[PATCH ssoma] extractor: backup state file when updating and fsync

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

The state file is important, so try not to lose it by
creating a backup before git writes it, and fsync the
result ASAP since git does not consider the config file
important enough.
---
 lib/Ssoma/Extractor.pm | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/lib/Ssoma/Extractor.pm b/lib/Ssoma/Extractor.pm
index afc9afd..7e2b5d1 100644
--- a/lib/Ssoma/Extractor.pm
+++ b/lib/Ssoma/Extractor.pm
@@ -7,6 +7,7 @@ use strict;
 use warnings;
 use Ssoma::Git;
 use Email::LocalDelivery;
+use IO::File;
 
 sub new {
 	my ($class, $git) = @_;
@@ -106,9 +107,32 @@ sub _extract {
 
 	# update the last-imported var
 	{
+		# This state file is important, and git does not fsync it.
+		if (open my $st, '<', $state) {
+			# clobber existing backup
+			my $bak = "$state.bak";
+			open my $bk, '>', $bak or die
+				"failed to open backup ($bak): $!";
+			my $size = -s $st;
+			my $r = read($st, my $buf, $size);
+			$st->close or die "close $state failed for copy: $!";
+			defined $r or die "failed read $size from $state: $!";
+			$r == $size or die "read ($r != $size) from $state";
+			$bk->write($buf) or die "failed to write $bak: $!";
+			defined($bk->flush) or die "flush $bak failed: $!";
+			defined($bk->sync) or die "fsync $bak failed: $!";
+			$bk->close or die "close $bak failed: $!";
+		}
+
 		local $ENV{GIT_CONFIG} = $state;
 		my $rv = system(qw/git config/, $lkey, $tip);
-		$rv == 0 or die "git config $lkey $tip failed: $? ($rv)\n";
+		$rv == 0 or die "git config $lkey $tip failed: $? ($rv)";
+
+		# git-config(1) does not fsync state files by default
+		open my $st, '+<', $state or
+				die "failed to open state ($state): $!";
+		defined($st->sync) or die "fsync $state failed: $!";
+		$st->close or die "close $state failed for fsync: $!";
 	}
 }
 
-- 
EW