Improve checked json casting (#10087)

This introduces new utility functions to get elements from JSON — in an ergonomic way and with nice error messages if the expected type does not match.

Co-authored-by: John Ericson <John.Ericson@Obsidian.Systems>

tests/unit/libfetchers/local.mk

@@ -0,0 +1,32 @@
+check: libfetchers-tests_RUN
+
+programs += libfetchers-tests
+
+libfetchers-tests_NAME = libnixfetchers-tests
+
+libfetchers-tests_ENV := _NIX_TEST_UNIT_DATA=$(d)/data
+
+libfetchers-tests_DIR := $(d)
+
+ifeq ($(INSTALL_UNIT_TESTS), yes)
+  libfetchers-tests_INSTALL_DIR := $(checkbindir)
+else
+  libfetchers-tests_INSTALL_DIR :=
+endif
+
+libfetchers-tests_SOURCES := $(wildcard $(d)/*.cc)
+
+libfetchers-tests_EXTRA_INCLUDES = \
+    -I tests/unit/libstore-support \
+    -I tests/unit/libutil-support \
+    $(INCLUDE_libfetchers) \
+    $(INCLUDE_libstore) \
+    $(INCLUDE_libutil)
+
+libfetchers-tests_CXXFLAGS += $(libfetchers-tests_EXTRA_INCLUDES)
+
+libfetchers-tests_LIBS = \
+    libstore-test-support libutil-test-support \
+    libfetchers libstore libutil
+
+libfetchers-tests_LDFLAGS := -lrapidcheck $(GTEST_LIBS)

tests/unit/libfetchers/public-key.cc

@@ -0,0 +1,18 @@
+#include <gtest/gtest.h>
+#include "fetchers.hh"
+#include "json-utils.hh"
+
+namespace nix {
+    TEST(PublicKey, jsonSerialization) {
+        auto json = nlohmann::json(fetchers::PublicKey { .key = "ABCDE" });
+
+        ASSERT_EQ(json, R"({ "key": "ABCDE", "type": "ssh-ed25519" })"_json);
+    }
+    TEST(PublicKey, jsonDeserialization) {
+        auto pubKeyJson = R"({ "key": "ABCDE", "type": "ssh-ed25519" })"_json;
+        fetchers::PublicKey pubKey = pubKeyJson;
+
+        ASSERT_EQ(pubKey.key, "ABCDE");
+        ASSERT_EQ(pubKey.type, "ssh-ed25519");
+    }
+}

tests/unit/libutil/json-utils.cc

@@ -3,6 +3,7 @@
 
 #include <gtest/gtest.h>
 
+#include "error.hh"
 #include "json-utils.hh"
 
 namespace nix {
@@ -55,4 +56,108 @@ TEST(from_json, vectorOfOptionalInts) {
     ASSERT_FALSE(vals.at(1).has_value());
 }
 
+TEST(valueAt, simpleObject) {
+    auto simple = R"({ "hello": "world" })"_json;
+
+    ASSERT_EQ(valueAt(getObject(simple), "hello"), "world");
+
+    auto nested = R"({ "hello": { "world": "" } })"_json;
+
+    auto & nestedObject = valueAt(getObject(nested), "hello");
+
+    ASSERT_EQ(valueAt(nestedObject, "world"), "");
+}
+
+TEST(valueAt, missingKey) {
+    auto json = R"({ "hello": { "nested": "world" } })"_json;
+
+    auto & obj = getObject(json);
+
+    ASSERT_THROW(valueAt(obj, "foo"), Error);
+}
+
+TEST(getObject, rightAssertions) {
+    auto simple = R"({ "object": {} })"_json;
+
+    ASSERT_EQ(getObject(valueAt(getObject(simple), "object")), (nlohmann::json::object_t {}));
+
+    auto nested = R"({ "object": { "object": {} } })"_json;
+
+    auto & nestedObject = getObject(valueAt(getObject(nested), "object"));
+
+    ASSERT_EQ(nestedObject, getObject(nlohmann::json::parse(R"({ "object": {} })")));
+    ASSERT_EQ(getObject(valueAt(getObject(nestedObject), "object")), (nlohmann::json::object_t {}));
+}
+
+TEST(getObject, wrongAssertions) {
+    auto json = R"({ "object": {}, "array": [], "string": "", "int": 0, "boolean": false })"_json;
+
+    auto & obj = getObject(json);
+
+    ASSERT_THROW(getObject(valueAt(obj, "array")), Error);
+    ASSERT_THROW(getObject(valueAt(obj, "string")), Error);
+    ASSERT_THROW(getObject(valueAt(obj, "int")), Error);
+    ASSERT_THROW(getObject(valueAt(obj, "boolean")), Error);
+}
+
+TEST(getArray, rightAssertions) {
+    auto simple = R"({ "array": [] })"_json;
+
+    ASSERT_EQ(getArray(valueAt(getObject(simple), "array")), (nlohmann::json::array_t {}));
+}
+
+TEST(getArray, wrongAssertions) {
+    auto json = R"({ "object": {}, "array": [], "string": "", "int": 0, "boolean": false })"_json;
+
+    ASSERT_THROW(getArray(valueAt(json, "object")), Error);
+    ASSERT_THROW(getArray(valueAt(json, "string")), Error);
+    ASSERT_THROW(getArray(valueAt(json, "int")), Error);
+    ASSERT_THROW(getArray(valueAt(json, "boolean")), Error);
+}
+
+TEST(getString, rightAssertions) {
+    auto simple = R"({ "string": "" })"_json;
+
+    ASSERT_EQ(getString(valueAt(getObject(simple), "string")), "");
+}
+
+TEST(getString, wrongAssertions) {
+    auto json = R"({ "object": {}, "array": [], "string": "", "int": 0, "boolean": false })"_json;
+
+    ASSERT_THROW(getString(valueAt(json, "object")), Error);
+    ASSERT_THROW(getString(valueAt(json, "array")), Error);
+    ASSERT_THROW(getString(valueAt(json, "int")), Error);
+    ASSERT_THROW(getString(valueAt(json, "boolean")), Error);
+}
+
+TEST(getInteger, rightAssertions) {
+    auto simple = R"({ "int": 0 })"_json;
+
+    ASSERT_EQ(getInteger(valueAt(getObject(simple), "int")), 0);
+}
+
+TEST(getInteger, wrongAssertions) {
+    auto json = R"({ "object": {}, "array": [], "string": "", "int": 0, "boolean": false })"_json;
+
+    ASSERT_THROW(getInteger(valueAt(json, "object")), Error);
+    ASSERT_THROW(getInteger(valueAt(json, "array")), Error);
+    ASSERT_THROW(getInteger(valueAt(json, "string")), Error);
+    ASSERT_THROW(getInteger(valueAt(json, "boolean")), Error);
+}
+
+TEST(getBoolean, rightAssertions) {
+    auto simple = R"({ "boolean": false })"_json;
+
+    ASSERT_EQ(getBoolean(valueAt(getObject(simple), "boolean")), false);
+}
+
+TEST(getBoolean, wrongAssertions) {
+    auto json = R"({ "object": {}, "array": [], "string": "", "int": 0, "boolean": false })"_json;
+
+    ASSERT_THROW(getBoolean(valueAt(json, "object")), Error);
+    ASSERT_THROW(getBoolean(valueAt(json, "array")), Error);
+    ASSERT_THROW(getBoolean(valueAt(json, "string")), Error);
+    ASSERT_THROW(getBoolean(valueAt(json, "int")), Error);
+}
+
 } /* namespace nix */