Add 'third_party/nix/' from commit 'be66c7a6b24e3c3c6157fd37b86c7203d14acf10' r/724

git-subtree-dir: third_party/nix
git-subtree-mainline: cf8cd640c1adf74a3706efbcb0ea4625da106fb2
git-subtree-split: be66c7a6b24e3c3c6157fd37b86c7203d14acf10

1 files changed, 817 insertions, 0 deletions

diff --git a/third_party/nix/src/libstore/remote-store.cc b/third_party/nix/src/libstore/remote-store.cc
new file mode 100644
index 000000000000..f34369d8fe0a
--- /dev/null
+++ b/third_party/nix/src/libstore/remote-store.cc
@@ -0,0 +1,817 @@
+#include "serialise.hh"
+#include "util.hh"
+#include "remote-store.hh"
+#include "worker-protocol.hh"
+#include "archive.hh"
+#include "affinity.hh"
+#include "globals.hh"
+#include "derivations.hh"
+#include "pool.hh"
+#include "finally.hh"
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include <cstring>
+
+namespace nix {
+
+
+Path readStorePath(Store & store, Source & from)
+{
+    Path path = readString(from);
+    store.assertStorePath(path);
+    return path;
+}
+
+
+template<class T> T readStorePaths(Store & store, Source & from)
+{
+    T paths = readStrings<T>(from);
+    for (auto & i : paths) store.assertStorePath(i);
+    return paths;
+}
+
+template PathSet readStorePaths(Store & store, Source & from);
+template Paths readStorePaths(Store & store, Source & from);
+
+/* TODO: Separate these store impls into different files, give them better names */
+RemoteStore::RemoteStore(const Params & params)
+    : Store(params)
+    , connections(make_ref<Pool<Connection>>(
+            std::max(1, (int) maxConnections),
+            [this]() { return openConnectionWrapper(); },
+            [this](const ref<Connection> & r) {
+                return
+                    r->to.good()
+                    && r->from.good()
+                    && std::chrono::duration_cast<std::chrono::seconds>(
+                        std::chrono::steady_clock::now() - r->startTime).count() < maxConnectionAge;
+            }
+            ))
+{
+}
+
+
+ref<RemoteStore::Connection> RemoteStore::openConnectionWrapper()
+{
+    if (failed)
+        throw Error("opening a connection to remote store '%s' previously failed", getUri());
+    try {
+        return openConnection();
+    } catch (...) {
+        failed = true;
+        throw;
+    }
+}
+
+
+UDSRemoteStore::UDSRemoteStore(const Params & params)
+    : Store(params)
+    , LocalFSStore(params)
+    , RemoteStore(params)
+{
+}
+
+
+UDSRemoteStore::UDSRemoteStore(std::string socket_path, const Params & params)
+    : Store(params)
+    , LocalFSStore(params)
+    , RemoteStore(params)
+    , path(socket_path)
+{
+}
+
+
+std::string UDSRemoteStore::getUri()
+{
+    if (path) {
+        return std::string("unix://") + *path;
+    } else {
+        return "daemon";
+    }
+}
+
+
+ref<RemoteStore::Connection> UDSRemoteStore::openConnection()
+{
+    auto conn = make_ref<Connection>();
+
+    /* Connect to a daemon that does the privileged work for us. */
+    conn->fd = socket(PF_UNIX, SOCK_STREAM
+        #ifdef SOCK_CLOEXEC
+        | SOCK_CLOEXEC
+        #endif
+        , 0);
+    if (!conn->fd)
+        throw SysError("cannot create Unix domain socket");
+    closeOnExec(conn->fd.get());
+
+    string socketPath = path ? *path : settings.nixDaemonSocketFile;
+
+    struct sockaddr_un addr;
+    addr.sun_family = AF_UNIX;
+    if (socketPath.size() + 1 >= sizeof(addr.sun_path))
+        throw Error(format("socket path '%1%' is too long") % socketPath);
+    strcpy(addr.sun_path, socketPath.c_str());
+
+    if (::connect(conn->fd.get(), (struct sockaddr *) &addr, sizeof(addr)) == -1)
+        throw SysError(format("cannot connect to daemon at '%1%'") % socketPath);
+
+    conn->from.fd = conn->fd.get();
