Add a Store::addToStore() variant that accepts a NAR

As a side effect, this ensures that signatures are propagated when
copying paths between stores.

Also refactored import/export to make use of this.

15 files changed, 235 insertions, 338 deletions

diff --git a/src/libstore/binary-cache-store.cc b/src/libstore/binary-cache-store.cc
index 41b1fa026a..b56f3ee8a1 100644
--- a/src/libstore/binary-cache-store.cc
+++ b/src/libstore/binary-cache-store.cc
@@ -46,8 +46,10 @@ Path BinaryCacheStore::narInfoFileFor(const Path & storePath)
     return storePathToHash(storePath) + ".narinfo";
 }
 
-void BinaryCacheStore::addToCache(const ValidPathInfo & info, ref<std::string> nar)
+void BinaryCacheStore::addToStore(const ValidPathInfo & info, const std::string & nar, bool repair)
 {
+    if (!repair && isValidPath(info.path)) return;
+
     /* Verify that all references are valid. This may do some .narinfo
        reads, but typically they'll already be cached. */
     for (auto & ref : info.references)
@@ -60,14 +62,13 @@ void BinaryCacheStore::addToCache(const ValidPathInfo & info, ref<std::string> n
         }
 
     auto narInfoFile = narInfoFileFor(info.path);
-    if (fileExists(narInfoFile)) return;
 
-    assert(nar->compare(0, narMagic.size(), narMagic) == 0);
+    assert(nar.compare(0, narMagic.size(), narMagic) == 0);
 
     auto narInfo = make_ref<NarInfo>(info);
 
-    narInfo->narSize = nar->size();
-    narInfo->narHash = hashString(htSHA256, *nar);
+    narInfo->narSize = nar.size();
+    narInfo->narHash = hashString(htSHA256, nar);
 
     if (info.narHash && info.narHash != narInfo->narHash)
         throw Error(format("refusing to copy corrupted path ‘%1%’ to binary cache") % info.path);
@@ -83,7 +84,7 @@ void BinaryCacheStore::addToCache(const ValidPathInfo & info, ref<std::string> n
     auto duration = std::chrono::duration_cast<std::chrono::milliseconds>(now2 - now1).count();
     printMsg(lvlTalkative, format("copying path ‘%1%’ (%2% bytes, compressed %3$.1f%% in %4% ms) to binary cache")
         % narInfo->path % narInfo->narSize
-        % ((1.0 - (double) narCompressed->size() / nar->size()) * 100.0)
+        % ((1.0 - (double) narCompressed->size() / nar.size()) * 100.0)
         % duration);
 
     /* Atomically write the NAR file. */
@@ -91,13 +92,13 @@ void BinaryCacheStore::addToCache(const ValidPathInfo & info, ref<std::string> n
         + (compression == "xz" ? ".xz" :
            compression == "bzip2" ? ".bz2" :
            "");
-    if (!fileExists(narInfo->url)) {
+    if (repair || !fileExists(narInfo->url)) {
         stats.narWrite++;
         upsertFile(narInfo->url, *narCompressed);
     } else
         stats.narWriteAverted++;
 
-    stats.narWriteBytes += nar->size();
+    stats.narWriteBytes += nar.size();
     stats.narWriteCompressedBytes += narCompressed->size();
     stats.narWriteCompressionTimeMs += duration;
 
@@ -141,7 +142,7 @@ void BinaryCacheStore::narFromPath(const Path & storePath, Sink & sink)
     /* Decompress the NAR. FIXME: would be nice to have the remote
        side do this. */
     try {
-        nar = decompress(info->compression, ref<std::string>(nar));
+        nar = decompress(info->compression, *nar);
     } catch (UnknownCompressionMethod &) {
         throw Error(format("binary cache path ‘%s’ uses unknown compression method ‘%s’")
             % storePath % info->compression);
@@ -156,51 +157,6 @@ void BinaryCacheStore::narFromPath(const Path & storePath, Sink & sink)
     sink((unsigned char *) nar->c_str(), nar->size());
 }
 
