path: root/src/libstore/build/derivation-goal.cc

#include "derivation-goal.hh"
#include "hook-instance.hh"
#include "worker.hh"
#include "builtins.hh"
#include "builtins/buildenv.hh"
#include "references.hh"
#include "finally.hh"
#include "util.hh"
#include "archive.hh"
#include "json.hh"
#include "compression.hh"
#include "worker-protocol.hh"
#include "topo-sort.hh"
#include "callback.hh"
#include "local-store.hh" // TODO remove, along with remaining downcasts

#include <regex>
#include <queue>

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <netdb.h>
#include <fcntl.h>
#include <termios.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/utsname.h>
#include <sys/resource.h>

#if HAVE_STATVFS
#include <sys/statvfs.h>
#endif

/* Includes required for chroot support. */
#if __linux__
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <netinet/ip.h>
#include <sys/personality.h>
#include <sys/mman.h>
#include <sched.h>
#include <sys/param.h>
#include <sys/mount.h>
#include <sys/syscall.h>
#if HAVE_SECCOMP
#include <seccomp.h>
#endif
#define pivot_root(new_root, put_old) (syscall(SYS_pivot_root, new_root, put_old))
#endif

#if __APPLE__
#include <spawn.h>
#include <sys/sysctl.h>
#endif

#include <pwd.h>
#include <grp.h>

#include <nlohmann/json.hpp>

namespace nix {

DerivationGoal::DerivationGoal(const StorePath & drvPath,
    const StringSet & wantedOutputs, Worker & worker, BuildMode buildMode)
    : Goal(worker)
    , useDerivation(true)
    , drvPath(drvPath)
    , wantedOutputs(wantedOutputs)
    , buildMode(buildMode)
{
    state = &DerivationGoal::getDerivation;
    name = fmt(
        "building of '%s' from .drv file",
        StorePathWithOutputs { drvPath, wantedOutputs }.to_string(worker.store));
    trace("created");

    mcExpectedBuilds = std::make_unique<MaintainCount<uint64_t>>(worker.expectedBuilds);
    worker.updateProgress();
}


DerivationGoal::DerivationGoal(const StorePath & drvPath, const BasicDerivation & drv,
    const StringSet & wantedOutputs, Worker & worker, BuildMode buildMode)
    : Goal(worker)
    , useDerivation(false)
    , drvPath(drvPath)
    , wantedOutputs(wantedOutputs)
    , buildMode(buildMode)
{
    this->drv = std::make_unique<Derivation>(drv);

    state = &DerivationGoal::haveDerivation;
    name = fmt(
        "building of '%s' from in-memory derivation",
        StorePathWithOutputs { drvPath, drv.outputNames() }.to_string(worker.store));
    trace("created");

    mcExpectedBuilds = std::make_unique<MaintainCount<uint64_t>>(worker.expectedBuilds);
    worker.updateProgress();

    /* Prevent the .chroot directory from being
       garbage-collected. (See isActiveTempFile() in gc.cc.) */
    worker.store.addTempRoot(this->drvPath);
}


DerivationGoal::~DerivationGoal()
{
    /* Careful: we should never ever throw an exception from a
       destructor. */
    try { closeLogFile(); } catch (...) { ignoreException(); }
}


string DerivationGoal::key()
{
    /* Ensure that derivations get built in order of their name,
       i.e. a derivation named "aardvark" always comes before
       "baboon". And substitution goals always happen before
       derivation goals (due to "b$"). */
    return "b$" + std::string(drvPath.name()) + "$" + worker.store.printStorePath(drvPath);
}


void DerivationGoal::killChild()
{
    hook.reset();
}


void DerivationGoal::timedOut(Error && ex)
{
    killChild();
    done(BuildResult::TimedOut, ex);
}


void DerivationGoal::work()
{
    (this->*state)();
}


void DerivationGoal::addWantedOutputs(const StringSet & outputs)
{
    /* If we already want all outputs, there is nothing to do. */
    if (wantedOutputs.empty()) return;

    if (outputs.empty()) {
        wantedOutputs.clear();
        needRestart = true;
    } else
        for (auto & i : outputs)
            if (wantedOutputs.insert(i).second)
                needRestart = true;
}


void DerivationGoal::getDerivation()
{
    trace("init");

    /* The first thing to do is to make sure that the derivation
       exists.  If it doesn't, it may be created through a
       substitute. */
    if (buildMode == bmNormal && worker.store.isValidPath(drvPath)) {
        loadDerivation();
        return;
    }

    addWaitee(upcast_goal(worker.makePathSubstitutionGoal(drvPath)));

    state = &DerivationGoal::loadDerivation;
}


void DerivationGoal::loadDerivation()
{
    trace("loading derivation");

    if (nrFailed != 0) {
        done(BuildResult::MiscFailure, Error("cannot build missing derivation '%s'", worker.store.printStorePath(drvPath)));
        return;
    }

    /* `drvPath' should already be a root, but let's be on the safe
       side: if the user forgot to make it a root, we wouldn't want
       things being garbage collected while we're busy. */
    worker.store.addTempRoot(drvPath);

    assert(worker.store.isValidPath(drvPath));