+    conn->to.fd = conn->fd.get();
+
+    conn->startTime = std::chrono::steady_clock::now();
+
+    initConnection(*conn);
+
+    return conn;
+}
+
+
+void RemoteStore::initConnection(Connection & conn)
+{
+    /* Send the magic greeting, check for the reply. */
+    try {
+        conn.to << WORKER_MAGIC_1;
+        conn.to.flush();
+        unsigned int magic = readInt(conn.from);
+        if (magic != WORKER_MAGIC_2) throw Error("protocol mismatch");
+
+        conn.from >> conn.daemonVersion;
+        if (GET_PROTOCOL_MAJOR(conn.daemonVersion) != GET_PROTOCOL_MAJOR(PROTOCOL_VERSION))
+            throw Error("Nix daemon protocol version not supported");
+        if (GET_PROTOCOL_MINOR(conn.daemonVersion) < 10)
+            throw Error("the Nix daemon version is too old");
+        conn.to << PROTOCOL_VERSION;
+
+        if (GET_PROTOCOL_MINOR(conn.daemonVersion) >= 14) {
+            int cpu = sameMachine() && settings.lockCPU ? lockToCurrentCPU() : -1;
+            if (cpu != -1)
+                conn.to << 1 << cpu;
+            else
+                conn.to << 0;
+        }
+
+        if (GET_PROTOCOL_MINOR(conn.daemonVersion) >= 11)
+            conn.to << false;
+
+        auto ex = conn.processStderr();
+        if (ex) std::rethrow_exception(ex);
+    }
+    catch (Error & e) {
+        throw Error("cannot open connection to remote store '%s': %s", getUri(), e.what());
+    }
+
+    setOptions(conn);
+}
+
+
+void RemoteStore::setOptions(Connection & conn)
+{
+    conn.to << wopSetOptions
+       << settings.keepFailed
+       << settings.keepGoing
+       << settings.tryFallback
+       << verbosity
+       << settings.maxBuildJobs
+       << settings.maxSilentTime
+       << true
+       << (settings.verboseBuild ? lvlError : lvlVomit)
+       << 0 // obsolete log type
+       << 0 /* obsolete print build trace */
+       << settings.buildCores
+       << settings.useSubstitutes;
+
+    if (GET_PROTOCOL_MINOR(conn.daemonVersion) >= 12) {
+        std::map<std::string, Config::SettingInfo> overrides;
+        globalConfig.getSettings(overrides, true);
+        overrides.erase(settings.keepFailed.name);
+        overrides.erase(settings.keepGoing.name);
+        overrides.erase(settings.tryFallback.name);
+        overrides.erase(settings.maxBuildJobs.name);
+        overrides.erase(settings.maxSilentTime.name);
+        overrides.erase(settings.buildCores.name);
+        overrides.erase(settings.useSubstitutes.name);
+        overrides.erase(settings.showTrace.name);
+        conn.to << overrides.size();
+        for (auto & i : overrides)
+            conn.to << i.first << i.second.value;
+    }
+
+    auto ex = conn.processStderr();
+    if (ex) std::rethrow_exception(ex);
+}
+
+
+/* A wrapper around Pool<RemoteStore::Connection>::Handle that marks
+   the connection as bad (causing it to be closed) if a non-daemon
+   exception is thrown before the handle is closed. Such an exception
+   causes a deviation from the expected protocol and therefore a
+   desynchronization between the client and daemon. */
+struct ConnectionHandle
+{
+    Pool<RemoteStore::Connection>::Handle handle;
+    bool daemonException = false;
+
+    ConnectionHandle(Pool<RemoteStore::Connection>::Handle && handle)
+        : handle(std::move(handle))
+    { }
+
+    ConnectionHandle(ConnectionHandle && h)
+        : handle(std::move(h.handle))
+    { }
+
+    ~ConnectionHandle()
+    {
+        if (!daemonException && std::uncaught_exception()) {
+            handle.markBad();
+            debug("closing daemon connection because of an exception");
+        }
+    }
+
+    RemoteStore::Connection * operator -> () { return &*handle; }
+