-void BinaryCacheStore::exportPath(const Path & storePath, Sink & sink)
-{
-    auto res = queryPathInfo(storePath);
-
-    narFromPath(storePath, sink);
-
-    // FIXME: check integrity of NAR.
-
-    sink << exportMagic << storePath << res->references << res->deriver << 0;
-}
-
-Paths BinaryCacheStore::importPaths(Source & source,
-    std::shared_ptr<FSAccessor> accessor)
-{
-    Paths res;
-    while (true) {
-        unsigned long long n = readLongLong(source);
-        if (n == 0) break;
-        if (n != 1) throw Error("input doesn't look like something created by ‘nix-store --export’");
-        res.push_back(importPath(source, accessor));
-    }
-    return res;
-}
-
-struct TeeSource : Source
-{
-    Source & readSource;
-    ref<std::string> data;
-    TeeSource(Source & readSource)
-        : readSource(readSource)
-        , data(make_ref<std::string>())
-    {
-    }
-    size_t read(unsigned char * data, size_t len)
-    {
-        size_t n = readSource.read(data, len);
-        this->data->append((char *) data, n);
-        return n;
-    }
-};
-
-struct NopSink : ParseSink
-{
-};
-
 std::shared_ptr<ValidPathInfo> BinaryCacheStore::queryPathInfoUncached(const Path & storePath)
 {
     auto narInfoFile = narInfoFileFor(storePath);
@@ -260,8 +216,7 @@ Path BinaryCacheStore::addToStore(const string & name, const Path & srcPath,
     ValidPathInfo info;
     info.path = makeFixedOutputPath(recursive, hashAlgo, h, name);
 
-    if (repair || !isValidPath(info.path))
-        addToCache(info, sink.s);
+    addToStore(info, *sink.s, repair);
 
     return info.path;
 }
@@ -276,7 +231,7 @@ Path BinaryCacheStore::addTextToStore(const string & name, const string & s,
     if (repair || !isValidPath(info.path)) {
         StringSink sink;
         dumpString(s, sink);
-        addToCache(info, sink.s);
+        addToStore(info, *sink.s, repair);
     }
 
     return info.path;
@@ -306,7 +261,7 @@ void BinaryCacheStore::buildPaths(const PathSet & paths, BuildMode buildMode)
         StringSink sink;
         dumpPath(storePath, sink);
 
-        addToCache(*info, sink.s);
+        addToStore(*info, *sink.s, buildMode == bmRepair);
     }
 }
 
@@ -343,7 +298,7 @@ struct BinaryCacheStoreAccessor : public FSAccessor
         if (i != nars.end()) return {i->second, restPath};
 
         StringSink sink;
-        store->exportPath(storePath, sink);
+        store->narFromPath(storePath, sink);
 
         auto accessor = makeNarAccessor(sink.s);
         nars.emplace(storePath, accessor);
@@ -381,36 +336,4 @@ ref<FSAccessor> BinaryCacheStore::getFSAccessor()
             std::dynamic_pointer_cast<BinaryCacheStore>(shared_from_this())));
 }
 
-Path BinaryCacheStore::importPath(Source & source, std::shared_ptr<FSAccessor> accessor)
-{
-    /* FIXME: some cut&paste of LocalStore::importPath(). */
-
-    /* Extract the NAR from the source. */
-    TeeSource tee(source);
-    NopSink sink;
-    parseDump(sink, tee);
-
-    uint32_t magic = readInt(source);
-    if (magic != exportMagic)
-        throw Error("Nix archive cannot be imported; wrong format");
-
-    ValidPathInfo info;
-    info.path = readStorePath(source);
-
-    info.references = readStorePaths<PathSet>(source);
-
-    readString(source); // deriver, don't care
-
-    bool haveSignature = readInt(source) == 1;
-    assert(!haveSignature);
-
-    addToCache(info, tee.data);
-
-    auto accessor_ = std::dynamic_pointer_cast<BinaryCacheStoreAccessor>(accessor);
-    if (accessor_)
-        accessor_->nars.emplace(info.path, makeNarAccessor(tee.data));
-
-    return info.path;
-}
-
 }
diff --git a/src/libstore/binary-cache-store.hh b/src/libstore/binary-cache-store.hh
index eb03c5f26d..cc6b98525e 100644
--- a/src/libstore/binary-cache-store.hh
+++ b/src/libstore/binary-cache-store.hh
@@ -46,8 +46,6 @@ private:
 
     std::string narInfoFileFor(const Path & storePath);
 
