Subject: bug#36350: [2.2.5] ‘read-headers’ blocks, thereby breaking web servers

From: Ludovic Courtès <[email-masked]>
Date: Mon, 24 Jun 2019 12:32:18 +0200

Hello,

In Guile 2.2.5, if you run:

  ./meta/guile examples/web/hello.scm &
  wget -O - http://localhost:8080

You’ll notice that ‘wget’ hangs (never receives a response) because the
server is actually stuck in a read(2) call that will never complete, in
‘read-headers’.

Reverting 73cde5ed7218a090ecee888870908af5445796f0 solves the problem.

AIUI, before that commit, ‘read-header-line’ would read exactly one
line.  After this change, it calls ‘lookahead-char’, which can block,
and that’s exactly what’s happening here.

I don’t know how HTTP continuation lines work, so I’m not sure what a
correct fix would look like.  Mark, WDYT?

I also noticed that there are no unit tests for (web server), which we
should probably address while we’re at it.  :-)

Thanks,
Ludo’.