nix-super/src/libstore/store-api.cc

#include "signature/local-keys.hh"
#include "source-accessor.hh"
#include "globals.hh"
#include "derived-path.hh"
#include "realisation.hh"
#include "derivations.hh"
#include "store-api.hh"
#include "util.hh"
#include "nar-info-disk-cache.hh"
#include "thread-pool.hh"
#include "url.hh"
#include "references.hh"
#include "archive.hh"
#include "callback.hh"
#include "git.hh"
#include "posix-source-accessor.hh"
// FIXME this should not be here, see TODO below on
// `addMultipleToStore`.
#include "worker-protocol.hh"
#include "signals.hh"
#include "users.hh"

#ifndef _WIN32
# include "remote-store.hh"
#endif

#include <nlohmann/json.hpp>
#include <regex>

using json = nlohmann::json;

namespace nix {


bool StoreDirConfig::isInStore(PathView path) const
{
    return isInDir(path, storeDir);
}


std::pair<StorePath, Path> StoreDirConfig::toStorePath(PathView path) const
{
    if (!isInStore(path))
        throw Error("path '%1%' is not in the Nix store", path);
    auto slash = path.find('/', storeDir.size() + 1);
    if (slash == Path::npos)
        return {parseStorePath(path), ""};
    else
        return {parseStorePath(path.substr(0, slash)), (Path) path.substr(slash)};
}


Path Store::followLinksToStore(std::string_view _path) const
{
    Path path = absPath(std::string(_path));
    while (!isInStore(path)) {
        if (!isLink(path)) break;
        auto target = readLink(path);
        path = absPath(target, dirOf(path));
    }
    if (!isInStore(path))
        throw BadStorePath("path '%1%' is not in the Nix store", path);
    return path;
}


StorePath Store::followLinksToStorePath(std::string_view path) const
{
    return toStorePath(followLinksToStore(path)).first;
}


/*
The exact specification of store paths is in `protocols/store-path.md`
in the Nix manual. These few functions implement that specification.

If changes to these functions go beyond mere implementation changes i.e.
also update the user-visible behavior, please update the specification
to match.
*/


StorePath StoreDirConfig::makeStorePath(std::string_view type,
    std::string_view hash, std::string_view name) const
{
    /* e.g., "source:sha256:1abc...:/nix/store:foo.tar.gz" */
    auto s = std::string(type) + ":" + std::string(hash)
        + ":" + storeDir + ":" + std::string(name);
    auto h = compressHash(hashString(HashAlgorithm::SHA256, s), 20);
    return StorePath(h, name);
}


StorePath StoreDirConfig::makeStorePath(std::string_view type,
    const Hash & hash, std::string_view name) const
{
    return makeStorePath(type, hash.to_string(HashFormat::Base16, true), name);
}


StorePath StoreDirConfig::makeOutputPath(std::string_view id,
    const Hash & hash, std::string_view name) const
{
    return makeStorePath("output:" + std::string { id }, hash, outputPathName(name, id));
}


/* Stuff the references (if any) into the type.  This is a bit
   hacky, but we can't put them in, say, <s2> (per the grammar above)
   since that would be ambiguous. */
static std::string makeType(
    const StoreDirConfig & store,
    std::string && type,
    const StoreReferences & references)
{
    for (auto & i : references.others) {
        type += ":";
        type += store.printStorePath(i);
    }
    if (references.self) type += ":self";
    return std::move(type);
}


StorePath StoreDirConfig::makeFixedOutputPath(std::string_view name, const FixedOutputInfo & info) const
{
    if (info.method == FileIngestionMethod::Git && info.hash.algo != HashAlgorithm::SHA1)
        throw Error("Git file ingestion must use SHA-1 hash");

    if (info.hash.algo == HashAlgorithm::SHA256 && info.method == FileIngestionMethod::Recursive) {
        return makeStorePath(makeType(*this, "source", info.references), info.hash, name);
    } else {
        if (!info.references.empty()) {
            throw Error("fixed output derivation '%s' is not allowed to refer to other store paths.\nYou may need to use the 'unsafeDiscardReferences' derivation attribute, see the manual for more details.",
                name);
        }
        // make a unique digest based on the parameters for creating this store object
        auto payload = "fixed:out:"
                + makeFileIngestionPrefix(info.method)
                + info.hash.to_string(HashFormat::Base16, true) + ":";
        auto digest = hashString(HashAlgorithm::SHA256, payload);
        return makeStorePath("output:out", digest, name);
    }
}


StorePath StoreDirConfig::makeFixedOutputPathFromCA(std::string_view name, const ContentAddressWithReferences & ca) const
{
    // New template
    return std::visit(overloaded {
        [&](const TextInfo & ti) {
            assert(ti.hash.algo == HashAlgorithm::SHA256);
            return makeStorePath(
                makeType(*this, "text", StoreReferences {
                    .others = ti.references,
                    .self = false,
                }),
                ti.hash,
                name);
        },
        [&](const FixedOutputInfo & foi) {
            return makeFixedOutputPath(name, foi);
        }
    }, ca.raw);
}


std::pair<StorePath, Hash> StoreDirConfig::computeStorePath(
    std::string_view name,
    SourceAccessor & accessor,
    const CanonPath & path,
    ContentAddressMethod method,
    HashAlgorithm hashAlgo,
    const StorePathSet & references,
    PathFilter & filter) const
{
    auto h = hashPath(accessor, path, method.getFileIngestionMethod(), hashAlgo, filter);
    return {
        makeFixedOutputPathFromCA(
            name,
            ContentAddressWithReferences::fromParts(
                method,
                h,
                {
                    .others = references,
                    .self = false,
                })),
        h,
    };
}


