From 763db9879ce48bd817f5b659b6a4168f7b711ec4 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Thu, 24 Jan 2019 19:07:26 +0100
Subject: [PATCH] Store the channel redirects in S3

---
 mirror-nixos-branch.pl | 55 +++++++++++++++++++-----------------------
 1 file changed, 25 insertions(+), 30 deletions(-)

diff --git a/mirror-nixos-branch.pl b/mirror-nixos-branch.pl
index 9c37fc6..4483852 100755
--- a/mirror-nixos-branch.pl
+++ b/mirror-nixos-branch.pl
@@ -25,8 +25,8 @@ my $channelDirRel = $channelName eq "nixpkgs-unstable" ? "nixpkgs" : "$1/$2";
 
 
 # Configuration.
-my $channelsDir = "/data/releases/channels";
-my $filesCache = "/data/releases/nixos-files.sqlite";
+my $TMPDIR = $ENV{'TMPDIR'} // "/tmp";
+my $filesCache = "${TMPDIR}/nixos-files.sqlite";
 my $bucketName = "nix-releases";
 
 $ENV{'GIT_DIR'} = "/home/hydra-mirror/nixpkgs-channels";
@@ -66,22 +66,27 @@ my $evalId = $releaseInfo->{jobsetevals}->[0] or die;
 my $evalUrl = "https://hydra.nixos.org/eval/$evalId";
 my $evalInfo = decode_json(fetch($evalUrl, 'application/json'));
 my $releasePrefix = "$channelDirRel/$releaseName";
+my $channelRedirect = "channels/$channelName";
 
 my $rev = $evalInfo->{jobsetevalinputs}->{nixpkgs}->{revision} or die;
 
 print STDERR "release is ‘$releaseName’ (build $releaseId), eval is $evalId, prefix is $releasePrefix, Git commit is $rev\n";
 
 # Guard against the channel going back in time.
-my @releaseUrl = split(/\//, read_file("$channelsDir/$channelName", err_mode => 'quiet') // "");
-my $curRelease = pop @releaseUrl;
-my $d = `NIX_PATH= nix-instantiate --eval -E "builtins.compareVersions (builtins.parseDrvName \\"$curRelease\\").version (builtins.parseDrvName \\"$releaseName\\").version"`;
-chomp $d;
-die "channel would go back in time from $curRelease to $releaseName, bailing out\n" if $d == 1;
-
-if ($bucket->head_key("$releasePrefix")) {
+my $redirect = $bucket->head_key($channelRedirect);
+if (defined $redirect->{'x-amz-website-redirect-location'}) {
+    my $curRelease = basename($redirect->{'x-amz-website-redirect-location'});
+    print STDERR "current channel version is $curRelease\n";
+    my $d = `NIX_PATH= nix-instantiate --eval -E "builtins.compareVersions (builtins.parseDrvName \\"$curRelease\\").version (builtins.parseDrvName \\"$releaseName\\").version"`;
+    chomp $d;
+    die "channel would go back in time from $curRelease to $releaseName, bailing out\n" if $d == 1;
+    exit if $d == 0;
+}
+    
+if ($bucket->head_key($releasePrefix)) {
     print STDERR "release already exists\n";
 } else {
-    my $tmpDir = "/data/releases/tmp/release-$channelName/$releaseName";
+    my $tmpDir = "$TMPDIR/release-$channelName/$releaseName";
     File::Path::make_path($tmpDir);
 
     write_file("$tmpDir/src-url", $evalUrl);
@@ -201,28 +206,18 @@ if ($bucket->head_key("$releasePrefix")) {
     File::Path::remove_tree($tmpDir);
 }
 
-# Prevent concurrent writes to the channels directory.
-open(my $lockfile, ">>", "$channelsDir/.htaccess.lock");
-flock($lockfile, LOCK_EX) or die "cannot acquire channels lock\n";
-
-# Update the channel.
-my $htaccess = "$channelsDir/.htaccess-$channelName";
-my $target = "https://releases.nixos.org/$releasePrefix";
-write_file($htaccess,
-           "Redirect /channels/$channelName $target\n" .
-           "Redirect /releases/nixos/channels/$channelName $target\n");
-
-my $channelLink = "$channelsDir/$channelName";
-if ((read_file($channelLink, err_mode => 'quiet') // "") ne $target) {
-    write_file("$channelLink.tmp", "$target");
-    rename("$channelLink.tmp", $channelLink) or die;
-}
-
-system("cat $channelsDir/.htaccess-nix* > $channelsDir/.htaccess.tmp") == 0 or die;
-rename("$channelsDir/.htaccess.tmp", "$channelsDir/.htaccess") or die;
+# Prevent concurrent writes to the repo.
+open(my $lockfile, ">>", "$TMPDIR/lock");
+flock($lockfile, LOCK_EX) or die "cannot acquire repo lock\n";
 
 # Update the nixpkgs-channels repo.
 system("git remote update origin >&2") == 0 or die;
 system("git push channels $rev:refs/heads/$channelName >&2") == 0 or die;
 
-flock($lockfile, LOCK_UN) or die "cannot release channels lock\n";
+flock($lockfile, LOCK_UN) or die "cannot release repo lock\n";
+
+# Update the channel redirect.
+$bucket->add_key($channelRedirect, "", {
+    'x-amz-website-redirect-location' => "/" . $releasePrefix,
+    'x-amz-acl' => "public-read"
+}) or die "failed to create redirect from $channelRedirect to $releasePrefix\n";