    /* Get the derivation. */
    drv = std::make_unique<Derivation>(worker.store.derivationFromPath(drvPath));

    haveDerivation();
}


void DerivationGoal::haveDerivation()
{
    trace("have derivation");

    if (drv->type() == DerivationType::CAFloating)
        settings.requireExperimentalFeature("ca-derivations");

    retrySubstitution = false;

    for (auto & i : drv->outputsAndOptPaths(worker.store))
        if (i.second.second)
            worker.store.addTempRoot(*i.second.second);

    auto outputHashes = staticOutputHashes(worker.store, *drv);
    for (auto &[outputName, outputHash] : outputHashes)
      initialOutputs.insert({
            outputName,
            InitialOutput{
                .wanted = true, // Will be refined later
                .outputHash = outputHash
            }
          });

    /* Check what outputs paths are not already valid. */
    checkPathValidity();
    bool allValid = true;
    for (auto & [_, status] : initialOutputs) {
        if (!status.wanted) continue;
        if (!status.known || !status.known->isValid()) {
            allValid = false;
            break;
        }
    }

    /* If they are all valid, then we're done. */
    if (allValid && buildMode == bmNormal) {
        done(BuildResult::AlreadyValid);
        return;
    }

    parsedDrv = std::make_unique<ParsedDerivation>(drvPath, *drv);


    /* We are first going to try to create the invalid output paths
       through substitutes.  If that doesn't work, we'll build
       them. */
    if (settings.useSubstitutes && parsedDrv->substitutesAllowed())
        for (auto & [_, status] : initialOutputs) {
            if (!status.wanted) continue;
            if (!status.known) {
                warn("do not know how to query for unknown floating content-addressed derivation output yet");
                /* Nothing to wait for; tail call */
                return DerivationGoal::gaveUpOnSubstitution();
            }
            addWaitee(upcast_goal(worker.makePathSubstitutionGoal(
                status.known->path,
                buildMode == bmRepair ? Repair : NoRepair,
                getDerivationCA(*drv))));
        }

    if (waitees.empty()) /* to prevent hang (no wake-up event) */
        outputsSubstitutionTried();
    else
        state = &DerivationGoal::outputsSubstitutionTried;
}


void DerivationGoal::outputsSubstitutionTried()
{
    trace("all outputs substituted (maybe)");

    if (nrFailed > 0 && nrFailed > nrNoSubstituters + nrIncompleteClosure && !settings.tryFallback) {
        done(BuildResult::TransientFailure,
            fmt("some substitutes for the outputs of derivation '%s' failed (usually happens due to networking issues); try '--fallback' to build derivation from source ",
                worker.store.printStorePath(drvPath)));
        return;
    }

    /*  If the substitutes form an incomplete closure, then we should
        build the dependencies of this derivation, but after that, we
        can still use the substitutes for this derivation itself.

        If the nrIncompleteClosure != nrFailed, we have another issue as well.
        In particular, it may be the case that the hole in the closure is
        an output of the current derivation, which causes a loop if retried.
     */
    if (nrIncompleteClosure > 0 && nrIncompleteClosure == nrFailed) retrySubstitution = true;

    nrFailed = nrNoSubstituters = nrIncompleteClosure = 0;

    if (needRestart) {
        needRestart = false;
        haveDerivation();
        return;
    }

    checkPathValidity();
    size_t nrInvalid = 0;
    for (auto & [_, status] : initialOutputs) {
        if (!status.wanted) continue;
        if (!status.known || !status.known->isValid())
            nrInvalid++;
    }

    if (buildMode == bmNormal && nrInvalid == 0) {
        done(BuildResult::Substituted);
        return;
    }
    if (buildMode == bmRepair && nrInvalid == 0) {
        repairClosure();
        return;
    }
    if (buildMode == bmCheck && nrInvalid > 0)
        throw Error("some outputs of '%s' are not valid, so checking is not possible",
            worker.store.printStorePath(drvPath));

    /* Nothing to wait for; tail call */
    gaveUpOnSubstitution();
}

/* At least one of the output paths could not be
   produced using a substitute.  So we have to build instead. */
void DerivationGoal::gaveUpOnSubstitution()
{
    /* Make sure checkPathValidity() from now on checks all
       outputs. */
    wantedOutputs.clear();

    /* The inputs must be built before we can build this goal. */
    if (useDerivation)
        for (auto & i : dynamic_cast<Derivation *>(drv.get())->inputDrvs)
            addWaitee(worker.makeDerivationGoal(i.first, i.second, buildMode == bmRepair ? bmRepair : bmNormal));

    for (auto & i : drv->inputSrcs) {
        if (worker.store.isValidPath(i)) continue;
        if (!settings.useSubstitutes)
            throw Error("dependency '%s' of '%s' does not exist, and substitution is disabled",
                worker.store.printStorePath(i), worker.store.printStorePath(drvPath));
        addWaitee(upcast_goal(worker.makePathSubstitutionGoal(i)));
    }

    if (waitees.empty()) /* to prevent hang (no wake-up event) */
        inputsRealised();
    else
        state = &DerivationGoal::inputsRealised;
}


void DerivationGoal::repairClosure()
{
    /* If we're repairing, we now know that our own outputs are valid.
       Now check whether the other paths in the outputs closure are
       good.  If not, then start derivation goals for the derivations
       that produced those outputs. */