+    void processStderr(Sink * sink = 0, Source * source = 0)
+    {
+        auto ex = handle->processStderr(sink, source);
+        if (ex) {
+            daemonException = true;
+            std::rethrow_exception(ex);
+        }
+    }
+};
+
+
+ConnectionHandle RemoteStore::getConnection()
+{
+    return ConnectionHandle(connections->get());
+}
+
+
+bool RemoteStore::isValidPathUncached(const Path & path)
+{
+    auto conn(getConnection());
+    conn->to << wopIsValidPath << path;
+    conn.processStderr();
+    return readInt(conn->from);
+}
+
+
+PathSet RemoteStore::queryValidPaths(const PathSet & paths, SubstituteFlag maybeSubstitute)
+{
+    auto conn(getConnection());
+    if (GET_PROTOCOL_MINOR(conn->daemonVersion) < 12) {
+        PathSet res;
+        for (auto & i : paths)
+            if (isValidPath(i)) res.insert(i);
+        return res;
+    } else {
+        conn->to << wopQueryValidPaths << paths;
+        conn.processStderr();
+        return readStorePaths<PathSet>(*this, conn->from);
+    }
+}
+
+
+PathSet RemoteStore::queryAllValidPaths()
+{
+    auto conn(getConnection());
+    conn->to << wopQueryAllValidPaths;
+    conn.processStderr();
+    return readStorePaths<PathSet>(*this, conn->from);
+}
+
+
+PathSet RemoteStore::querySubstitutablePaths(const PathSet & paths)
+{
+    auto conn(getConnection());
+    if (GET_PROTOCOL_MINOR(conn->daemonVersion) < 12) {
+        PathSet res;
+        for (auto & i : paths) {
+            conn->to << wopHasSubstitutes << i;
+            conn.processStderr();
+            if (readInt(conn->from)) res.insert(i);
+        }
+        return res;
+    } else {
+        conn->to << wopQuerySubstitutablePaths << paths;
+        conn.processStderr();
+        return readStorePaths<PathSet>(*this, conn->from);
+    }
+}
+
+
+void RemoteStore::querySubstitutablePathInfos(const PathSet & paths,
+    SubstitutablePathInfos & infos)
+{
+    if (paths.empty()) return;
+
+    auto conn(getConnection());
+
+    if (GET_PROTOCOL_MINOR(conn->daemonVersion) < 12) {
+
+        for (auto & i : paths) {
+            SubstitutablePathInfo info;
+            conn->to << wopQuerySubstitutablePathInfo << i;
+            conn.processStderr();
+            unsigned int reply = readInt(conn->from);
+            if (reply == 0) continue;
+            info.deriver = readString(conn->from);
+            if (info.deriver != "") assertStorePath(info.deriver);
+            info.references = readStorePaths<PathSet>(*this, conn->from);
+            info.downloadSize = readLongLong(conn->from);
+            info.narSize = readLongLong(conn->from);
+            infos[i] = info;
+        }
+
+    } else {
+
+        conn->to << wopQuerySubstitutablePathInfos << paths;
+        conn.processStderr();
+        size_t count = readNum<size_t>(conn->from);
+        for (size_t n = 0; n < count; n++) {
+            Path path = readStorePath(*this, conn->from);
+            SubstitutablePathInfo & info(infos[path]);
+            info.deriver = readString(conn->from);
+            if (info.deriver != "") assertStorePath(info.deriver);
+            info.references = readStorePaths<PathSet>(*this, conn->from);
+            info.downloadSize = readLongLong(conn->from);
+            info.narSize = readLongLong(conn->from);
+        }
+
+    }
+}
+
+
+void RemoteStore::queryPathInfoUncached(const Path & path,
+    Callback<std::shared_ptr<ValidPathInfo>> callback) noexcept
+{
+    try {
+        std::shared_ptr<ValidPathInfo> info;
+        {
+            auto conn(getConnection());
+            conn->to << wopQueryPathInfo << path;
+            try {
+                conn.processStderr();
+            } catch (Error & e) {
+                // Ugly backwards compatibility hack.
