nix-copy-closure: Fix race condition
There is a long-standing race condition when copying a closure to a remote machine, particularly affecting build-remote.pl: the client first asks the remote machine which paths it already has, then copies over the missing paths. If the garbage collector kicks in on the remote machine between the first and second step, the already-present paths may be deleted. The missing paths may then refer to deleted paths, causing nix-copy-closure to fail. The client now performs both steps using a single remote Nix call (using ‘nix-store --serve’), locking all paths in the closure while querying. I changed the --serve protocol a bit (getting rid of QueryCommand), so this breaks the SSH substituter from older versions. But it was marked experimental anyway. Fixes #141.
This commit is contained in:
Eelco Dolstra
parent
2c3a8f787b
commit
04170d06bf
4 changed files with 137 additions and 61 deletions
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@ -4,6 +4,15 @@ use strict;
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use Nix::Config;
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use Nix::Store;
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use List::Util qw(sum);
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use IPC::Open2;
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sub readInt {
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my ($from) = @_;
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my $resp;
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sysread($from, $resp, 8) == 8 or die "did not receive valid reply from remote host\n";
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return unpack("L<x4", $resp);
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}
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sub copyTo {
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@ -20,14 +29,76 @@ sub copyTo {
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# Ignore exit status because this is just an optimisation.
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}
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# Start ‘nix-store --serve’ on the remote host.
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my ($from, $to);
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my $pid = open2($from, $to, "ssh $sshHost @{$sshOpts} nix-store --serve --write");
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# Do the handshake.
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eval {
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my $SERVE_MAGIC_1 = 0x390c9deb; # FIXME
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my $clientVersion = 0x200;
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syswrite($to, pack("L<x4L<x4", $SERVE_MAGIC_1, $clientVersion)) or die;
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die "did not get valid handshake from remote host\n" if readInt($from) != 0x5452eecb;
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my $serverVersion = readInt($from);
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die "unsupported server version\n" if $serverVersion < 0x200 || $serverVersion >= 0x300;
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};
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if ($@) {
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chomp $@;
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warn "$@; falling back to old closure copying method\n";
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return oldCopyTo(\@closure, @_);
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}
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# Send the "query valid paths" command with the "lock" option
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# enabled. This prevens a race where the remote host
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# garbage-collect paths that are already there.
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my $req = pack("L<x4L<x4L<x4", 1, 1, scalar @closure);
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for my $s (@closure) {
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my $len = length $s;
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$req .= pack("L<x4", $len);
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$req .= $s;
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$req .= "\000" x (8 - $len % 8) if $len % 8;
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}
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syswrite($to, $req) or die;
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# Get back the set of paths that are already valid on the remote host.
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my %present;
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my $n = readInt($from);
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while ($n--) {
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my $len = readInt($from);
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my $s;
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sysread($from, $s, $len) == $len or die;
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$present{$s} = 1;
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sysread($from, $s, 8 - $len % 8) if $len % 8; # skip padding
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}
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my @missing = grep { !$present{$_} } @closure;
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return if !@missing;
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# Send the "import paths" command.
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syswrite($to, pack("L<x4", 4)) or die;
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exportPaths(fileno($to), $sign, @missing);
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readInt($from) == 1 or die;
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# Shut down the server process.
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close $to;
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waitpid $pid, 0;
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}
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# For backwards compatibility with Nix <= 1.7. Will be removed
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# eventually.
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sub oldCopyTo {
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my ($closure, $sshHost, $sshOpts, $storePaths, $compressor, $decompressor,
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$includeOutputs, $dryRun, $sign, $progressViewer, $useSubstitutes) = @_;
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# Ask the remote host which paths are invalid. Because of limits
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# to the command line length, do this in chunks. Eventually,
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# we'll want to use ‘--from-stdin’, but we can't rely on the
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# target having this option yet.
