init: tcp connect latency and jitter tester

.github/workflows/ci.yml

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+name: ci
+
+on:
+  push:
+    branches: [master]
+
+jobs:
+  build:
+    runs-on: windows-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ilammy/msvc-dev-cmd@v1
+      - run: cmake -B build
+      - run: cmake --build build --config Release

.gitignore

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+build/
+.claude/
+*.obj
+*.exe
+*.pdb
+*.ilk

CMakeLists.txt

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+cmake_minimum_required(VERSION 3.16)
+project(pingpp CXX)
+
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+
+add_executable(pingpp src/main.cpp)
+
+if(WIN32)
+    target_link_libraries(pingpp ws2_32)
+endif()

README.md

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+# pingpp
+
+меряет задержку и джиттер до хостов через обычный TCP-connect, без ICMP и прав администратора. удобно быстро глянуть какая VPN-нода бодрее.
+
+```mermaid
+sequenceDiagram
+    loop 5 попыток
+        pingpp->>Host: TCP connect
+        Host-->>pingpp: SYN-ACK
+        Note over pingpp: засекли время
+    end
+    pingpp->>pingpp: avg / min / max / jitter
+```
+
+## сборка
+
+```
+cmake -B build
+cmake --build build --config Release
+```
+
+## юзать
+
+```
+build\Release\pingpp.exe 1.1.1.1:443 vpn.example.com:51820
+```

src/main.cpp

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+#define NOMINMAX
+#include <winsock2.h>
+#include <ws2tcpip.h>
+#include <windows.h>
+#include <iostream>
+#include <string>
+#include <vector>
+#include <chrono>
+#include <cmath>
+#include <algorithm>
+
+#pragma comment(lib, "ws2_32.lib")
+
+struct Target {
+    std::string host;
+    uint16_t port;
+};
+
+static bool parse_target(const std::string& s, Target& t) {
+    size_t colon = s.rfind(':');
+    if (colon == std::string::npos) return false;
+    t.host = s.substr(0, colon);
+    try {
+        t.port = static_cast<uint16_t>(std::stoi(s.substr(colon + 1)));
+    } catch (...) {
+        return false;
+    }
+    return true;
+}
+
+static bool tcp_connect_once(const Target& t, double& ms) {
+    addrinfo hints{};
+    hints.ai_family = AF_UNSPEC;
+    hints.ai_socktype = SOCK_STREAM;
+    addrinfo* res = nullptr;
+    std::string portstr = std::to_string(t.port);
+    if (getaddrinfo(t.host.c_str(), portstr.c_str(), &hints, &res) != 0 || !res) return false;
+
+    SOCKET s = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
+    if (s == INVALID_SOCKET) { freeaddrinfo(res); return false; }
+
+    u_long nonblock = 1;
+    ioctlsocket(s, FIONBIO, &nonblock);
+
+    auto start = std::chrono::steady_clock::now();
+    int rc = connect(s, res->ai_addr, static_cast<int>(res->ai_addrlen));
+    bool ok = false;
+
+    if (rc == 0) {
+        ok = true;
+    } else if (WSAGetLastError() == WSAEWOULDBLOCK) {
+        fd_set writefds;
+        FD_ZERO(&writefds);
+        FD_SET(s, &writefds);
+        timeval tv{};
+        tv.tv_sec = 2;
+        tv.tv_usec = 0;
+        if (select(0, nullptr, &writefds, nullptr, &tv) > 0) {
+            int err = 0;
+            int errlen = sizeof(err);
+            getsockopt(s, SOL_SOCKET, SO_ERROR, reinterpret_cast<char*>(&err), &errlen);
+            ok = (err == 0);
+        }
+    }
+
+    auto end = std::chrono::steady_clock::now();
+    ms = std::chrono::duration<double, std::milli>(end - start).count();
+
+    closesocket(s);
+    freeaddrinfo(res);
+    return ok;
+}
+
+int main(int argc, char** argv) {
+    if (argc < 2) {
+        std::cerr << "usage: pingpp <host:port> [host:port ...]" << std::endl;
+        return 1;
+    }
+
+    WSADATA wsa;
+    if (WSAStartup(MAKEWORD(2, 2), &wsa) != 0) {
+        std::cerr << "WSAStartup failed" << std::endl;
+        return 1;
+    }
+
+    const int attempts = 5;
+
+    for (int i = 1; i < argc; ++i) {
+        Target t;
+        if (!parse_target(argv[i], t)) {
+            std::cout << argv[i] << ": bad format, use host:port" << std::endl;
+            continue;
+        }
+
+        std::vector<double> times;
+        for (int a = 0; a < attempts; ++a) {
+            double ms;
+            if (tcp_connect_once(t, ms)) times.push_back(ms);
+        }
+
+        std::cout << t.host << ":" << t.port << " -> ";
+        if (times.empty()) {
+            std::cout << "no response" << std::endl;
+            continue;
+        }
+
+        double sum = 0, mn = times[0], mx = times[0];
+        for (double v : times) { sum += v; mn = std::min(mn, v); mx = std::max(mx, v); }
+        double avg = sum / times.size();
+
+        double var = 0;
+        for (double v : times) var += (v - avg) * (v - avg);
+        double jitter = std::sqrt(var / times.size());
+
+        std::cout << times.size() << "/" << attempts << " ok, avg " << avg << " ms, "
+            << "min " << mn << " ms, max " << mx << " ms, jitter " << jitter << " ms" << std::endl;
+    }
+
+    WSACleanup();
+    return 0;
+}