secs-gem/tests/test_metrics_prometheus.cpp

// Prometheus exporter test.  Spins up the registry + HTTP server on a
// loopback port, scrapes via raw TCP, and asserts the text-exposition
// format renders correctly with counters, gauges, labels, and HELP/TYPE
// metadata.

#include <doctest/doctest.h>

#include <asio.hpp>
#include <chrono>
#include <memory>
#include <string>

#include "secsgem/metrics/prometheus.hpp"

using namespace secsgem::metrics;
using namespace std::chrono_literals;

namespace {

// Fire one HTTP GET / against the server and return the body.
std::string scrape(asio::io_context& io, uint16_t port) {
  asio::ip::tcp::socket sock(io);
  asio::error_code ec;
  sock.connect({asio::ip::address_v4::loopback(), port}, ec);
  REQUIRE_FALSE(ec);
  const std::string req = "GET /metrics HTTP/1.1\r\nHost: localhost\r\n\r\n";
  asio::write(sock, asio::buffer(req), ec);
  REQUIRE_FALSE(ec);
  asio::streambuf buf;
  asio::read(sock, buf, ec);
  // EOF is expected (server closes after reply).
  REQUIRE((ec == asio::error::eof || !ec));
  std::istream is(&buf);
  std::string line, headers, body;
  bool in_body = false;
  while (std::getline(is, line)) {
    if (in_body) body += line + "\n";
    else if (line == "\r" || line.empty()) in_body = true;
    else headers += line + "\n";
  }
  return body;
}

}  // namespace

TEST_CASE("Prometheus: render counters and gauges") {
  Registry r;
  r.describe("secsgem_messages_total", "messages dispatched", MetricType::Counter);
  r.inc("secsgem_messages_total", {{"dir", "rx"}, {"stream", "1"}}, 3);
  r.inc("secsgem_messages_total", {{"dir", "tx"}, {"stream", "1"}}, 5);
  r.set_gauge("secsgem_spool_depth", 42);

  const auto text = r.render();
  CHECK(text.find("# HELP secsgem_messages_total messages dispatched")
        != std::string::npos);
  CHECK(text.find("# TYPE secsgem_messages_total counter") != std::string::npos);
  CHECK(text.find("secsgem_messages_total{dir=\"rx\",stream=\"1\"} 3")
        != std::string::npos);
  CHECK(text.find("secsgem_messages_total{dir=\"tx\",stream=\"1\"} 5")
        != std::string::npos);
  CHECK(text.find("# TYPE secsgem_spool_depth gauge") != std::string::npos);
  CHECK(text.find("secsgem_spool_depth 42") != std::string::npos);
}

TEST_CASE("Prometheus: HTTP server serves /metrics") {
  asio::io_context server_io;
  auto reg = std::make_shared<Registry>();
  reg->describe("secsgem_test_total", "test counter", MetricType::Counter);
  reg->inc("secsgem_test_total", {{"path", "happy"}}, 7);
  reg->set_gauge("secsgem_test_gauge", 3.14);

  // Port 0 → OS picks a free one.
  auto server = std::make_shared<PrometheusServer>(server_io, 0, reg);
  server->start();
  const auto port = server->port();

  std::thread server_thread([&] { server_io.run(); });

  // Give the acceptor a tick to arm.
  std::this_thread::sleep_for(50ms);

  asio::io_context client_io;
  const auto body = scrape(client_io, port);

  CHECK(body.find("secsgem_test_total{path=\"happy\"} 7") != std::string::npos);
  CHECK(body.find("secsgem_test_gauge 3.14") != std::string::npos);

  server_io.stop();
  server_thread.join();
}

TEST_CASE("Prometheus: live updates picked up on next scrape") {
  asio::io_context server_io;
  auto reg = std::make_shared<Registry>();
  auto server = std::make_shared<PrometheusServer>(server_io, 0, reg);
  server->start();
  const auto port = server->port();
  std::thread server_thread([&] { server_io.run(); });
  std::this_thread::sleep_for(50ms);

  reg->inc("secsgem_dynamic_total", {{"k", "v"}});
  asio::io_context c1;
  auto body1 = scrape(c1, port);
  CHECK(body1.find("secsgem_dynamic_total{k=\"v\"} 1") != std::string::npos);

  reg->inc("secsgem_dynamic_total", {{"k", "v"}}, 4);
  asio::io_context c2;
  auto body2 = scrape(c2, port);
  CHECK(body2.find("secsgem_dynamic_total{k=\"v\"} 5") != std::string::npos);

  server_io.stop();
  server_thread.join();
}