[benchmarks] Microbenchmark for dynamic_routing_table (drt_node perf)

benchmarks/bench_drt.cc

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+/**
+ * bench_drt.cc �Microbenchmark for dynamic_routing_table
+ *
+ * Measures:
+ *   1. Route registration (insert) throughput
+ *   2. Route lookup (find) throughput �both hits and misses
+ *   3. Peak RSS (memory footprint)
+ *
+ * Build (Linux/WSL):
+ *   g++ -O2 -std=c++20 -I ../libraries/http_server -o bench_drt bench_drt.cc
+ *
+ * Usage:
+ *   ./bench_drt [num_iterations]    (default: 5)
+ */
+
+#include <algorithm>
+#include <chrono>
+#include <cstdint>
+#include <cstdio>
+#include <iostream>
+#include <numeric>
+#include <random>
+#include <string>
+#include <vector>
+
+// For RSS measurement on Linux
+#ifdef __linux__
+#include <fstream>
+#include <unistd.h>
+#endif
+
+#include "http_server/dynamic_routing_table.hh"
+
+// ─── Route value type matching lithium's usage ───────────────────────────────
+
+using handler_fn = void (*)(int);
+
+struct route_value {
+  int method;
+  handler_fn handler;
+};
+
+// ─── Helpers ─────────────────────────────────────────────────────────────────
+
+static void dummy_handler(int) {}
+
+static long get_rss_kb() {
+#ifdef __linux__
+  std::ifstream status("/proc/self/status");
+  std::string line;
+  while (std::getline(status, line)) {
+    if (line.rfind("VmRSS:", 0) == 0) {
+      long kb = 0;
+      std::sscanf(line.c_str(), "VmRSS: %ld", &kb);
+      return kb;
+    }
+  }
+#endif
+  return -1;
+}
+
+using hi_res_clock = std::chrono::high_resolution_clock;
+using ns = std::chrono::nanoseconds;
+
+// ─── Route generators ────────────────────────────────────────────────────────
+
+static std::vector<std::string> generate_routes() {
+  // Mix of static, parameterized, and deep paths �realistic REST API surface
+  std::vector<std::string> routes;
+
+  // Static CRUD-style routes (typical REST API)
+  const char* resources[] = {"users", "posts", "comments", "articles", "products",
+                             "orders", "invoices", "sessions", "teams", "projects",
+                             "tasks", "events", "files", "images", "tags",
+                             "categories", "settings", "notifications", "messages", "logs"};
+
+  for (auto res : resources) {
+    routes.push_back(std::string("/api/v1/") + res);
+    routes.push_back(std::string("/api/v1/") + res + "/{{id}}");
+    routes.push_back(std::string("/api/v1/") + res + "/{{id}}/details");
+    routes.push_back(std::string("/api/v1/") + res + "/{{id}}/edit");
+    routes.push_back(std::string("/api/v1/") + res + "/{{id}}/delete");
+    routes.push_back(std::string("/api/v2/") + res);
+    routes.push_back(std::string("/api/v2/") + res + "/{{id}}");
+  }
+
+  // Deeper nested routes
+  routes.push_back("/api/v1/users/{{user_id}}/posts/{{post_id}}/comments");
+  routes.push_back("/api/v1/users/{{user_id}}/posts/{{post_id}}/comments/{{comment_id}}");
+  routes.push_back("/api/v1/teams/{{team_id}}/projects/{{project_id}}/tasks");
+  routes.push_back("/api/v1/teams/{{team_id}}/projects/{{project_id}}/tasks/{{task_id}}");
+  routes.push_back("/api/v1/organizations/{{org_id}}/teams/{{team_id}}/members");
+
+  // Static utility routes
+  routes.push_back("/health");
+  routes.push_back("/metrics");
+  routes.push_back("/api/v1/auth/login");
+  routes.push_back("/api/v1/auth/logout");
+  routes.push_back("/api/v1/auth/refresh");
+  routes.push_back("/api/v1/search");
+  routes.push_back("/api/v1/export");
+
+  return routes;
+}
+
+static std::vector<std::string> generate_lookup_urls(std::mt19937& rng) {
+  // Concrete URLs that would match the parameterized routes
+  std::vector<std::string> urls;
+
+  const char* resources[] = {"users", "posts", "comments", "articles", "products",
+                             "orders", "invoices", "sessions", "teams", "projects"};
+
+  for (auto res : resources) {
+    for (int id = 1; id <= 50; id++) {
+      urls.push_back(std::string("/api/v1/") + res + "/" + std::to_string(id));
+      urls.push_back(std::string("/api/v1/") + res + "/" + std::to_string(id) + "/details");
+    }
+    urls.push_back(std::string("/api/v1/") + res);
+    urls.push_back(std::string("/api/v2/") + res);
+  }
+
+  // Some deep nested lookups
+  for (int i = 1; i <= 20; i++) {
+    urls.push_back("/api/v1/users/" + std::to_string(i) + "/posts/" +
+                   std::to_string(i * 10) + "/comments");
+  }
+
+  // Static routes
+  urls.push_back("/health");
+  urls.push_back("/metrics");
+  urls.push_back("/api/v1/auth/login");
+  urls.push_back("/api/v1/search");
+
+  // Shuffle for realistic access pattern
+  std::shuffle(urls.begin(), urls.end(), rng);
+  return urls;
+}
+
+static std::vector<std::string> generate_miss_urls() {
