Initial commit: wireframe packet capture/analysis tool

Terminal packet capture and analysis tool built to learn the C++
memory model (byte layout, alignment, endianness, std::span over
unowned buffers) via a real capture pipeline.

- Hand-rolled L2-L4 decoders (Ethernet, IPv4, IPv6 with extension
  header walking, TCP, UDP) over std::span, no struct-casting
- L7 dissector interface with DNS, HTTP, and TLS SNI implementations
- pcapng read/write for Wireshark-compatible capture files
- Bounded capture queue: drop-on-backpressure for live capture,
  blocking push for faithful file replay
- Kernel-level BPF filtering (-f) and a separate display-only search
  (-g / interactive) that doesn't touch what's captured
- Replay mode (-r) reads a saved pcapng file back through the same
  pipeline as live capture, no root or live device needed
- pcap_stats() surfaces kernel/interface drops invisible to the
  capture queue's own counter
- Three frontends sharing one CaptureSession setup path: CLI, TUI
  (FTXUI, primary), GUI (Dear ImGui + SDL3, secondary)
- 89 unit tests (doctest) plus 9 libFuzzer harnesses covering every
  hand-rolled parser; fuzzing found and fixed a real OOM in the
  pcapng reader (unbounded allocation from an untrusted length field)

1 files changed, 280 insertions, 0 deletions

diff --git a/src/gui_main.cpp b/src/gui_main.cpp
new file mode 100644
index 0000000..d5d4518
--- /dev/null
+++ b/src/gui_main.cpp
@@ -0,0 +1,280 @@
+// GUI frontend (secondary to the TUI - see PLAN.md Decisions). Same
+// capture/decode/filter/pcapng pipeline as main.cpp's CLI/TUI modes,
+// via wireframe::CaptureSession - not a hand-copied setup path, so it
+// can't drift on datalink validation, filter errors, or the
+// pcap_breakloop() shutdown hook the way two independent
+// implementations eventually would.
+//
+// Dear ImGui + SDL3 (see CMakeLists.txt for the toolkit decision).
+
+#include <SDL3/SDL.h>
+#include <imgui.h>
+#include <imgui_impl_sdl3.h>
+#include <imgui_impl_sdlrenderer3.h>
+
+#include <atomic>
+#include <cstdio>
+#include <cstring>
+#include <deque>
+#include <mutex>
+#include <optional>
+#include <span>
+#include <string>
+#include <thread>
+
+#include "wireframe/capture_session.hpp"
+#include "wireframe/search.hpp"
+#include "wireframe/summarize.hpp"
+
+namespace {
+
+struct PacketRow {
+    std::string summary;
+    std::vector<unsigned char> data;
+};
+
+constexpr std::size_t kMaxRows = 5000;  // cap memory; oldest rows scroll off
+
+struct SharedState {
+    std::mutex mutex;
+    std::deque<PacketRow> rows;
+    std::uint64_t packet_count = 0;
+    bool replay_finished = false;  // guarded by mutex, like rows/packet_count
+    // Set once the consumer loop drains and exits from an explicit stop
+    // (the window's quit action or an external SIGINT/SIGTERM) - but
+    // NOT when a replay simply reaches end-of-file on its own, since the
+    // point of replaying a file is browsing/searching it afterward, not
+    // watching it flash by and vanish. The render loop watches this so
+    // an external signal still closes the whole app in every other case
+    // - not just the capture, leaving a frozen window behind - the
+    // same single shutdown path run_tui() uses.
