Merge branch 'substitute-fetchers' into ipfs-git-ipld

obsidiansystems · Jun 22, 2020 · 62d6ee0 · 62d6ee0
2 parents f85fc65 + 74b83c4
commit 62d6ee0
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diff --git a/src/libexpr/primops/fetchTree.cc b/src/libexpr/primops/fetchTree.cc
@@ -134,6 +134,20 @@ static void fetch(EvalState & state, const Pos & pos, Value * * args, Value & v,
     if (evalSettings.pureEval && !expectedHash)
         throw Error("in pure evaluation mode, '%s' requires a 'sha256' argument", who);
 
+    // try to substitute if we can
+    if (settings.useSubstitutes && expectedHash) {
+        auto substitutableStorePath = fetchers::trySubstitute(state.store,
+            unpack ? FileIngestionMethod::Recursive : FileIngestionMethod::Flat, *expectedHash, name);
+        if (substitutableStorePath) {
+            auto substitutablePath = state.store->toRealPath(*substitutableStorePath);
+            if (state.allowedPaths)
+                state.allowedPaths->insert(substitutablePath);
+
+            mkString(v, substitutablePath, PathSet({substitutablePath}));
+            return;
+        }
+    }
+
     auto storePath =
         unpack
         ? fetchers::downloadTarball(state.store, *url, name, (bool) expectedHash).storePath

diff --git a/src/libfetchers/fetchers.cc b/src/libfetchers/fetchers.cc
@@ -72,4 +72,22 @@ std::pair<Tree, std::shared_ptr<const Input>> Input::fetchTree(ref<Store> store)
     return {std::move(tree), input};
 }
 
+std::optional<StorePath> trySubstitute(ref<Store> store, FileIngestionMethod ingestionMethod,
+    Hash hash, std::string_view name)
+{
+    auto substitutablePath = store->makeFixedOutputPath(ingestionMethod, hash, name);
+
+    try {
+        store->ensurePath(substitutablePath);
+
+        debug("using substituted path '%s'", store->printStorePath(substitutablePath));
+
+        return substitutablePath;
+    } catch (Error & e) {
+        debug("substitution of path '%s' failed: %s", store->printStorePath(substitutablePath), e.what());
+    }
+
+    return std::nullopt;
+}
+
 }
diff --git a/src/libfetchers/fetchers.hh b/src/libfetchers/fetchers.hh
@@ -100,4 +100,7 @@ Tree downloadTarball(
     const std::string & name,
     bool immutable);
 
+std::optional<StorePath> trySubstitute(ref<Store> store, FileIngestionMethod ingestionMethod,
+    Hash hash, std::string_view name);
+
 }