1 files changed, 147 insertions, 0 deletions
diff --git a/src/libstore/fetchers/registry.cc b/src/libstore/fetchers/registry.cc
new file mode 100644
index 000000000..9c74f118d
--- /dev/null
+++ b/src/libstore/fetchers/registry.cc
@@ -0,0 +1,147 @@
+#include "registry.hh"
+#include "util.hh"
+#include "fetchers.hh"
+#include "globals.hh"
+#include "download.hh"
+
+#include <nlohmann/json.hpp>
+
+namespace nix::fetchers {
+
+std::shared_ptr<Registry> Registry::read(
+    const Path & path, RegistryType type)
+{
+    auto registry = std::make_shared<Registry>(type);
+
+    if (!pathExists(path))
+        return std::make_shared<Registry>(type);
+
+    auto json = nlohmann::json::parse(readFile(path));
+
+    auto version = json.value("version", 0);
+    if (version != 1)
+        throw Error("flake registry '%s' has unsupported version %d", path, version);
+
+    auto flakes = json["flakes"];
+    for (auto i = flakes.begin(); i != flakes.end(); ++i) {
+        // FIXME: remove 'uri' soon.
+        auto url = i->value("url", i->value("uri", ""));
+        if (url.empty())
+            throw Error("flake registry '%s' lacks a 'url' attribute for entry '%s'",
+                path, i.key());
+        registry->entries.push_back(
+            {inputFromURL(i.key()), inputFromURL(url)});
+    }
+
+    return registry;
+}
+
+void Registry::write(const Path & path)
+{
+    nlohmann::json json;
+    json["version"] = 1;
+    for (auto & elem : entries)
+        json["flakes"][elem.first->to_string()] = { {"url", elem.second->to_string()} };
+    createDirs(dirOf(path));
+    writeFile(path, json.dump(4));
+}
+
+void Registry::add(
+    const std::shared_ptr<const Input> & from,
+    const std::shared_ptr<const Input> & to)
+{
+    entries.emplace_back(from, to);
+}
+
+void Registry::remove(const std::shared_ptr<const Input> & input)
+{
+    // FIXME: use C++20 std::erase.
+    for (auto i = entries.begin(); i != entries.end(); )
+        if (*i->first == *input)
+            i = entries.erase(i);
+        else
+            ++i;
+}
+
+Path getUserRegistryPath()
+{
+    return getHome() + "/.config/nix/registry.json";
+}
+
+std::shared_ptr<Registry> getUserRegistry()
+{
+    return Registry::read(getUserRegistryPath(), Registry::User);
+}
+
+static std::shared_ptr<Registry> flagRegistry =
+    std::make_shared<Registry>(Registry::Flag);
+
+std::shared_ptr<Registry> getFlagRegistry()
+{
+    return flagRegistry;
+}
+
+void overrideRegistry(
+    const std::shared_ptr<const Input> & from,
+    const std::shared_ptr<const Input> & to)
+{
+    flagRegistry->add(from, to);
+}
+
+static std::shared_ptr<Registry> getGlobalRegistry(ref<Store> store)
+{
+    static auto reg = [&]() {
+        auto path = settings.flakeRegistry;
+
+        if (!hasPrefix(path, "/")) {
+            CachedDownloadRequest request(path);
+            request.name = "flake-registry.json";
+            request.gcRoot = true;
+            path = getDownloader()->downloadCached(store, request).path;
+        }
+
+        return Registry::read(path, Registry::Global);
+    }();
+
+    return reg;
+}
+
+Registries getRegistries(ref<Store> store)
+{
+    Registries registries;
+    registries.push_back(getFlagRegistry());
+    registries.push_back(getUserRegistry());
+    registries.push_back(getGlobalRegistry(store));
+    return registries;
+}
+
+std::shared_ptr<const Input> lookupInRegistries(
+    ref<Store> store,
+    std::shared_ptr<const Input> input)
+{
+    int n = 0;
+
+ restart:
+
+    n++;
+    if (n > 100) throw Error("cycle detected in flake registr for '%s'", input);
+
+    for (auto & registry : getRegistries(store)) {
+        // FIXME: O(n)
+        for (auto & entry : registry->entries) {
+            if (entry.first->contains(*input)) {
+                input = entry.second->applyOverrides(
+                    !entry.first->getRef() && input->getRef() ? input->getRef() : std::optional<std::string>(),
+                    !entry.first->getRev() && input->getRev() ? input->getRev() : std::optional<Hash>());
+                goto restart;
+            }
+        }
+    }
+
+    if (!input->isDirect())
+        throw Error("cannot find flake '%s' in the flake registries", input->to_string());
+
+    return input;
+}
+
+}