implement external Message-ID finder

Currently, this looks at other public-inbox configurations
served in the same process.  In the future, it will generate
links to other Message-ID lookup endpoints.

1 files changed, 92 insertions, 0 deletions

diff --git a/lib/PublicInbox/ExtMsg.pm b/lib/PublicInbox/ExtMsg.pm
new file mode 100644
index 00000000..1c0887cd
--- /dev/null
+++ b/lib/PublicInbox/ExtMsg.pm
@@ -0,0 +1,92 @@
+# Copyright (C) 2015 all contributors <meta@public-inbox.org>
+# License: AGPLv3 or later (https://www.gnu.org/licenses/agpl-3.0.txt)
+package PublicInbox::ExtMsg;
+use strict;
+use warnings;
+use URI::Escape qw(uri_escape_utf8);
+use PublicInbox::Hval;
+use PublicInbox::MID qw/mid_compress mid2path/;
+
+sub ext_msg {
+        my ($ctx) = @_;
+        my $pi_config = $ctx->{pi_config};
+        my $listname = $ctx->{listname};
+        my $mid = $ctx->{mid};
+        my $cmid = mid_compress($mid);
+
+        eval { require PublicInbox::Search };
+        my $have_xap = $@ ? 0 : 1;
+        my @nox;
+
+        foreach my $k (keys %$pi_config) {
+                $k =~ /\Apublicinbox\.([A-Z0-9a-z-]+)\.url\z/ or next;
+                my $list = $1;
+                next if $list eq $listname;
+
+                my $git_dir = $pi_config->{"publicinbox.$list.mainrepo"};
+                defined $git_dir or next;
+
+                my $url = $pi_config->{"publicinbox.$list.url"};
+                defined $url or next;
+
+                $url =~ s!/+\z!!;
+
+                # try to find the URL with Xapian to avoid forking
+                if ($have_xap) {
+                        my $doc_id = eval {
+                                my $s = PublicInbox::Search->new($git_dir);
+                                $s->find_unique_doc_id('mid', $cmid);
+                        };
+                        if ($@) {
+                                # xapian not configured for this repo
+                        } else {
+                                # maybe we found it!
+                                return r302($url, $cmid) if (defined $doc_id);
+
+                                # no point in trying the fork fallback if we
+                                # know Xapian is up-to-date but missing the
+                                # message in the current repo
+                                next;
+                        }
+                }
+
+                # queue up for forking after we've tried Xapian on all of them
+                push @nox, { git_dir => $git_dir, url => $url };
+        }
+
+        # Xapian not installed or configured for some repos
+        my $path = "HEAD:" . mid2path($cmid);
+
+        foreach my $n (@nox) {
+                my @cmd = ('git', "--git-dir=$n->{git_dir}", 'cat-file',
+                           '-t', $path);
+                my $pid = open my $fh, '-|';
+                defined $pid or die "fork failed: $!\n";
+
+                if ($pid == 0) {
+                        open STDERR, '>', '/dev/null'; # ignore errors
+                        exec @cmd or die "exec failed: $!\n";
+                } else {
+                        my $type = eval { local $/; <$fh> };
+                        close $fh;
+                        if ($? == 0 && $type eq "blob\n") {
+                                return r302($n->{url}, $cmid);
+                        }
+                }
+        }
+
+        # Fall back to external repos
+
+        [404, ['Content-Type'=>'text/plain'], ['Not found']];
+}
+
+# Redirect to another public-inbox which is mapped by $pi_config
+sub r302 {
+        my ($url, $mid) = @_;
+        $url .= '/' . uri_escape_utf8($mid) . '/';
+        [ 302,
+          [ 'Location' => $url, 'Content-Type' => 'text/plain' ],
+          [ "Redirecting to\n$url\n" ] ]
+}
+
+1;