nix/src/libstore/daemon.cc

#include "daemon.hh"
#include "monitor-fd.hh"
#include "worker-protocol.hh"
#include "store-api.hh"
#include "finally.hh"
#include "affinity.hh"
#include "archive.hh"
#include "derivations.hh"
#include "args.hh"

namespace nix::daemon {

Sink & operator << (Sink & sink, const Logger::Fields & fields)
{
    sink << fields.size();
    for (auto & f : fields) {
        sink << f.type;
        if (f.type == Logger::Field::tInt)
            sink << f.i;
        else if (f.type == Logger::Field::tString)
            sink << f.s;
        else abort();
    }
    return sink;
}

/* Logger that forwards log messages to the client, *if* we're in a
   state where the protocol allows it (i.e., when canSendStderr is
   true). */
struct TunnelLogger : public Logger
{
    FdSink & to;

    struct State
    {
        bool canSendStderr = false;
        std::vector<std::string> pendingMsgs;
    };

    Sync<State> state_;

    unsigned int clientVersion;

    TunnelLogger(FdSink & to, unsigned int clientVersion)
        : to(to), clientVersion(clientVersion) { }

    void enqueueMsg(const std::string & s)
    {
        auto state(state_.lock());

        if (state->canSendStderr) {
            assert(state->pendingMsgs.empty());
            try {
                to(s);
                to.flush();
            } catch (...) {
                /* Write failed; that means that the other side is
                   gone. */
                state->canSendStderr = false;
                throw;
            }
        } else
            state->pendingMsgs.push_back(s);
    }

    void log(Verbosity lvl, const FormatOrString & fs) override
    {
        if (lvl > verbosity) return;

        StringSink buf;
        buf << STDERR_NEXT << (fs.s + "\n");
        enqueueMsg(*buf.s);
    }

    void logEI(const ErrorInfo & ei) override
    {
        if (ei.level > verbosity) return;

        std::stringstream oss;
        showErrorInfo(oss, ei, false);

        StringSink buf;
        buf << STDERR_NEXT << oss.str();
        enqueueMsg(*buf.s);
    }

    /* startWork() means that we're starting an operation for which we
       want to send out stderr to the client. */
    void startWork()
    {
        auto state(state_.lock());
        state->canSendStderr = true;

        for (auto & msg : state->pendingMsgs)
            to(msg);

        state->pendingMsgs.clear();

        to.flush();
    }

    /* stopWork() means that we're done; stop sending stderr to the
       client. */
    void stopWork(bool success = true, const string & msg = "", unsigned int status = 0)
    {
        auto state(state_.lock());

        state->canSendStderr = false;

        if (success)
            to << STDERR_LAST;
        else {
            to << STDERR_ERROR << msg;
            if (status != 0) to << status;
        }
    }

    void startActivity(ActivityId act, Verbosity lvl, ActivityType type,
        const std::string & s, const Fields & fields, ActivityId parent) override
    {
        if (GET_PROTOCOL_MINOR(clientVersion) < 20) {
            if (!s.empty())
                log(lvl, s + "...");
            return;
        }

        StringSink buf;
        buf << STDERR_START_ACTIVITY << act << lvl << type << s << fields << parent;
        enqueueMsg(*buf.s);
    }

    void stopActivity(ActivityId act) override
    {
        if (GET_PROTOCOL_MINOR(clientVersion) < 20) return;
        StringSink buf;
        buf << STDERR_STOP_ACTIVITY << act;
        enqueueMsg(*buf.s);
    }

    void result(ActivityId act, ResultType type, const Fields & fields) override
    {
        if (GET_PROTOCOL_MINOR(clientVersion) < 20) return;
        StringSink buf;
        buf << STDERR_RESULT << act << type << fields;
        enqueueMsg(*buf.s);
    }
};

struct TunnelSink : Sink
{
    Sink & to;
    TunnelSink(Sink & to) : to(to) { }
    virtual void operator () (const unsigned char * data, size_t len)
    {
        to << STDERR_WRITE;
        writeString(data, len, to);
    }
};