StorePath Store::addToStore(
    std::string_view name,
    SourceAccessor & accessor,
    const CanonPath & path,
    ContentAddressMethod method,
    HashAlgorithm hashAlgo,
    const StorePathSet & references,
    PathFilter & filter,
    RepairFlag repair)
{
    FileSerialisationMethod fsm;
    switch (method.getFileIngestionMethod()) {
    case FileIngestionMethod::Flat:
        fsm = FileSerialisationMethod::Flat;
        break;
    case FileIngestionMethod::Recursive:
        fsm = FileSerialisationMethod::Recursive;
        break;
    case FileIngestionMethod::Git:
        // Use NAR; Git is not a serialization method
        fsm = FileSerialisationMethod::Recursive;
        break;
    }
    auto source = sinkToSource([&](Sink & sink) {
        dumpPath(accessor, path, sink, fsm, filter);
    });
    return addToStoreFromDump(*source, name, fsm, method, hashAlgo, references, repair);
}

void Store::addMultipleToStore(
    PathsSource & pathsToCopy,
    Activity & act,
    RepairFlag repair,
    CheckSigsFlag checkSigs)
{
    std::atomic<size_t> nrDone{0};
    std::atomic<size_t> nrFailed{0};
    std::atomic<uint64_t> bytesExpected{0};
    std::atomic<uint64_t> nrRunning{0};

    using PathWithInfo = std::pair<ValidPathInfo, std::unique_ptr<Source>>;

    std::map<StorePath, PathWithInfo *> infosMap;
    StorePathSet storePathsToAdd;
    for (auto & thingToAdd : pathsToCopy) {
        infosMap.insert_or_assign(thingToAdd.first.path, &thingToAdd);
        storePathsToAdd.insert(thingToAdd.first.path);
    }

    auto showProgress = [&]() {
        act.progress(nrDone, pathsToCopy.size(), nrRunning, nrFailed);
    };

    ThreadPool pool;

    processGraph<StorePath>(pool,
        storePathsToAdd,

        [&](const StorePath & path) {

            auto & [info, _] = *infosMap.at(path);

            if (isValidPath(info.path)) {
                nrDone++;
                showProgress();
                return StorePathSet();
            }

            bytesExpected += info.narSize;
            act.setExpected(actCopyPath, bytesExpected);

            return info.references;
        },

        [&](const StorePath & path) {
            checkInterrupt();

            auto & [info_, source_] = *infosMap.at(path);
            auto info = info_;
            info.ultimate = false;

            /* Make sure that the Source object is destroyed when
               we're done. In particular, a SinkToSource object must
               be destroyed to ensure that the destructors on its
               stack frame are run; this includes
               LegacySSHStore::narFromPath()'s connection lock. */
            auto source = std::move(source_);

            if (!isValidPath(info.path)) {
                MaintainCount<decltype(nrRunning)> mc(nrRunning);
                showProgress();
                try {
                    addToStore(info, *source, repair, checkSigs);
                } catch (Error & e) {
                    nrFailed++;
                    if (!settings.keepGoing)
                        throw e;
                    printMsg(lvlError, "could not copy %s: %s", printStorePath(path), e.what());
                    showProgress();
                    return;
                }
            }

            nrDone++;
            showProgress();
        });
}

void Store::addMultipleToStore(
    Source & source,
    RepairFlag repair,
    CheckSigsFlag checkSigs)
{
    auto expected = readNum<uint64_t>(source);
    for (uint64_t i = 0; i < expected; ++i) {
        // FIXME we should not be using the worker protocol here, let
        // alone the worker protocol with a hard-coded version!
        auto info = WorkerProto::Serialise<ValidPathInfo>::read(*this,
            WorkerProto::ReadConn {
                .from = source,
                .version = 16,
            });
        info.ultimate = false;
        addToStore(info, source, repair, checkSigs);
    }
}


/*
The aim of this function is to compute in one pass the correct ValidPathInfo for
the files that we are trying to add to the store. To accomplish that in one
pass, given the different kind of inputs that we can take (normal nar archives,
nar archives with non SHA-256 hashes, and flat files), we set up a net of sinks
and aliases. Also, since the dataflow is obfuscated by this, we include here a
graphviz diagram:

digraph graphname {
    node [shape=box]
    fileSource -> narSink
    narSink [style=dashed]
    narSink -> unsualHashTee [style = dashed, label = "Recursive && !SHA-256"]
    narSink -> narHashSink [style = dashed, label = "else"]
    unsualHashTee -> narHashSink
    unsualHashTee -> caHashSink
    fileSource -> parseSink
    parseSink [style=dashed]
    parseSink-> fileSink [style = dashed, label = "Flat"]
    parseSink -> blank [style = dashed, label = "Recursive"]
    fileSink -> caHashSink
}
*/
ValidPathInfo Store::addToStoreSlow(
    std::string_view name,
    SourceAccessor & accessor,
    const CanonPath & srcPath,
    ContentAddressMethod method, HashAlgorithm hashAlgo,
    const StorePathSet & references,
    std::optional<Hash> expectedCAHash)
{
    HashSink narHashSink { HashAlgorithm::SHA256 };
    HashSink caHashSink { hashAlgo };

    /* Note that fileSink and unusualHashTee must be mutually exclusive, since
       they both write to caHashSink. Note that that requisite is currently true
       because the former is only used in the flat case. */
    RegularFileSink fileSink { caHashSink };
    TeeSink unusualHashTee { narHashSink, caHashSink };

    auto & narSink = method == FileIngestionMethod::Recursive && hashAlgo != HashAlgorithm::SHA256
        ? static_cast<Sink &>(unusualHashTee)
        : narHashSink;

