tarball.cc: Use ETags

6 files changed, 99 insertions, 42 deletions

diff --git a/src/libstore/fetchers/cache.cc b/src/libstore/fetchers/cache.cc
index 4c88b64c5..14a84744a 100644
--- a/src/libstore/fetchers/cache.cc
+++ b/src/libstore/fetchers/cache.cc
@@ -66,6 +66,19 @@ struct CacheImpl : Cache
         ref<Store> store,
         const Attrs & inAttrs) override
     {
+        if (auto res = lookupExpired(store, inAttrs)) {
+            if (!res->expired)
+                return std::make_pair(std::move(res->infoAttrs), std::move(res->storePath));
+            debug("ignoring expired cache entry '%s'",
+                attrsToJson(inAttrs).dump());
+        }
+        return {};
+    }
+
+    std::optional<Result> lookupExpired(
+        ref<Store> store,
+        const Attrs & inAttrs) override
+    {
         auto state(_state.lock());
 
         auto inAttrsJson = attrsToJson(inAttrs).dump();
@@ -81,11 +94,6 @@ struct CacheImpl : Cache
         auto immutable = stmt.getInt(2) != 0;
         auto timestamp = stmt.getInt(3);
 
-        if (!immutable && (settings.tarballTtl.get() == 0 || timestamp + settings.tarballTtl < time(0))) {
-            debug("ignoring expired cache entry '%s'", inAttrsJson);
-            return {};
-        }
-
         store->addTempRoot(storePath);
         if (!store->isValidPath(storePath)) {
             // FIXME: we could try to substitute 'storePath'.
@@ -96,7 +104,11 @@ struct CacheImpl : Cache
         debug("using cache entry '%s' -> '%s', '%s'",
             inAttrsJson, infoJson, store->printStorePath(storePath));
 
-        return {{jsonToAttrs(nlohmann::json::parse(infoJson)), std::move(storePath)}};
+        return Result {
+            .expired = !immutable && (settings.tarballTtl.get() == 0 || timestamp + settings.tarballTtl < time(0)),
+            .infoAttrs = jsonToAttrs(nlohmann::json::parse(infoJson)),
+            .storePath = std::move(storePath)
+        };
     }
 };
 
diff --git a/src/libstore/fetchers/cache.hh b/src/libstore/fetchers/cache.hh
index ba2d30629..a25b05985 100644
--- a/src/libstore/fetchers/cache.hh
+++ b/src/libstore/fetchers/cache.hh
@@ -17,6 +17,17 @@ struct Cache
     virtual std::optional<std::pair<Attrs, StorePath>> lookup(
         ref<Store> store,
         const Attrs & inAttrs) = 0;
+
+    struct Result
+    {
+        bool expired = false;
+        Attrs infoAttrs;
+        StorePath storePath;
+    };
+
+    virtual std::optional<Result> lookupExpired(
+        ref<Store> store,
+        const Attrs & inAttrs) = 0;
 };
 
 ref<Cache> getCache();
diff --git a/src/libstore/fetchers/fetchers.hh b/src/libstore/fetchers/fetchers.hh
index 0a028cf7a..9c931dfa1 100644
--- a/src/libstore/fetchers/fetchers.hh
+++ b/src/libstore/fetchers/fetchers.hh
@@ -93,7 +93,13 @@ std::unique_ptr<Input> inputFromAttrs(const Attrs & attrs);
 
 void registerInputScheme(std::unique_ptr<InputScheme> && fetcher);
 
-StorePath downloadFile(
+struct DownloadFileResult
+{
+    StorePath storePath;
+    std::string etag;
+};
+
+DownloadFileResult downloadFile(
     ref<Store> store,
     const std::string & url,
     const std::string & name,
diff --git a/src/libstore/fetchers/github.cc b/src/libstore/fetchers/github.cc
index 1041b98a5..0fef456df 100644
--- a/src/libstore/fetchers/github.cc
+++ b/src/libstore/fetchers/github.cc
@@ -81,7 +81,7 @@ struct GitHubInput : Input
             auto json = nlohmann::json::parse(
                 readFile(
                     store->toRealPath(
-                        downloadFile(store, url, "source", false))));
+                        downloadFile(store, url, "source", false).storePath)));
             rev = Hash(json["sha"], htSHA1);
             debug("HEAD revision for '%s' is %s", url, rev->gitRev());
         }
diff --git a/src/libstore/fetchers/registry.cc b/src/libstore/fetchers/registry.cc
index 0aac18375..638e6e50a 100644
--- a/src/libstore/fetchers/registry.cc
+++ b/src/libstore/fetchers/registry.cc
@@ -130,7 +130,7 @@ static std::shared_ptr<Registry> getGlobalRegistry(ref<Store> store)
         if (!hasPrefix(path, "/"))
             // FIXME: register as GC root.
             // FIXME: if download fails, use previous version if available.
-            path = store->toRealPath(downloadFile(store, path, "flake-registry.json", false));
+            path = store->toRealPath(downloadFile(store, path, "flake-registry.json", false).storePath);
 
         return Registry::read(path, Registry::Global);
     }();
diff --git a/src/libstore/fetchers/tarball.cc b/src/libstore/fetchers/tarball.cc
index bbc96d70b..53971ec2b 100644
--- a/src/libstore/fetchers/tarball.cc
+++ b/src/libstore/fetchers/tarball.cc
@@ -9,7 +9,7 @@
 
 namespace nix::fetchers {
 
-StorePath downloadFile(
+DownloadFileResult downloadFile(
     ref<Store> store,
     const std::string & url,
     const std::string & name,
@@ -23,37 +23,54 @@ StorePath downloadFile(
         {"name", name},
     });
 
