From d1c222d9bd4bbf94536bf8262c85f4551a34e416 Mon Sep 17 00:00:00 2001
From: Kefu Chai <kefu.chai@scylladb.com>
Date: Sun, 26 Jan 2025 16:17:55 +0800
Subject: [PATCH] config: specialize config_from_string() for sstring

Specialize config_from_string() for sstring to resolve lexical_cast
stream state parsing limitation. This enables correct handling of empty
string configurations, such as setting an empty value in CQL:

```cql
UPDATE system.config SET value='' WHERE
name='allowed_repair_based_node_ops';
```
Previous implementation using boost::lexical_cast would fail due to
EOF stream state, incorrectly rejecting valid empty string conversions.

Fixes scylladb/scylladb#22491
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>

Closes scylladb/scylladb#22492
---
 db/config.cc                     | 7 +++++++
 test/boost/virtual_table_test.cc | 7 +++++++
 utils/config_file_impl.hh        | 3 +++
 3 files changed, 17 insertions(+)

diff --git a/db/config.cc b/db/config.cc
index 65eca08626..8a3495d434 100644
--- a/db/config.cc
+++ b/db/config.cc
@@ -20,6 +20,7 @@
 
 #include <seastar/core/coroutine.hh>
 #include <seastar/core/format.hh>
+#include <seastar/core/sstring.hh>
 #include <seastar/json/json_elements.hh>
 #include <seastar/util/log.hh>
 #include <seastar/util/log-cli.hh>
@@ -115,6 +116,12 @@ config_from_string(std::string_view value) {
     }
 }
 
+template <>
+sstring
+config_from_string(std::string_view value) {
+    return sstring(value);
+}
+
 template <>
 const config_type& config_type_for<bool>() {
     static config_type ct("bool", value_to_json<bool>);
diff --git a/test/boost/virtual_table_test.cc b/test/boost/virtual_table_test.cc
index d8a3e589e5..df39568dc6 100644
--- a/test/boost/virtual_table_test.cc
+++ b/test/boost/virtual_table_test.cc
@@ -95,6 +95,13 @@ SEASTAR_THREAD_TEST_CASE(test_system_config_table_update) {
     }).get();
 }
 
+SEASTAR_THREAD_TEST_CASE(test_system_config_table_set_empty) {
+    do_with_cql_env_thread([] (cql_test_env& env) {
+        env.execute_cql(format("UPDATE system.config SET value = '' WHERE name = 'allowed_repair_based_node_ops';")).get();
+        BOOST_REQUIRE_EQUAL(env.local_db().get_config().allowed_repair_based_node_ops(), sstring());
+    }).get();
+}
+
 SEASTAR_THREAD_TEST_CASE(test_system_config_table_no_live_update) {
     do_with_cql_env_thread([] (cql_test_env& env) {
         BOOST_REQUIRE_THROW(
diff --git a/utils/config_file_impl.hh b/utils/config_file_impl.hh
index 18909cfe0f..7fb0a2d624 100644
--- a/utils/config_file_impl.hh
+++ b/utils/config_file_impl.hh
@@ -27,6 +27,9 @@ T config_from_string(std::string_view string_representation) {
 template <>
 bool config_from_string(std::string_view string_representation);
 
+template <>
+sstring config_from_string(std::string_view string_representation);
+
 }
 
 namespace YAML {