+    std::atomic<bool> capture_alive{true};
+};
+
+void consumer_loop(wireframe::CaptureSession& session, wireframe::CaptureQueue& queue,
+                    SharedState& state) {
+    while (auto packet = queue.pop()) {
+        std::span<const unsigned char> bytes{packet->data};
+        std::string summary = wireframe::summarize_packet(bytes, session.datalink());
+
+        if (auto* writer = session.pcapng_writer()) {
+            writer->write_packet(/*interface_id=*/0, packet->ts_sec, packet->ts_usec, bytes,
+                                  packet->original_len);
+        }
+
+        std::lock_guard<std::mutex> lock(state.mutex);
+        state.rows.push_back({std::move(summary), std::move(packet->data)});
+        if (state.rows.size() > kMaxRows) state.rows.pop_front();
+        ++state.packet_count;
+    }
+    if (session.is_replay() && !session.stop_requested()) {
+        std::lock_guard<std::mutex> lock(state.mutex);
+        state.replay_finished = true;
+    } else {
+        state.capture_alive.store(false);
+    }
+}
+
+}  // namespace
+
+int main(int argc, char** argv) {
+    wireframe::CaptureSessionOptions options;
+    for (int i = 1; i < argc; ++i) {
+        if (std::strcmp(argv[i], "-w") == 0 && i + 1 < argc) {
+            options.pcapng_output_path = argv[++i];
+        } else if (std::strcmp(argv[i], "-f") == 0 && i + 1 < argc) {
+            options.filter_expr = argv[++i];
+        } else if (std::strcmp(argv[i], "-r") == 0 && i + 1 < argc) {
+            options.replay_input_path = argv[++i];
+        } else if (options.device.empty()) {
+            options.device = argv[i];
+        }
+    }
+
+    wireframe::CaptureSession session;
+    if (auto err = session.open(options)) {
+        std::fprintf(stderr, "%s\n", err->c_str());
+        return 1;
+    }
+    session.install_signal_handlers();
+
+    if (!SDL_Init(SDL_INIT_VIDEO)) {
+        std::fprintf(stderr, "SDL_Init failed: %s\n", SDL_GetError());
+        return 1;
+    }
+
+    SDL_Window* window =
+        SDL_CreateWindow("wireframe", 1000, 650, SDL_WINDOW_RESIZABLE | SDL_WINDOW_HIDDEN);
+    if (window == nullptr) {
+        std::fprintf(stderr, "SDL_CreateWindow failed: %s\n", SDL_GetError());
+        SDL_Quit();
+        return 1;
+    }
+    SDL_Renderer* renderer = SDL_CreateRenderer(window, nullptr);
+    if (renderer == nullptr) {
+        std::fprintf(stderr, "SDL_CreateRenderer failed: %s\n", SDL_GetError());
+        SDL_DestroyWindow(window);
+        SDL_Quit();
+        return 1;
+    }
+    SDL_SetWindowPosition(window, SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED);
+    SDL_ShowWindow(window);
+
+    IMGUI_CHECKVERSION();
+    ImGui::CreateContext();
+    ImGui::GetIO().IniFilename = nullptr;  // no layout file: this is a fixed, simple layout
+    ImGui_ImplSDL3_InitForSDLRenderer(window, renderer);
+    ImGui_ImplSDLRenderer3_Init(renderer);
+
+    wireframe::CaptureQueue queue(4096);
+    SharedState state;
+    std::thread capture_thread = session.start_capture_thread(queue);
+    std::thread consumer_thread(consumer_loop, std::ref(session), std::ref(queue),
+                                 std::ref(state));
+
+    int selected_row = -1;
+    bool quit = false;
+    char search_buf[256] = {};
+    ImGuiIO& io = ImGui::GetIO();
+    while (!quit && state.capture_alive.load()) {
+        SDL_Event event;
+        while (SDL_PollEvent(&event)) {
+            ImGui_ImplSDL3_ProcessEvent(&event);
+            if (event.type == SDL_EVENT_QUIT) {
+                quit = true;
+                session.request_stop();
+            }
+            // io.WantCaptureKeyboard reflects whether an ImGui widget
+            // (the search box) held keyboard focus as of the last
+            // completed frame - without this check, Escape would quit
+            // the whole app while the user is just trying to clear a
+            // search term, instead of doing what the TUI's Escape does
+            // in the same context (clear the term, stay open).
+            if (event.type == SDL_EVENT_KEY_DOWN && event.key.key == SDLK_ESCAPE &&
+                !io.WantCaptureKeyboard) {
+                quit = true;
+                session.request_stop();
+            }
+        }
+
+        ImGui_ImplSDLRenderer3_NewFrame();
+        ImGui_ImplSDL3_NewFrame();
+        ImGui::NewFrame();
+
+        ImGui::SetNextWindowPos(ImVec2(0, 0));
+        ImGui::SetNextWindowSize(io.DisplaySize);
+        ImGui::Begin("wireframe", nullptr,
+                      ImGuiWindowFlags_NoTitleBar | ImGuiWindowFlags_NoResize |
+                          ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoCollapse);
+
+        if (session.is_replay()) {
+            ImGui::Text("replaying %s (%s)", session.device().c_str(),
+                        pcap_datalink_val_to_name(session.datalink()));
+        } else {
+            ImGui::Text("capturing on %s (%s)", session.device().c_str(),
+                        pcap_datalink_val_to_name(session.datalink()));
+        }
+        ImGui::SameLine();
+        ImGui::SetNextItemWidth(300);
+        ImGui::InputTextWithHint("##search", "search (display filter, not capture filter)",
+                                  search_buf, sizeof(search_buf));
+        if (ImGui::IsItemFocused() && ImGui::IsKeyPressed(ImGuiKey_Escape)) {
+            search_buf[0] = '\0';  // same behavior as the TUI's Esc-while-searching
+        }
+        std::string search_term(search_buf);
+        ImGui::Separator();
+
+        float details_height = 160.0f;
+        std::size_t shown = 0;
+        ImGui::BeginChild("packet_list", ImVec2(0, -details_height - 8), ImGuiChildFlags_Borders);
+        {
+            std::lock_guard<std::mutex> lock(state.mutex);
+            for (std::size_t i = 0; i < state.rows.size(); ++i) {
+                if (!wireframe::matches_search(state.rows[i].summary, search_term)) continue;
+                ++shown;
+
+                // ImGui derives a widget's ID from its label text by
+                // default; two rows with identical summary text (e.g.