    /* Functionally, this means that fileSource will yield the content of
       srcPath. The fact that we use scratchpadSink as a temporary buffer here
       is an implementation detail. */
    auto fileSource = sinkToSource([&](Sink & scratchpadSink) {
        accessor.dumpPath(srcPath, scratchpadSink);
    });

    /* tapped provides the same data as fileSource, but we also write all the
       information to narSink. */
    TeeSource tapped { *fileSource, narSink };

    NullFileSystemObjectSink blank;
    auto & parseSink = method.getFileIngestionMethod() == FileIngestionMethod::Flat
        ? (FileSystemObjectSink &) fileSink
        : (FileSystemObjectSink &) blank; // for recursive or git we do recursive

    /* The information that flows from tapped (besides being replicated in
       narSink), is now put in parseSink. */
    parseDump(parseSink, tapped);

    /* We extract the result of the computation from the sink by calling
       finish. */
    auto [narHash, narSize] = narHashSink.finish();

    auto hash = method == FileIngestionMethod::Recursive && hashAlgo == HashAlgorithm::SHA256
        ? narHash
        : method == FileIngestionMethod::Git
        ? git::dumpHash(hashAlgo, accessor, srcPath).hash
        : caHashSink.finish().first;

    if (expectedCAHash && expectedCAHash != hash)
        throw Error("hash mismatch for '%s'", srcPath);


    ValidPathInfo info {
        *this,
        name,
        ContentAddressWithReferences::fromParts(
            method,
            hash,
            {
                .others = references,
                .self = false,
            }),
        narHash,
    };
    info.narSize = narSize;

    if (!isValidPath(info.path)) {
        auto source = sinkToSource([&](Sink & scratchpadSink) {
            accessor.dumpPath(srcPath, scratchpadSink);
        });
        addToStore(info, *source);
    }

    return info;
}

StringSet StoreConfig::getDefaultSystemFeatures()
{
    auto res = settings.systemFeatures.get();

    if (experimentalFeatureSettings.isEnabled(Xp::CaDerivations))
        res.insert("ca-derivations");

    if (experimentalFeatureSettings.isEnabled(Xp::RecursiveNix))
        res.insert("recursive-nix");

    return res;
}

Store::Store(const Params & params)
    : StoreConfig(params)
    , state({(size_t) pathInfoCacheSize})
{
    assertLibStoreInitialized();
}


std::string Store::getUri()
{
    return "";
}

bool Store::PathInfoCacheValue::isKnownNow()
{
    std::chrono::duration ttl = didExist()
        ? std::chrono::seconds(settings.ttlPositiveNarInfoCache)
        : std::chrono::seconds(settings.ttlNegativeNarInfoCache);

    return std::chrono::steady_clock::now() < time_point + ttl;
}

std::map<std::string, std::optional<StorePath>> Store::queryStaticPartialDerivationOutputMap(const StorePath & path)
{
    std::map<std::string, std::optional<StorePath>> outputs;
    auto drv = readInvalidDerivation(path);
    for (auto & [outputName, output] : drv.outputsAndOptPaths(*this)) {
        outputs.emplace(outputName, output.second);
    }
    return outputs;
}

std::map<std::string, std::optional<StorePath>> Store::queryPartialDerivationOutputMap(
    const StorePath & path,
    Store * evalStore_)
{
    auto & evalStore = evalStore_ ? *evalStore_ : *this;

    auto outputs = evalStore.queryStaticPartialDerivationOutputMap(path);

    if (!experimentalFeatureSettings.isEnabled(Xp::CaDerivations))
        return outputs;

    auto drv = evalStore.readInvalidDerivation(path);
    auto drvHashes = staticOutputHashes(*this, drv);
    for (auto & [outputName, hash] : drvHashes) {
        auto realisation = queryRealisation(DrvOutput{hash, outputName});
        if (realisation) {
            outputs.insert_or_assign(outputName, realisation->outPath);
        } else {
            // queryStaticPartialDerivationOutputMap is not guaranteed
            // to return std::nullopt for outputs which are not
            // statically known.
            outputs.insert({outputName, std::nullopt});
        }
    }

    return outputs;
}

OutputPathMap Store::queryDerivationOutputMap(const StorePath & path, Store * evalStore) {
    auto resp = queryPartialDerivationOutputMap(path, evalStore);
    OutputPathMap result;
    for (auto & [outName, optOutPath] : resp) {
        if (!optOutPath)
            throw MissingRealisation(printStorePath(path), outName);
        result.insert_or_assign(outName, *optOutPath);
    }
    return result;
}

StorePathSet Store::queryDerivationOutputs(const StorePath & path)
{
    auto outputMap = this->queryDerivationOutputMap(path);
    StorePathSet outputPaths;
    for (auto & i: outputMap) {
        outputPaths.emplace(std::move(i.second));
    }
    return outputPaths;
}


void Store::querySubstitutablePathInfos(const StorePathCAMap & paths, SubstitutablePathInfos & infos)
{
    if (!settings.useSubstitutes) return;
    for (auto & sub : getDefaultSubstituters()) {
        for (auto & path : paths) {
            if (infos.count(path.first))
                // Choose first succeeding substituter.
                continue;

            auto subPath(path.first);