    /* Get the output closure. */
    auto outputs = queryDerivationOutputMap();
    StorePathSet outputClosure;
    for (auto & i : outputs) {
        if (!wantOutput(i.first, wantedOutputs)) continue;
        worker.store.computeFSClosure(i.second, outputClosure);
    }

    /* Filter out our own outputs (which we have already checked). */
    for (auto & i : outputs)
        outputClosure.erase(i.second);

    /* Get all dependencies of this derivation so that we know which
       derivation is responsible for which path in the output
       closure. */
    StorePathSet inputClosure;
    if (useDerivation) worker.store.computeFSClosure(drvPath, inputClosure);
    std::map<StorePath, StorePath> outputsToDrv;
    for (auto & i : inputClosure)
        if (i.isDerivation()) {
            auto depOutputs = worker.store.queryPartialDerivationOutputMap(i);
            for (auto & j : depOutputs)
                if (j.second)
                    outputsToDrv.insert_or_assign(*j.second, i);
        }

    /* Check each path (slow!). */
    for (auto & i : outputClosure) {
        if (worker.pathContentsGood(i)) continue;
        printError(
            "found corrupted or missing path '%s' in the output closure of '%s'",
            worker.store.printStorePath(i), worker.store.printStorePath(drvPath));
        auto drvPath2 = outputsToDrv.find(i);
        if (drvPath2 == outputsToDrv.end())
            addWaitee(upcast_goal(worker.makePathSubstitutionGoal(i, Repair)));
        else
            addWaitee(worker.makeDerivationGoal(drvPath2->second, StringSet(), bmRepair));
    }

    if (waitees.empty()) {
        done(BuildResult::AlreadyValid);
        return;
    }

    state = &DerivationGoal::closureRepaired;
}


void DerivationGoal::closureRepaired()
{
    trace("closure repaired");
    if (nrFailed > 0)
        throw Error("some paths in the output closure of derivation '%s' could not be repaired",
            worker.store.printStorePath(drvPath));
    done(BuildResult::AlreadyValid);
}


void DerivationGoal::inputsRealised()
{
    trace("all inputs realised");

    if (nrFailed != 0) {
        if (!useDerivation)
            throw Error("some dependencies of '%s' are missing", worker.store.printStorePath(drvPath));
        done(BuildResult::DependencyFailed, Error(
                "%s dependencies of derivation '%s' failed to build",
                nrFailed, worker.store.printStorePath(drvPath)));
        return;
    }

    if (retrySubstitution) {
        haveDerivation();
        return;
    }

    /* Gather information necessary for computing the closure and/or
       running the build hook. */

    /* Determine the full set of input paths. */

    /* First, the input derivations. */
    if (useDerivation) {
        auto & fullDrv = *dynamic_cast<Derivation *>(drv.get());

        if (settings.isExperimentalFeatureEnabled("ca-derivations") &&
            ((!fullDrv.inputDrvs.empty() && derivationIsCA(fullDrv.type()))
            || fullDrv.type() == DerivationType::DeferredInputAddressed)) {
            /* We are be able to resolve this derivation based on the
               now-known results of dependencies. If so, we become a stub goal
               aliasing that resolved derivation goal */
            std::optional attempt = fullDrv.tryResolve(worker.store);
            assert(attempt);
            Derivation drvResolved { *std::move(attempt) };

            auto pathResolved = writeDerivation(worker.store, drvResolved);
            resolvedDrv = drvResolved;

            auto msg = fmt("Resolved derivation: '%s' -> '%s'",
                worker.store.printStorePath(drvPath),
                worker.store.printStorePath(pathResolved));
            act = std::make_unique<Activity>(*logger, lvlInfo, actBuildWaiting, msg,
                Logger::Fields {
                       worker.store.printStorePath(drvPath),
                       worker.store.printStorePath(pathResolved),
                   });

            auto resolvedGoal = worker.makeDerivationGoal(
                pathResolved, wantedOutputs, buildMode);
            addWaitee(resolvedGoal);

            state = &DerivationGoal::resolvedFinished;
            return;
        }

        for (auto & [depDrvPath, wantedDepOutputs] : fullDrv.inputDrvs) {
            /* Add the relevant output closures of the input derivation
               `i' as input paths.  Only add the closures of output paths
               that are specified as inputs. */
            assert(worker.store.isValidPath(drvPath));
            auto outputs = worker.store.queryPartialDerivationOutputMap(depDrvPath);
            for (auto & j : wantedDepOutputs) {
                if (outputs.count(j) > 0) {
                    auto optRealizedInput = outputs.at(j);
                    if (!optRealizedInput)
                        throw Error(
                            "derivation '%s' requires output '%s' from input derivation '%s', which is supposedly realized already, yet we still don't know what path corresponds to that output",
                            worker.store.printStorePath(drvPath), j, worker.store.printStorePath(depDrvPath));
                    worker.store.computeFSClosure(*optRealizedInput, inputPaths);
                } else
                    throw Error(
                        "derivation '%s' requires non-existent output '%s' from input derivation '%s'",
                        worker.store.printStorePath(drvPath), j, worker.store.printStorePath(depDrvPath));
            }
        }
    }

