* Install NixManifest.pm, NixConfig.pm and GeneratePatches.pm under

  the Nix:: namespace.

4 files changed, 728 insertions, 2 deletions

diff --git a/perl/Makefile.am b/perl/Makefile.am
index 548708a33..a459bdc87 100644
--- a/perl/Makefile.am
+++ b/perl/Makefile.am
@@ -2,7 +2,9 @@ perlversion := $(shell perl -e 'use Config; print $$Config{version};')
 perlarchname := $(shell perl -e 'use Config; print $$Config{archname};')
 perllibdir = $(libdir)/perl5/site_perl/$(perlversion)/$(perlarchname)
 
-install-exec-local: lib/Nix/*.pm
+all: lib/Nix/Config.pm
+
+install-exec-local: lib/Nix/*.pm lib/Nix/Config.pm
 	$(INSTALL) -d $(DESTDIR)$(perllibdir)/Nix
 	$(INSTALL_DATA) lib/Nix/*.pm $(DESTDIR)$(perllibdir)/Nix
 	$(INSTALL) -d $(DESTDIR)$(perllibdir)/auto/Nix/Store
@@ -22,4 +24,6 @@ AM_CXXFLAGS = \
 lib/Nix/Store.cc: lib/Nix/Store.xs
 	xsubpp $^ -output $@
 
-EXTRA_DIST = lib/Nix/*.pm lib/Nix/Store.xs
+EXTRA_DIST = lib/Nix/Store.pm lib/Nix/Manifest.pm lib/Nix/Config.pm.in lib/Nix/Store.xs
+
+include ../substitute.mk
diff --git a/perl/lib/Nix/Config.pm.in b/perl/lib/Nix/Config.pm.in
new file mode 100644
index 000000000..658305fd9
--- /dev/null
+++ b/perl/lib/Nix/Config.pm.in
@@ -0,0 +1,25 @@
+package Nix::Config;
+
+$binDir = $ENV{"NIX_BIN_DIR"} || "@bindir@";
+$libexecDir = $ENV{"NIX_LIBEXEC_DIR"} || "@libexecdir@";
+$manifestDir = $ENV{"NIX_MANIFESTS_DIR"} || "@localstatedir@/nix/manifests";
+$logDir = $ENV{"NIX_LOG_DIR"} || "@localstatedir@/log/nix";
+
+$bzip2 = $ENV{"NIX_BZIP2"} || "@bzip2@";
+$curl = "@curl@";
+
+sub readConfig {
+    my %config;
+    my $config = "@sysconfdir@/nix/nix.conf";
+    return unless -f $config;
+    
+    open CONFIG, "<$config" or die "cannot open `$config'";
+    while (<CONFIG>) {
+        /^\s*([\w|-]+)\s*=\s*(.*)$/ or next;
+        $config{$1} = $2;
+        print "|$1| -> |$2|\n";
+    }
+    close CONFIG;
+}
+
+return 1;
diff --git a/perl/lib/Nix/GeneratePatches.pm b/perl/lib/Nix/GeneratePatches.pm
new file mode 100644
index 000000000..f9d83c49c
--- /dev/null
+++ b/perl/lib/Nix/GeneratePatches.pm
@@ -0,0 +1,340 @@
+package Nix::GeneratePatches;
+
+use strict;
+use File::Temp qw(tempdir);
+use File::stat;
+use Nix::Config;
+use Nix::Manifest;
+
+our @ISA = qw(Exporter);
+our @EXPORT = qw(generatePatches propagatePatches copyPatches);
+
+
+# Some patch generations options.
+
+# Max size of NAR archives to generate patches for.
+my $maxNarSize = $ENV{"NIX_MAX_NAR_SIZE"};
+$maxNarSize = 160 * 1024 * 1024 if !defined $maxNarSize;
+
+# If patch is bigger than this fraction of full archive, reject.
+my $maxPatchFraction = $ENV{"NIX_PATCH_FRACTION"};
+$maxPatchFraction = 0.60 if !defined $maxPatchFraction;
+
+my $timeLimit = $ENV{"NIX_BSDIFF_TIME_LIMIT"};
+$timeLimit = 180 if !defined $timeLimit;
+
+my $hashAlgo = "sha256";
+
+
+sub findOutputPaths {
+    my $narFiles = shift;
+
+    my %outPaths;
+    
+    foreach my $p (keys %{$narFiles}) {
+
+        # Ignore derivations.