            // Recompute store path so that we can use a different store root.
            if (path.second) {
                subPath = makeFixedOutputPathFromCA(
                    path.first.name(),
                    ContentAddressWithReferences::withoutRefs(*path.second));
                if (sub->storeDir == storeDir)
                    assert(subPath == path.first);
                if (subPath != path.first)
                    debug("replaced path '%s' with '%s' for substituter '%s'", printStorePath(path.first), sub->printStorePath(subPath), sub->getUri());
            } else if (sub->storeDir != storeDir) continue;

            debug("checking substituter '%s' for path '%s'", sub->getUri(), sub->printStorePath(subPath));
            try {
                auto info = sub->queryPathInfo(subPath);

                if (sub->storeDir != storeDir && !(info->isContentAddressed(*sub) && info->references.empty()))
                    continue;

                auto narInfo = std::dynamic_pointer_cast<const NarInfo>(
                    std::shared_ptr<const ValidPathInfo>(info));
                infos.insert_or_assign(path.first, SubstitutablePathInfo{
                    .deriver = info->deriver,
                    .references = info->references,
                    .downloadSize = narInfo ? narInfo->fileSize : 0,
                    .narSize = info->narSize,
                });
            } catch (InvalidPath &) {
            } catch (SubstituterDisabled &) {
            } catch (Error & e) {
                if (settings.tryFallback)
                    logError(e.info());
                else
                    throw;
            }
        }
    }
}


bool Store::isValidPath(const StorePath & storePath)
{
    {
        auto state_(state.lock());
        auto res = state_->pathInfoCache.get(std::string(storePath.to_string()));
        if (res && res->isKnownNow()) {
            stats.narInfoReadAverted++;
            return res->didExist();
        }
    }

    if (diskCache) {
        auto res = diskCache->lookupNarInfo(getUri(), std::string(storePath.hashPart()));
        if (res.first != NarInfoDiskCache::oUnknown) {
            stats.narInfoReadAverted++;
            auto state_(state.lock());
            state_->pathInfoCache.upsert(std::string(storePath.to_string()),
                res.first == NarInfoDiskCache::oInvalid ? PathInfoCacheValue{} : PathInfoCacheValue { .value = res.second });
            return res.first == NarInfoDiskCache::oValid;
        }
    }

    bool valid = isValidPathUncached(storePath);

    if (diskCache && !valid)
        // FIXME: handle valid = true case.
        diskCache->upsertNarInfo(getUri(), std::string(storePath.hashPart()), 0);

    return valid;
}


/* Default implementation for stores that only implement
   queryPathInfoUncached(). */
bool Store::isValidPathUncached(const StorePath & path)
{
    try {
        queryPathInfo(path);
        return true;
    } catch (InvalidPath &) {
        return false;
    }
}


ref<const ValidPathInfo> Store::queryPathInfo(const StorePath & storePath)
{
    std::promise<ref<const ValidPathInfo>> promise;

    queryPathInfo(storePath,
        {[&](std::future<ref<const ValidPathInfo>> result) {
            try {
                promise.set_value(result.get());
            } catch (...) {
                promise.set_exception(std::current_exception());
            }
        }});

    return promise.get_future().get();
}


static bool goodStorePath(const StorePath & expected, const StorePath & actual)
{
    return
        expected.hashPart() == actual.hashPart()
        && (expected.name() == Store::MissingName || expected.name() == actual.name());
}


std::optional<std::shared_ptr<const ValidPathInfo>> Store::queryPathInfoFromClientCache(const StorePath & storePath)
{
    auto hashPart = std::string(storePath.hashPart());

    {
        auto res = state.lock()->pathInfoCache.get(std::string(storePath.to_string()));
        if (res && res->isKnownNow()) {
            stats.narInfoReadAverted++;
            if (res->didExist())
                return std::make_optional(res->value);
            else
                return std::make_optional(nullptr);
        }
    }

    if (diskCache) {
        auto res = diskCache->lookupNarInfo(getUri(), hashPart);
        if (res.first != NarInfoDiskCache::oUnknown) {
            stats.narInfoReadAverted++;
            {
                auto state_(state.lock());
                state_->pathInfoCache.upsert(std::string(storePath.to_string()),
                    res.first == NarInfoDiskCache::oInvalid ? PathInfoCacheValue{} : PathInfoCacheValue{ .value = res.second });
                if (res.first == NarInfoDiskCache::oInvalid ||
                    !goodStorePath(storePath, res.second->path))
                    return std::make_optional(nullptr);
            }
            assert(res.second);
            return std::make_optional(res.second);
        }
    }

    return std::nullopt;
}


void Store::queryPathInfo(const StorePath & storePath,
    Callback<ref<const ValidPathInfo>> callback) noexcept
{
    auto hashPart = std::string(storePath.hashPart());

    try {
        auto r = queryPathInfoFromClientCache(storePath);
        if (r.has_value()) {
            std::shared_ptr<const ValidPathInfo> & info = *r;
            if (info)
                return callback(ref(info));
            else
                throw InvalidPath("path '%s' is not valid", printStorePath(storePath));
        }
    } catch (...) { return callback.rethrow(); }

    auto callbackPtr = std::make_shared<decltype(callback)>(std::move(callback));

    queryPathInfoUncached(storePath,
        {[this, storePath, hashPart, callbackPtr](std::future<std::shared_ptr<const ValidPathInfo>> fut) {

            try {
                auto info = fut.get();

                if (diskCache)
                    diskCache->upsertNarInfo(getUri(), hashPart, info);

                {
                    auto state_(state.lock());
                    state_->pathInfoCache.upsert(std::string(storePath.to_string()), PathInfoCacheValue { .value = info });
                }

                if (!info || !goodStorePath(storePath, info->path)) {
                    stats.narInfoMissing++;
                    throw InvalidPath("path '%s' is not valid", printStorePath(storePath));
                }