    /* Second, the input sources. */
    worker.store.computeFSClosure(drv->inputSrcs, inputPaths);

    debug("added input paths %s", worker.store.showPaths(inputPaths));

    /* What type of derivation are we building? */
    derivationType = drv->type();

    /* Don't repeat fixed-output derivations since they're already
       verified by their output hash.*/
    nrRounds = derivationIsFixed(derivationType) ? 1 : settings.buildRepeat + 1;

    /* Okay, try to build.  Note that here we don't wait for a build
       slot to become available, since we don't need one if there is a
       build hook. */
    state = &DerivationGoal::tryToBuild;
    worker.wakeUp(shared_from_this());

    result = BuildResult();
}

void DerivationGoal::started() {
    auto msg = fmt(
        buildMode == bmRepair ? "repairing outputs of '%s'" :
        buildMode == bmCheck ? "checking outputs of '%s'" :
        nrRounds > 1 ? "building '%s' (round %d/%d)" :
        "building '%s'", worker.store.printStorePath(drvPath), curRound, nrRounds);
    fmt("building '%s'", worker.store.printStorePath(drvPath));
    if (hook) msg += fmt(" on '%s'", machineName);
    act = std::make_unique<Activity>(*logger, lvlInfo, actBuild, msg,
        Logger::Fields{worker.store.printStorePath(drvPath), hook ? machineName : "", curRound, nrRounds});
    mcRunningBuilds = std::make_unique<MaintainCount<uint64_t>>(worker.runningBuilds);
    worker.updateProgress();
}

void DerivationGoal::tryToBuild()
{
    trace("trying to build");

    /* Obtain locks on all output paths, if the paths are known a priori.

       The locks are automatically released when we exit this function or Nix
       crashes.  If we can't acquire the lock, then continue; hopefully some
       other goal can start a build, and if not, the main loop will sleep a few
       seconds and then retry this goal. */
    PathSet lockFiles;
    /* FIXME: Should lock something like the drv itself so we don't build same
       CA drv concurrently */
    if (dynamic_cast<LocalStore *>(&worker.store))
        /* If we aren't a local store, we might need to use the local store as
           a build remote, but that would cause a deadlock. */
        /* FIXME: Make it so we can use ourselves as a build remote even if we
           are the local store (separate locking for building vs scheduling? */
        /* FIXME: find some way to lock for scheduling for the other stores so
           a forking daemon with --store still won't farm out redundant builds.
           */
        for (auto & i : drv->outputsAndOptPaths(worker.store))
            if (i.second.second)
                lockFiles.insert(worker.store.Store::toRealPath(*i.second.second));

    if (!outputLocks.lockPaths(lockFiles, "", false)) {
        if (!actLock)
            actLock = std::make_unique<Activity>(*logger, lvlWarn, actBuildWaiting,
                fmt("waiting for lock on %s", yellowtxt(showPaths(lockFiles))));
        worker.waitForAWhile(shared_from_this());
        return;
    }

    actLock.reset();

    /* Now check again whether the outputs are valid.  This is because
       another process may have started building in parallel.  After
       it has finished and released the locks, we can (and should)
       reuse its results.  (Strictly speaking the first check can be
       omitted, but that would be less efficient.)  Note that since we
       now hold the locks on the output paths, no other process can
       build this derivation, so no further checks are necessary. */
    checkPathValidity();
    bool allValid = true;
    for (auto & [_, status] : initialOutputs) {
        if (!status.wanted) continue;
        if (!status.known || !status.known->isValid()) {
            allValid = false;
            break;
        }
    }
    if (buildMode != bmCheck && allValid) {
        debug("skipping build of derivation '%s', someone beat us to it", worker.store.printStorePath(drvPath));
        outputLocks.setDeletion(true);
        done(BuildResult::AlreadyValid);
        return;
    }

    /* If any of the outputs already exist but are not valid, delete
       them. */
    for (auto & [_, status] : initialOutputs) {
        if (!status.known || status.known->isValid()) continue;
        auto storePath = status.known->path;
        debug("removing invalid path '%s'", worker.store.printStorePath(status.known->path));
        deletePath(worker.store.Store::toRealPath(storePath));
    }