+        next if ($p =~ /\.drv$/);
+        
+        # Ignore builders (too much ambiguity -- they're all called
+        # `builder.sh').
+        next if ($p =~ /\.sh$/);
+        next if ($p =~ /\.patch$/);
+        
+        # Don't bother including tar files etc.
+        next if ($p =~ /\.tar$/ || $p =~ /\.tar\.(gz|bz2|Z|lzma|xz)$/ || $p =~ /\.zip$/ || $p =~ /\.bin$/ || $p =~ /\.tgz$/ || $p =~ /\.rpm$/ || $p =~ /cvs-export$/ || $p =~ /fetchhg$/);
+
+        $outPaths{$p} = 1;
+    }
+
+    return %outPaths;
+}
+
+
+sub getNameVersion {
+    my $p = shift;
+    $p =~ /\/[0-9a-z]+((?:-[a-zA-Z][^\/-]*)+)([^\/]*)$/;
+    my $name = $1;
+    my $version = $2;
+    return undef unless defined $name && defined $version;
+    $name =~ s/^-//;
+    $version =~ s/^-//;
+    return ($name, $version);
+}
+
+
+# A quick hack to get a measure of the `distance' between two
+# versions: it's just the position of the first character that differs
+# (or 999 if they are the same).
+sub versionDiff {
+    my $s = shift;
+    my $t = shift;
+    my $i;
+    return 999 if $s eq $t;
+    for ($i = 0; $i < length $s; $i++) {
+        return $i if $i >= length $t or
+            substr($s, $i, 1) ne substr($t, $i, 1);
+    }
+    return $i;
+}
+
+
+sub getNarBz2 {
+    my $narPath = shift;
+    my $narFiles = shift;
+    my $storePath = shift;
+    
+    my $narFileList = $$narFiles{$storePath};
+    die "missing path $storePath" unless defined $narFileList;
+
+    my $narFile = @{$narFileList}[0];
+    die unless defined $narFile;
+
+    $narFile->{url} =~ /\/([^\/]+)$/;
+    die unless defined $1;
+    return "$narPath/$1";
+}
+
+
+sub containsPatch {
+    my $patches = shift;
+    my $storePath = shift;
+    my $basePath = shift;
+    my $patchList = $$patches{$storePath};
+    return 0 if !defined $patchList;
+    my $found = 0;
+    foreach my $patch (@{$patchList}) {
+        # !!! baseHash might differ
+        return 1 if $patch->{basePath} eq $basePath;
+    }
+    return 0;
+}
+
+
+sub generatePatches {
+    my ($srcNarFiles, $dstNarFiles, $srcPatches, $dstPatches, $narPath, $patchesPath, $patchesURL, $tmpDir) = @_;
+
+    my %srcOutPaths = findOutputPaths $srcNarFiles;
+    my %dstOutPaths = findOutputPaths $dstNarFiles;
+
+    # For each output path in the destination, see if we need to / can
+    # create a patch.
+
+    print STDERR "creating patches...\n";
+
+    foreach my $p (keys %dstOutPaths) {
+
+        # If exactly the same path already exists in the source, skip it.
+        next if defined $srcOutPaths{$p};
+    
+        print "  $p\n";
+
+        # If not, then we should find the paths in the source that are
+        # `most' likely to be present on a system that wants to
+        # install this path.
+
+        (my $name, my $version) = getNameVersion $p;
+        next unless defined $name && defined $version;
+
+        my @closest = ();
+        my $closestVersion;
+        my $minDist = -1; # actually, larger means closer
+
+        # Find all source paths with the same name.