                (*callbackPtr)(ref<const ValidPathInfo>(info));
            } catch (...) { callbackPtr->rethrow(); }
        }});
}

void Store::queryRealisation(const DrvOutput & id,
        Callback<std::shared_ptr<const Realisation>> callback) noexcept
{

    try {
        if (diskCache) {
            auto [cacheOutcome, maybeCachedRealisation]
                = diskCache->lookupRealisation(getUri(), id);
            switch (cacheOutcome) {
            case NarInfoDiskCache::oValid:
                debug("Returning a cached realisation for %s", id.to_string());
                callback(maybeCachedRealisation);
                return;
            case NarInfoDiskCache::oInvalid:
                debug(
                    "Returning a cached missing realisation for %s",
                    id.to_string());
                callback(nullptr);
                return;
            case NarInfoDiskCache::oUnknown:
                break;
            }
        }
    } catch (...) {
        return callback.rethrow();
    }

    auto callbackPtr
        = std::make_shared<decltype(callback)>(std::move(callback));

    queryRealisationUncached(
        id,
        { [this, id, callbackPtr](
              std::future<std::shared_ptr<const Realisation>> fut) {
            try {
                auto info = fut.get();

                if (diskCache) {
                    if (info)
                        diskCache->upsertRealisation(getUri(), *info);
                    else
                        diskCache->upsertAbsentRealisation(getUri(), id);
                }

                (*callbackPtr)(std::shared_ptr<const Realisation>(info));

            } catch (...) {
                callbackPtr->rethrow();
            }
        } });
}

std::shared_ptr<const Realisation> Store::queryRealisation(const DrvOutput & id)
{
    using RealPtr = std::shared_ptr<const Realisation>;
    std::promise<RealPtr> promise;

    queryRealisation(id,
        {[&](std::future<RealPtr> result) {
            try {
                promise.set_value(result.get());
            } catch (...) {
                promise.set_exception(std::current_exception());
            }
        }});

    return promise.get_future().get();
}

void Store::substitutePaths(const StorePathSet & paths)
{
    std::vector<DerivedPath> paths2;
    for (auto & path : paths)
        if (!path.isDerivation())
            paths2.emplace_back(DerivedPath::Opaque{path});
    uint64_t downloadSize, narSize;
    StorePathSet willBuild, willSubstitute, unknown;
    queryMissing(paths2,
        willBuild, willSubstitute, unknown, downloadSize, narSize);

    if (!willSubstitute.empty())
        try {
            std::vector<DerivedPath> subs;
            for (auto & p : willSubstitute) subs.emplace_back(DerivedPath::Opaque{p});
            buildPaths(subs);
        } catch (Error & e) {
            logWarning(e.info());
        }
}


StorePathSet Store::queryValidPaths(const StorePathSet & paths, SubstituteFlag maybeSubstitute)
{
    struct State
    {
        size_t left;
        StorePathSet valid;
        std::exception_ptr exc;
    };

    Sync<State> state_(State{paths.size(), StorePathSet()});

    std::condition_variable wakeup;
    ThreadPool pool;

    auto doQuery = [&](const StorePath & path) {
        checkInterrupt();
        queryPathInfo(path, {[path, &state_, &wakeup](std::future<ref<const ValidPathInfo>> fut) {
            auto state(state_.lock());
            try {
                auto info = fut.get();
                state->valid.insert(path);
            } catch (InvalidPath &) {
            } catch (...) {
                state->exc = std::current_exception();
            }
            assert(state->left);
            if (!--state->left)
                wakeup.notify_one();
        }});
    };

    for (auto & path : paths)
        pool.enqueue(std::bind(doQuery, path));

    pool.process();

    while (true) {
        auto state(state_.lock());
        if (!state->left) {
            if (state->exc) std::rethrow_exception(state->exc);
            return std::move(state->valid);
        }
        state.wait(wakeup);
    }
}


/* Return a string accepted by decodeValidPathInfo() that
   registers the specified paths as valid.  Note: it's the
   responsibility of the caller to provide a closure. */
std::string Store::makeValidityRegistration(const StorePathSet & paths,
    bool showDerivers, bool showHash)
{
    std::string s = "";

    for (auto & i : paths) {
        s += printStorePath(i) + "\n";

        auto info = queryPathInfo(i);

        if (showHash) {
            s += info->narHash.to_string(HashFormat::Base16, false) + "\n";
            s += fmt("%1%\n", info->narSize);
        }

        auto deriver = showDerivers && info->deriver ? printStorePath(*info->deriver) : "";
        s += deriver + "\n";

        s += fmt("%1%\n", info->references.size());

        for (auto & j : info->references)
            s += printStorePath(j) + "\n";
    }

    return s;
}


StorePathSet Store::exportReferences(const StorePathSet & storePaths, const StorePathSet & inputPaths)
{
    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", printStorePath(storePath));

        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 = derivationFromPath(j);
            for (auto & k : drv.outputsAndOptPaths(*this)) {
                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");
                computeFSClosure(*k.second.second, paths);
            }
        }
    }

    return paths;
}


const Store::Stats & Store::getStats()
{
    {
        auto state_(state.lock());
        stats.pathInfoCacheSize = state_->pathInfoCache.size();
    }
    return stats;
}


static std::string makeCopyPathMessage(
    std::string_view srcUri,
    std::string_view dstUri,
    std::string_view storePath)
{
    return srcUri == "local" || srcUri == "daemon"
        ? fmt("copying path '%s' to '%s'", storePath, dstUri)
        : dstUri == "local" || dstUri == "daemon"
        ? fmt("copying path '%s' from '%s'", storePath, srcUri)
        : fmt("copying path '%s' from '%s' to '%s'", storePath, srcUri, dstUri);
}


void copyStorePath(
    Store & srcStore,
    Store & dstStore,
    const StorePath & storePath,
    RepairFlag repair,
    CheckSigsFlag checkSigs)
{
    /* Bail out early (before starting a download from srcStore) if
       dstStore already has this path. */
    if (!repair && dstStore.isValidPath(storePath))
        return;

    auto srcUri = srcStore.getUri();
    auto dstUri = dstStore.getUri();
    auto storePathS = srcStore.printStorePath(storePath);
    Activity act(*logger, lvlInfo, actCopyPath,
        makeCopyPathMessage(srcUri, dstUri, storePathS),
        {storePathS, srcUri, dstUri});
    PushActivity pact(act.id);

    auto info = srcStore.queryPathInfo(storePath);

    uint64_t total = 0;

