firefox/testing/web-platform/tests/fetch/h1-parsing/resources/README.md

blue-with-0x00-in-a-header.asis is a copy from ../../images/blue.png with the following prepended using Control Pictures to signify actual newlines and 0x00:

HTTP/1.1 200 AN IMAGE␍␊
Content-Type: image/png␍␊
Custom: ␀␍␊␍␊