struct TunnelSource : BufferedSource
{
    Source & from;
    BufferedSink & to;
    TunnelSource(Source & from, BufferedSink & to) : from(from), to(to) { }
    size_t readUnbuffered(unsigned char * data, size_t len) override
    {
        to << STDERR_READ << len;
        to.flush();
        size_t n = readString(data, len, from);
        if (n == 0) throw EndOfFile("unexpected end-of-file");
        return n;
    }
};

struct ClientSettings
{
    bool keepFailed;
    bool keepGoing;
    bool tryFallback;
    Verbosity verbosity;
    unsigned int maxBuildJobs;
    time_t maxSilentTime;
    bool verboseBuild;
    unsigned int buildCores;
    bool useSubstitutes;
    StringMap overrides;

    void apply(TrustedFlag trusted)
    {
        settings.keepFailed = keepFailed;
        settings.keepGoing = keepGoing;
        settings.tryFallback = tryFallback;
        nix::verbosity = verbosity;
        settings.maxBuildJobs.assign(maxBuildJobs);
        settings.maxSilentTime = maxSilentTime;
        settings.verboseBuild = verboseBuild;
        settings.buildCores = buildCores;
        settings.useSubstitutes = useSubstitutes;

        for (auto & i : overrides) {
            auto & name(i.first);
            auto & value(i.second);

            auto setSubstituters = [&](Setting<Strings> & res) {
                if (name != res.name && res.aliases.count(name) == 0)
                    return false;
                StringSet trusted = settings.trustedSubstituters;
                for (auto & s : settings.substituters.get())
                    trusted.insert(s);
                Strings subs;
                auto ss = tokenizeString<Strings>(value);
                for (auto & s : ss)
                    if (trusted.count(s))
                        subs.push_back(s);
                    else
                        warn("ignoring untrusted substituter '%s'", s);
                res = subs;
                return true;
            };

            try {
                if (name == "ssh-auth-sock") // obsolete
                    ;
                else if (trusted
                    || name == settings.buildTimeout.name
                    || name == "connect-timeout"
                    || (name == "builders" && value == ""))
                    settings.set(name, value);
                else if (setSubstituters(settings.substituters))
                    ;
                else if (setSubstituters(settings.extraSubstituters))
                    ;
                else
                    debug("ignoring the client-specified setting '%s', because it is a restricted setting and you are not a trusted user", name);
            } catch (UsageError & e) {
                warn(e.what());
            }
        }
    }
};

static void performOp(TunnelLogger * logger, ref<Store> store,
    TrustedFlag trusted, RecursiveFlag recursive, unsigned int clientVersion,
    Source & from, BufferedSink & to, unsigned int op)
{
    switch (op) {

    case wopIsValidPath: {
        auto path = store->parseStorePath(readString(from));
        logger->startWork();
        bool result = store->isValidPath(path);
        logger->stopWork();
        to << result;
        break;
    }

    case wopQueryValidPaths: {
        auto paths = readStorePaths<StorePathSet>(*store, from);
        logger->startWork();
        auto res = store->queryValidPaths(paths);
        logger->stopWork();
        writeStorePaths(*store, to, res);
        break;
    }

    case wopHasSubstitutes: {
        auto path = store->parseStorePath(readString(from));
        logger->startWork();
        StorePathSet paths; // FIXME
        paths.insert(path);
        auto res = store->querySubstitutablePaths(paths);
        logger->stopWork();
        to << (res.count(path) != 0);
        break;
    }

    case wopQuerySubstitutablePaths: {
        auto paths = readStorePaths<StorePathSet>(*store, from);
        logger->startWork();
        auto res = store->querySubstitutablePaths(paths);
        logger->stopWork();
        writeStorePaths(*store, to, res);
        break;
    }

    case wopQueryPathHash: {
        auto path = store->parseStorePath(readString(from));
        logger->startWork();
        auto hash = store->queryPathInfo(path)->narHash;
        logger->stopWork();
        to << hash.to_string(Base16, false);
        break;
    }

