More detailed error message for SystemError exceptions (#6756)

* a more detailed error message for SystemError exceptions

* update error message

* fix windows message

CHANGELOG.md

@@ -19,6 +19,7 @@
 
 ### Internals
 * Prebuilt binaries for non-Apple platforms are no longer published as nothing was using them ([PR #6746](https://github.com/realm/realm-core/pull/6746)).
+* SystemError exceptions now have a more detailed error message. ([#6739](https://github.com/realm/realm-core/issues/6739))
 
 ----------------------------------------------
 

src/realm/exceptions.hpp

@@ -355,13 +355,14 @@ class FileAccessError : public RuntimeError {
 
 struct SystemError : RuntimeError {
     SystemError(std::error_code err, std::string_view msg)
-        : RuntimeError(ErrorCodes::SystemError, msg)
+        : RuntimeError(ErrorCodes::SystemError,
+                       util::format("%1 (SystemError %2: %3)", msg, err.value(), err.message()))
     {
         const_cast<Status&>(to_status()).set_std_error_code(err);
     }
 
     SystemError(int err_no, std::string_view msg)
-        : SystemError(std::error_code(err_no, std::system_category()), msg)
+        : SystemError(std::error_code(err_no, std::generic_category()), msg)
     {
     }
 

test/object-store/sync/app.cpp

@@ -2771,7 +2771,8 @@ TEST_CASE("app: sync integration", "[sync][app][baas]") {
                 sync_error_handler_called.store(true);
                 REQUIRE(error.get_system_error() ==
                         sync::make_error_code(realm::sync::ProtocolError::bad_authentication));
-                REQUIRE(error.reason() == "Unable to refresh the user access token.");
+                REQUIRE_THAT(std::string(error.reason()),
+                             Catch::Matchers::ContainsSubstring("Unable to refresh the user access token."));
             };
             auto r = Realm::get_shared_realm(config);
             timed_wait_for([&] {
@@ -2871,7 +2872,8 @@ TEST_CASE("app: sync integration", "[sync][app][baas]") {
                 sync_error_handler_called.store(true);
                 REQUIRE(error.get_system_error() ==
                         sync::make_error_code(realm::sync::ProtocolError::bad_authentication));
-                REQUIRE(error.reason() == "Unable to refresh the user access token.");
+                REQUIRE_THAT(std::string(error.reason()),
+                             Catch::Matchers::ContainsSubstring("Unable to refresh the user access token."));
             };
 
             auto transport = static_cast<SynchronousTestTransport*>(session.transport());
@@ -3101,8 +3103,9 @@ TEST_CASE("app: sync integration", "[sync][app][baas]") {
 
         auto error = wait_for_future(std::move(pf.future), std::chrono::minutes(5)).get();
         REQUIRE(error.get_system_error() == make_error_code(sync::ProtocolError::limits_exceeded));
-        REQUIRE(error.reason() == "Sync websocket closed because the server received a message that was too large: "
-                                  "read limited at 16777217 bytes");
+        REQUIRE_THAT(std::string(error.reason()),
+                     Catch::Matchers::ContainsSubstring("Sync websocket closed because the server received a message "
+                                                        "that was too large: read limited at 16777217 bytes"));
         REQUIRE(error.is_client_reset_requested());
         REQUIRE(error.server_requests_action == sync::ProtocolErrorInfo::Action::ClientReset);
     }

test/test_util_file.cpp

@@ -304,4 +304,17 @@ TEST(Utils_File_Lock)
     CHECK_NOT(f2.try_rw_lock_exclusive());
 }
 
+TEST(Utils_File_SystemErrorMessage)
+{
+    std::error_code err = std::make_error_code(std::errc::too_many_files_open);
+    std::string_view message = "my message";
+#ifdef _WIN32
+    std::string expected = util::format("%1 (SystemError %2: %3)", message, err.value(), "too many files open");
+#else
+    std::string expected = util::format("%1 (SystemError %2: %3)", message, err.value(), "Too many open files");
+#endif
+    CHECK_THROW_CONTAINING_MESSAGE(throw SystemError(err, message), expected);
+    CHECK_THROW_CONTAINING_MESSAGE(throw SystemError(err.value(), message), expected);
+}
+
 #endif