Add test for url accumulation bug

tests/test_http_handler.cpp

@@ -3,6 +3,7 @@
 #include "http_handler.hpp"
 #include "server.hpp"
 
+#include <chrono>
 #include <doctest/doctest.h>
 #include <fcntl.h>
 #include <poll.h>
@@ -198,3 +199,70 @@ TEST_CASE("HTTP pipelined POST requests race condition") {
   server->shutdown();
   runThread.join();
 }
+
+TEST_CASE("HTTP URL split across multiple writes") {
+  weaseldb::Config config;
+  HttpHandler handler(config);
+  auto server = Server::create(config, handler, {});
+  int fd = server->create_local_connection();
+
+  auto runThread = std::thread{[&]() { server->run(); }};
+
+  // Test URL accumulation by splitting the URL across multiple writes
+  // This would have caught the original bug where URL string_view pointed
+  // to llhttp's internal buffer that gets reused between writes
+
+  // Split "GET /metrics HTTP/1.1\r\n" across multiple writes
+  std::string part1 = "GET /met";
+  std::string part2 = "rics HTTP/1.1\r\n";
+  std::string headers = "Host: localhost\r\n"
+                        "Connection: close\r\n"
+                        "\r\n";
+
+  // Write URL in two parts - this tests URL accumulation
+  int w1 = write(fd, part1.c_str(), part1.size());
+  REQUIRE(w1 == static_cast<int>(part1.size()));
+
+  // Attempt to trigger separate llhttp parsing calls
+  std::this_thread::sleep_for(std::chrono::milliseconds(1));
+
+  int w2 = write(fd, part2.c_str(), part2.size());
+  REQUIRE(w2 == static_cast<int>(part2.size()));
+
+  int w3 = write(fd, headers.c_str(), headers.size());
+  REQUIRE(w3 == static_cast<int>(headers.size()));
+
+  // Read response
+  char buf[4096];
+  int total_read = 0;
+  bool found_metrics_response = false;
+
+  while (total_read < 4000) {
+    int r = read(fd, buf + total_read, sizeof(buf) - total_read - 1);
+    if (r <= 0)
+      break;
+    total_read += r;
+
+    buf[total_read] = '\0';
+    std::string response(buf, total_read);
+
+    // Check for successful metrics response (not 404)
+    if (response.find("HTTP/1.1 200 OK") != std::string::npos &&
+        response.find("text/plain; version=0.0.4") != std::string::npos) {
+      found_metrics_response = true;
+      break;
+    }
+
+    // Check for 404 which would indicate URL accumulation failed
+    if (response.find("HTTP/1.1 404") != std::string::npos) {
+      FAIL("Got 404 - URL accumulation failed, split URL was not properly "
+           "reconstructed");
+    }
+  }
+
+  REQUIRE(found_metrics_response);
+
+  close(fd);
+  server->shutdown();
+  runThread.join();
+}