+
+        foreach my $q (keys %srcOutPaths) {
+            (my $name2, my $version2) = getNameVersion $q;
+            next unless defined $name2 && defined $version2;
+
+            if ($name eq $name2) {
+
+                my $srcSystem = @{$$dstNarFiles{$p}}[0]->{system};
+                my $dstSystem = @{$$srcNarFiles{$q}}[0]->{system};
+                if (defined $srcSystem && defined $dstSystem && $srcSystem ne $dstSystem) {
+                    print "    SKIPPING $q due to different systems ($srcSystem vs. $dstSystem)\n";
+                    next;
+                }
+
+                # If the sizes differ too much, then skip.  This
+                # disambiguates between, e.g., a real component and a
+                # wrapper component (cf. Firefox in Nixpkgs).
+                my $srcSize = @{$$srcNarFiles{$q}}[0]->{size};
+                my $dstSize = @{$$dstNarFiles{$p}}[0]->{size};
+                my $ratio = $srcSize / $dstSize;
+                $ratio = 1 / $ratio if $ratio < 1;
+                # print "  SIZE $srcSize $dstSize $ratio $q\n";
+
+                if ($ratio >= 3) {
+                    print "    SKIPPING $q due to size ratio $ratio ($srcSize vs. $dstSize)\n";
+                    next;
+                }
+
+                # If there are multiple matching names, include the
+                # ones with the closest version numbers.
+                my $dist = versionDiff $version, $version2;
+                if ($dist > $minDist) {
+                    $minDist = $dist;
+                    @closest = ($q);
+                    $closestVersion = $version2;
+                } elsif ($dist == $minDist) {
+                    push @closest, $q;
+                }
+            }
+        }
+
+        if (scalar(@closest) == 0) {
+            print "    NO BASE: $p\n";
+            next;
+        }
+
+        foreach my $closest (@closest) {
+
+            # Generate a patch between $closest and $p.
+            print STDERR "  $p <- $closest\n";
+
+            # If the patch already exists, skip it.
+            if (containsPatch($srcPatches, $p, $closest) ||
+                containsPatch($dstPatches, $p, $closest))
+            {
+                print "    skipping, already exists\n";
+                next;
+            }
+
+            my $srcNarBz2 = getNarBz2 $narPath, $srcNarFiles, $closest;
+            my $dstNarBz2 = getNarBz2 $narPath, $dstNarFiles, $p;
+
+            if (! -f $srcNarBz2) {
+                warn "patch source archive $srcNarBz2 is missing\n";
+                next;
+            }
+
+            system("$Nix::Config::bzip2 -d < $srcNarBz2 > $tmpDir/A") == 0
+                or die "cannot unpack $srcNarBz2";
+
+            if (stat("$tmpDir/A")->size >= $maxNarSize) {
+                print "    skipping, source is too large\n";
+                next;
+            }
+        
+            system("$Nix::Config::bzip2 -d < $dstNarBz2 > $tmpDir/B") == 0
+                or die "cannot unpack $dstNarBz2";
+
+            if (stat("$tmpDir/B")->size >= $maxNarSize) {
+                print "    skipping, destination is too large\n";
+                next;
+            }
+        
+            my $time1 = time();
+            my $res = system("ulimit -t $timeLimit; $Nix::Config::libexecDir/bsdiff $tmpDir/A $tmpDir/B $tmpDir/DIFF");
+            my $time2 = time();
+            if ($res) {
+                warn "binary diff computation aborted after ", $time2 - $time1, " seconds\n";
+                next;
+            }
+
+            my $baseHash = `$Nix::Config::binDir/nix-hash --flat --type $hashAlgo --base32 $tmpDir/A` or die;
+            chomp $baseHash;
+
+            my $narHash = `$Nix::Config::binDir/nix-hash --flat --type $hashAlgo --base32 $tmpDir/B` or die;
+            chomp $narHash;
+
+            my $narDiffHash = `$Nix::Config::binDir/nix-hash --flat --type $hashAlgo --base32 $tmpDir/DIFF` or die;
+            chomp $narDiffHash;
+
+            my $narDiffSize = stat("$tmpDir/DIFF")->size;
+            my $dstNarBz2Size = stat($dstNarBz2)->size;
+
+            print "    size $narDiffSize; full size $dstNarBz2Size; ", $time2 - $time1, " seconds\n";
+        
+            if ($narDiffSize >= $dstNarBz2Size) {
+                print "    rejecting; patch bigger than full archive\n";
+                next;
+            }
+    
+            if ($narDiffSize / $dstNarBz2Size >= $maxPatchFraction) {
+                print "    rejecting; patch too large relative to full archive\n";
+                next;
+            }
+    
+            my $finalName = "$narDiffHash.nar-bsdiff";
+
+            if (-e "$patchesPath/$finalName") {
+                print "    not copying, already exists\n";
+            }
+
+            else {
+                system("cp '$tmpDir/DIFF' '$patchesPath/$finalName.tmp'") == 0
+                    or die "cannot copy diff";
+                rename("$patchesPath/$finalName.tmp", "$patchesPath/$finalName")
+                    or die "cannot rename $patchesPath/$finalName.tmp";
+            }
+        
+            # Add the patch to the manifest.
