5 files changed, 53 insertions, 68 deletions
diff --git a/src/libstore/binary-cache-store.cc b/src/libstore/binary-cache-store.cc
index 556fa3d59355..67607ab3d43a 100644
--- a/src/libstore/binary-cache-store.cc
+++ b/src/libstore/binary-cache-store.cc
@@ -17,66 +17,6 @@
 
 namespace nix {
 
-/* Given requests for a path /nix/store/<x>/<y>, this accessor will
-   first download the NAR for /nix/store/<x> from the binary cache,
-   build a NAR accessor for that NAR, and use that to access <y>. */
-struct BinaryCacheStoreAccessor : public FSAccessor
-{
-    ref<BinaryCacheStore> store;
-
-    std::map<Path, ref<FSAccessor>> nars;
-
-    BinaryCacheStoreAccessor(ref<BinaryCacheStore> store)
-        : store(store)
-    {
-    }
-
-    std::pair<ref<FSAccessor>, Path> fetch(const Path & path_)
-    {
-        auto path = canonPath(path_);
-
-        auto storePath = store->toStorePath(path);
-        std::string restPath = std::string(path, storePath.size());
-
-        if (!store->isValidPath(storePath))
-            throw InvalidPath(format("path '%1%' is not a valid store path") % storePath);
-
-        auto i = nars.find(storePath);
-        if (i != nars.end()) return {i->second, restPath};
-
-        StringSink sink;
-        store->narFromPath(storePath, sink);
-
-        auto accessor = makeNarAccessor(sink.s);
-        nars.emplace(storePath, accessor);
-        return {accessor, restPath};
-    }
-
-    Stat stat(const Path & path) override
-    {
-        auto res = fetch(path);
-        return res.first->stat(res.second);
-    }
-
-    StringSet readDirectory(const Path & path) override
-    {
-        auto res = fetch(path);
-        return res.first->readDirectory(res.second);
-    }
-
-    std::string readFile(const Path & path) override
-    {
-        auto res = fetch(path);
-        return res.first->readFile(res.second);
-    }
-
-    std::string readLink(const Path & path) override
-    {
-        auto res = fetch(path);
-        return res.first->readLink(res.second);
-    }
-};
-
 BinaryCacheStore::BinaryCacheStore(const Params & params)
     : Store(params)
 {
@@ -161,7 +101,7 @@ void BinaryCacheStore::addToStore(const ValidPathInfo & info, const ref<std::str
     if (info.narHash && info.narHash != narInfo->narHash)
         throw Error(format("refusing to copy corrupted path '%1%' to binary cache") % info.path);
 
-    auto accessor_ = std::dynamic_pointer_cast<BinaryCacheStoreAccessor>(accessor);
+    auto accessor_ = std::dynamic_pointer_cast<RemoteFSAccessor>(accessor);
 
     /* Optionally write a JSON file containing a listing of the
        contents of the NAR. */
@@ -174,8 +114,10 @@ void BinaryCacheStore::addToStore(const ValidPathInfo & info, const ref<std::str
 
             auto narAccessor = makeNarAccessor(nar);
 
-            if (accessor_)
+            if (accessor_) {
                 accessor_->nars.emplace(info.path, narAccessor);
+                accessor_->addToCache(info.path, *nar);
+            }
 
             std::function<void(const Path &, JSONPlaceholder &)> recurse;
 
@@ -220,8 +162,10 @@ void BinaryCacheStore::addToStore(const ValidPathInfo & info, const ref<std::str
     }
 
     else {
-        if (accessor_)
+        if (accessor_) {
             accessor_->nars.emplace(info.path, makeNarAccessor(nar));
+            accessor_->addToCache(info.path, *nar);
+        }
     }
 
