Integrate render into /metrics handler

src/http_handler.cpp

@@ -1,10 +1,19 @@
 #include "http_handler.hpp"
-#include "arena_allocator.hpp"
-#include "perfetto_categories.hpp"
+
 #include <cstring>
 #include <string>
 #include <strings.h>
 
+#include "arena_allocator.hpp"
+#include "format.hpp"
+#include "metric.hpp"
+#include "perfetto_categories.hpp"
+
+auto requests_counter_family = metric::create_counter(
+    "weaseldb_http_requests_total", "Total http requests");
+thread_local auto metrics_counter =
+    requests_counter_family.create({{"path", "/metrics"}});
+
 // HttpConnectionState implementation
 HttpConnectionState::HttpConnectionState(ArenaAllocator &arena)
     : current_header_field_buf(ArenaStlAllocator<char>(&arena)),
@@ -227,10 +236,44 @@ void HttpHandler::handleDeleteRetention(Connection &conn,
 
 void HttpHandler::handleGetMetrics(Connection &conn,
                                    const HttpConnectionState &state) {
-  // TODO: Implement metrics collection and formatting
-  sendResponse(conn, 200, "text/plain",
-               "# WeaselDB metrics\nweaseldb_requests_total 0\n",
-               state.connection_close);
+  metrics_counter.inc();
+  ArenaAllocator &arena = conn.get_arena();
+  auto metrics_span = metric::render(arena);
+
+  // Calculate total size for the response body
+  size_t total_size = 0;
+  for (const auto &sv : metrics_span) {
+    total_size += sv.size();
+  }
+
+  auto *http_state = static_cast<HttpConnectionState *>(conn.user_data);
+
+  // Build HTTP response headers using arena
+  std::string_view headers;
+  if (state.connection_close) {
+    headers = static_format(
+        arena, "HTTP/1.1 200 OK\r\n",
+        "Content-Type: text/plain; version=0.0.4\r\n",
+        "Content-Length: ", static_cast<uint64_t>(total_size), "\r\n",
+        "X-Response-ID: ", static_cast<int64_t>(http_state->request_id), "\r\n",
+        "Connection: close\r\n", "\r\n");
+    conn.close_after_send();
+  } else {
+    headers = static_format(
+        arena, "HTTP/1.1 200 OK\r\n",
+        "Content-Type: text/plain; version=0.0.4\r\n",
+        "Content-Length: ", static_cast<uint64_t>(total_size), "\r\n",
+        "X-Response-ID: ", static_cast<int64_t>(http_state->request_id), "\r\n",
+        "Connection: keep-alive\r\n", "\r\n");
+  }
+
+  // Send headers
+  conn.append_message(headers, false);
+
+  // Send body in chunks
+  for (const auto &sv : metrics_span) {
+    conn.append_message(sv, false);
+  }
 }
 
 void HttpHandler::handleGetOk(Connection &conn,