    /* Don't do a remote build if the derivation has the attribute
       `preferLocalBuild' set.  Also, check and repair modes are only
       supported for local builds. */
    bool buildLocally = buildMode != bmNormal || parsedDrv->willBuildLocally(worker.store);

    if (!buildLocally) {
        switch (tryBuildHook()) {
            case rpAccept:
                /* Yes, it has started doing so.  Wait until we get
                   EOF from the hook. */
                actLock.reset();
                result.startTime = time(0); // inexact
                state = &DerivationGoal::buildDone;
                started();
                return;
            case rpPostpone:
                /* Not now; wait until at least one child finishes or
                   the wake-up timeout expires. */
                if (!actLock)
                    actLock = std::make_unique<Activity>(*logger, lvlWarn, actBuildWaiting,
                        fmt("waiting for a machine to build '%s'", yellowtxt(worker.store.printStorePath(drvPath))));
                worker.waitForAWhile(shared_from_this());
                outputLocks.unlock();
                return;
            case rpDecline:
                /* We should do it ourselves. */
                break;
        }
    }

    actLock.reset();

    state = &DerivationGoal::tryLocalBuild;
    worker.wakeUp(shared_from_this());
}

void DerivationGoal::tryLocalBuild() {
    throw Error(
        "unable to build with a primary store that isn't a local store; "
        "either pass a different '--store' or enable remote builds."
        "\nhttps://nixos.org/nix/manual/#chap-distributed-builds");
}


static void chmod_(const Path & path, mode_t mode)
{
    if (chmod(path.c_str(), mode) == -1)
        throw SysError("setting permissions on '%s'", path);
}


/* Move/rename path 'src' to 'dst'. Temporarily make 'src' writable if
   it's a directory and we're not root (to be able to update the
   directory's parent link ".."). */
static void movePath(const Path & src, const Path & dst)
{
    auto st = lstat(src);

    bool changePerm = (geteuid() && S_ISDIR(st.st_mode) && !(st.st_mode & S_IWUSR));

    if (changePerm)
        chmod_(src, st.st_mode | S_IWUSR);

    if (rename(src.c_str(), dst.c_str()))
        throw SysError("renaming '%1%' to '%2%'", src, dst);

    if (changePerm)
        chmod_(dst, st.st_mode);
}


void replaceValidPath(const Path & storePath, const Path & tmpPath)
{
    /* We can't atomically replace storePath (the original) with
       tmpPath (the replacement), so we have to move it out of the
       way first.  We'd better not be interrupted here, because if
       we're repairing (say) Glibc, we end up with a broken system. */
    Path oldPath = (format("%1%.old-%2%-%3%") % storePath % getpid() % random()).str();
    if (pathExists(storePath))
        movePath(storePath, oldPath);

    try {
        movePath(tmpPath, storePath);
    } catch (...) {
        try {
            // attempt to recover
            movePath(oldPath, storePath);
        } catch (...) {
            ignoreException();
        }
        throw;
    }

    deletePath(oldPath);
}


int DerivationGoal::getChildStatus()
{
    return hook->pid.kill();
}


void DerivationGoal::closeReadPipes()
{
    hook->builderOut.readSide = -1;
    hook->fromHook.readSide = -1;
}


void DerivationGoal::cleanupHookFinally()
{
}


void DerivationGoal::cleanupPreChildKill()
{
}


void DerivationGoal::cleanupPostChildKill()
{
}


bool DerivationGoal::cleanupDecideWhetherDiskFull()
{
    return false;
}


void DerivationGoal::cleanupPostOutputsRegisteredModeCheck()
{
}


void DerivationGoal::cleanupPostOutputsRegisteredModeNonCheck()
{
}


void DerivationGoal::buildDone()
{
    trace("build done");

    Finally releaseBuildUser([&](){ this->cleanupHookFinally(); });

    cleanupPreChildKill();

    /* Since we got an EOF on the logger pipe, the builder is presumed
       to have terminated.  In fact, the builder could also have
       simply have closed its end of the pipe, so just to be sure,
       kill it. */
    int status = getChildStatus();

    debug("builder process for '%s' finished", worker.store.printStorePath(drvPath));

    result.timesBuilt++;
    result.stopTime = time(0);

    /* So the child is gone now. */
    worker.childTerminated(this);

    /* Close the read side of the logger pipe. */
    closeReadPipes();

    /* Close the log file. */
    closeLogFile();

    cleanupPostChildKill();

    bool diskFull = false;

    try {

        /* Check the exit status. */
        if (!statusOk(status)) {

            diskFull |= cleanupDecideWhetherDiskFull();

            auto msg = fmt("builder for '%s' %s",
                yellowtxt(worker.store.printStorePath(drvPath)),
                statusToString(status));

            if (!logger->isVerbose() && !logTail.empty()) {
                msg += fmt(";\nlast %d log lines:\n", logTail.size());
                for (auto & line : logTail) {
                    msg += "> ";
                    msg += line;
                    msg += "\n";
                }
                msg += fmt("For full logs, run '" ANSI_BOLD "nix log %s" ANSI_NORMAL "'.",
                    worker.store.printStorePath(drvPath));
            }

            if (diskFull)
                msg += "\nnote: build failure may have been caused by lack of free disk space";

            throw BuildError(msg);
        }

        /* Compute the FS closure of the outputs and register them as
           being valid. */
        registerOutputs();

        if (settings.postBuildHook != "") {
            Activity act(*logger, lvlInfo, actPostBuildHook,
                fmt("running post-build-hook '%s'", settings.postBuildHook),
                Logger::Fields{worker.store.printStorePath(drvPath)});
            PushActivity pact(act.id);
            StorePathSet outputPaths;
            for (auto i : drv->outputs) {
                outputPaths.insert(finalOutputs.at(i.first));
            }
            std::map<std::string, std::string> hookEnvironment = getEnv();

            hookEnvironment.emplace("DRV_PATH", worker.store.printStorePath(drvPath));
            hookEnvironment.emplace("OUT_PATHS", chomp(concatStringsSep(" ", worker.store.printStorePathSet(outputPaths))));