+                if (e.msg().find("is not valid") != std::string::npos)
+                    throw InvalidPath(e.what());
+                throw;
+            }
+            if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 17) {
+                bool valid; conn->from >> valid;
+                if (!valid) throw InvalidPath(format("path '%s' is not valid") % path);
+            }
+            info = std::make_shared<ValidPathInfo>();
+            info->path = path;
+            info->deriver = readString(conn->from);
+            if (info->deriver != "") assertStorePath(info->deriver);
+            info->narHash = Hash(readString(conn->from), htSHA256);
+            info->references = readStorePaths<PathSet>(*this, conn->from);
+            conn->from >> info->registrationTime >> info->narSize;
+            if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 16) {
+                conn->from >> info->ultimate;
+                info->sigs = readStrings<StringSet>(conn->from);
+                conn->from >> info->ca;
+            }
+        }
+        callback(std::move(info));
+    } catch (...) { callback.rethrow(); }
+}
+
+
+void RemoteStore::queryReferrers(const Path & path,
+    PathSet & referrers)
+{
+    auto conn(getConnection());
+    conn->to << wopQueryReferrers << path;
+    conn.processStderr();
+    PathSet referrers2 = readStorePaths<PathSet>(*this, conn->from);
+    referrers.insert(referrers2.begin(), referrers2.end());
+}
+
+
+PathSet RemoteStore::queryValidDerivers(const Path & path)
+{
+    auto conn(getConnection());
+    conn->to << wopQueryValidDerivers << path;
+    conn.processStderr();
+    return readStorePaths<PathSet>(*this, conn->from);
+}
+
+
+PathSet RemoteStore::queryDerivationOutputs(const Path & path)
+{
+    auto conn(getConnection());
+    conn->to << wopQueryDerivationOutputs << path;
+    conn.processStderr();
+    return readStorePaths<PathSet>(*this, conn->from);
+}
+
+
+PathSet RemoteStore::queryDerivationOutputNames(const Path & path)
+{
+    auto conn(getConnection());
+    conn->to << wopQueryDerivationOutputNames << path;
+    conn.processStderr();
+    return readStrings<PathSet>(conn->from);
+}
+
+
+Path RemoteStore::queryPathFromHashPart(const string & hashPart)
+{
+    auto conn(getConnection());
+    conn->to << wopQueryPathFromHashPart << hashPart;
+    conn.processStderr();
+    Path path = readString(conn->from);
+    if (!path.empty()) assertStorePath(path);
+    return path;
+}
+
+
+void RemoteStore::addToStore(const ValidPathInfo & info, Source & source,
+    RepairFlag repair, CheckSigsFlag checkSigs, std::shared_ptr<FSAccessor> accessor)
+{
+    auto conn(getConnection());
+
+    if (GET_PROTOCOL_MINOR(conn->daemonVersion) < 18) {
+        conn->to << wopImportPaths;
+
+        auto source2 = sinkToSource([&](Sink & sink) {
+            sink << 1 // == path follows
+                ;
+            copyNAR(source, sink);
+            sink
+                << exportMagic
+                << info.path
+                << info.references
+                << info.deriver
+                << 0 // == no legacy signature
+                << 0 // == no path follows
+                ;
+        });
+
+        conn.processStderr(0, source2.get());
+
+        auto importedPaths = readStorePaths<PathSet>(*this, conn->from);
+        assert(importedPaths.size() <= 1);
+    }
+
+    else {
+        conn->to << wopAddToStoreNar
+                 << info.path << info.deriver << info.narHash.to_string(Base16, false)
+                 << info.references << info.registrationTime << info.narSize
+                 << info.ultimate << info.sigs << info.ca
+                 << repair << !checkSigs;
+        bool tunnel = GET_PROTOCOL_MINOR(conn->daemonVersion) >= 21;
+        if (!tunnel) copyNAR(source, conn->to);
+        conn.processStderr(0, tunnel ? &source : nullptr);
+    }
+}
+
+
+Path RemoteStore::addToStore(const string & name, const Path & _srcPath,
+    bool recursive, HashType hashAlgo, PathFilter & filter, RepairFlag repair)
+{
+    if (repair) throw Error("repairing is not supported when building through the Nix daemon");
+
+    auto conn(getConnection());
+
+    Path srcPath(absPath(_srcPath));
+
+    conn->to << wopAddToStore << name
+       << ((hashAlgo == htSHA256 && recursive) ? 0 : 1) /* backwards compatibility hack */
+       << (recursive ? 1 : 0)
+       << printHashType(hashAlgo);
+
+    try {
+        conn->to.written = 0;
+        conn->to.warn = true;
+        connections->incCapacity();
+        {
+            Finally cleanup([&]() { connections->decCapacity(); });
+            dumpPath(srcPath, conn->to, filter);
+        }
+        conn->to.warn = false;
+        conn.processStderr();
+    } catch (SysError & e) {
+        /* Daemon closed while we were sending the path. Probably OOM
