From 2fa5b3e9600b80589e8e5240a3e6904244fc885d Mon Sep 17 00:00:00 2001
From: Andrew Noyes <andrew@weaselab.dev>
Date: Wed, 3 Sep 2025 13:57:23 -0400
Subject: [PATCH] Instrument connections

---
 src/connection.cpp | 47 ++++++++++++++++++++++++++++++++++++++++++++++
 src/server.cpp     |  1 +
 2 files changed, 48 insertions(+)

diff --git a/src/connection.cpp b/src/connection.cpp
index ff14a7d..b2c462c 100644
--- a/src/connection.cpp
+++ b/src/connection.cpp
@@ -5,8 +5,29 @@
 #include <cstdio>
 #include <cstdlib>
 
+#include "metric.hpp"
 #include "server.hpp" // Need this for release_back_to_server implementation
 
+namespace {
+// Thread-local metric instances
+thread_local auto connections_total =
+    metric::create_counter("weaseldb_connections_total",
+                           "Total number of connections accepted")
+        .create({});
+thread_local auto connections_active =
+    metric::create_gauge("weaseldb_connections_active",
+                         "Number of currently active connections")
+        .create({});
+thread_local auto bytes_read =
+    metric::create_counter("weaseldb_bytes_read_total",
+                           "Total number of bytes read from clients")
+        .create({});
+thread_local auto bytes_written =
+    metric::create_counter("weaseldb_bytes_written_total",
+                           "Total number of bytes written to clients")
+        .create({});
+} // namespace
+
 // Static thread-local storage for iovec buffer
 static thread_local std::vector<struct iovec> g_iovec_buffer{IOV_MAX};
 
@@ -16,6 +37,11 @@ Connection::Connection(struct sockaddr_storage addr, int fd, int64_t id,
     : fd_(fd), id_(id), epoll_index_(epoll_index), addr_(addr), arena_(),
       handler_(handler), server_(server.weak_from_this()) {
   server.active_connections_.fetch_add(1, std::memory_order_relaxed);
+
+  // Increment connection metrics using thread-local instances
+  connections_total.inc();
+  connections_active.inc();
+
   assert(handler_);
   handler_->on_connection_established(*this);
 }
@@ -27,6 +53,10 @@ Connection::~Connection() {
   if (auto server_ptr = server_.lock()) {
     server_ptr->active_connections_.fetch_sub(1, std::memory_order_relaxed);
   }
+
+  // Decrement active connections gauge
+  connections_active.dec();
+
   int e = close(fd_);
   if (e == -1 && errno != EINTR) {
     perror("close");
@@ -63,11 +93,18 @@ int Connection::readBytes(char *buf, size_t buffer_size) {
     if (r == 0) {
       return -1;
     }
+
+    // Increment bytes read metric
+    if (r > 0) {
+      bytes_read.inc(r);
+    }
+
     return r;
   }
 }
 
 bool Connection::writeBytes() {
+  ssize_t total_bytes_written = 0;
   while (!messages_.empty()) {
     // Build iovec array up to IOV_MAX limit using thread-local vector
     assert(g_iovec_buffer.size() == IOV_MAX);
@@ -93,6 +130,10 @@ bool Connection::writeBytes() {
           continue; // Standard practice: retry on signal interruption
         }
         if (errno == EAGAIN) {
+          // Increment bytes written metric before returning
+          if (total_bytes_written > 0) {
+            bytes_written.inc(total_bytes_written);
+          }
           return false;
         }
         perror("writev");
@@ -102,6 +143,7 @@ bool Connection::writeBytes() {
     }
 
     assert(w > 0);
+    total_bytes_written += w;
 
     // Handle partial writes by updating string_view data/size
     size_t bytes_written = static_cast<size_t>(w);
@@ -123,5 +165,10 @@ bool Connection::writeBytes() {
   }
   assert(messages_.empty());
 
+  // Increment bytes written metric
+  if (total_bytes_written > 0) {
+    bytes_written.inc(total_bytes_written);
+  }
+
   return false;
 }
diff --git a/src/server.cpp b/src/server.cpp
index 3a02a77..77fde1f 100644
--- a/src/server.cpp
+++ b/src/server.cpp
@@ -487,6 +487,7 @@ void Server::process_connection_writes(std::unique_ptr<Connection> &conn,
   if ((events & EPOLLOUT) || ((events & EPOLLIN) && conn->hasMessages())) {
     bool had_messages = conn->hasMessages();
     bool error = conn->writeBytes();
+
     if (error) {
       conn.reset(); // Connection should be closed
       return;