            RunOptions opts(settings.postBuildHook, {});
            opts.environment = hookEnvironment;

            struct LogSink : Sink {
                Activity & act;
                std::string currentLine;

                LogSink(Activity & act) : act(act) { }

                void operator() (std::string_view data) override {
                    for (auto c : data) {
                        if (c == '\n') {
                            flushLine();
                        } else {
                            currentLine += c;
                        }
                    }
                }

                void flushLine() {
                    act.result(resPostBuildLogLine, currentLine);
                    currentLine.clear();
                }

                ~LogSink() {
                    if (currentLine != "") {
                        currentLine += '\n';
                        flushLine();
                    }
                }
            };
            LogSink sink(act);

            opts.standardOut = &sink;
            opts.mergeStderrToStdout = true;
            runProgram2(opts);
        }

        if (buildMode == bmCheck) {
            cleanupPostOutputsRegisteredModeCheck();
            done(BuildResult::Built);
            return;
        }

        cleanupPostOutputsRegisteredModeNonCheck();

        /* Repeat the build if necessary. */
        if (curRound++ < nrRounds) {
            outputLocks.unlock();
            state = &DerivationGoal::tryToBuild;
            worker.wakeUp(shared_from_this());
            return;
        }

        /* It is now safe to delete the lock files, since all future
           lockers will see that the output paths are valid; they will
           not create new lock files with the same names as the old
           (unlinked) lock files. */
        outputLocks.setDeletion(true);
        outputLocks.unlock();

    } catch (BuildError & e) {
        outputLocks.unlock();

        BuildResult::Status st = BuildResult::MiscFailure;

        if (hook && WIFEXITED(status) && WEXITSTATUS(status) == 101)
            st = BuildResult::TimedOut;

        else if (hook && (!WIFEXITED(status) || WEXITSTATUS(status) != 100)) {
        }

        else {
            st =
                dynamic_cast<NotDeterministic*>(&e) ? BuildResult::NotDeterministic :
                statusOk(status) ? BuildResult::OutputRejected :
                derivationIsImpure(derivationType) || diskFull ? BuildResult::TransientFailure :
                BuildResult::PermanentFailure;
        }

        done(st, e);
        return;
    }

    done(BuildResult::Built);
}

void DerivationGoal::resolvedFinished() {
    assert(resolvedDrv);

    auto resolvedHashes = staticOutputHashes(worker.store, *resolvedDrv);

    // `wantedOutputs` might be empty, which means “all the outputs”
    auto realWantedOutputs = wantedOutputs;
    if (realWantedOutputs.empty())
        realWantedOutputs = resolvedDrv->outputNames();

    for (auto & wantedOutput : realWantedOutputs) {
        assert(initialOutputs.count(wantedOutput) != 0);
        assert(resolvedHashes.count(wantedOutput) != 0);
        auto realisation = worker.store.queryRealisation(
                DrvOutput{resolvedHashes.at(wantedOutput), wantedOutput}
        );
        // We've just built it, but maybe the build failed, in which case the
        // realisation won't be there
        if (realisation) {
            auto newRealisation = *realisation;
            newRealisation.id = DrvOutput{initialOutputs.at(wantedOutput).outputHash, wantedOutput};
            worker.store.registerDrvOutput(newRealisation);
        } else {
            // If we don't have a realisation, then it must mean that something
            // failed when building the resolved drv
            assert(!result.success());
        }
    }

    // This is potentially a bit fishy in terms of error reporting. Not sure
    // how to do it in a cleaner way
    amDone(nrFailed == 0 ? ecSuccess : ecFailed, ex);
}

HookReply DerivationGoal::tryBuildHook()
{
    if (!worker.tryBuildHook || !useDerivation) return rpDecline;

    if (!worker.hook)
        worker.hook = std::make_unique<HookInstance>();

    try {

        /* Send the request to the hook. */
        worker.hook->sink
            << "try"
            << (worker.getNrLocalBuilds() < settings.maxBuildJobs ? 1 : 0)
            << drv->platform
            << worker.store.printStorePath(drvPath)
            << parsedDrv->getRequiredSystemFeatures();
        worker.hook->sink.flush();

