C API: Add nix_store_real_path

src/libstore-c/nix_api_store.cc

@@ -100,6 +100,18 @@ bool nix_store_is_valid_path(nix_c_context * context, Store * store, StorePath *
     NIXC_CATCH_ERRS_RES(false);
 }
 
+nix_err nix_store_real_path(
+    nix_c_context * context, Store * store, StorePath * path, nix_get_string_callback callback, void * user_data)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto res = store->ptr->toRealPath(path->path);
+        return call_nix_get_string_callback(res, callback, user_data);
+    }
+    NIXC_CATCH_ERRS
+}
+
 StorePath * nix_store_parse_path(nix_c_context * context, Store * store, const char * path)
 {
     if (context)

src/libstore-c/nix_api_store.h

@@ -149,6 +149,26 @@ void nix_store_path_free(StorePath * p);
  * @return true or false, error info in context
  */
 bool nix_store_is_valid_path(nix_c_context * context, Store * store, StorePath * path);
+
+/**
+ * @brief Get the physical location of a store path
+ *
+ * A store may reside at a different location than its `storeDir` suggests.
+ * This situation is called a relocated store.
+ * Relocated stores are used during NixOS installation, as well as in restricted computing environments that don't offer
+ * a writable `/nix/store`.
+ *
+ * Not all types of stores support this operation.
+ *
+ * @param[in] context Optional, stores error information
+ * @param[in] store nix store reference
+ * @param[in] path the path to get the real path from
+ * @param[in] callback called with the real path
+ * @param[in] user_data arbitrary data, passed to the callback when it's called.
+ */
+nix_err nix_store_real_path(
+    nix_c_context * context, Store * store, StorePath * path, nix_get_string_callback callback, void * user_data);
+
 // nix_err nix_store_ensure(Store*, const char*);
 // nix_err nix_store_build_paths(Store*);
 /**

src/libstore-tests/nix_api_store.cc

@@ -119,4 +119,84 @@ TEST_F(nix_api_store_test, nix_store_is_valid_path_not_in_store)
     ASSERT_EQ(false, nix_store_is_valid_path(ctx, store, path));
 }
 
+TEST_F(nix_api_store_test, nix_store_real_path)
+{
+    StorePath * path = nix_store_parse_path(ctx, store, (nixStoreDir + PATH_SUFFIX).c_str());
+    std::string rp;
+    auto ret = nix_store_real_path(ctx, store, path, OBSERVE_STRING(rp));
+    assert_ctx_ok();
+    ASSERT_EQ(NIX_OK, ret);
+    // Assumption: we're not testing with a relocated store
+    ASSERT_STREQ((nixStoreDir + PATH_SUFFIX).c_str(), rp.c_str());
+
+    nix_store_path_free(path);
 }
+
+TEST_F(nix_api_util_context, nix_store_real_path_relocated)
+{
+    if (nix::getEnv("HOME").value_or("") == "/homeless-shelter") {
+        // Can't open default store from within sandbox
+        GTEST_SKIP();
+    }
+    auto tmp = nix::createTempDir();
+    std::string storeRoot = tmp + "/store";
+    std::string stateDir = tmp + "/state";
+    std::string logDir = tmp + "/log";
+    const char * rootkv[] = {"root", storeRoot.c_str()};
+    const char * statekv[] = {"state", stateDir.c_str()};
+    const char * logkv[] = {"log", logDir.c_str()};
+    // const char * rokv[] = {"read-only", "true"};
+    const char ** kvs[] = {rootkv, statekv, logkv, NULL};
+
+    nix_libstore_init(ctx);
+    assert_ctx_ok();
+
+    Store * store = nix_store_open(ctx, "local", kvs);
+    assert_ctx_ok();
+    ASSERT_NE(store, nullptr);
+
+    std::string nixStoreDir;
+    auto ret = nix_store_get_storedir(ctx, store, OBSERVE_STRING(nixStoreDir));
+    ASSERT_EQ(NIX_OK, ret);
+    ASSERT_STREQ(NIX_STORE_DIR, nixStoreDir.c_str());
+
+    StorePath * path = nix_store_parse_path(ctx, store, (nixStoreDir + PATH_SUFFIX).c_str());
+    assert_ctx_ok();
+    ASSERT_NE(path, nullptr);
+
+    std::string rp;
+    ret = nix_store_real_path(ctx, store, path, OBSERVE_STRING(rp));
+    assert_ctx_ok();
+    ASSERT_EQ(NIX_OK, ret);
+
+    // Assumption: we're not testing with a relocated store
+    ASSERT_STREQ((storeRoot + NIX_STORE_DIR + PATH_SUFFIX).c_str(), rp.c_str());
+
+    nix_store_path_free(path);
+}
+
+TEST_F(nix_api_util_context, nix_store_real_path_binary_cache)
+{
+    if (nix::getEnv("HOME").value_or("") == "/homeless-shelter") {
+        // TODO: override NIX_CACHE_HOME?
+        // skipping test in sandbox because narinfo cache can't be written
+        GTEST_SKIP();
+    }
+
+    Store * store = nix_store_open(ctx, "https://cache.nixos.org", nullptr);
+    assert_ctx_ok();
+    ASSERT_NE(store, nullptr);
+
+    std::string path_raw = std::string(NIX_STORE_DIR) + PATH_SUFFIX;
+    StorePath * path = nix_store_parse_path(ctx, store, path_raw.c_str());
+    assert_ctx_ok();
+    ASSERT_NE(path, nullptr);
+
+    std::string rp;
+    auto ret = nix_store_real_path(ctx, store, path, OBSERVE_STRING(rp));
+    assert_ctx_ok();
+    ASSERT_EQ(NIX_OK, ret);
+    ASSERT_STREQ(path_raw.c_str(), rp.c_str());
+}
+
+} // namespace nixC