+            addPatch $dstPatches, $p,
+                { url => "$patchesURL/$finalName", hash => "$hashAlgo:$narDiffHash"
+                , size => $narDiffSize, basePath => $closest, baseHash => "$hashAlgo:$baseHash"
+                , narHash => "$hashAlgo:$narHash", patchType => "nar-bsdiff"
+                };
+        }
+    }
+}
+
+
+# Propagate useful patches from $srcPatches to $dstPatches.  A patch
+# is useful if it produces either paths in the $dstNarFiles or paths
+# that can be used as the base for other useful patches.
+sub propagatePatches {
+    my ($srcPatches, $dstNarFiles, $dstPatches) = @_;
+
+    print STDERR "propagating patches...\n";
+
+    my $changed;
+    do {
+        # !!! we repeat this to reach the transitive closure; inefficient
+        $changed = 0;
+
+        print STDERR "loop\n";
+
+        my %dstBasePaths;
+        foreach my $q (keys %{$dstPatches}) {
+            foreach my $patch (@{$$dstPatches{$q}}) {
+                $dstBasePaths{$patch->{basePath}} = 1;
+            }
+        }
+
+        foreach my $p (keys %{$srcPatches}) {
+            my $patchList = $$srcPatches{$p};
+
+            my $include = 0;
+
+            # Is path $p included in the destination?  If so, include
+            # patches that produce it.
+            $include = 1 if defined $$dstNarFiles{$p};
+
+            # Is path $p a path that serves as a base for paths in the
+            # destination?  If so, include patches that produce it.
+            # !!! check baseHash
+            $include = 1 if defined $dstBasePaths{$p};
+
+            if ($include) {
+                foreach my $patch (@{$patchList}) {
+                    $changed = 1 if addPatch $dstPatches, $p, $patch;
+                }
+            }
+        
+        }
+    
+    } while $changed;
+}
+
+
+# Add all new patches in $srcPatches to $dstPatches.
+sub copyPatches {
+    my ($srcPatches, $dstPatches) = @_;
+    foreach my $p (keys %{$srcPatches}) {
+        addPatch $dstPatches, $p, $_ foreach @{$$srcPatches{$p}};
+    }
+}
+
+
+return 1;
diff --git a/perl/lib/Nix/Manifest.pm b/perl/lib/Nix/Manifest.pm
new file mode 100644
index 000000000..7790cfe3b
--- /dev/null
+++ b/perl/lib/Nix/Manifest.pm
@@ -0,0 +1,357 @@
+package Nix::Manifest;
+
+use strict;
+use DBI;
+use Cwd;
+use File::stat;
+use File::Path;
+use Fcntl ':flock';
+use Nix::Config;
+
+our @ISA = qw(Exporter);
+our @EXPORT = qw(readManifest writeManifest updateManifestDB addPatch);
+
+
+sub addNAR {
+    my ($narFiles, $storePath, $info) = @_;
+    
+    $$narFiles{$storePath} = []
+        unless defined $$narFiles{$storePath};
+
+    my $narFileList = $$narFiles{$storePath};
+
+    my $found = 0;
+    foreach my $narFile (@{$narFileList}) {
+        $found = 1 if $narFile->{url} eq $info->{url};
+    }
+    
+    push @{$narFileList}, $info if !$found;
+}
+
+
+sub addPatch {
+    my ($patches, $storePath, $patch) = @_;
+
+    $$patches{$storePath} = []
+        unless defined $$patches{$storePath};
+
+    my $patchList = $$patches{$storePath};
+
+    my $found = 0;
+    foreach my $patch2 (@{$patchList}) {
+        $found = 1 if
+            $patch2->{url} eq $patch->{url} &&
+            $patch2->{basePath} eq $patch->{basePath};
+    }
+    
+    push @{$patchList}, $patch if !$found;