        /* Read the first line of input, which should be a word indicating
           whether the hook wishes to perform the build. */
        string reply;
        while (true) {
            auto s = [&]() {
                try {
                    return readLine(worker.hook->fromHook.readSide.get());
                } catch (Error & e) {
                    e.addTrace({}, "while reading the response from the build hook");
                    throw e;
                }
            }();
            if (handleJSONLogMessage(s, worker.act, worker.hook->activities, true))
                ;
            else if (string(s, 0, 2) == "# ") {
                reply = string(s, 2);
                break;
            }
            else {
                s += "\n";
                writeToStderr(s);
            }
        }

        debug("hook reply is '%1%'", reply);

        if (reply == "decline")
            return rpDecline;
        else if (reply == "decline-permanently") {
            worker.tryBuildHook = false;
            worker.hook = 0;
            return rpDecline;
        }
        else if (reply == "postpone")
            return rpPostpone;
        else if (reply != "accept")
            throw Error("bad hook reply '%s'", reply);

    } catch (SysError & e) {
        if (e.errNo == EPIPE) {
            printError(
                "build hook died unexpectedly: %s",
                chomp(drainFD(worker.hook->fromHook.readSide.get())));
            worker.hook = 0;
            return rpDecline;
        } else
            throw;
    }

    hook = std::move(worker.hook);

    try {
        machineName = readLine(hook->fromHook.readSide.get());
    } catch (Error & e) {
        e.addTrace({}, "while reading the machine name from the build hook");
        throw e;
    }

    /* Tell the hook all the inputs that have to be copied to the
       remote system. */
    worker_proto::write(worker.store, hook->sink, inputPaths);

    /* Tell the hooks the missing outputs that have to be copied back
       from the remote system. */
    {
        StringSet missingOutputs;
        for (auto & [outputName, status] : initialOutputs) {
            // XXX: Does this include known CA outputs?
            if (buildMode != bmCheck && status.known && status.known->isValid()) continue;
            missingOutputs.insert(outputName);
        }
        worker_proto::write(worker.store, hook->sink, missingOutputs);
    }

    hook->sink = FdSink();
    hook->toHook.writeSide = -1;

    /* Create the log file and pipe. */
    Path logFile = openLogFile();

    set<int> fds;
    fds.insert(hook->fromHook.readSide.get());
    fds.insert(hook->builderOut.readSide.get());
    worker.childStarted(shared_from_this(), fds, false, false);

    return rpAccept;
}


StorePathSet DerivationGoal::exportReferences(const StorePathSet & storePaths)
{
    StorePathSet paths;

    for (auto & storePath : storePaths) {
        if (!inputPaths.count(storePath))
            throw BuildError("cannot export references of path '%s' because it is not in the input closure of the derivation", worker.store.printStorePath(storePath));

        worker.store.computeFSClosure({storePath}, paths);
    }

    /* If there are derivations in the graph, then include their
       outputs as well.  This is useful if you want to do things
       like passing all build-time dependencies of some path to a
       derivation that builds a NixOS DVD image. */
    auto paths2 = paths;

    for (auto & j : paths2) {
        if (j.isDerivation()) {
            Derivation drv = worker.store.derivationFromPath(j);
            for (auto & k : drv.outputsAndOptPaths(worker.store)) {
                if (!k.second.second)
                    /* FIXME: I am confused why we are calling
                       `computeFSClosure` on the output path, rather than
                       derivation itself. That doesn't seem right to me, so I
                       won't try to implemented this for CA derivations. */
                    throw UnimplementedError("exportReferences on CA derivations is not yet implemented");
                worker.store.computeFSClosure(*k.second.second, paths);
            }
        }
    }

    return paths;
}


void DerivationGoal::registerOutputs()
{
    /* When using a build hook, the build hook can register the output
       as valid (by doing `nix-store --import').  If so we don't have
       to do anything here.

       We can only early return when the outputs are known a priori. For
       floating content-addressed derivations this isn't the case.
     */
    for (auto & [outputName, optOutputPath] : worker.store.queryPartialDerivationOutputMap(drvPath)) {
        if (!wantOutput(outputName, wantedOutputs))
            continue;
        if (!optOutputPath)
            throw BuildError(
                "output '%s' from derivation '%s' does not have a known output path",
                outputName, worker.store.printStorePath(drvPath));
        auto & outputPath = *optOutputPath;
        if (!worker.store.isValidPath(outputPath))
            throw BuildError(
                "output '%s' from derivation '%s' is supposed to be at '%s' but that path is not valid",
                outputName, worker.store.printStorePath(drvPath), worker.store.printStorePath(outputPath));

        finalOutputs.insert_or_assign(outputName, outputPath);
    }
}

Path DerivationGoal::openLogFile()
{
    logSize = 0;

    if (!settings.keepLog) return "";

    auto baseName = std::string(baseNameOf(worker.store.printStorePath(drvPath)));

    /* Create a log file. */
    Path logDir;
    if (auto localStore = dynamic_cast<LocalStore *>(&worker.store))
        logDir = localStore->logDir;
    else
        logDir = settings.nixLogDir;
    Path dir = fmt("%s/%s/%s/", logDir, LocalFSStore::drvsLogDir, string(baseName, 0, 2));
    createDirs(dir);