-    if (auto res = getCache()->lookup(store, inAttrs))
-        return std::move(res->second);
+    auto cached = getCache()->lookupExpired(store, inAttrs);
 
-    // FIXME: use ETag.
+    if (cached && !cached->expired)
+        return {
+            .storePath = std::move(cached->storePath),
+            .etag = getStrAttr(cached->infoAttrs, "etag")
+        };
 
     DownloadRequest request(url);
+    if (cached)
+        request.expectedETag = getStrAttr(cached->infoAttrs, "etag");
     auto res = getDownloader()->download(request);
 
     // FIXME: write to temporary file.
 
-    StringSink sink;
-    dumpString(*res.data, sink);
-    auto hash = hashString(htSHA256, *res.data);
-    ValidPathInfo info(store->makeFixedOutputPath(false, hash, name));
-    info.narHash = hashString(htSHA256, *sink.s);
-    info.narSize = sink.s->size();
-    info.ca = makeFixedOutputCA(false, hash);
-    store->addToStore(info, sink.s, NoRepair, NoCheckSigs);
-
     Attrs infoAttrs({
         {"etag", res.etag},
     });
 
+    std::optional<StorePath> storePath;
+
+    if (res.cached) {
+        assert(cached);
+        assert(request.expectedETag == res.etag);
+        storePath = std::move(cached->storePath);
+    } else {
+        StringSink sink;
+        dumpString(*res.data, sink);
+        auto hash = hashString(htSHA256, *res.data);
+        ValidPathInfo info(store->makeFixedOutputPath(false, hash, name));
+        info.narHash = hashString(htSHA256, *sink.s);
+        info.narSize = sink.s->size();
+        info.ca = makeFixedOutputCA(false, hash);
+        store->addToStore(info, sink.s, NoRepair, NoCheckSigs);
+        storePath = std::move(info.path);
+    }
+
     getCache()->add(
         store,
         inAttrs,
         infoAttrs,
-        info.path.clone(),
+        *storePath,
         immutable);
 
-    return std::move(info.path);
+    return {
+        .storePath = std::move(*storePath),
+        .etag = res.etag,
+    };
 }
 
 Tree downloadTarball(
@@ -68,41 +85,52 @@ Tree downloadTarball(
         {"name", name},
     });
 
-    if (auto res = getCache()->lookup(store, inAttrs))
+    auto cached = getCache()->lookupExpired(store, inAttrs);
+
+    if (cached && !cached->expired)
         return Tree {
-            .actualPath = store->toRealPath(res->second),
-            .storePath = std::move(res->second),
+            .actualPath = store->toRealPath(cached->storePath),
+            .storePath = std::move(cached->storePath),
             .info = TreeInfo {
-                .lastModified = getIntAttr(res->first, "lastModified"),
+                .lastModified = getIntAttr(cached->infoAttrs, "lastModified"),
             },
         };
 
-    auto tarball = downloadFile(store, url, name, immutable);
-
-    Path tmpDir = createTempDir();
-    AutoDelete autoDelete(tmpDir, true);
-    unpackTarfile(store->toRealPath(tarball), tmpDir);
-    auto members = readDirectory(tmpDir);
-    if (members.size() != 1)
-        throw nix::Error("tarball '%s' contains an unexpected number of top-level files", url);
-    auto topDir = tmpDir + "/" + members.begin()->name;
-    auto lastModified = lstat(topDir).st_mtime;
-    auto unpackedStorePath = store->addToStore(name, topDir, true, htSHA256, defaultPathFilter, NoRepair);
+    auto res = downloadFile(store, url, name, immutable);
+
+    std::optional<StorePath> unpackedStorePath;
+    time_t lastModified;
+
+    if (cached && res.etag != "" && getStrAttr(cached->infoAttrs, "etag") == res.etag) {
+        unpackedStorePath = std::move(cached->storePath);
+        lastModified = getIntAttr(cached->infoAttrs, "lastModified");
+    } else {
+        Path tmpDir = createTempDir();
+        AutoDelete autoDelete(tmpDir, true);
+        unpackTarfile(store->toRealPath(res.storePath), tmpDir);
+        auto members = readDirectory(tmpDir);
+        if (members.size() != 1)
+            throw nix::Error("tarball '%s' contains an unexpected number of top-level files", url);
+        auto topDir = tmpDir + "/" + members.begin()->name;
+        lastModified = lstat(topDir).st_mtime;
+        unpackedStorePath = store->addToStore(name, topDir, true, htSHA256, defaultPathFilter, NoRepair);
+    }
 
     Attrs infoAttrs({
         {"lastModified", lastModified},
+        {"etag", res.etag},
     });
 
     getCache()->add(
         store,
         inAttrs,
         infoAttrs,
-        unpackedStorePath,
+        *unpackedStorePath,
         immutable);
 
     return Tree {
-        .actualPath = store->toRealPath(unpackedStorePath),
-        .storePath = std::move(unpackedStorePath),
+        .actualPath = store->toRealPath(*unpackedStorePath),
+        .storePath = std::move(*unpackedStorePath),
         .info = TreeInfo {
             .lastModified = lastModified,
         },