+                // repeated ICMP lines) would otherwise collide on the
+                // same ID. PushID(index) makes each row's ID unique
+                // regardless of what text it displays.
+                ImGui::PushID(static_cast<int>(i));
+                bool is_selected = (selected_row == static_cast<int>(i));
+                if (ImGui::Selectable(state.rows[i].summary.c_str(), is_selected)) {
+                    selected_row = static_cast<int>(i);
+                }
+                ImGui::PopID();
+            }
+            // Auto-scroll to the newest row unless the user has scrolled up
+            // to look at something (a manual scroll leaves the view short
+            // of the max, which is what we check here).
+            if (ImGui::GetScrollY() >= ImGui::GetScrollMaxY() - 1.0f) {
+                ImGui::SetScrollHereY(1.0f);
+            }
+        }
+        ImGui::EndChild();
+
+        ImGui::BeginChild("packet_details", ImVec2(0, details_height), ImGuiChildFlags_Borders);
+        {
+            std::lock_guard<std::mutex> lock(state.mutex);
+            if (selected_row >= 0 && selected_row < static_cast<int>(state.rows.size())) {
+                for (const auto& line : wireframe::hex_dump_lines(state.rows[selected_row].data)) {
+                    ImGui::TextUnformatted(line.c_str());
+                }
+            } else {
+                ImGui::TextDisabled("select a packet to see its hex dump");
+            }
+        }
+        ImGui::EndChild();
+
+        ImGui::Separator();
+        {
+            std::lock_guard<std::mutex> lock(state.mutex);
+            const char* finished = state.replay_finished ? "  [replay finished]" : "";
+            if (search_term.empty()) {
+                ImGui::Text("packets: %llu%s  dropped: %llu  (Esc to quit)",
+                            static_cast<unsigned long long>(state.packet_count), finished,
+                            static_cast<unsigned long long>(queue.dropped()));
+            } else {
+                ImGui::Text("packets: %llu (%zu shown)%s  dropped: %llu  (Esc to clear search)",
+                            static_cast<unsigned long long>(state.packet_count), shown, finished,
+                            static_cast<unsigned long long>(queue.dropped()));
+            }
+        }
+        // Kernel/interface-level drops: a traffic spike can drop
+        // packets before libpcap ever hands them to our callback,
+        // which the queue-side counter above can't see.
+        if (auto stats = session.stats()) {
+            if (stats->dropped > 0 || stats->if_dropped > 0) {
+                ImGui::TextColored(ImVec4(1.0f, 0.6f, 0.2f, 1.0f),
+                                    "kernel/interface dropped %u/%u (received %u)", stats->dropped,
+                                    stats->if_dropped, stats->received);
+            }
+        }
+
+        ImGui::End();
+
+        ImGui::Render();
+        SDL_SetRenderDrawColor(renderer, 30, 30, 30, 255);
+        SDL_RenderClear(renderer);
+        ImGui_ImplSDLRenderer3_RenderDrawData(ImGui::GetDrawData(), renderer);
+        SDL_RenderPresent(renderer);
+    }
+
+    session.request_stop();
+    capture_thread.join();
+    consumer_thread.join();
+
+    if (queue.dropped() > 0) {
+        std::fprintf(stderr, "dropped %llu packets (render side fell behind)\n",
+                     static_cast<unsigned long long>(queue.dropped()));
+    }
+
+    ImGui_ImplSDLRenderer3_Shutdown();
+    ImGui_ImplSDL3_Shutdown();
+    ImGui::DestroyContext();
+    SDL_DestroyRenderer(renderer);
+    SDL_DestroyWindow(window);
+    SDL_Quit();
+    return 0;
+}