    case wopQueryReferences:
    case wopQueryReferrers:
    case wopQueryValidDerivers:
    case wopQueryDerivationOutputs: {
        auto path = store->parseStorePath(readString(from));
        logger->startWork();
        StorePathSet paths;
        if (op == wopQueryReferences)
            for (auto & i : store->queryPathInfo(path)->references)
                paths.insert(i);
        else if (op == wopQueryReferrers)
            store->queryReferrers(path, paths);
        else if (op == wopQueryValidDerivers)
            paths = store->queryValidDerivers(path);
        else paths = store->queryDerivationOutputs(path);
        logger->stopWork();
        writeStorePaths(*store, to, paths);
        break;
    }

    case wopQueryDerivationOutputNames: {
        auto path = store->parseStorePath(readString(from));
        logger->startWork();
        auto names = store->readDerivation(path).outputNames();
        logger->stopWork();
        to << names;
        break;
    }

    case wopQueryDerivationOutputMap: {
        auto path = store->parseStorePath(readString(from));
        logger->startWork();
        auto outputs = store->queryPartialDerivationOutputMap(path);
        logger->stopWork();
        worker_proto::write(*store, to, outputs);
        break;
    }

    case wopQueryDeriver: {
        auto path = store->parseStorePath(readString(from));
        logger->startWork();
        auto info = store->queryPathInfo(path);
        logger->stopWork();
        to << (info->deriver ? store->printStorePath(*info->deriver) : "");
        break;
    }

    case wopQueryPathFromHashPart: {
        auto hashPart = readString(from);
        logger->startWork();
        auto path = store->queryPathFromHashPart(hashPart);
        logger->stopWork();
        to << (path ? store->printStorePath(*path) : "");
        break;
    }

    case wopAddToStore: {
        if (GET_PROTOCOL_MINOR(clientVersion) >= 25) {
            auto name = readString(from);
            auto camStr = readString(from);
            auto refs = readStorePaths<StorePathSet>(*store, from);

            logger->startWork();
            StorePath path = [&]() -> StorePath {
                // NB: FramedSource must be out of scope before logger->stopWork();
                ContentAddressMethod contentAddressMethod = parseContentAddressMethod(camStr);
                FramedSource source(from);
                return std::visit(overloaded {
                    [&](TextHashMethod &_) -> StorePath {
                        // We could stream this by changing Store
                        std::string contents = source.drain();
                        return store->addTextToStore(name, contents, refs);
                    },
                    [&](FixedOutputHashMethod &fohm) -> StorePath {
                        if (!refs.empty())
                            throw UnimplementedError("cannot yet have refs with flat or nar-hashed data");
                        return store->addToStoreFromDump(source, name, fohm.fileIngestionMethod, fohm.hashType);
                    },
                }, contentAddressMethod);
            }();
            logger->stopWork();

            to << store->printStorePath(path);

        } else {
            HashType hashAlgo;
            std::string baseName;
            FileIngestionMethod method;
            {
                bool fixed;
                uint8_t recursive;
                std::string hashAlgoRaw;
                from >> baseName >> fixed /* obsolete */ >> recursive >> hashAlgoRaw;
                if (recursive > (uint8_t) FileIngestionMethod::Recursive)
                    throw Error("unsupported FileIngestionMethod with value of %i; you may need to upgrade nix-daemon", recursive);
                method = FileIngestionMethod { recursive };
                /* Compatibility hack. */
                if (!fixed) {
                    hashAlgoRaw = "sha256";
                    method = FileIngestionMethod::Recursive;
                }
                hashAlgo = parseHashType(hashAlgoRaw);
            }

            StringSink saved;
            TeeSource savedNARSource(from, saved);
            RetrieveRegularNARSink savedRegular { saved };

            if (method == FileIngestionMethod::Recursive) {
                /* Get the entire NAR dump from the client and save it to
                  a string so that we can pass it to
                  addToStoreFromDump(). */
                ParseSink sink; /* null sink; just parse the NAR */
                parseDump(sink, savedNARSource);
            } else
                parseDump(savedRegular, from);

            logger->startWork();
            if (!savedRegular.regular) throw Error("regular file expected");

