Give the parser a following request, and it will create a bad environment header:
GET / HTTP/1.0
Maybe it should return -1 with a bad character in HTTP field names.
Test is at https://gist.github.com/4021280
update picohttpparser to 8edde15 fixing issue #5
Thank you for reporting the issue.
examine the first char of header name (fixes kazuho/p5-http-parser-xs#5)