Fix config rewrite overwrite the first rename-command with the last o…

…ne (#429)

For example, we have below rename-commands in the config file:
```
rename-command KEYS KEYS_NEW
rename-command GET  GET_NEW
rename-command SET  SET_NEW
```
then `rename-command KEYS KEYS_NEW` would be overwriten to
`rename-command SET  SET_NEW` since we didn't skip the `rename-command`
correctly in config rewrite.

src/config.cc

@@ -536,6 +536,11 @@ Status Config::Rewrite() {
   std::vector<std::string> lines;
   std::map<std::string, std::string> new_config;
   for (const auto &iter : fields_) {
+    if (iter.first == "rename-command") {
+      // We should NOT overwrite the rename command since it cannot be rewritten in-flight,
+      // so skip it here to avoid rewriting it as new item.
+      continue;
+    }
     new_config[iter.first] = iter.second->ToString();
   }
 

tests/config_test.cc

@@ -2,6 +2,8 @@
 #include "server.h"
 #include <map>
 #include <vector>
+#include <fstream>
+#include <iostream>
 #include <gtest/gtest.h>
 
 TEST(Config, GetAndSet) {
@@ -104,6 +106,28 @@ TEST(Config, GetAndSet) {
   }
 }
 
+TEST(Config, Rewrite) {
+  const char *path = "test.conf";
+  unlink(path);
+
+  std::ostringstream string_stream;
+  string_stream << "rename-command KEYS KEYS_NEW" << "\n";
+  string_stream << "rename-command GET GET_NEW" << "\n";
+  string_stream << "rename-command SET SET_NEW" << "\n";
+  std::ofstream output_file(path, std::ios::out);
+  output_file.write(string_stream.str().c_str(), string_stream.str().size());
+  output_file.close();
+
+  Config config;
+  Redis::PopulateCommands();
+  ASSERT_TRUE(config.Load(path).IsOK());
+  ASSERT_TRUE(config.Rewrite().IsOK());
+  // Need to re-populate the command table since it has renamed by the previous
+  Redis::PopulateCommands();
+  ASSERT_TRUE(config.Load(path).IsOK());
+  unlink(path);
+}
+
 TEST(Namespace, Add) {
   const char *path = "test.conf";
   unlink(path);