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my @missing = ();
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my @missing;
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my $missingSize = 0;
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while (scalar(@closure) > 0) {
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my @ps = splice(@closure, 0, 1500);
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while (scalar(@$closure) > 0) {
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my @ps = splice(@$closure, 0, 1500);
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open(READ, "set -f; ssh $sshHost @{$sshOpts} nix-store --check-validity --print-invalid @ps|");
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while (<READ>) {
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chomp;
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@ -58,7 +58,7 @@ static std::pair<FdSink, FdSource> connect(const string & conn)
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static void substitute(std::pair<FdSink, FdSource> & pipes, Path storePath, Path destPath)
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{
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writeInt(cmdSubstitute, pipes.first);
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writeInt(cmdDumpStorePath, pipes.first);
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writeString(storePath, pipes.first);
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pipes.first.flush();
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restorePath(destPath, pipes.second);
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@ -68,20 +68,20 @@ static void substitute(std::pair<FdSink, FdSource> & pipes, Path storePath, Path
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static void query(std::pair<FdSink, FdSource> & pipes)
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{
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writeInt(cmdQuery, pipes.first);
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for (string line; getline(std::cin, line);) {
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Strings tokenized = tokenizeString<Strings>(line);
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string cmd = tokenized.front();
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tokenized.pop_front();
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if (cmd == "have") {
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writeInt(qCmdHave, pipes.first);
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writeInt(cmdQueryValidPaths, pipes.first);
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writeInt(0, pipes.first); // don't lock
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writeStrings(tokenized, pipes.first);
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pipes.first.flush();
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PathSet paths = readStrings<PathSet>(pipes.second);
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foreach (PathSet::iterator, i, paths)
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std::cout << *i << std::endl;
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} else if (cmd == "info") {
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writeInt(qCmdInfo, pipes.first);
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writeInt(cmdQueryPathInfos, pipes.first);
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writeStrings(tokenized, pipes.first);
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pipes.first.flush();
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while (1) {
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@ -869,8 +869,12 @@ static void opClearFailedPaths(Strings opFlags, Strings opArgs)
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/* Serve the nix store in a way usable by a restricted ssh user. */
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static void opServe(Strings opFlags, Strings opArgs)
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{
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if (!opArgs.empty() || !opFlags.empty())
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throw UsageError("no arguments or flags expected");
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bool writeAllowed = false;
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foreach (Strings::iterator, i, opFlags)
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if (*i == "--write") writeAllowed = true;
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else throw UsageError(format("unknown flag `%1%'") % *i);
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if (!opArgs.empty()) throw UsageError("no arguments expected");
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FdSource in(STDIN_FILENO);
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FdSink out(STDOUT_FILENO);
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@ -883,23 +887,26 @@ static void opServe(Strings opFlags, Strings opArgs)
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out.flush();
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readInt(in); // Client version, unused for now
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ServeCommand cmd = (ServeCommand) readInt(in);
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switch (cmd) {
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case cmdQuery:
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while (true) {
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QueryCommand qCmd;
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ServeCommand cmd;
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try {
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qCmd = (QueryCommand) readInt(in);
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cmd = (ServeCommand) readInt(in);
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} catch (EndOfFile & e) {
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break;
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}
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switch (qCmd) {
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case qCmdHave: {
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switch (cmd) {
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case cmdQueryValidPaths: {
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bool lock = readInt(in);
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PathSet paths = readStorePaths<PathSet>(in);
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if (lock && writeAllowed)
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for (auto & path : paths)
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store->addTempRoot(path);
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writeStrings(store->queryValidPaths(paths), out);
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out.flush();
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break;
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}
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case qCmdInfo: {
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case cmdQueryPathInfos: {
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PathSet paths = readStorePaths<PathSet>(in);
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// !!! Maybe we want a queryPathInfos?
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foreach (PathSet::iterator, i, paths) {
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@ -914,19 +921,22 @@ static void opServe(Strings opFlags, Strings opArgs)
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writeLongLong(info.narSize, out);
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}
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writeString("", out);
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break;
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}
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default:
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throw Error(format("unknown serve query `%1%'") % cmd);
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}
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out.flush();
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}
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break;
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case cmdSubstitute:
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}
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case cmdDumpStorePath:
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dumpPath(readStorePath(in), out);
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out.flush();
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break;
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case cmdImportPaths:
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if (!writeAllowed) throw Error("importing paths not allowed");
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store->importPaths(false, in);
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writeInt(1, out); // indicate success
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out.flush();
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break;
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default:
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throw Error(format("unknown serve command `%1%'") % cmd);
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throw Error(format("unknown serve command %1%") % cmd);
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}
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}
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}
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@ -2,23 +2,18 @@
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namespace nix {
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#define SERVE_MAGIC_1 0x390c9deb
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#define SERVE_MAGIC_2 0x5452eecb
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#define SERVE_PROTOCOL_VERSION 0x101
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#define SERVE_PROTOCOL_VERSION 0x200
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#define GET_PROTOCOL_MAJOR(x) ((x) & 0xff00)
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#define GET_PROTOCOL_MINOR(x) ((x) & 0x00ff)
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typedef enum {
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cmdQuery = 0,
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cmdSubstitute = 1,
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cmdQueryValidPaths = 1,
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cmdQueryPathInfos = 2,
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cmdDumpStorePath = 3,
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cmdImportPaths = 4,
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} ServeCommand;
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typedef enum {
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qCmdHave = 0,
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qCmdInfo = 1,
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} QueryCommand;
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}
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