[PATCH] http: yield body->getline running time

[Eric Wong <e@80x24.org>]

We cannot let a client monopolize the single-threaded server
even if it can drain the socket buffer faster than we can
emit data.

While we're at it, acknowledge the this behavior (which happens
naturally) in httpd/async.

The same idea is present in NNTP for the long_response code.

This is the HTTP followup to:
commit 0d0fde0bff97 ("nntp: introduce long response API for streaming")
commit 79d8bfedcdd2 ("nntp: avoid signals for long responses")
---
 lib/PublicInbox/HTTP.pm        | 5 ++++-
 lib/PublicInbox/HTTPD/Async.pm | 4 +++-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/lib/PublicInbox/HTTP.pm b/lib/PublicInbox/HTTP.pm
index fcbd758..6df1c3f 100644
--- a/lib/PublicInbox/HTTP.pm
+++ b/lib/PublicInbox/HTTP.pm
@@ -265,10 +265,13 @@ sub getline_response {
 	my $pull = $self->{pull} = sub {
 		local $/ = \8192;
 		my $forward = $self->{forward};
+		# limit our own running time for fairness with other
+		# clients and to avoid buffering too much:
+		my $n = 100;
 		while ($forward && defined(my $buf = $forward->getline)) {
 			$write->($buf);
 			last if $self->{closed};
-			if ($self->{write_buf_size}) {
+			if ((--$n) <= 0 || $self->{write_buf_size}) {
 				$self->write($self->{pull});
 				return;
 			}
diff --git a/lib/PublicInbox/HTTPD/Async.pm b/lib/PublicInbox/HTTPD/Async.pm
index add07ce..fadf2d3 100644
--- a/lib/PublicInbox/HTTPD/Async.pm
+++ b/lib/PublicInbox/HTTPD/Async.pm
@@ -45,7 +45,9 @@ sub async_pass {
 				$self->watch_read(0);
 				$io->write($restart_read); # D::S::write
 			}
-			return; # stay in watch_read
+			# stay in watch_read, but let other clients
+			# get some work done, too.
+			return;
 		} elsif (!defined $r) {
 			return if $!{EAGAIN} || $!{EINTR};
 		}