            // FIXME: try to stream directly from `from`.
            StringSource dumpSource { *saved.s };
            auto path = store->addToStoreFromDump(dumpSource, baseName, method, hashAlgo);
            logger->stopWork();

            to << store->printStorePath(path);
        }
        break;
    }

    case wopAddTextToStore: {
        string suffix = readString(from);
        string s = readString(from);
        auto refs = readStorePaths<StorePathSet>(*store, from);
        logger->startWork();
        auto path = store->addTextToStore(suffix, s, refs, NoRepair);
        logger->stopWork();
        to << store->printStorePath(path);
        break;
    }

    case wopExportPath: {
        auto path = store->parseStorePath(readString(from));
        readInt(from); // obsolete
        logger->startWork();
        TunnelSink sink(to);
        store->exportPath(path, sink);
        logger->stopWork();
        to << 1;
        break;
    }

    case wopImportPaths: {
        logger->startWork();
        TunnelSource source(from, to);
        auto paths = store->importPaths(source,
            trusted ? NoCheckSigs : CheckSigs);
        logger->stopWork();
        Strings paths2;
        for (auto & i : paths) paths2.push_back(store->printStorePath(i));
        to << paths2;
        break;
    }

    case wopBuildPaths: {
        std::vector<StorePathWithOutputs> drvs;
        for (auto & s : readStrings<Strings>(from))
            drvs.push_back(store->parsePathWithOutputs(s));
        BuildMode mode = bmNormal;
        if (GET_PROTOCOL_MINOR(clientVersion) >= 15) {
            mode = (BuildMode) readInt(from);

            /* Repairing is not atomic, so disallowed for "untrusted"
               clients.  */
            if (mode == bmRepair && !trusted)
                throw Error("repairing is not allowed because you are not in 'trusted-users'");
        }
        logger->startWork();
        store->buildPaths(drvs, mode);
        logger->stopWork();
        to << 1;
        break;
    }

    case wopBuildDerivation: {
        auto drvPath = store->parseStorePath(readString(from));
        BasicDerivation drv;
        readDerivation(from, *store, drv, Derivation::nameFromPath(drvPath));
        BuildMode buildMode = (BuildMode) readInt(from);
        logger->startWork();

        /* Content-addressed derivations are trustless because their output paths
           are verified by their content alone, so any derivation is free to
           try to produce such a path.

           Input-addressed derivation output paths, however, are calculated
           from the derivation closure that produced them---even knowing the
           root derivation is not enough. That the output data actually came
           from those derivations is fundamentally unverifiable, but the daemon
           trusts itself on that matter. The question instead is whether the
           submitted plan has rights to the output paths it wants to fill, and
           at least the derivation closure proves that.

           It would have been nice if input-address algorithm merely depended
           on the build time closure, rather than depending on the derivation
           closure. That would mean input-addressed paths used at build time
           would just be trusted and not need their own evidence. This is in
           fact fine as the same guarantees would hold *inductively*: either
           the remote builder has those paths and already trusts them, or it
           needs to build them too and thus their evidence must be provided in
           turn.  The advantage of this variant algorithm is that the evidence
           for input-addressed paths which the remote builder already has
           doesn't need to be sent again.

           That said, now that we have floating CA derivations, it is better
           that people just migrate to those which also solve this problem, and
           others. It's the same migration difficulty with strictly more
           benefit.