-    void addToCache(const ValidPathInfo & info, ref<std::string> nar);
-
 public:
 
     bool isValidPathUncached(const Path & path) override;
@@ -82,6 +80,9 @@ public:
     void querySubstitutablePathInfos(const PathSet & paths,
         SubstitutablePathInfos & infos) override;
 
+    void addToStore(const ValidPathInfo & info, const std::string & nar,
+        bool repair = false) override;
+
     Path addToStore(const string & name, const Path & srcPath,
         bool recursive = true, HashType hashAlgo = htSHA256,
         PathFilter & filter = defaultPathFilter, bool repair = false) override;
@@ -91,13 +92,6 @@ public:
 
     void narFromPath(const Path & path, Sink & sink) override;
 
-    void exportPath(const Path & path, Sink & sink) override;
-
-    Paths importPaths(Source & source,
-        std::shared_ptr<FSAccessor> accessor) override;
-
-    Path importPath(Source & source, std::shared_ptr<FSAccessor> accessor);
-
     void buildPaths(const PathSet & paths, BuildMode buildMode = bmNormal) override;
 
     BuildResult buildDerivation(const Path & drvPath, const BasicDerivation & drv,
diff --git a/src/libstore/builtins.cc b/src/libstore/builtins.cc
index a4785d6905..e1ce36e922 100644
--- a/src/libstore/builtins.cc
+++ b/src/libstore/builtins.cc
@@ -31,7 +31,7 @@ void builtinFetchurl(const BasicDerivation & drv)
     auto unpack = drv.env.find("unpack");
     if (unpack != drv.env.end() && unpack->second == "1") {
         if (string(*data.data, 0, 6) == string("\xfd" "7zXZ\0", 6))
-            data.data = decompress("xz", ref<std::string>(data.data));
+            data.data = decompress("xz", *data.data);
         StringSource source(*data.data);
         restorePath(storePath, source);
     } else
diff --git a/src/libstore/export-import.cc b/src/libstore/export-import.cc
new file mode 100644
index 0000000000..4ec01add30
--- /dev/null
+++ b/src/libstore/export-import.cc
@@ -0,0 +1,136 @@
+#include "store-api.hh"
+#include "archive.hh"
+#include "worker-protocol.hh"
+
+#include <algorithm>
+
+namespace nix {
+
+struct HashAndWriteSink : Sink
+{
+    Sink & writeSink;
+    HashSink hashSink;
+    HashAndWriteSink(Sink & writeSink) : writeSink(writeSink), hashSink(htSHA256)
+    {
+    }
+    virtual void operator () (const unsigned char * data, size_t len)
+    {
+        writeSink(data, len);
+        hashSink(data, len);
+    }
+    Hash currentHash()
+    {
+        return hashSink.currentHash().first;
+    }
+};
+
+void Store::exportPaths(const Paths & paths, Sink & sink)
+{
+    Paths sorted = topoSortPaths(PathSet(paths.begin(), paths.end()));
+    std::reverse(sorted.begin(), sorted.end());
+
+    std::string doneLabel("paths exported");
+    logger->incExpected(doneLabel, sorted.size());
+
+    for (auto & path : sorted) {
+        Activity act(*logger, lvlInfo, format("exporting path ‘%s’") % path);
+        sink << 1;
+        exportPath(path, sink);
+        logger->incProgress(doneLabel);
+    }
+
+    sink << 0;
+}
+
+void Store::exportPath(const Path & path, Sink & sink)
+{
+    auto info = queryPathInfo(path);
+
+    HashAndWriteSink hashAndWriteSink(sink);
+
+    narFromPath(path, hashAndWriteSink);
+
+    /* Refuse to export paths that have changed.  This prevents
+       filesystem corruption from spreading to other machines.
+       Don't complain if the stored hash is zero (unknown). */
+    Hash hash = hashAndWriteSink.currentHash();
+    if (hash != info->narHash && info->narHash != Hash(info->narHash.type))
+        throw Error(format("hash of path ‘%1%’ has changed from ‘%2%’ to ‘%3%’!") % path
+            % printHash(info->narHash) % printHash(hash));
+
+    hashAndWriteSink << exportMagic << path << info->references << info->deriver << 0;
+}
+
+struct TeeSource : Source
+{
+    Source & readSource;
+    ref<std::string> data;
+    TeeSource(Source & readSource)
+        : readSource(readSource)
+        , data(make_ref<std::string>())
+    {
+    }
+    size_t read(unsigned char * data, size_t len)
+    {
+        size_t n = readSource.read(data, len);
+        this->data->append((char *) data, n);
+        return n;
+    }
+};
+
+struct NopSink : ParseSink
+{
+};
+
+Paths Store::importPaths(Source & source, std::shared_ptr<FSAccessor> accessor)
+{
+    Paths res;
+    while (true) {
+        unsigned long long n = readLongLong(source);
+        if (n == 0) break;
+        if (n != 1) throw Error("input doesn't look like something created by ‘nix-store --export’");
+
+        /* Extract the NAR from the source. */
+        TeeSource tee(source);
+        NopSink sink;
+        parseDump(sink, tee);
+
+        uint32_t magic = readInt(source);
+        if (magic != exportMagic)
+            throw Error("Nix archive cannot be imported; wrong format");
+
+        ValidPathInfo info;
+
+        info.path = readStorePath(source);
+
+        Activity act(*logger, lvlInfo, format("importing path ‘%s’") % info.path);
+
+        info.references = readStorePaths<PathSet>(source);
+
+        info.deriver = readString(source);
+        if (info.deriver != "") assertStorePath(info.deriver);
+
+        info.narHash = hashString(htSHA256, *tee.data);
+        info.narSize = tee.data->size();
+
+        // Ignore optional legacy signature.
+        if (readInt(source) == 1)
+            readString(source);
+
+        addToStore(info, *tee.data);
+
+        // FIXME: implement accessors?
+        assert(!accessor);
+#if 0
+        auto accessor_ = std::dynamic_pointer_cast<BinaryCacheStoreAccessor>(accessor);
+        if (accessor_)
+            accessor_->nars.emplace(info.path, makeNarAccessor(tee.data));
+#endif
+
+        res.push_back(info.path);
+    }
+
+    return res;
+}
+
+}
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index 42e4ab9f4a..ff434d0589 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -901,6 +901,40 @@ void LocalStore::invalidatePath(State & state, const Path & path)
 }
 
