feat(server): support config set for some flags (#1624)

1. add tcp_keepalive flag
2. support config set for the following flags: tcp_keepalive,dir,requirepass,masterauth
3. more print details when failing on dbfilename flag validation

Signed-off-by: adi_holden <adi@dragonflydb.io>

src/facade/dragonfly_listener.cc

@@ -7,7 +7,6 @@
 #ifdef DFLY_USE_SSL
 #include <openssl/ssl.h>
 #endif
-
 #include "base/flags.h"
 #include "base/logging.h"
 #include "facade/dragonfly_connection.h"
@@ -27,6 +26,9 @@ ABSL_FLAG(string, tls_cert_file, "", "cert file for tls connections");
 ABSL_FLAG(string, tls_key_file, "", "key file for tls connections");
 ABSL_FLAG(string, tls_ca_cert_file, "", "ca signed certificate to validate tls connections");
 ABSL_FLAG(string, tls_ca_cert_dir, "", "ca signed certificates directory");
+ABSL_FLAG(uint32_t, tcp_keepalive, 300,
+          "the period in seconds of inactivity after which keep-alives are triggerred,"
+          "the duration until an inactive connection is terminated is twice the specified time");
 
 #if 0
 enum TlsClientAuth {
@@ -99,21 +101,19 @@ SSL_CTX* CreateSslServerCntx() {
 }
 #endif
 
-bool ConfigureKeepAlive(int fd, unsigned interval_sec) {
-  DCHECK_GT(interval_sec, 3u);
-
+bool ConfigureKeepAlive(int fd) {
   int val = 1;
   if (setsockopt(fd, SOL_SOCKET, SO_KEEPALIVE, &val, sizeof(val)) < 0)
     return false;
 
-  val = interval_sec;
+  val = absl::GetFlag(FLAGS_tcp_keepalive);
   if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPIDLE, &val, sizeof(val)) < 0)
     return false;
 
   /* Send next probes after the specified interval. Note that we set the
    * delay as interval / 3, as we send three probes before detecting
    * an error (see the next setsockopt call). */
-  val = interval_sec / 3;
+  val = std::max(val / 3, 1);
   if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPINTVL, &val, sizeof(val)) < 0)
     return false;
 
@@ -153,12 +153,11 @@ util::Connection* Listener::NewConnection(ProactorBase* proactor) {
 
 error_code Listener::ConfigureServerSocket(int fd) {
   int val = 1;
-  constexpr int kInterval = 300;  // 300 seconds is ok to start checking for liveness.
 
   if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val)) < 0) {
     LOG(WARNING) << "Could not set reuse addr on socket " << SafeErrorMessage(errno);
   }
-  bool success = ConfigureKeepAlive(fd, kInterval);
+  bool success = ConfigureKeepAlive(fd);
 
   if (!success) {
     int myerr = errno;

src/server/config_registry.cc

@@ -21,6 +21,10 @@ ConfigRegistry& ConfigRegistry::Register(std::string_view name, WriteCb cb) {
   return *this;
 }
 
+ConfigRegistry& ConfigRegistry::Register(std::string_view name) {
+  return Register(name, [](const absl::CommandLineFlag& flag) { return true; });
+}
+
 // Returns true if the value was updated.
 bool ConfigRegistry::Set(std::string_view config_name, std::string_view value) {
   unique_lock lk(mu_);

src/server/config_registry.h

@@ -15,6 +15,7 @@ class ConfigRegistry {
   using WriteCb = std::function<bool(const absl::CommandLineFlag&)>;
 
   ConfigRegistry& Register(std::string_view name, WriteCb cb);
+  ConfigRegistry& Register(std::string_view name);
 
   // Returns true if the value was updated.
   bool Set(std::string_view config_name, std::string_view value);

src/server/main_service.cc

@@ -622,6 +622,11 @@ void Service::Init(util::AcceptServer* acceptor, std::vector<facade::Listener*>
     return true;
   });
 
+  config_registry.Register("dir");
+  config_registry.Register("requirepass");
+  config_registry.Register("masterauth");
+  config_registry.Register("tcp_keepalive");
+
   pp_.Await([](uint32_t index, ProactorBase* pb) { ServerState::Init(index); });
 
   uint32_t shard_num = GetFlag(FLAGS_num_shards);

src/server/server_family.cc

@@ -388,7 +388,7 @@ GenericError ValidateFilename(const fs::path& filename, bool new_version) {
 
   if (!filename.parent_path().empty() && !is_cloud_path) {
     return {absl::StrCat("filename may not contain directory separators (Got \"", filename.c_str(),
-                         "\")")};
+                         "\"). dbfilename should specify the filename without the directory")};
   }
 
   if (!filename.has_extension()) {