    Path logFileName = fmt("%s/%s%s", dir, string(baseName, 2),
        settings.compressLog ? ".bz2" : "");

    fdLogFile = open(logFileName.c_str(), O_CREAT | O_WRONLY | O_TRUNC | O_CLOEXEC, 0666);
    if (!fdLogFile) throw SysError("creating log file '%1%'", logFileName);

    logFileSink = std::make_shared<FdSink>(fdLogFile.get());

    if (settings.compressLog)
        logSink = std::shared_ptr<CompressionSink>(makeCompressionSink("bzip2", *logFileSink));
    else
        logSink = logFileSink;

    return logFileName;
}


void DerivationGoal::closeLogFile()
{
    auto logSink2 = std::dynamic_pointer_cast<CompressionSink>(logSink);
    if (logSink2) logSink2->finish();
    if (logFileSink) logFileSink->flush();
    logSink = logFileSink = 0;
    fdLogFile = -1;
}


bool DerivationGoal::isReadDesc(int fd)
{
    return fd == hook->builderOut.readSide.get();
}


void DerivationGoal::handleChildOutput(int fd, const string & data)
{
    if (isReadDesc(fd))
    {
        logSize += data.size();
        if (settings.maxLogSize && logSize > settings.maxLogSize) {
            killChild();
            done(
                BuildResult::LogLimitExceeded,
                Error("%s killed after writing more than %d bytes of log output",
                    getName(), settings.maxLogSize));
            return;
        }

        for (auto c : data)
            if (c == '\r')
                currentLogLinePos = 0;
            else if (c == '\n')
                flushLine();
            else {
                if (currentLogLinePos >= currentLogLine.size())
                    currentLogLine.resize(currentLogLinePos + 1);
                currentLogLine[currentLogLinePos++] = c;
            }

        if (logSink) (*logSink)(data);
    }

    if (hook && fd == hook->fromHook.readSide.get()) {
        for (auto c : data)
            if (c == '\n') {
                handleJSONLogMessage(currentHookLine, worker.act, hook->activities, true);
                currentHookLine.clear();
            } else
                currentHookLine += c;
    }
}


void DerivationGoal::handleEOF(int fd)
{
    if (!currentLogLine.empty()) flushLine();
    worker.wakeUp(shared_from_this());
}


void DerivationGoal::flushLine()
{
    if (handleJSONLogMessage(currentLogLine, *act, builderActivities, false))
        ;

    else {
        logTail.push_back(currentLogLine);
        if (logTail.size() > settings.logLines) logTail.pop_front();

        act->result(resBuildLogLine, currentLogLine);
    }

    currentLogLine = "";
    currentLogLinePos = 0;
}


std::map<std::string, std::optional<StorePath>> DerivationGoal::queryPartialDerivationOutputMap()
{
    if (!useDerivation || drv->type() != DerivationType::CAFloating) {
        std::map<std::string, std::optional<StorePath>> res;
        for (auto & [name, output] : drv->outputs)
            res.insert_or_assign(name, output.path(worker.store, drv->name, name));
        return res;
    } else {
        return worker.store.queryPartialDerivationOutputMap(drvPath);
    }
}

OutputPathMap DerivationGoal::queryDerivationOutputMap()
{
    if (!useDerivation || drv->type() != DerivationType::CAFloating) {
        OutputPathMap res;
        for (auto & [name, output] : drv->outputsAndOptPaths(worker.store))
            res.insert_or_assign(name, *output.second);
        return res;
    } else {
        return worker.store.queryDerivationOutputMap(drvPath);
    }
}


void DerivationGoal::checkPathValidity()
{
    bool checkHash = buildMode == bmRepair;
    for (auto & i : queryPartialDerivationOutputMap()) {
        InitialOutput & info = initialOutputs.at(i.first);
        info.wanted = wantOutput(i.first, wantedOutputs);
        if (i.second) {
            auto outputPath = *i.second;
            info.known = {
                .path = outputPath,
                .status = !worker.store.isValidPath(outputPath)
                    ? PathStatus::Absent
                    : !checkHash || worker.pathContentsGood(outputPath)
                    ? PathStatus::Valid
                    : PathStatus::Corrupt,
            };
        }
        if (settings.isExperimentalFeatureEnabled("ca-derivations")) {
            if (auto real = worker.store.queryRealisation(
                    DrvOutput{initialOutputs.at(i.first).outputHash, i.first})) {
                info.known = {
                    .path = real->outPath,
                    .status = PathStatus::Valid,
                };
            }
        }
    }
}


void DerivationGoal::done(BuildResult::Status status, std::optional<Error> ex)
{
    result.status = status;
    if (ex)
        result.errorMsg = ex->what();
    amDone(result.success() ? ecSuccess : ecFailed, ex);
    if (result.status == BuildResult::TimedOut)
        worker.timedOut = true;
    if (result.status == BuildResult::PermanentFailure)
        worker.permanentFailure = true;

    mcExpectedBuilds.reset();
    mcRunningBuilds.reset();

    if (result.success()) {
        if (status == BuildResult::Built)
            worker.doneBuilds++;
    } else {
        if (status != BuildResult::DependencyFailed)
            worker.failedBuilds++;
    }

    worker.updateProgress();
}


}