+  return {
+    "/api/v3/users",
+    "/api/v1/nonexistent",
+    "/api/v1/users/123/unknown",
+    "/totally/wrong/path",
+    "/api/v1/users/123/posts/456/comments/789/replies",
+    "/",
+    "/api",
+  };
+}
+
+// ─── Benchmark runners ───────────────────────────────────────────────────────
+
+struct bench_result {
+  double insert_ns_per_op;
+  double lookup_hit_ns_per_op;
+  double lookup_miss_ns_per_op;
+  long rss_after_insert_kb;
+};
+
+static bench_result run_once(const std::vector<std::string>& routes,
+                            const std::vector<std::string>& lookup_urls,
+                            const std::vector<std::string>& miss_urls,
+                            int lookup_multiplier) {
+  bench_result result{};
+
+  long rss_before = get_rss_kb();
+
+  // ── Insert benchmark ──
+  li::dynamic_routing_table<route_value> table;
+  auto t0 = hi_res_clock::now();
+  for (auto& r : routes) {
+    auto& v = table[r];
+    v.method = 1;
+    v.handler = dummy_handler;
+  }
+  auto t1 = hi_res_clock::now();
+  result.insert_ns_per_op =
+      (double)std::chrono::duration_cast<ns>(t1 - t0).count() / routes.size();
+
+  result.rss_after_insert_kb = get_rss_kb() - rss_before;
+
+  // ── Lookup hit benchmark ──
+  volatile int sink = 0; // prevent optimizer from eliminating lookups
+  auto t2 = hi_res_clock::now();
+  for (int rep = 0; rep < lookup_multiplier; rep++) {
+    for (auto& url : lookup_urls) {
+      auto it = table.find(url);
+      if (it != table.end())
+        sink += it->second.method;
+    }
+  }
+  auto t3 = hi_res_clock::now();
+  long total_hits = (long)lookup_urls.size() * lookup_multiplier;
+  result.lookup_hit_ns_per_op =
+      (double)std::chrono::duration_cast<ns>(t3 - t2).count() / total_hits;
+
+  // ── Lookup miss benchmark ──
+  auto t4 = hi_res_clock::now();
+  for (int rep = 0; rep < lookup_multiplier * 10; rep++) {
+    for (auto& url : miss_urls) {
+      auto it = table.find(url);
+      if (it != table.end())
+        sink += it->second.method;
+    }
+  }
+  auto t5 = hi_res_clock::now();
+  long total_misses = (long)miss_urls.size() * lookup_multiplier * 10;
+  result.lookup_miss_ns_per_op =
+      (double)std::chrono::duration_cast<ns>(t5 - t4).count() / total_misses;
+
+  return result;
+}
+
+// ─── Main ────────────────────────────────────────────────────────────────────
+
+int main(int argc, char** argv) {
+  int iterations = 5;
+  if (argc > 1)
+    iterations = std::atoi(argv[1]);
+  if (iterations < 1)
+    iterations = 5;
+
+  const int lookup_multiplier{1000}; // multiply lookups for stable timing
+
+  auto routes = generate_routes();
+  std::mt19937 rng(42); // deterministic seed
+  auto lookup_urls = generate_lookup_urls(rng);
+  auto miss_urls = generate_miss_urls();
+
+  std::printf("═══════════════════════════════════════════════════════\n");
+  std::printf("  dynamic_routing_table benchmark\n");
+  std::printf("═══════════════════════════════════════════════════════\n");
+  std::printf("  Routes registered  : %zu\n", routes.size());
+  std::printf("  Lookup URLs (hits) : %zu × %d = %ld\n", lookup_urls.size(),
+              lookup_multiplier, (long)lookup_urls.size() * lookup_multiplier);
+  std::printf("  Lookup URLs (miss) : %zu × %d = %ld\n", miss_urls.size(),
+              lookup_multiplier * 10, (long)miss_urls.size() * lookup_multiplier * 10);
+  std::printf("  Iterations         : %d\n", iterations);
+  std::printf("───────────────────────────────────────────────────────\n\n");
+
+  std::vector<double> insert_times, hit_times, miss_times;
+  long last_rss = 0;
+
+  for (int i = 0; i < iterations; i++) {
+    auto r = run_once(routes, lookup_urls, miss_urls, lookup_multiplier);
+    insert_times.push_back(r.insert_ns_per_op);
+    hit_times.push_back(r.lookup_hit_ns_per_op);
+    miss_times.push_back(r.lookup_miss_ns_per_op);
+    last_rss = r.rss_after_insert_kb;
+    std::printf("  [iter %d]  insert: %7.1f ns/op  |  hit: %6.1f ns/op  |  miss: %6.1f ns/op\n",
+                i + 1, r.insert_ns_per_op, r.lookup_hit_ns_per_op, r.lookup_miss_ns_per_op);
+  }
+
+  // Compute medians
+  auto median = [](std::vector<double> v) {
+    std::sort(v.begin(), v.end());
+    size_t n = v.size();
+    return (n % 2 == 0) ? (v[n / 2 - 1] + v[n / 2]) / 2.0 : v[n / 2];
+  };
+
+  std::printf("\n───────────────────────────────────────────────────────\n");
+  std::printf("  MEDIAN  insert: %7.1f ns/op  |  hit: %6.1f ns/op  |  miss: %6.1f ns/op\n",
+              median(insert_times), median(hit_times), median(miss_times));
+  if (last_rss > 0)
+    std::printf("  RSS delta after insert: ~%ld KB\n", last_rss);
+  std::printf("═══════════════════════════════════════════════════════\n");
+
+  return 0;
+}