 
+void LocalStore::addToStore(const ValidPathInfo & info, const std::string & nar, bool repair)
+{
+    addTempRoot(info.path);
+
+    if (repair || !isValidPath(info.path)) {
+
+        PathLocks outputLock;
+
+        /* Lock the output path.  But don't lock if we're being called
+           from a build hook (whose parent process already acquired a
+           lock on this path). */
+        Strings locksHeld = tokenizeString<Strings>(getEnv("NIX_HELD_LOCKS"));
+        if (find(locksHeld.begin(), locksHeld.end(), info.path) == locksHeld.end())
+            outputLock.lockPaths({info.path});
+
+        if (repair || !isValidPath(info.path)) {
+
+            deletePath(info.path);
+
+            StringSource source(nar);
+            restorePath(info.path, source);
+
+            canonicalisePathMetaData(info.path, -1);
+
+            optimisePath(info.path); // FIXME: combine with hashPath()
+
+            registerValidPath(info);
+        }
+
+        outputLock.setDeletion(true);
+    }
+}
+
+
 Path LocalStore::addToStoreFromDump(const string & dump, const string & name,
     bool recursive, HashType hashAlgo, bool repair)
 {
@@ -1016,69 +1050,6 @@ Path LocalStore::addTextToStore(const string & name, const string & s,
 }
 