+           or I/O error. */
+        if (e.errNo == EPIPE)
+            try {
+                conn.processStderr();
+            } catch (EndOfFile & e) { }
+        throw;
+    }
+
+    return readStorePath(*this, conn->from);
+}
+
+
+Path RemoteStore::addTextToStore(const string & name, const string & s,
+    const PathSet & references, RepairFlag repair)
+{
+    if (repair) throw Error("repairing is not supported when building through the Nix daemon");
+
+    auto conn(getConnection());
+    conn->to << wopAddTextToStore << name << s << references;
+
+    conn.processStderr();
+    return readStorePath(*this, conn->from);
+}
+
+
+void RemoteStore::buildPaths(const PathSet & drvPaths, BuildMode buildMode)
+{
+    auto conn(getConnection());
+    conn->to << wopBuildPaths;
+    if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 13) {
+        conn->to << drvPaths;
+        if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 15)
+            conn->to << buildMode;
+        else
+            /* Old daemons did not take a 'buildMode' parameter, so we
+               need to validate it here on the client side.  */
+            if (buildMode != bmNormal)
+                throw Error("repairing or checking is not supported when building through the Nix daemon");
+    } else {
+        /* For backwards compatibility with old daemons, strip output
+           identifiers. */
+        PathSet drvPaths2;
+        for (auto & i : drvPaths)
+            drvPaths2.insert(string(i, 0, i.find('!')));
+        conn->to << drvPaths2;
+    }
+    conn.processStderr();
+    readInt(conn->from);
+}
+
+
+BuildResult RemoteStore::buildDerivation(const Path & drvPath, const BasicDerivation & drv,
+    BuildMode buildMode)
+{
+    auto conn(getConnection());
+    conn->to << wopBuildDerivation << drvPath << drv << buildMode;
+    conn.processStderr();
+    BuildResult res;
+    unsigned int status;
+    conn->from >> status >> res.errorMsg;
+    res.status = (BuildResult::Status) status;
+    return res;
+}
+
+
+void RemoteStore::ensurePath(const Path & path)
+{
+    auto conn(getConnection());
+    conn->to << wopEnsurePath << path;
+    conn.processStderr();
+    readInt(conn->from);
+}
+
+
+void RemoteStore::addTempRoot(const Path & path)
+{
+    auto conn(getConnection());
+    conn->to << wopAddTempRoot << path;
+    conn.processStderr();
+    readInt(conn->from);
+}
+
+
+void RemoteStore::addIndirectRoot(const Path & path)
+{
+    auto conn(getConnection());
+    conn->to << wopAddIndirectRoot << path;
+    conn.processStderr();
+    readInt(conn->from);
+}
+
+
+void RemoteStore::syncWithGC()
+{
+    auto conn(getConnection());
+    conn->to << wopSyncWithGC;
+    conn.processStderr();
+    readInt(conn->from);
+}
+
+
+Roots RemoteStore::findRoots(bool censor)
+{
+    auto conn(getConnection());
+    conn->to << wopFindRoots;
+    conn.processStderr();
+    size_t count = readNum<size_t>(conn->from);
+    Roots result;
+    while (count--) {
+        Path link = readString(conn->from);
+        Path target = readStorePath(*this, conn->from);
+        result[target].emplace(link);
+    }
+    return result;
+}
+
+
+void RemoteStore::collectGarbage(const GCOptions & options, GCResults & results)
+{
+    auto conn(getConnection());
+
+    conn->to
+        << wopCollectGarbage << options.action << options.pathsToDelete << options.ignoreLiveness
+        << options.maxFreed
+        /* removed options */
+        << 0 << 0 << 0;
+
+    conn.processStderr();
+
+    results.paths = readStrings<PathSet>(conn->from);
+    results.bytesFreed = readLongLong(conn->from);
+    readLongLong(conn->from); // obsolete
+
+    {
+        auto state_(Store::state.lock());
+        state_->pathInfoCache.clear();
+    }
+}
+
+
+void RemoteStore::optimiseStore()
+{
+    auto conn(getConnection());
+    conn->to << wopOptimiseStore;
+    conn.processStderr();
+    readInt(conn->from);
+}
+
+
+bool RemoteStore::verifyStore(bool checkContents, RepairFlag repair)
+{
+    auto conn(getConnection());
+    conn->to << wopVerifyStore << checkContents << repair;
+    conn.processStderr();
+    return readInt(conn->from);
+}
+
+
+void RemoteStore::addSignatures(const Path & storePath, const StringSet & sigs)
+{
+    auto conn(getConnection());
+    conn->to << wopAddSignatures << storePath << sigs;
+    conn.processStderr();
+    readInt(conn->from);
+}
+
+
+void RemoteStore::queryMissing(const PathSet & targets,
+    PathSet & willBuild, PathSet & willSubstitute, PathSet & unknown,
+    unsigned long long & downloadSize, unsigned long long & narSize)
+{
+    {
+        auto conn(getConnection());
+        if (GET_PROTOCOL_MINOR(conn->daemonVersion) < 19)
+            // Don't hold the connection handle in the fallback case
+            // to prevent a deadlock.