    // recompute store path on the chance dstStore does it differently
    if (info->ca && info->references.empty()) {
        auto info2 = make_ref<ValidPathInfo>(*info);
        info2->path = dstStore.makeFixedOutputPathFromCA(
            info->path.name(),
            info->contentAddressWithReferences().value());
        if (dstStore.storeDir == srcStore.storeDir)
            assert(info->path == info2->path);
        info = info2;
    }

    if (info->ultimate) {
        auto info2 = make_ref<ValidPathInfo>(*info);
        info2->ultimate = false;
        info = info2;
    }

    auto source = sinkToSource([&](Sink & sink) {
        LambdaSink progressSink([&](std::string_view data) {
            total += data.size();
            act.progress(total, info->narSize);
        });
        TeeSink tee { sink, progressSink };
        srcStore.narFromPath(storePath, tee);
    }, [&]() {
           throw EndOfFile("NAR for '%s' fetched from '%s' is incomplete", srcStore.printStorePath(storePath), srcStore.getUri());
    });

    dstStore.addToStore(*info, *source, repair, checkSigs);
}


std::map<StorePath, StorePath> copyPaths(
    Store & srcStore,
    Store & dstStore,
    const RealisedPath::Set & paths,
    RepairFlag repair,
    CheckSigsFlag checkSigs,
    SubstituteFlag substitute)
{
    StorePathSet storePaths;
    std::set<Realisation> toplevelRealisations;
    for (auto & path : paths) {
        storePaths.insert(path.path());
        if (auto realisation = std::get_if<Realisation>(&path.raw)) {
            experimentalFeatureSettings.require(Xp::CaDerivations);
            toplevelRealisations.insert(*realisation);
        }
    }
    auto pathsMap = copyPaths(srcStore, dstStore, storePaths, repair, checkSigs, substitute);

    ThreadPool pool;

    try {
        // Copy the realisation closure
        processGraph<Realisation>(
            pool, Realisation::closure(srcStore, toplevelRealisations),
            [&](const Realisation & current) -> std::set<Realisation> {
                std::set<Realisation> children;
                for (const auto & [drvOutput, _] : current.dependentRealisations) {
                    auto currentChild = srcStore.queryRealisation(drvOutput);
                    if (!currentChild)
                        throw Error(
                            "incomplete realisation closure: '%s' is a "
                            "dependency of '%s' but isn't registered",
                            drvOutput.to_string(), current.id.to_string());
                    children.insert(*currentChild);
                }
                return children;
            },
            [&](const Realisation& current) -> void {
                dstStore.registerDrvOutput(current, checkSigs);
            });
    } catch (MissingExperimentalFeature & e) {
        // Don't fail if the remote doesn't support CA derivations is it might
        // not be within our control to change that, and we might still want
        // to at least copy the output paths.
        if (e.missingFeature == Xp::CaDerivations)
            ignoreException();
        else
            throw;
    }

    return pathsMap;
}

std::map<StorePath, StorePath> copyPaths(
    Store & srcStore,
    Store & dstStore,
    const StorePathSet & storePaths,
    RepairFlag repair,
    CheckSigsFlag checkSigs,
    SubstituteFlag substitute)
{
    auto valid = dstStore.queryValidPaths(storePaths, substitute);

    StorePathSet missing;
    for (auto & path : storePaths)
        if (!valid.count(path)) missing.insert(path);

    Activity act(*logger, lvlInfo, actCopyPaths, fmt("copying %d paths", missing.size()));

    // In the general case, `addMultipleToStore` requires a sorted list of
    // store paths to add, so sort them right now
    auto sortedMissing = srcStore.topoSortPaths(missing);
    std::reverse(sortedMissing.begin(), sortedMissing.end());

    std::map<StorePath, StorePath> pathsMap;
    for (auto & path : storePaths)
        pathsMap.insert_or_assign(path, path);

    Store::PathsSource pathsToCopy;

    auto computeStorePathForDst = [&](const ValidPathInfo & currentPathInfo) -> StorePath {
        auto storePathForSrc = currentPathInfo.path;
        auto storePathForDst = storePathForSrc;
        if (currentPathInfo.ca && currentPathInfo.references.empty()) {
            storePathForDst = dstStore.makeFixedOutputPathFromCA(
                currentPathInfo.path.name(),
                currentPathInfo.contentAddressWithReferences().value());
            if (dstStore.storeDir == srcStore.storeDir)
                assert(storePathForDst == storePathForSrc);
            if (storePathForDst != storePathForSrc)
                debug("replaced path '%s' to '%s' for substituter '%s'",
                        srcStore.printStorePath(storePathForSrc),
                        dstStore.printStorePath(storePathForDst),
                        dstStore.getUri());
        }
        return storePathForDst;
    };

