impl(bigquery): Json parsing changes for custom BigQuery library (#14918)

Author: jsrinnn

google/cloud/bigquery/v2/minimal/internal/json_utils.h

@@ -101,7 +101,20 @@ bool SafeGetToWithNullable(ResponseType& value, bool& is_null,
   if (i != j.end()) {
     // BQ sends null type values which crashes get_to() so check for null.
     if (!i->is_null()) {
-      i->get_to(value);
+      // JSON value for the field, from the server, can be anything.
+      // In 80% cases its a string value at which point we retrieve
+      // the string value.
+      // For any other values, (like nested Arrays or objects) we just give back
+      // a string to be parsed by the caller. The library has no idea what to
+      // expect in the value field it can be anything based on what the client
+      // sends hence its not feasible to parse here. This is best done on the
+      // client side based on the client-usecase and column schema returned by
+      // the server for each of these values.
+      if (i->type() == nlohmann::json::value_t::string) {
+        i->get_to(value);
+      } else {
+        value = i->dump();
+      }
     } else {
       is_null = true;
     }

google/cloud/bigquery/v2/minimal/internal/json_utils_test.cc

@@ -277,6 +277,57 @@ TEST(JsonUtilsTest, SafeGetToWithNullableNonNull) {
   EXPECT_FALSE(is_null);
 }
 
+TEST(JsonUtilsTest, SafeGetToWithNullableString) {
+  auto const* const key = "v";
+  auto constexpr kJsonText = R"({"v":"Apple"})";
+  auto json = nlohmann::json::parse(kJsonText, nullptr, false);
+  EXPECT_TRUE(json.is_object());
+
+  std::string val;
+  bool is_null;
+  EXPECT_TRUE(SafeGetToWithNullable(val, is_null, json, key));
+  EXPECT_EQ(val, "Apple");
+}
+
+TEST(JsonUtilsTest, SafeGetToWithNullableStringAsNumber) {
+  auto const* const key = "v";
+  auto constexpr kJsonText = R"({"v":"123"})";
+  auto json = nlohmann::json::parse(kJsonText, nullptr, false);
+  EXPECT_TRUE(json.is_object());
+
+  std::string val;
+  bool is_null;
+  EXPECT_TRUE(SafeGetToWithNullable(val, is_null, json, key));
+  EXPECT_EQ(val, "123");
+}
+
+TEST(JsonUtilsTest, SafeGetToWithNullableStringAsFloat) {
+  auto const* const key = "v";
+  auto constexpr kJsonText = R"({"v":"123.123"})";
+  auto json = nlohmann::json::parse(kJsonText, nullptr, false);
+  EXPECT_TRUE(json.is_object());
+
+  std::string val;
+  bool is_null;
+  EXPECT_TRUE(SafeGetToWithNullable(val, is_null, json, key));
+  EXPECT_EQ(val, "123.123");
+}
+
+TEST(JsonUtilsTest, SafeGetToWithNullableStringAsArray) {
+  auto const* const key = "v";
+  auto constexpr kExpectedJsonText =
+      R"([{"v":"1"},{"v":"2"},{"v":"3"},{"v":"4"},{"v":"5"}])";
+  auto constexpr kJsonText =
+      R"({"v":[{"v":"1"},{"v":"2"},{"v":"3"},{"v":"4"},{"v":"5"}]})";
+  auto json = nlohmann::json::parse(kJsonText, nullptr, false);
+  EXPECT_TRUE(json.is_object());
+
+  std::string val;
+  bool is_null;
+  EXPECT_TRUE(SafeGetToWithNullable(val, is_null, json, key));
+  EXPECT_EQ(val, kExpectedJsonText);
+}
+
 GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_END
 }  // namespace bigquery_v2_minimal_internal
 }  // namespace cloud