+
+    return !$found;
+}
+
+
+sub readManifest_ {
+    my ($manifest, $addNAR, $addPatch) = @_;
+
+    open MANIFEST, "<$manifest"
+        or die "cannot open `$manifest': $!";
+
+    my $inside = 0;
+    my $type;
+
+    my $manifestVersion = 2;
+
+    my ($storePath, $url, $hash, $size, $basePath, $baseHash, $patchType);
+    my ($narHash, $narSize, $references, $deriver, $copyFrom, $system);
+
+    while (<MANIFEST>) {
+        chomp;
+        s/\#.*$//g;
+        next if (/^$/);
+
+        if (!$inside) {
+
+            if (/^\s*(\w*)\s*\{$/) {
+                $type = $1;
+                $type = "narfile" if $type eq "";
+                $inside = 1;
+                undef $storePath;
+                undef $url;
+                undef $hash;
+                undef $size;
+                undef $narHash;
+                undef $narSize;
+                undef $basePath;
+                undef $baseHash;
+                undef $patchType;
+                undef $system;
+                $references = "";
+                $deriver = "";
+	    }
+
+        } else {
+            
+            if (/^\}$/) {
+                $inside = 0;
+
+                if ($type eq "narfile") {
+                    &$addNAR($storePath,
+                        { url => $url, hash => $hash, size => $size
+                        , narHash => $narHash, narSize => $narSize
+                        , references => $references
+                        , deriver => $deriver
+                        , system => $system
+                        });
+                }
+
+                elsif ($type eq "patch") {
+                    &$addPatch($storePath,
+                        { url => $url, hash => $hash, size => $size
+                        , basePath => $basePath, baseHash => $baseHash
+                        , narHash => $narHash, narSize => $narSize
+                        , patchType => $patchType
+                        });
+                }
+
+            }
+            
+            elsif (/^\s*StorePath:\s*(\/\S+)\s*$/) { $storePath = $1; }
+            elsif (/^\s*CopyFrom:\s*(\/\S+)\s*$/) { $copyFrom = $1; }
+            elsif (/^\s*Hash:\s*(\S+)\s*$/) { $hash = $1; }
+            elsif (/^\s*URL:\s*(\S+)\s*$/) { $url = $1; }
+            elsif (/^\s*Size:\s*(\d+)\s*$/) { $size = $1; }
+            elsif (/^\s*SuccOf:\s*(\/\S+)\s*$/) { } # obsolete
+            elsif (/^\s*BasePath:\s*(\/\S+)\s*$/) { $basePath = $1; }
+            elsif (/^\s*BaseHash:\s*(\S+)\s*$/) { $baseHash = $1; }
+            elsif (/^\s*Type:\s*(\S+)\s*$/) { $patchType = $1; }
+            elsif (/^\s*NarHash:\s*(\S+)\s*$/) { $narHash = $1; }
+            elsif (/^\s*NarSize:\s*(\d+)\s*$/) { $narSize = $1; }
+            elsif (/^\s*References:\s*(.*)\s*$/) { $references = $1; }
+            elsif (/^\s*Deriver:\s*(\S+)\s*$/) { $deriver = $1; }
+            elsif (/^\s*ManifestVersion:\s*(\d+)\s*$/) { $manifestVersion = $1; }
+            elsif (/^\s*System:\s*(\S+)\s*$/) { $system = $1; }
+
+            # Compatibility;
+            elsif (/^\s*NarURL:\s*(\S+)\s*$/) { $url = $1; }
+            elsif (/^\s*MD5:\s*(\S+)\s*$/) { $hash = "md5:$1"; }
+
+        }
+    }
+
+    close MANIFEST;
+
+    return $manifestVersion;
+}
+
+
+sub readManifest {