    // total is accessed by each copy, which are each handled in separate threads
    std::atomic<uint64_t> total = 0;

    for (auto & missingPath : sortedMissing) {
        auto info = srcStore.queryPathInfo(missingPath);

        auto storePathForDst = computeStorePathForDst(*info);
        pathsMap.insert_or_assign(missingPath, storePathForDst);

        ValidPathInfo infoForDst = *info;
        infoForDst.path = storePathForDst;

        auto source = sinkToSource([&](Sink & sink) {
            // We can reasonably assume that the copy will happen whenever we
            // read the path, so log something about that at that point
            auto srcUri = srcStore.getUri();
            auto dstUri = dstStore.getUri();
            auto storePathS = srcStore.printStorePath(missingPath);
            Activity act(*logger, lvlInfo, actCopyPath,
                makeCopyPathMessage(srcUri, dstUri, storePathS),
                {storePathS, srcUri, dstUri});
            PushActivity pact(act.id);

            LambdaSink progressSink([&](std::string_view data) {
                total += data.size();
                act.progress(total, info->narSize);
            });
            TeeSink tee { sink, progressSink };

            srcStore.narFromPath(missingPath, tee);
        });
        pathsToCopy.push_back(std::pair{infoForDst, std::move(source)});
    }

    dstStore.addMultipleToStore(pathsToCopy, act, repair, checkSigs);

    return pathsMap;
}

void copyClosure(
    Store & srcStore,
    Store & dstStore,
    const RealisedPath::Set & paths,
    RepairFlag repair,
    CheckSigsFlag checkSigs,
    SubstituteFlag substitute)
{
    if (&srcStore == &dstStore) return;

    RealisedPath::Set closure;
    RealisedPath::closure(srcStore, paths, closure);

    copyPaths(srcStore, dstStore, closure, repair, checkSigs, substitute);
}

void copyClosure(
    Store & srcStore,
    Store & dstStore,
    const StorePathSet & storePaths,
    RepairFlag repair,
    CheckSigsFlag checkSigs,
    SubstituteFlag substitute)
{
    if (&srcStore == &dstStore) return;

    StorePathSet closure;
    srcStore.computeFSClosure(storePaths, closure);
    copyPaths(srcStore, dstStore, closure, repair, checkSigs, substitute);
}

std::optional<ValidPathInfo> decodeValidPathInfo(const Store & store, std::istream & str, std::optional<HashResult> hashGiven)
{
    std::string path;
    getline(str, path);
    if (str.eof()) { return {}; }
    if (!hashGiven) {
        std::string s;
        getline(str, s);
        auto narHash = Hash::parseAny(s, HashAlgorithm::SHA256);
        getline(str, s);
        auto narSize = string2Int<uint64_t>(s);
        if (!narSize) throw Error("number expected");
        hashGiven = { narHash, *narSize };
    }
    ValidPathInfo info(store.parseStorePath(path), hashGiven->first);
    info.narSize = hashGiven->second;
    std::string deriver;
    getline(str, deriver);
    if (deriver != "") info.deriver = store.parseStorePath(deriver);
    std::string s;
    getline(str, s);
    auto n = string2Int<int>(s);
    if (!n) throw Error("number expected");
    while ((*n)--) {
        getline(str, s);
        info.references.insert(store.parseStorePath(s));
    }
    if (!str || str.eof()) throw Error("missing input");
    return std::optional<ValidPathInfo>(std::move(info));
}


std::string StoreDirConfig::showPaths(const StorePathSet & paths)
{
    std::string s;
    for (auto & i : paths) {
        if (s.size() != 0) s += ", ";
        s += "'" + printStorePath(i) + "'";
    }
    return s;
}


std::string showPaths(const PathSet & paths)
{
    return concatStringsSep(", ", quoteStrings(paths));
}


Derivation Store::derivationFromPath(const StorePath & drvPath)
{
    ensurePath(drvPath);
    return readDerivation(drvPath);
}

static Derivation readDerivationCommon(Store & store, const StorePath & drvPath, bool requireValidPath)
{
    auto accessor = store.getFSAccessor(requireValidPath);
    try {
        return parseDerivation(store,
            accessor->readFile(CanonPath(store.printStorePath(drvPath))),
            Derivation::nameFromPath(drvPath));
    } catch (FormatError & e) {
        throw Error("error parsing derivation '%s': %s", store.printStorePath(drvPath), e.msg());
    }
}

std::optional<StorePath> Store::getBuildDerivationPath(const StorePath & path)
{

    if (!path.isDerivation()) {
        try {
            auto info = queryPathInfo(path);
            if (!info->deriver) return std::nullopt;
            return *info->deriver;
        } catch (InvalidPath &) {
            return std::nullopt;
        }
    }

    if (!experimentalFeatureSettings.isEnabled(Xp::CaDerivations) || !isValidPath(path))
        return path;

    auto drv = readDerivation(path);
    if (!drv.type().hasKnownOutputPaths()) {
        // The build log is actually attached to the corresponding
        // resolved derivation, so we need to get it first
        auto resolvedDrv = drv.tryResolve(*this);
        if (resolvedDrv)
            return writeDerivation(*this, *resolvedDrv, NoRepair, true);
    }

    return path;
}

Derivation Store::readDerivation(const StorePath & drvPath)
{ return readDerivationCommon(*this, drvPath, true); }

Derivation Store::readInvalidDerivation(const StorePath & drvPath)
{ return readDerivationCommon(*this, drvPath, false); }

