[RFC 3/3] input_pipe: handle noncanonical TTY

[Eric Wong]

lei could get a TTY in noncanonical mode for stdin, so rely on
VMIN+VTIME to get the desired non-blocking semantics we'd expect
from a pipe or socket.  This ought to prevent read(2) (Perl sysread)
from returning zero when we really want to hit EAGAIN.
---
 lib/PublicInbox/InputPipe.pm | 33 ++++++++++++++++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

diff --git a/lib/PublicInbox/InputPipe.pm b/lib/PublicInbox/InputPipe.pm
index 39aefab2..8358ddd6 100644
--- a/lib/PublicInbox/InputPipe.pm
+++ b/lib/PublicInbox/InputPipe.pm
@@ -6,6 +6,31 @@ package PublicInbox::InputPipe;
 use v5.12;
 use parent qw(PublicInbox::DS);
 use PublicInbox::Syscall qw(EPOLLIN);
+use POSIX ();
+use Carp qw(croak carp);
+
+# I'm not sure what I'm doing w.r.t terminals.
+# FIXME needs non-interactive tests
+sub unblock_tty ($) {
+       my ($self) = @_;
+       my $fd = fileno($self->{sock});
+       my $t = POSIX::Termios->new;
+       $t->getattr($fd) or croak("tcgetattr($fd): $!");
+       return if $t->getlflag & POSIX::ICANON; # line-oriented, good
+
+       # make noncanonical mode TTYs behave like a O_NONBLOCK pipe.
+       # O_NONBLOCK itself isn't well-defined, here, so rely on VMIN + VTIME
+       my ($vmin, $vtime) = ($t->getcc(POSIX::VMIN), $t->getcc(POSIX::VTIME));
+       return if $vmin == 1 && $vtime == 0;
+
+       $t->setcc(POSIX::VMIN, 1); # 1 byte minimum
+       $t->setcc(POSIX::VTIME, 0); # no timeout
+       $t->setattr($fd, POSIX::TCSANOW) or croak("tcsetattr($fd): $!");
+
+       $t->setcc(POSIX::VMIN, $vmin);
+       $t->setcc(POSIX::VTIME, $vtime);
+       $self->{restore_termios} = $t;
+}
 
 sub consume {
        my ($in, $cb, @args) = @_;
@@ -16,11 +41,17 @@ sub consume {
                $self->requeue;
        } elsif (-p $in || -s _) { # O_NONBLOCK for sockets and pipes
                $in->blocking(0);
-       } # TODO: tty
+       } elsif (-t $in) { # isatty(3) can't use `_' stat cache
+               unblock_tty($self);
+       }
 }
 
 sub close {
        my ($self) = @_;
+       if (my $t = delete($self->{restore_termios})) {
+               my $fd = fileno($self->{sock} // return);
+               $t->setattr($fd, POSIX::TCSANOW) or carp("tcsetattr($fd): $!")
+       }
        $self->{-need_rq} ? delete($self->{sock}) : $self->SUPER::close
 }