 
-struct HashAndWriteSink : Sink
-{
-    Sink & writeSink;
-    HashSink hashSink;
-    HashAndWriteSink(Sink & writeSink) : writeSink(writeSink), hashSink(htSHA256)
-    {
-    }
-    virtual void operator () (const unsigned char * data, size_t len)
-    {
-        writeSink(data, len);
-        hashSink(data, len);
-    }
-    Hash currentHash()
-    {
-        return hashSink.currentHash().first;
-    }
-};
-
-
-void LocalStore::exportPath(const Path & path, Sink & sink)
-{
-    assertStorePath(path);
-
-    printMsg(lvlTalkative, format("exporting path ‘%1%’") % path);
-
-    auto info = queryPathInfo(path);
-
-    HashAndWriteSink hashAndWriteSink(sink);
-
-    dumpPath(path, hashAndWriteSink);
-
-    /* Refuse to export paths that have changed.  This prevents
-       filesystem corruption from spreading to other machines.
-       Don't complain if the stored hash is zero (unknown). */
-    Hash hash = hashAndWriteSink.currentHash();
-    if (hash != info->narHash && info->narHash != Hash(info->narHash.type))
-        throw Error(format("hash of path ‘%1%’ has changed from ‘%2%’ to ‘%3%’!") % path
-            % printHash(info->narHash) % printHash(hash));
-
-    hashAndWriteSink << exportMagic << path << info->references << info->deriver;
-
-    hashAndWriteSink << 0; // backwards compatibility
-}
-
-
-struct HashAndReadSource : Source
-{
-    Source & readSource;
-    HashSink hashSink;
-    bool hashing;
-    HashAndReadSource(Source & readSource) : readSource(readSource), hashSink(htSHA256)
-    {
-        hashing = true;
-    }
-    size_t read(unsigned char * data, size_t len)
-    {
-        size_t n = readSource.read(data, len);
-        if (hashing) hashSink(data, n);
-        return n;
-    }
-};
-
-
 /* Create a temporary directory in the store that won't be
    garbage-collected. */
 Path LocalStore::createTempDirInStore()
@@ -1095,103 +1066,6 @@ Path LocalStore::createTempDirInStore()
 }
 
 
-Path LocalStore::importPath(Source & source)
-{
-    HashAndReadSource hashAndReadSource(source);
-
-    /* We don't yet know what store path this archive contains (the
-       store path follows the archive data proper), and besides, we
-       don't know yet whether the signature is valid. */
-    Path tmpDir = createTempDirInStore();
-    AutoDelete delTmp(tmpDir);
-    Path unpacked = tmpDir + "/unpacked";
-
-    restorePath(unpacked, hashAndReadSource);
-
-    uint32_t magic = readInt(hashAndReadSource);
-    if (magic != exportMagic)
-        throw Error("Nix archive cannot be imported; wrong format");
-
-    Path dstPath = readStorePath(hashAndReadSource);
-
-    printMsg(lvlTalkative, format("importing path ‘%1%’") % dstPath);
-
-    PathSet references = readStorePaths<PathSet>(hashAndReadSource);
-
-    Path deriver = readString(hashAndReadSource);
-    if (deriver != "") assertStorePath(deriver);
-
-    Hash hash = hashAndReadSource.hashSink.finish().first;
-    hashAndReadSource.hashing = false;
-
-    bool haveSignature = readInt(hashAndReadSource) == 1;
-
-    if (haveSignature)
-        // Ignore legacy signature.
-        readString(hashAndReadSource);
-
-    /* Do the actual import. */
-
-    /* !!! way too much code duplication with addTextToStore() etc. */
-    addTempRoot(dstPath);
-
-    if (!isValidPath(dstPath)) {
-
-        PathLocks outputLock;
-
-        /* Lock the output path.  But don't lock if we're being called
-           from a build hook (whose parent process already acquired a
-           lock on this path). */
-        Strings locksHeld = tokenizeString<Strings>(getEnv("NIX_HELD_LOCKS"));
-        if (find(locksHeld.begin(), locksHeld.end(), dstPath) == locksHeld.end())
-            outputLock.lockPaths(singleton<PathSet, Path>(dstPath));
-
-        if (!isValidPath(dstPath)) {
-
-            deletePath(dstPath);
-
-            if (rename(unpacked.c_str(), dstPath.c_str()) == -1)
-                throw SysError(format("cannot move ‘%1%’ to ‘%2%’")
-                    % unpacked % dstPath);
-
-            canonicalisePathMetaData(dstPath, -1);
-
-            /* !!! if we were clever, we could prevent the hashPath()
-               here. */
-            HashResult hash = hashPath(htSHA256, dstPath);
-
-            optimisePath(dstPath); // FIXME: combine with hashPath()
-
-            ValidPathInfo info;
-            info.path = dstPath;
-            info.narHash = hash.first;
-            info.narSize = hash.second;
-            info.references = references;
-            info.deriver = deriver != "" && isValidPath(deriver) ? deriver : "";
-            registerValidPath(info);
-        }
-
-        outputLock.setDeletion(true);
-    }
-
-    return dstPath;
-}
-
-
-Paths LocalStore::importPaths(Source & source,
-    std::shared_ptr<FSAccessor> accessor)
-{
-    Paths res;
-    while (true) {
-        unsigned long long n = readLongLong(source);
-        if (n == 0) break;
-        if (n != 1) throw Error("input doesn't look like something created by ‘nix-store --export’");
-        res.push_back(importPath(source));
-    }
-    return res;
-}
-
-
 void LocalStore::invalidatePathChecked(const Path & path)
 {
     assertStorePath(path);
diff --git a/src/libstore/local-store.hh b/src/libstore/local-store.hh
index d3cde74081..e714f8e0fe 100644
--- a/src/libstore/local-store.hh
+++ b/src/libstore/local-store.hh
@@ -112,6 +112,9 @@ public:
     void querySubstitutablePathInfos(const PathSet & paths,
         SubstitutablePathInfos & infos) override;
 