}

#ifndef _WIN32
# include "local-store.hh"
# include "uds-remote-store.hh"
#endif


namespace nix {

/* Split URI into protocol+hierarchy part and its parameter set. */
std::pair<std::string, Store::Params> splitUriAndParams(const std::string & uri_)
{
    auto uri(uri_);
    Store::Params params;
    auto q = uri.find('?');
    if (q != std::string::npos) {
        params = decodeQuery(uri.substr(q + 1));
        uri = uri_.substr(0, q);
    }
    return {uri, params};
}

#ifdef _WIN32 // Unused on Windows because the next `#ifndef`
[[maybe_unused]]
#endif
static bool isNonUriPath(const std::string & spec)
{
    return
        // is not a URL
        spec.find("://") == std::string::npos
        // Has at least one path separator, and so isn't a single word that
        // might be special like "auto"
        && spec.find("/") != std::string::npos;
}

std::shared_ptr<Store> openFromNonUri(const std::string & uri, const Store::Params & params)
{
    // TODO reenable on Windows once we have `LocalStore` and
    // `UDSRemoteStore`.
    #ifndef _WIN32
    if (uri == "" || uri == "auto") {
        auto stateDir = getOr(params, "state", settings.nixStateDir);
        if (access(stateDir.c_str(), R_OK | W_OK) == 0)
            return std::make_shared<LocalStore>(params);
        else if (pathExists(settings.nixDaemonSocketFile))
            return std::make_shared<UDSRemoteStore>(params);
        #if __linux__
        else if (!pathExists(stateDir)
            && params.empty()
            && !isRootUser()
            && !getEnv("NIX_STORE_DIR").has_value()
            && !getEnv("NIX_STATE_DIR").has_value())
        {
            /* If /nix doesn't exist, there is no daemon socket, and
               we're not root, then automatically set up a chroot
               store in ~/.local/share/nix/root. */
            auto chrootStore = getDataDir() + "/nix/root";
            if (!pathExists(chrootStore)) {
                try {
                    createDirs(chrootStore);
                } catch (Error & e) {
                    return std::make_shared<LocalStore>(params);
                }
                warn("'%s' does not exist, so Nix will use '%s' as a chroot store", stateDir, chrootStore);
            } else
                debug("'%s' does not exist, so Nix will use '%s' as a chroot store", stateDir, chrootStore);
            Store::Params params2;
            params2["root"] = chrootStore;
            return std::make_shared<LocalStore>(params2);
        }
        #endif
        else
            return std::make_shared<LocalStore>(params);
    } else if (uri == "daemon") {
        return std::make_shared<UDSRemoteStore>(params);
    } else if (uri == "local") {
        return std::make_shared<LocalStore>(params);
    } else if (isNonUriPath(uri)) {
        Store::Params params2 = params;
        params2["root"] = absPath(uri);
        return std::make_shared<LocalStore>(params2);
    } else {
        return nullptr;
    }
    #else
    return nullptr;
    #endif
}

// The `parseURL` function supports both IPv6 URIs as defined in
// RFC2732, but also pure addresses. The latter one is needed here to
// connect to a remote store via SSH (it's possible to do e.g. `ssh root@::1`).
//
// This function now ensures that a usable connection string is available:
// * If the store to be opened is not an SSH store, nothing will be done.
// * If the URL looks like `root@[::1]` (which is allowed by the URL parser and probably
//   needed to pass further flags), it
//   will be transformed into `root@::1` for SSH (same for `[::1]` -> `::1`).
// * If the URL looks like `root@::1` it will be left as-is.
// * In any other case, the string will be left as-is.
static std::string extractConnStr(const std::string &proto, const std::string &connStr)
{
    if (proto.rfind("ssh") != std::string::npos) {
        std::smatch result;
        std::regex v6AddrRegex("^((.*)@)?\\[(.*)\\]$");

        if (std::regex_match(connStr, result, v6AddrRegex)) {
            if (result[1].matched) {
                return result.str(1) + result.str(3);
            }
            return result.str(3);
        }
    }

    return connStr;
}

ref<Store> openStore(const std::string & uri_,
    const Store::Params & extraParams)
{
    auto params = extraParams;
    try {
        auto parsedUri = parseURL(uri_);
        params.insert(parsedUri.query.begin(), parsedUri.query.end());

        auto baseURI = extractConnStr(
            parsedUri.scheme,
            parsedUri.authority.value_or("") + parsedUri.path
        );

        for (auto implem : *Implementations::registered) {
            if (implem.uriSchemes.count(parsedUri.scheme)) {
                auto store = implem.create(parsedUri.scheme, baseURI, params);
                if (store) {
                    experimentalFeatureSettings.require(store->experimentalFeature());
                    store->init();
                    store->warnUnknownSettings();
                    return ref<Store>(store);
                }
            }
        }
    }
    catch (BadURL &) {
        auto [uri, uriParams] = splitUriAndParams(uri_);
        params.insert(uriParams.begin(), uriParams.end());

        if (auto store = openFromNonUri(uri, params)) {
            experimentalFeatureSettings.require(store->experimentalFeature());
            store->warnUnknownSettings();
            return ref<Store>(store);
        }
    }

    throw Error("don't know how to open Nix store '%s'", uri_);
}

std::list<ref<Store>> getDefaultSubstituters()
{
    static auto stores([]() {
        std::list<ref<Store>> stores;

        StringSet done;

        auto addStore = [&](const std::string & uri) {
            if (!done.insert(uri).second) return;
            try {
                stores.push_back(openStore(uri));
            } catch (Error & e) {
                logWarning(e.info());
            }
        };

        for (auto uri : settings.substituters.get())
            addStore(uri);

        stores.sort([](ref<Store> & a, ref<Store> & b) {
            return a->priority < b->priority;
        });

        return stores;
    } ());

    return stores;
}

std::vector<StoreFactory> * Implementations::registered = 0;

}