           Lastly, do note that when we parse fixed-output content-addressed
           derivations, we throw out the precomputed output paths and just
           store the hashes, so there aren't two competing sources of truth an
           attacker could exploit. */
        if (drv.type() == DerivationType::InputAddressed && !trusted)
            throw Error("you are not privileged to build input-addressed derivations");

        /* Make sure that the non-input-addressed derivations that got this far
           are in fact content-addressed if we don't trust them. */
        assert(derivationIsCA(drv.type()) || trusted);

        auto res = store->buildDerivation(drvPath, drv, buildMode);
        logger->stopWork();
        to << res.status << res.errorMsg;
        break;
    }

    case wopEnsurePath: {
        auto path = store->parseStorePath(readString(from));
        logger->startWork();
        store->ensurePath(path);
        logger->stopWork();
        to << 1;
        break;
    }

    case wopAddTempRoot: {
        auto path = store->parseStorePath(readString(from));
        logger->startWork();
        store->addTempRoot(path);
        logger->stopWork();
        to << 1;
        break;
    }

    case wopAddIndirectRoot: {
        Path path = absPath(readString(from));
        logger->startWork();
        store->addIndirectRoot(path);
        logger->stopWork();
        to << 1;
        break;
    }

    case wopSyncWithGC: {
        logger->startWork();
        store->syncWithGC();
        logger->stopWork();
        to << 1;
        break;
    }

    case wopFindRoots: {
        logger->startWork();
        Roots roots = store->findRoots(!trusted);
        logger->stopWork();

        size_t size = 0;
        for (auto & i : roots)
            size += i.second.size();

        to << size;

        for (auto & [target, links] : roots)
            for (auto & link : links)
                to << link << store->printStorePath(target);

        break;
    }

    case wopCollectGarbage: {
        GCOptions options;
        options.action = (GCOptions::GCAction) readInt(from);
        options.pathsToDelete = readStorePaths<StorePathSet>(*store, from);
        from >> options.ignoreLiveness >> options.maxFreed;
        // obsolete fields
        readInt(from);
        readInt(from);
        readInt(from);

        GCResults results;

        logger->startWork();
        if (options.ignoreLiveness)
            throw Error("you are not allowed to ignore liveness");
        store->collectGarbage(options, results);
        logger->stopWork();

        to << results.paths << results.bytesFreed << 0 /* obsolete */;

        break;
    }

    case wopSetOptions: {

        ClientSettings clientSettings;

        clientSettings.keepFailed = readInt(from);
        clientSettings.keepGoing = readInt(from);
        clientSettings.tryFallback = readInt(from);
        clientSettings.verbosity = (Verbosity) readInt(from);
        clientSettings.maxBuildJobs = readInt(from);
        clientSettings.maxSilentTime = readInt(from);
        readInt(from); // obsolete useBuildHook
        clientSettings.verboseBuild = lvlError == (Verbosity) readInt(from);
        readInt(from); // obsolete logType
        readInt(from); // obsolete printBuildTrace
        clientSettings.buildCores = readInt(from);
        clientSettings.useSubstitutes = readInt(from);

        if (GET_PROTOCOL_MINOR(clientVersion) >= 12) {
            unsigned int n = readInt(from);
            for (unsigned int i = 0; i < n; i++) {
                string name = readString(from);
                string value = readString(from);
                clientSettings.overrides.emplace(name, value);
            }
        }

        logger->startWork();

        // FIXME: use some setting in recursive mode. Will need to use
        // non-global variables.
        if (!recursive)
            clientSettings.apply(trusted);

        logger->stopWork();
        break;
    }

    case wopQuerySubstitutablePathInfo: {
        auto path = store->parseStorePath(readString(from));
        logger->startWork();
        SubstitutablePathInfos infos;
        store->querySubstitutablePathInfos({{path, std::nullopt}}, infos);
        logger->stopWork();
        auto i = infos.find(path);
        if (i == infos.end())
            to << 0;
        else {
            to << 1
               << (i->second.deriver ? store->printStorePath(*i->second.deriver) : "");
            writeStorePaths(*store, to, i->second.references);
            to << i->second.downloadSize
               << i->second.narSize;
        }
        break;
    }