+    void addToStore(const ValidPathInfo & info, const std::string & nar,
+        bool repair) override;
+
     Path addToStore(const string & name, const Path & srcPath,
         bool recursive = true, HashType hashAlgo = htSHA256,
         PathFilter & filter = defaultPathFilter, bool repair = false) override;
@@ -126,11 +129,6 @@ public:
     Path addTextToStore(const string & name, const string & s,
         const PathSet & references, bool repair = false) override;
 
-    void exportPath(const Path & path, Sink & sink) override;
-
-    Paths importPaths(Source & source,
-        std::shared_ptr<FSAccessor> accessor) override;
-
     void buildPaths(const PathSet & paths, BuildMode buildMode) override;
 
     BuildResult buildDerivation(const Path & drvPath, const BasicDerivation & drv,
@@ -229,8 +227,6 @@ private:
 
     Path createTempDirInStore();
 
-    Path importPath(Source & source);
-
     void checkDerivationOutputs(const Path & drvPath, const Derivation & drv);
 
     typedef std::unordered_set<ino_t> InodeHash;
diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index 1616f98f00..1a6afe46bb 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -326,6 +326,12 @@ Path RemoteStore::queryPathFromHashPart(const string & hashPart)
 }
 
 
+void RemoteStore::addToStore(const ValidPathInfo & info, const std::string & nar, bool repair)
+{
+    throw Error("RemoteStore::addToStore() not implemented");
+}
+
+
 Path RemoteStore::addToStore(const string & name, const Path & _srcPath,
     bool recursive, HashType hashAlgo, PathFilter & filter, bool repair)
 {
@@ -373,25 +379,6 @@ Path RemoteStore::addTextToStore(const string & name, const string & s,
 }
 
 
-void RemoteStore::exportPath(const Path & path, Sink & sink)
-{
-    auto conn(connections->get());
-    conn->to << wopExportPath << path << 0;
-    conn->processStderr(&sink); /* sink receives the actual data */
-    readInt(conn->from);
-}
-
-
-Paths RemoteStore::importPaths(Source & source,
-    std::shared_ptr<FSAccessor> accessor)
-{
-    auto conn(connections->get());
-    conn->to << wopImportPaths;
-    conn->processStderr(0, &source);
-    return readStorePaths<Paths>(conn->from);
-}
-
-
 void RemoteStore::buildPaths(const PathSet & drvPaths, BuildMode buildMode)
 {
     auto conn(connections->get());
diff --git a/src/libstore/remote-store.hh b/src/libstore/remote-store.hh
index f4fd96a614..0757f82e89 100644
--- a/src/libstore/remote-store.hh
+++ b/src/libstore/remote-store.hh
@@ -51,6 +51,9 @@ public:
     void querySubstitutablePathInfos(const PathSet & paths,
         SubstitutablePathInfos & infos) override;
 
+    void addToStore(const ValidPathInfo & info, const std::string & nar,
+        bool repair) override;
+
     Path addToStore(const string & name, const Path & srcPath,
         bool recursive = true, HashType hashAlgo = htSHA256,
         PathFilter & filter = defaultPathFilter, bool repair = false) override;
@@ -58,11 +61,6 @@ public:
     Path addTextToStore(const string & name, const string & s,
         const PathSet & references, bool repair = false) override;
 
