanager.com/ 
      https://www.google-analytics.com/ 
      https://vk.com/ 
      https://mc.yandex.ru/ 
      https://top-fwz1.mail.ru/ 
      https://static.criteo.net/ 
      https://yastatic.net/s3/metrika/
      https://sslwidget.criteo.com/
      https://apis.google.com/
      https://cdn.ampproject.org/v0.js
      https://cdn.ampproject.org/v0/amp-sidebar-0.1.js
      https://cdn.ampproject.org/v0/amp-form-0.1.js
      https://cdn.ampproject.org/v0/amp-accordion-0.1.js;
    frame-src 'self' 'unsafe-eval' 'unsafe-inline'
      https://www.opentrainer.ru
      https://mc.webvisor.com 
      https://mc.webvisor.org 
      http://webvisor.com
      https://mc.yandex.ru 
      https://www.opentrainer.ru/trainer-api/school/singlegame/ 
      http://www.adobe.com/go/getflashplayer 
      https://www.facebook.com/tr/ 
      https://staticxx.facebook.com/connect/xd_arbiter/r/
      https://www.youtube.com/embed/ 
      https://i.ytimg.com/vi/
      https://vk.com/widget_community.php
      https://www.facebook.com/v2.6/plugins/
      https://www.youtube.com/subscribe_embed
      https://accounts.google.com/o/oauth2/postmessageRelay
      https://9215081.fls.doubleclick.net/;
    frame-ancestors 'self' http://webvisor.com;
    style-src 'self' 'unsafe-inline' 
      https://tagmanager.google.com/
      https://fonts.googleapis.com/;
    img-src 'self' 'unsafe-inline' 'unsafe-eval'
      https://s3.open-broker.ru/
      https://opentrainer.ru/images/tinymce/
      https://ssl.gstatic.com/
      https://vk.com/
      https://www.google-analytics.com/
      https://pixel.open-broker.ru/ 
      https://stats.g.doubleclick.net/
      https://www.google.com/ads/
      https://www.google.ru/ads/
      https://www.facebook.com/tr/
      https://mc.yandex.ru/clmap/
      https://www.googletagmanager.com/
      https://i.ytimg.com/vi/
      https://mc.yandex.ru/metrika/
Referrer-Policy: no-referrer-when-downgrade

While Firefox and cURL still parse line-folded headers like these, the HTTP specification seems to have deprecated them stating that new implementation should not produce them. Crates like httparse seem to have decided to not support them at all due to this, c.f. seanmonstar/httparse#68

#97 contains a quick fix, but again I am not convinced that we should bloat attohttpc to support obsolete functionality.