    case wopQuerySubstitutablePathInfos: {
        SubstitutablePathInfos infos;
        StorePathCAMap pathsMap = {};
        if (GET_PROTOCOL_MINOR(clientVersion) < 22) {
            auto paths = readStorePaths<StorePathSet>(*store, from);
            for (auto & path : paths)
                pathsMap.emplace(path, std::nullopt);
        } else
            pathsMap = readStorePathCAMap(*store, from);
        logger->startWork();
        store->querySubstitutablePathInfos(pathsMap, infos);
        logger->stopWork();
        to << infos.size();
        for (auto & i : infos) {
            to << store->printStorePath(i.first)
               << (i.second.deriver ? store->printStorePath(*i.second.deriver) : "");
            writeStorePaths(*store, to, i.second.references);
            to << i.second.downloadSize << i.second.narSize;
        }
        break;
    }

    case wopQueryAllValidPaths: {
        logger->startWork();
        auto paths = store->queryAllValidPaths();
        logger->stopWork();
        writeStorePaths(*store, to, paths);
        break;
    }

    case wopQueryPathInfo: {
        auto path = store->parseStorePath(readString(from));
        std::shared_ptr<const ValidPathInfo> info;
        logger->startWork();
        try {
            info = store->queryPathInfo(path);
        } catch (InvalidPath &) {
            if (GET_PROTOCOL_MINOR(clientVersion) < 17) throw;
        }
        logger->stopWork();
        if (info) {
            if (GET_PROTOCOL_MINOR(clientVersion) >= 17)
                to << 1;
            to << (info->deriver ? store->printStorePath(*info->deriver) : "")
               << info->narHash.to_string(Base16, false);
            writeStorePaths(*store, to, info->references);
            to << info->registrationTime << info->narSize;
            if (GET_PROTOCOL_MINOR(clientVersion) >= 16) {
                to << info->ultimate
                   << info->sigs
                   << renderContentAddress(info->ca);
            }
        } else {
            assert(GET_PROTOCOL_MINOR(clientVersion) >= 17);
            to << 0;
        }
        break;
    }

    case wopOptimiseStore:
        logger->startWork();
        store->optimiseStore();
        logger->stopWork();
        to << 1;
        break;

    case wopVerifyStore: {
        bool checkContents, repair;
        from >> checkContents >> repair;
        logger->startWork();
        if (repair && !trusted)
            throw Error("you are not privileged to repair paths");
        bool errors = store->verifyStore(checkContents, (RepairFlag) repair);
        logger->stopWork();
        to << errors;
        break;
    }

    case wopAddSignatures: {
        auto path = store->parseStorePath(readString(from));
        StringSet sigs = readStrings<StringSet>(from);
        logger->startWork();
        if (!trusted)
            throw Error("you are not privileged to add signatures");
        store->addSignatures(path, sigs);
        logger->stopWork();
        to << 1;
        break;
    }

    case wopNarFromPath: {
        auto path = store->parseStorePath(readString(from));
        logger->startWork();
        logger->stopWork();
        dumpPath(store->toRealPath(path), to);
        break;
    }

    case wopAddToStoreNar: {
        bool repair, dontCheckSigs;
        auto path = store->parseStorePath(readString(from));
        auto deriver = readString(from);
        auto narHash = Hash::parseAny(readString(from), htSHA256);
        ValidPathInfo info { path, narHash };
        if (deriver != "")
            info.deriver = store->parseStorePath(deriver);
        info.references = readStorePaths<StorePathSet>(*store, from);
        from >> info.registrationTime >> info.narSize >> info.ultimate;
        info.sigs = readStrings<StringSet>(from);
        info.ca = parseContentAddressOpt(readString(from));
        from >> repair >> dontCheckSigs;
        if (!trusted && dontCheckSigs)
            dontCheckSigs = false;
        if (!trusted)
            info.ultimate = false;

        if (GET_PROTOCOL_MINOR(clientVersion) >= 23) {
            logger->startWork();
            {
                FramedSource source(from);
                store->addToStore(info, source, (RepairFlag) repair,
                    dontCheckSigs ? NoCheckSigs : CheckSigs);
            }
            logger->stopWork();
        }

        else {
            std::unique_ptr<Source> source;
            if (GET_PROTOCOL_MINOR(clientVersion) >= 21)
                source = std::make_unique<TunnelSource>(from, to);
            else {
                StringSink saved;
                TeeSource tee { from, saved };
                ParseSink ether;
                parseDump(ether, tee);
                source = std::make_unique<StringSource>(std::move(*saved.s));
            }

            logger->startWork();