-    void exportPath(const Path & path, Sink & sink) override;
-
-    Paths importPaths(Source & source,
-        std::shared_ptr<FSAccessor> accessor) override;
-
     void buildPaths(const PathSet & paths, BuildMode buildMode) override;
 
     BuildResult buildDerivation(const Path & drvPath, const BasicDerivation & drv,
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index c6cc46c609..8600def627 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -363,10 +363,9 @@ void copyStorePath(ref<Store> srcStore, ref<Store> dstStore,
     auto info = srcStore->queryPathInfo(storePath);
 
     StringSink sink;
-    srcStore->exportPaths({storePath}, sink);
+    srcStore->narFromPath({storePath}, sink);
 
-    StringSource source(*sink.s);
-    dstStore->importPaths(source, 0);
+    dstStore->addToStore(*info, *sink.s);
 }
 
 
@@ -406,16 +405,6 @@ string showPaths(const PathSet & paths)
 }
 
 
-void Store::exportPaths(const Paths & paths, Sink & sink)
-{
-    for (auto & i : paths) {
-        sink << 1;
-        exportPath(i, sink);
-    }
-    sink << 0;
-}
-
-
 std::string ValidPathInfo::fingerprint() const
 {
     if (narSize == 0 || !narHash)
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index 95ad5136d9..f680e951f8 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -19,7 +19,7 @@ namespace nix {
 /* Size of the hash part of store paths, in base-32 characters. */
 const size_t storePathHashLen = 32; // i.e. 160 bits
 
-/* Magic header of exportPath() output. */
+/* Magic header of exportPath() output (obsolete). */
 const uint32_t exportMagic = 0x4558494e;
 
 
@@ -253,6 +253,10 @@ public:
     virtual void querySubstitutablePathInfos(const PathSet & paths,
         SubstitutablePathInfos & infos) = 0;
 
+    /* Import a path into the store. */
+    virtual void addToStore(const ValidPathInfo & info, const std::string & nar,
+        bool repair = false) = 0;
+
     /* Copy the contents of a path to the store and register the
        validity the resulting path.  The resulting path is returned.
        The function object `filter' can be used to exclude files (see
@@ -269,21 +273,6 @@ public:
     /* Write a NAR dump of a store path. */
     virtual void narFromPath(const Path & path, Sink & sink) = 0;
 
-    /* Export a store path, that is, create a NAR dump of the store
-       path and append its references and its deriver. */
-    virtual void exportPath(const Path & path, Sink & sink) = 0;
-
-    /* Export multiple paths in the format expected by ‘nix-store
-       --import’. */
-    void exportPaths(const Paths & paths, Sink & sink);
-
-    /* Import a sequence of NAR dumps created by exportPaths() into
-       the Nix store. Optionally, the contents of the NARs are
-       preloaded into the specified FS accessor to speed up subsequent
-       access. */
-    virtual Paths importPaths(Source & source,
-        std::shared_ptr<FSAccessor> accessor) = 0;
-
     /* For each path, if it's a derivation, build it.  Building a
        derivation means ensuring that the output paths are valid.  If
        they are already valid, this is a no-op.  Otherwise, validity
@@ -397,6 +386,19 @@ public:
        relation.  If p refers to q, then p preceeds q in this list. */
     Paths topoSortPaths(const PathSet & paths);
 
+    /* Export multiple paths in the format expected by ‘nix-store
+       --import’. */
+    void exportPaths(const Paths & paths, Sink & sink);
+
+    void exportPath(const Path & path, Sink & sink);
+
+    /* Import a sequence of NAR dumps created by exportPaths() into
+       the Nix store. Optionally, the contents of the NARs are
+       preloaded into the specified FS accessor to speed up subsequent
+       access. */
+    Paths importPaths(Source & source,
+        std::shared_ptr<FSAccessor> accessor);
+
     struct Stats
     {
         std::atomic<uint64_t> narInfoRead{0};
diff --git a/src/libstore/worker-protocol.hh b/src/libstore/worker-protocol.hh
index d133328d1e..7ff0553a01 100644
--- a/src/libstore/worker-protocol.hh
+++ b/src/libstore/worker-protocol.hh
@@ -25,7 +25,7 @@ typedef enum {
     wopAddIndirectRoot = 12,
     wopSyncWithGC = 13,
     wopFindRoots = 14,
-    wopExportPath = 16,
+    wopExportPath = 16, // obsolete
     wopQueryDeriver = 18, // obsolete
     wopSetOptions = 19,
     wopCollectGarbage = 20,
@@ -35,7 +35,7 @@ typedef enum {
     wopQueryFailedPaths = 24,
     wopClearFailedPaths = 25,
     wopQueryPathInfo = 26,
-    wopImportPaths = 27,
+    wopImportPaths = 27, // obsolete
     wopQueryDerivationOutputNames = 28,
     wopQueryPathFromHashPart = 29,
     wopQuerySubstitutablePathInfos = 30,
diff --git a/src/libutil/compression.cc b/src/libutil/compression.cc
index ec63855f6c..cd2cc9cc10 100644
--- a/src/libutil/compression.cc
+++ b/src/libutil/compression.cc
@@ -173,26 +173,26 @@ static ref<std::string> decompressBzip2(const std::string & in)
     }
 }
 
