gcf2: libgit2-based git cat-file alternative

Having tens of thousands of inboxes and associated git processes
won't work well, so we'll use libgit2 to access the object DB
directly.  We only care about OID lookups and won't need to rely
on per-repo revision names or paths.

The Git::Raw XS package won't be used since its manpages don't
promise a stable API.  Since we already use Inline::C and have
experience with I::C when it comes to compatibility, this only
introduces libgit2 itself as a source of new incompatibilities.

This also provides an excuse for me to writev(2) to reduce
syscalls, but liburing is on the horizon for next year.

1 files changed, 112 insertions, 0 deletions

diff --git a/t/gcf2.t b/t/gcf2.t
new file mode 100644
index 00000000..c67efb6c
--- /dev/null
+++ b/t/gcf2.t
@@ -0,0 +1,112 @@
+#!perl -w
+# Copyright (C) 2020 all contributors <meta@public-inbox.org>
+# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
+use strict;
+use PublicInbox::TestCommon;
+use Test::More;
+use Fcntl qw(:seek);
+use IO::Handle ();
+use POSIX qw(_exit);
+require_mods('PublicInbox::Gcf2');
+use_ok 'PublicInbox::Gcf2';
+my $gcf2 = PublicInbox::Gcf2::new();
+is(ref($gcf2), 'PublicInbox::Gcf2', '::new works');
+chomp(my $objdir = xqx([qw(git rev-parse --git-path objects)]));
+if ($objdir =~ /\A--git-path\n/) { # git <2.5
+        chomp($objdir = xqx([qw(git rev-parse --git-dir)]));
+        $objdir .= '/objects';
+        $objdir = undef unless -d $objdir;
+}
+
+my $COPYING = 'dba13ed2ddf783ee8118c6a581dbf75305f816a3';
+open my $agpl, '<', 'COPYING' or BAIL_OUT "AGPL-3 missing: $!";
+$agpl = do { local $/; <$agpl> };
+
+SKIP: {
+        skip 'not in git worktree', 15 unless defined($objdir);
+        $gcf2->add_alternate($objdir);
+        open my $fh, '+>', undef or BAIL_OUT "open: $!";
+        my $fd = fileno($fh);
+        $fh->autoflush(1);
+
+        $gcf2->cat_oid($fd, 'invalid');
+        seek($fh, 0, SEEK_SET) or BAIL_OUT "seek: $!";
+        is(do { local $/; <$fh> }, "invalid missing\n", 'got missing message');
+
+        seek($fh, 0, SEEK_SET) or BAIL_OUT "seek: $!";
+        $gcf2->cat_oid($fd, '0'x40);
+        seek($fh, 0, SEEK_SET) or BAIL_OUT "seek: $!";
+        is(do { local $/; <$fh> }, ('0'x40)." missing\n",
+                'got missing message for 0x40');
+
+        seek($fh, 0, SEEK_SET) or BAIL_OUT "seek: $!";
+        $gcf2->cat_oid($fd, $COPYING);
+        my $buf;
+        my $ck_copying = sub {
+                my ($desc) = @_;
+                seek($fh, 0, SEEK_SET) or BAIL_OUT "seek: $!";
+                is(<$fh>, "$COPYING blob 34520\n", 'got expected header');
+                $buf = do { local $/; <$fh> };
+                is(chop($buf), "\n", 'got trailing \\n');
+                is($buf, $agpl, "AGPL matches ($desc)");
+        };
+        $ck_copying->('regular file');
+
+        $^O eq 'linux' or skip('pipe tests are Linux-only', 12);
+        my $size = -s $fh;
+        for my $blk (1, 0) {
+                my ($r, $w);
+                pipe($r, $w) or BAIL_OUT $!;
+                fcntl($w, 1031, 4096) or
+                        skip('Linux too old for F_SETPIPE_SZ', 12);
+                $w->blocking($blk);
+                seek($fh, 0, SEEK_SET) or BAIL_OUT "seek: $!";
+                truncate($fh, 0) or BAIL_OUT "truncate: $!";
+                defined(my $pid = fork) or BAIL_OUT "fork: $!";
+                if ($pid == 0) {
+                        close $w;
+                        tick; # wait for parent to block on writev
+                        $buf = do { local $/; <$r> };
+                        print $fh $buf or _exit(1);
+                        _exit(0);
+                }
+                $gcf2->cat_oid(fileno($w), $COPYING);
+                close $w or BAIL_OUT "close: $!";
+                is(waitpid($pid, 0), $pid, 'child exited');
+                is($?, 0, 'no error in child');
+                $ck_copying->("pipe blocking($blk)");
+
+                pipe($r, $w) or BAIL_OUT $!;
+                fcntl($w, 1031, 4096) or BAIL_OUT $!;
+                $w->blocking($blk);
+                close $r;
+                local $SIG{PIPE} = 'IGNORE';
+                eval { $gcf2->cat_oid(fileno($w), $COPYING) };
+                like($@, qr/writev error:/, 'got writev error');
+        }
+}
+
+if (my $nr = $ENV{TEST_LEAK_NR}) {
+        open my $null, '>', '/dev/null' or BAIL_OUT "open /dev/null: $!";
+        my $fd = fileno($null);
+        my $cat = $ENV{TEST_LEAK_CAT} // 10;
+        diag "checking for leaks... (TEST_LEAK_NR=$nr TEST_LEAK_CAT=$cat)";
+        local $SIG{PIPE} = 'IGNORE';
+        my ($r, $w);
+        pipe($r, $w);
+        close $r;
+        my $broken = fileno($w);
+        for (1..$nr) {
+                my $obj = PublicInbox::Gcf2::new();
+                if (defined($objdir)) {
+                        $obj->add_alternate($objdir);
+                        for (1..$cat) {
+                                $obj->cat_oid($fd, $COPYING);
+                                eval { $obj->cat_oid($broken, $COPYING) };
+                                $obj->cat_oid($fd, '0'x40);
+                                $obj->cat_oid($fd, 'invalid');
+                        }
+                }
+        }
+}
+done_testing;