            // FIXME: race if addToStore doesn't read source?
            store->addToStore(info, *source, (RepairFlag) repair,
                dontCheckSigs ? NoCheckSigs : CheckSigs);

            logger->stopWork();
        }

        break;
    }

    case wopQueryMissing: {
        std::vector<StorePathWithOutputs> targets;
        for (auto & s : readStrings<Strings>(from))
            targets.push_back(store->parsePathWithOutputs(s));
        logger->startWork();
        StorePathSet willBuild, willSubstitute, unknown;
        uint64_t downloadSize, narSize;
        store->queryMissing(targets, willBuild, willSubstitute, unknown, downloadSize, narSize);
        logger->stopWork();
        writeStorePaths(*store, to, willBuild);
        writeStorePaths(*store, to, willSubstitute);
        writeStorePaths(*store, to, unknown);
        to << downloadSize << narSize;
        break;
    }

    default:
        throw Error("invalid operation %1%", op);
    }
}

void processConnection(
    ref<Store> store,
    FdSource & from,
    FdSink & to,
    TrustedFlag trusted,
    RecursiveFlag recursive,
    std::function<void(Store &)> authHook)
{
    auto monitor = !recursive ? std::make_unique<MonitorFdHup>(from.fd) : nullptr;

    /* Exchange the greeting. */
    unsigned int magic = readInt(from);
    if (magic != WORKER_MAGIC_1) throw Error("protocol mismatch");
    to << WORKER_MAGIC_2 << PROTOCOL_VERSION;
    to.flush();
    unsigned int clientVersion = readInt(from);

    if (clientVersion < 0x10a)
        throw Error("the Nix client version is too old");

    auto tunnelLogger = new TunnelLogger(to, clientVersion);
    auto prevLogger = nix::logger;
    // FIXME
    if (!recursive)
        logger = tunnelLogger;

    unsigned int opCount = 0;

    Finally finally([&]() {
        _isInterrupted = false;
        prevLogger->log(lvlDebug, fmt("%d operations", opCount));
    });

    if (GET_PROTOCOL_MINOR(clientVersion) >= 14 && readInt(from)) {
        auto affinity = readInt(from);
        setAffinityTo(affinity);
    }

    readInt(from); // obsolete reserveSpace

    /* Send startup error messages to the client. */
    tunnelLogger->startWork();

    try {

        /* If we can't accept clientVersion, then throw an error
           *here* (not above). */
        authHook(*store);

        tunnelLogger->stopWork();
        to.flush();

        /* Process client requests. */
        while (true) {
            WorkerOp op;
            try {
                op = (WorkerOp) readInt(from);
            } catch (Interrupted & e) {
                break;
            } catch (EndOfFile & e) {
                break;
            }

            opCount++;

            try {
                performOp(tunnelLogger, store, trusted, recursive, clientVersion, from, to, op);
            } catch (Error & e) {
                /* If we're not in a state where we can send replies, then
                   something went wrong processing the input of the
                   client.  This can happen especially if I/O errors occur
                   during addTextToStore() / importPath().  If that
                   happens, just send the error message and exit. */
                bool errorAllowed = tunnelLogger->state_.lock()->canSendStderr;
                tunnelLogger->stopWork(false, e.msg(), e.status);
                if (!errorAllowed) throw;
            } catch (std::bad_alloc & e) {
                tunnelLogger->stopWork(false, "Nix daemon out of memory", 1);
                throw;
            }

            to.flush();

            assert(!tunnelLogger->state_.lock()->canSendStderr);
        };

    } catch (std::exception & e) {
        tunnelLogger->stopWork(false, e.what(), 1);
        to.flush();
        return;
    }
}

}