+    my ($manifest, $narFiles, $patches) = @_;
+    readManifest_($manifest,
+        sub { addNAR($narFiles, @_); },
+        sub { addPatch($patches, @_); } );
+}
+
+
+sub writeManifest {
+    my ($manifest, $narFiles, $patches, $noCompress) = @_;
+
+    open MANIFEST, ">$manifest.tmp"; # !!! check exclusive
+
+    print MANIFEST "version {\n";
+    print MANIFEST "  ManifestVersion: 3\n";
+    print MANIFEST "}\n";
+
+    foreach my $storePath (sort (keys %{$narFiles})) {
+        my $narFileList = $$narFiles{$storePath};
+        foreach my $narFile (@{$narFileList}) {
+            print MANIFEST "{\n";
+            print MANIFEST "  StorePath: $storePath\n";
+            print MANIFEST "  NarURL: $narFile->{url}\n";
+            print MANIFEST "  Hash: $narFile->{hash}\n" if defined $narFile->{hash};
+            print MANIFEST "  Size: $narFile->{size}\n" if defined $narFile->{size};
+            print MANIFEST "  NarHash: $narFile->{narHash}\n";
+            print MANIFEST "  NarSize: $narFile->{narSize}\n" if $narFile->{narSize};
+            print MANIFEST "  References: $narFile->{references}\n"
+                if defined $narFile->{references} && $narFile->{references} ne "";
+            print MANIFEST "  Deriver: $narFile->{deriver}\n"
+                if defined $narFile->{deriver} && $narFile->{deriver} ne "";
+            print MANIFEST "  System: $narFile->{system}\n" if defined $narFile->{system};
+            print MANIFEST "}\n";
+        }
+    }
+    
+    foreach my $storePath (sort (keys %{$patches})) {
+        my $patchList = $$patches{$storePath};
+        foreach my $patch (@{$patchList}) {
+            print MANIFEST "patch {\n";
+            print MANIFEST "  StorePath: $storePath\n";
+            print MANIFEST "  NarURL: $patch->{url}\n";
+            print MANIFEST "  Hash: $patch->{hash}\n";
+            print MANIFEST "  Size: $patch->{size}\n";
+            print MANIFEST "  NarHash: $patch->{narHash}\n";
+            print MANIFEST "  NarSize: $patch->{narSize}\n" if $patch->{narSize};
+            print MANIFEST "  BasePath: $patch->{basePath}\n";
+            print MANIFEST "  BaseHash: $patch->{baseHash}\n";
+            print MANIFEST "  Type: $patch->{patchType}\n";
+            print MANIFEST "}\n";
+        }
+    }
+    
+    
+    close MANIFEST;
+
+    rename("$manifest.tmp", $manifest)
+        or die "cannot rename $manifest.tmp: $!";
+
+
+    # Create a bzipped manifest.
+    unless (defined $noCompress) {
+	system("$Nix::Config::bzip2 < $manifest > $manifest.bz2.tmp") == 0
+	    or die "cannot compress manifest";
+
+	rename("$manifest.bz2.tmp", "$manifest.bz2")
+	    or die "cannot rename $manifest.bz2.tmp: $!";
+    }
+}
+
+
+sub updateManifestDB {
+    my $manifestDir = $Nix::Config::manifestDir;
+
+    mkpath($manifestDir);
+    
+    my $dbPath = "$manifestDir/cache.sqlite";
+
+    # Open/create the database.
+    our $dbh = DBI->connect("dbi:SQLite:dbname=$dbPath", "", "")
+        or die "cannot open database `$dbPath'";
+    $dbh->{RaiseError} = 1;
+    $dbh->{PrintError} = 0;
+
+    $dbh->do("pragma foreign_keys = on");
+    $dbh->do("pragma synchronous = off"); # we can always reproduce the cache
+    $dbh->do("pragma journal_mode = truncate");
+
+    # Initialise the database schema, if necessary.