     /* Compress the NAR. */
@@ -379,7 +323,7 @@ Path BinaryCacheStore::addTextToStore(const string & name, const string & s,
 
 ref<FSAccessor> BinaryCacheStore::getFSAccessor()
 {
-    return make_ref<RemoteFSAccessor>(ref<Store>(shared_from_this()));
+    return make_ref<RemoteFSAccessor>(ref<Store>(shared_from_this()), localNarCache);
 }
 
 std::shared_ptr<std::string> BinaryCacheStore::getBuildLog(const Path & path)
diff --git a/src/libstore/binary-cache-store.hh b/src/libstore/binary-cache-store.hh
index f9c1c2cbe8a8..d3b0e0bd9332 100644
--- a/src/libstore/binary-cache-store.hh
+++ b/src/libstore/binary-cache-store.hh
@@ -18,6 +18,7 @@ public:
     const Setting<std::string> compression{this, "xz", "compression", "NAR compression method ('xz', 'bzip2', or 'none')"};
     const Setting<bool> writeNARListing{this, false, "write-nar-listing", "whether to write a JSON file listing the files in each NAR"};
     const Setting<Path> secretKeyFile{this, "", "secret-key", "path to secret key used to sign the binary cache"};
+    const Setting<Path> localNarCache{this, "", "local-nar-cache", "path to a local cache of NARs"};
 
 private:
 
diff --git a/src/libstore/remote-fs-accessor.cc b/src/libstore/remote-fs-accessor.cc
index 098151f8c0f6..ba9620a175bb 100644
--- a/src/libstore/remote-fs-accessor.cc
+++ b/src/libstore/remote-fs-accessor.cc
@@ -3,10 +3,29 @@
 
 namespace nix {
 
-
-RemoteFSAccessor::RemoteFSAccessor(ref<Store> store)
+RemoteFSAccessor::RemoteFSAccessor(ref<Store> store, const Path & cacheDir)
     : store(store)
+    , cacheDir(cacheDir)
 {
+    if (cacheDir != "")
+        createDirs(cacheDir);
+}
+
+Path RemoteFSAccessor::makeCacheFile(const Path & storePath)
+{
+    assert(cacheDir != "");
+    return fmt("%s/%s.nar", cacheDir, storePathToHash(storePath));
+}
+
+void RemoteFSAccessor::addToCache(const Path & storePath, const std::string & nar)
+{
+    try {
+        if (cacheDir == "") return;
+        /* FIXME: do this asynchronously. */
+        writeFile(makeCacheFile(storePath), nar);
+    } catch (...) {
+        ignoreException();
+    }
 }
 
 std::pair<ref<FSAccessor>, Path> RemoteFSAccessor::fetch(const Path & path_)
@@ -23,7 +42,16 @@ std::pair<ref<FSAccessor>, Path> RemoteFSAccessor::fetch(const Path & path_)
     if (i != nars.end()) return {i->second, restPath};
 
     StringSink sink;
-    store->narFromPath(storePath, sink);
+
+    try {
+        if (cacheDir != "")
+            *sink.s = nix::readFile(makeCacheFile(storePath));
+    } catch (SysError &) { }
+
+    if (sink.s->empty()) {
+        store->narFromPath(storePath, sink);
+        addToCache(storePath, *sink.s);
+    }
 
     auto accessor = makeNarAccessor(sink.s);
     nars.emplace(storePath, accessor);
diff --git a/src/libstore/remote-fs-accessor.hh b/src/libstore/remote-fs-accessor.hh
index 28f36c8296e1..2a3fc01eff58 100644
--- a/src/libstore/remote-fs-accessor.hh
+++ b/src/libstore/remote-fs-accessor.hh
@@ -12,10 +12,20 @@ class RemoteFSAccessor : public FSAccessor
 
     std::map<Path, ref<FSAccessor>> nars;
 
+    Path cacheDir;
+
     std::pair<ref<FSAccessor>, Path> fetch(const Path & path_);
+
+    friend class BinaryCacheStore;
+
+    Path makeCacheFile(const Path & storePath);
+
+    void addToCache(const Path & storePath, const std::string & nar);
+
 public:
 
-    RemoteFSAccessor(ref<Store> store);
+    RemoteFSAccessor(ref<Store> store,
+        const /* FIXME: use std::optional */ Path & cacheDir = "");
 
     Stat stat(const Path & path) override;
 
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index fa6ade75002a..3bc5e4c57c95 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -619,6 +619,8 @@ void copyPaths(ref<Store> srcStore, ref<Store> dstStore, const PathSet & storePa
     for (auto & path : storePaths)
         if (!valid.count(path)) missing.insert(path);
 
+    if (missing.empty()) return;
+
     Activity act(*logger, lvlInfo, actCopyPaths, fmt("copying %d paths", missing.size()));
 
     std::atomic<size_t> nrDone{0};