Fix AnyEvent socket EOF and interpreter callback recursion

[fglock]

Summary

Restore AnyEvent::HTTPD 0.93 compatibility by fixing two independently reproducible PerlOnJava runtime defects:

1. The JVM backend does not deliver socket EOF promptly after the HTTP server disconnects.
2. The interpreter backend aborts with StackOverflowError while executing AnyEvent condition-variable callbacks.

The distribution is pure Perl. These should be reusable AnyEvent/socket/runtime fixes rather than CPAN source patches.

The archived CPAN random-tester run is 20260825-135237-11904, target AnyEvent::HTTPD. Its report says Unknown test outcome, but focused reproduction attributes that incomplete result to the defects below.

System-Perl baseline

The exact prerequisite versions were built in an isolated library using system Perl so that AnyEvent's generated constants.pl came from the same interpreter running the tests:

• AnyEvent 7.17
• AnyEvent::HTTP 2.25
• Object::Event 1.23
• AnyEvent::HTTPD 0.93

With ordinary loopback socket access, the unchanged upstream suite passes:

All tests successful.
Files=13, Tests=64
Result: PASS

The suite completes in approximately two seconds.

JVM backend: delayed/missing EOF

Focused test:

timeout 45 ./jperl t/01_basic_request.t

Observed:

1..4
test_connect timed out at .../AnyEvent/HTTPD/Util.pm line 70.
ok 1 - the path of the request URL was ok
ok 2 - the path of the second request URL was ok
ok 3 - Correct method used
ok 4 - the response text was ok

The response bytes arrive, but the client does not receive EOF. The test only completes after its internal 15-second AnyEvent::Handle timeout returns the accumulated response.

For an HTTP/1.0 request without keep-alive, upstream closes the connection promptly. AnyEvent::HTTPD::HTTPConnection::do_disconnect performs the following sequence:

shutdown $self->{hdl}->{fh}, 1;
$self->{hdl}->on_read(sub {});
$self->{hdl}->on_eof(undef);
my $timer;
$timer = AE::timer 2, 0, sub {
 undef $timer;
 delete $self->{hdl};
};

Likely investigation areas are socket shutdown, EOF propagation through AnyEvent::Handle, destruction/close of the retained filehandle, and timer-driven handle release. A focused project-owned test should determine which layer owns the defect.

Interpreter backend: callback recursion/stack overflow

Focused test:

timeout 45 ./jperl --interpreter t/01_basic_request.t

Observed:

1..4
# No tests run!
Interpreter error in AnyEvent.pm line 2061: null
StackOverflowError

AnyEvent 7.17 line 2061 is the condition-variable end callback invocation:

sub end {
 return if --$_[0]{_ae_counter};
 &{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
}

The JVM stack repeatedly cycles through interpreted callback application and bytecode execution. Reduce this to a small callback/condvar reproducer and fix interpreter callback dispatch or recursion independently of the socket EOF problem.

Context and impact

Core AnyEvent is currently installed under a distropref that skips its broad upstream suite because it includes unsupported fork and optional event-loop surfaces. That policy does not explain this failure: AnyEvent::HTTPD is a downstream, non-forking loopback acceptance gate, and its complete suite passes under system Perl.

The CPAN reports contain many AnyEvent-family modules, including numerous passing downstream distributions. Correct socket teardown and interpreter callback execution therefore have broader value than this one HTTP server.

Acceptance criteria

• Add a permanent, standard-Perl-validated regression for prompt EOF after the relevant shutdown/handle-release sequence.
• Make the JVM-focused t/01_basic_request.t complete without the 15-second test_connect timed out warning.
• Add a small standard-Perl-validated interpreter regression for the condition-variable callback shape around AnyEvent.pm line 2061.
• Make the interpreter-focused test complete without StackOverflowError.
• Run the unchanged AnyEvent::HTTPD 0.93 suite successfully on PerlOnJava: 13 files and 64 tests.
• Verify both backends where the runtime surface is shared.
• Refresh the CPAN compatibility classification from Unknown test outcome to PASS once the bounded suite completes reliably.