+            goto fallback;
+        conn->to << wopQueryMissing << targets;
+        conn.processStderr();
+        willBuild = readStorePaths<PathSet>(*this, conn->from);
+        willSubstitute = readStorePaths<PathSet>(*this, conn->from);
+        unknown = readStorePaths<PathSet>(*this, conn->from);
+        conn->from >> downloadSize >> narSize;
+        return;
+    }
+
+ fallback:
+    return Store::queryMissing(targets, willBuild, willSubstitute,
+        unknown, downloadSize, narSize);
+}
+
+
+void RemoteStore::connect()
+{
+    auto conn(getConnection());
+}
+
+
+unsigned int RemoteStore::getProtocol()
+{
+    auto conn(connections->get());
+    return conn->daemonVersion;
+}
+
+
+void RemoteStore::flushBadConnections()
+{
+    connections->flushBad();
+}
+
+
+RemoteStore::Connection::~Connection()
+{
+    try {
+        to.flush();
+    } catch (...) {
+        ignoreException();
+    }
+}
+
+
+static Logger::Fields readFields(Source & from)
+{
+    Logger::Fields fields;
+    size_t size = readInt(from);
+    for (size_t n = 0; n < size; n++) {
+        auto type = (decltype(Logger::Field::type)) readInt(from);
+        if (type == Logger::Field::tInt)
+            fields.push_back(readNum<uint64_t>(from));
+        else if (type == Logger::Field::tString)
+            fields.push_back(readString(from));
+        else
+            throw Error("got unsupported field type %x from Nix daemon", (int) type);
+    }
+    return fields;
+}
+
+
+std::exception_ptr RemoteStore::Connection::processStderr(Sink * sink, Source * source)
+{
+    to.flush();
+
+    while (true) {
+
+        auto msg = readNum<uint64_t>(from);
+
+        if (msg == STDERR_WRITE) {
+            string s = readString(from);
+            if (!sink) throw Error("no sink");
+            (*sink)(s);
+        }
+
+        else if (msg == STDERR_READ) {
+            if (!source) throw Error("no source");
+            size_t len = readNum<size_t>(from);
+            auto buf = std::make_unique<unsigned char[]>(len);
+            writeString(buf.get(), source->read(buf.get(), len), to);
+            to.flush();
+        }
+
+        else if (msg == STDERR_ERROR) {
+            string error = readString(from);
+            unsigned int status = readInt(from);
+            return std::make_exception_ptr(Error(status, error));
+        }
+
+        else if (msg == STDERR_NEXT)
+            printError(chomp(readString(from)));
+
+        else if (msg == STDERR_START_ACTIVITY) {
+            auto act = readNum<ActivityId>(from);
+            auto lvl = (Verbosity) readInt(from);
+            auto type = (ActivityType) readInt(from);
+            auto s = readString(from);
+            auto fields = readFields(from);
+            auto parent = readNum<ActivityId>(from);
+            logger->startActivity(act, lvl, type, s, fields, parent);
+        }
+
+        else if (msg == STDERR_STOP_ACTIVITY) {
+            auto act = readNum<ActivityId>(from);
+            logger->stopActivity(act);
+        }
+
+        else if (msg == STDERR_RESULT) {
+            auto act = readNum<ActivityId>(from);
+            auto type = (ResultType) readInt(from);
+            auto fields = readFields(from);
+            logger->result(act, type, fields);
+        }
+
+        else if (msg == STDERR_LAST)
+            break;
+
+        else
+            throw Error("got unknown message type %x from Nix daemon", msg);
+    }
+
+    return nullptr;
+}
+
+static std::string uriScheme = "unix://";
+
+static RegisterStoreImplementation regStore([](
+    const std::string & uri, const Store::Params & params)
+    -> std::shared_ptr<Store>
+{
+    if (std::string(uri, 0, uriScheme.size()) != uriScheme) return 0;
+    return std::make_shared<UDSRemoteStore>(std::string(uri, uriScheme.size()), params);
+});
+
+}