-ref<std::string> compress(const std::string & method, ref<std::string> in)
+ref<std::string> compress(const std::string & method, const std::string & in)
 {
     if (method == "none")
-        return in;
+        return make_ref<std::string>(in);
     else if (method == "xz")
-        return compressXZ(*in);
+        return compressXZ(in);
     else if (method == "bzip2")
-        return compressBzip2(*in);
+        return compressBzip2(in);
     else
         throw UnknownCompressionMethod(format("unknown compression method ‘%s’") % method);
 }
 
-ref<std::string> decompress(const std::string & method, ref<std::string> in)
+ref<std::string> decompress(const std::string & method, const std::string & in)
 {
     if (method == "none")
-        return in;
+        return make_ref<std::string>(in);
     else if (method == "xz")
-        return decompressXZ(*in);
+        return decompressXZ(in);
     else if (method == "bzip2")
-        return decompressBzip2(*in);
+        return decompressBzip2(in);
     else
         throw UnknownCompressionMethod(format("unknown compression method ‘%s’") % method);
 }
diff --git a/src/libutil/compression.hh b/src/libutil/compression.hh
index 33c465df84..ed3c463865 100644
--- a/src/libutil/compression.hh
+++ b/src/libutil/compression.hh
@@ -7,9 +7,9 @@
 
 namespace nix {
 
-ref<std::string> compress(const std::string & method, ref<std::string> in);
+ref<std::string> compress(const std::string & method, const std::string & in);
 
-ref<std::string> decompress(const std::string & method, ref<std::string> in);
+ref<std::string> decompress(const std::string & method, const std::string & in);
 
 MakeError(UnknownCompressionMethod, Error);
 
diff --git a/src/nix-store/nix-store.cc b/src/nix-store/nix-store.cc
index d63adaff32..99fee5c65f 100644
--- a/src/nix-store/nix-store.cc
+++ b/src/nix-store/nix-store.cc
@@ -503,7 +503,7 @@ static void opReadLog(Strings opFlags, Strings opArgs)
             }
 
             else if (pathExists(logBz2Path)) {
-                std::cout << *decompress("bzip2", make_ref<std::string>(readFile(logBz2Path)));
+                std::cout << *decompress("bzip2", readFile(logBz2Path));
                 found = true;
                 break;
             }
@@ -703,9 +703,7 @@ static void opExport(Strings opFlags, Strings opArgs)
         throw UsageError(format("unknown flag ‘%1%’") % i);
 
     FdSink sink(STDOUT_FILENO);
-    Paths sorted = store->topoSortPaths(PathSet(opArgs.begin(), opArgs.end()));
-    reverse(sorted.begin(), sorted.end());
-    store->exportPaths(sorted, sink);
+    store->exportPaths(opArgs, sink);
 }
 
 
diff --git a/src/nix/command.cc b/src/nix/command.cc
index c8d91737d8..253c9686ba 100644
--- a/src/nix/command.cc
+++ b/src/nix/command.cc
@@ -108,7 +108,7 @@ void StorePathsCommand::run(ref<Store> store)
             PathSet closure;
             for (auto & storePath : storePaths)
                 store->computeFSClosure(storePath, closure, false, false);
-            storePaths = store->topoSortPaths(closure);
+            storePaths = Paths(closure.begin(), closure.end());
         }
     }