+    $dbh->do(<<EOF);
+        create table if not exists Manifests (
+            id        integer primary key autoincrement not null,
+            path      text unique not null,
+            timestamp integer not null
+        );
+EOF
+    
+    $dbh->do(<<EOF);
+        create table if not exists NARs (
+            id               integer primary key autoincrement not null,
+            manifest         integer not null,
+            storePath        text not null,
+            url              text not null,
+            hash             text,
+            size             integer,
+            narHash          text,
+            narSize          integer,
+            refs             text,
+            deriver          text,
+            system           text,
+            foreign key (manifest) references Manifests(id) on delete cascade
+        );
+EOF
+
+    $dbh->do("create index if not exists NARs_storePath on NARs(storePath)");
+
+    $dbh->do(<<EOF);
+        create table if not exists Patches (
+            id               integer primary key autoincrement not null,
+            manifest         integer not null,
+            storePath        text not null,
+            basePath         text not null,
+            baseHash         text not null,
+            url              text not null,
+            hash             text,
+            size             integer,
+            narHash          text,
+            narSize          integer,
+            patchType        text not null,
+            foreign key (manifest) references Manifests(id) on delete cascade
+        );
+EOF
+
+    $dbh->do("create index if not exists Patches_storePath on Patches(storePath)");
+
+    # Acquire an exclusive lock to ensure that only one process
+    # updates the DB at the same time.  This isn't really necessary,
+    # but it prevents work duplication and lock contention in SQLite.
+    my $lockFile = "$manifestDir/cache.lock";
+    open MAINLOCK, ">>$lockFile" or die "unable to acquire lock ‘$lockFile’: $!\n";
+    flock(MAINLOCK, LOCK_EX) or die;
+
+    $dbh->begin_work;
+
+    # Read each manifest in $manifestDir and add it to the database,
+    # unless we've already done so on a previous run.
+    my %seen;
+    
+    for my $manifest (glob "$manifestDir/*.nixmanifest") {
+        $manifest = Cwd::abs_path($manifest);
+        my $timestamp = lstat($manifest)->mtime;
+        $seen{$manifest} = 1;
+
+        next if scalar @{$dbh->selectcol_arrayref(
+            "select 1 from Manifests where path = ? and timestamp = ?",
+            {}, $manifest, $timestamp)} == 1;
+
+        print STDERR "caching $manifest...\n";
+        
+        $dbh->do("delete from Manifests where path = ?", {}, $manifest);
+                 
+        $dbh->do("insert into Manifests(path, timestamp) values (?, ?)",
+                 {}, $manifest, $timestamp);
+
+        our $id = $dbh->last_insert_id("", "", "", "");
+
+        sub addNARToDB {
+            my ($storePath, $narFile) = @_;
+            $dbh->do(
+                "insert into NARs(manifest, storePath, url, hash, size, narHash, " .
+                "narSize, refs, deriver, system) values (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)",
+                {}, $id, $storePath, $narFile->{url}, $narFile->{hash}, $narFile->{size},
+                $narFile->{narHash}, $narFile->{narSize}, $narFile->{references},
+                $narFile->{deriver}, $narFile->{system});
+        };
+        
+        sub addPatchToDB {
+            my ($storePath, $patch) = @_;
+            $dbh->do(
+                "insert into Patches(manifest, storePath, basePath, baseHash, url, hash, " .
+                "size, narHash, narSize, patchType) values (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)",
+                {}, $id, $storePath, $patch->{basePath}, $patch->{baseHash}, $patch->{url},
+                $patch->{hash}, $patch->{size}, $patch->{narHash}, $patch->{narSize},
+                $patch->{patchType});
+        };
+
+        my $version = readManifest_($manifest, \&addNARToDB, \&addPatchToDB);
+        
+        if ($version < 3) {
+            die "you have an old-style manifest `$manifest'; please delete it";
+        }
+        if ($version >= 10) {
+            die "manifest `$manifest' is too new; please delete it or upgrade Nix";
+        }
+    }
+
+    # Removed cached information for removed manifests from the DB.
+    foreach my $manifest (@{$dbh->selectcol_arrayref("select path from Manifests")}) {
+        next if defined $seen{$manifest};
+        $dbh->do("delete from Manifests where path = ?", {}, $manifest);
+    }
+
+    $dbh->commit;
+
+    close MAINLOCK;
+
+    return $dbh;
+}
+
+
+return 1;