Monitor command (#427)

feat(server): support monitor command - allowing user to debug commands
from all connections by using a connection as monitors for the this
(#344)

Signed-off-by: Boaz Sade <boaz@dragonflydb.io>

src/server/server_state.cc

@@ -0,0 +1,51 @@
+// Copyright 2022, DragonflyDB authors.  All rights reserved.
+// See LICENSE for licensing terms.
+//
+
+#include "server/server_state.h"
+
+#include "base/logging.h"
+#include "server/conn_context.h"
+
+namespace dfly {
+
+void MonitorsRepo::Add(ConnectionContext* connection) {
+  VLOG(1) << "register connection "
+          << " at address 0x" << std::hex << (const void*)connection << " for thread "
+          << util::ProactorBase::GetIndex();
+
+  monitors_.push_back(connection);
+}
+
+void MonitorsRepo::Send(const std::string& msg) {
+  if (!monitors_.empty()) {
+    VLOG(1) << "thread " << util::ProactorBase::GetIndex() << " sending monitor message '" << msg
+            << "' for " << monitors_.size();
+    for (auto monitor_conn : monitors_) {
+      monitor_conn->SendMonitorMsg(msg);
+    }
+  }
+}
+
+void MonitorsRepo::Remove(const ConnectionContext* conn) {
+  auto it = std::find_if(monitors_.begin(), monitors_.end(),
+                         [&conn](const auto& val) { return val == conn; });
+  if (it != monitors_.end()) {
+    VLOG(1) << "removing connection 0x" << std::hex << (const void*)conn << " releasing token";
+    monitors_.erase(it);
+  } else {
+    VLOG(1) << "no connection 0x" << std::hex << (const void*)conn
+            << " found in the registered list here";
+  }
+}
+
+void MonitorsRepo::NotifyChangeCount(bool added) {
+  if (added) {
+    ++global_count_;
+  } else {
+    DCHECK(global_count_ > 0);
+    --global_count_;
+  }
+}
+
+}  // end of namespace dfly