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, 326 insertions, 0 deletions

diff --git a/src/main.cpp b/src/main.cpp
new file mode 100644
index 0000000..3a3e925
--- /dev/null
+++ b/src/main.cpp
@@ -0,0 +1,326 @@
+// Stage 2 (PLAN.md): Ethernet/IP/TCP/UDP decoders producing a live
+// packet-list line per capture. The TUI itself is still an open
+// question (PLAN.md), so this prints to stdout for now; -x keeps the
+// stage-1 hex dump available underneath each summary.
+//
+// Stage 3: -w <file> writes the same capture out as pcapng alongside
+// the summary, so files stay Wireshark-compatible (PLAN.md).
+//
+// Stage 4: capture thread -> bounded CaptureQueue -> render loop on
+// the main thread (PLAN.md's architecture sketch). The capture thread
+// only copies raw bytes into the queue; decoding, printing, and
+// pcapng-writing all happen on the consumer side, so a slow render
+// path can never block the capture thread - a full queue drops the
+// packet and counts it instead.
+//
+// Stage 5: L7 dissectors register into an L7Registry keyed by port
+// (wireframe/l7/dissector.hpp) and get consulted from summarize_packet
+// once TCP/UDP decode a port number. DNS is the first one, proving the
+// interface against real traffic rather than synthetic bytes.
+//
+// IPv6: dispatched by version nibble rather than assumed absent --
+// every live-capture test so far has shown real IPv6 background
+// traffic silently dropped once the decoder only handled IPv4.
+//
+// Stage 6: -f <expr> compiles a tcpdump-style BPF expression via
+// libpcap's own compiler (wireframe/filter.hpp) and installs it with
+// pcap_setfilter(), filtering in the kernel before packets ever reach
+// userspace - rather than hand-rolling a second BPF parser.
+//
+// Device-open/datalink-validate/filter/pcapng/signal-handler setup all
+// goes through wireframe::CaptureSession (wireframe/capture_session.hpp)
+// - the same one gui_main.cpp uses - so the CLI/TUI and GUI frontends
+// can't drift apart on that setup path.
+
+#include <pcap.h>
+
+#include <cstdio>
+#include <cstring>
+#include <deque>
+#include <mutex>
+#include <optional>
+#include <span>
+#include <string>
+#include <thread>
+
+#include <ftxui/component/component.hpp>
+#include <ftxui/component/screen_interactive.hpp>
+#include <ftxui/dom/elements.hpp>
+
+#include "wireframe/capture_session.hpp"
+#include "wireframe/search.hpp"
+#include "wireframe/summarize.hpp"
+
+namespace {
+
+// Queue capacity: how many packets can be buffered between the capture
+// thread and the render loop before new packets get dropped. Sized as
+// a fixed constant rather than a flag - tune later if a real workload
+// needs it, not speculatively now.
+constexpr std::size_t kQueueCapacity = 4096;
+
+void hex_dump(std::span<const unsigned char> bytes) {
+    for (const auto& line : wireframe::hex_dump_lines(bytes)) {
+        std::printf("%s\n", line.c_str());
+    }
+    std::printf("\n");
+}
+
+struct RenderOptions {
+    bool verbose_hex;
+    int datalink;
+    wireframe::pcapng::Writer* pcapng_writer;
+    std::string search_term;  // display filter - see wireframe/search.hpp
+};
+
+void render_packet(const wireframe::CapturedPacket& packet, const RenderOptions& opts) {
+    std::span<const unsigned char> bytes{packet.data};
+
+    std::string line = wireframe::summarize_packet(bytes, opts.datalink);
+
+    // -g is a display filter, not a capture filter: still written to
+    // -w regardless of whether it matches, since -w should reflect
+    // what was actually captured (that's -f's job), not what's shown.
+    if (opts.pcapng_writer) {
+        opts.pcapng_writer->write_packet(/*interface_id=*/0, packet.ts_sec, packet.ts_usec, bytes,
+                                          packet.original_len);
+    }
+
+    if (!wireframe::matches_search(line, opts.search_term)) return;
+
+    std::printf("%s\n", line.c_str());
+    if (opts.verbose_hex) hex_dump(bytes);
+
+    // Flush per packet: stdout is fully buffered off a tty, and this is
+    // a live capture tool, not a batch one.
+    std::fflush(stdout);
+}
+
+// TUI mode (-t): a scrolling packet list in a full-screen view, built
+// with FTXUI (see NAMES.md-adjacent decision: chosen over notcurses for
+// pure-C++ portability - no C build-system/dependency chain to fight
+// on every platform PLAN.md targets, and genuine Windows console
+// support, which notcurses lacks).
+//
+// A dedicated consumer thread pops from the capture queue and appends
+// formatted rows to shared state; the UI thread just redraws on
+// Event::Custom. 'q'/Esc triggers the same pcap_breakloop() shutdown
+// path as Ctrl-C, so there's one shutdown sequence, not two: breakloop
+// -> capture thread's pcap_loop returns -> queue.stop() -> consumer
+// drains and calls screen.Exit() -> screen.Loop() returns.
+void run_tui(wireframe::CaptureSession& session, wireframe::CaptureQueue& queue,
+             RenderOptions& opts) {
+    using namespace ftxui;
+
+    constexpr std::size_t kMaxRows = 2000;  // cap memory; oldest rows scroll off
+
+    std::mutex state_mutex;
+    std::deque<std::string> rows;
+    std::uint64_t packet_count = 0;
+
+    // '/' search: a display filter over `rows`, independent of the
+    // capture itself (wireframe/search.hpp) - typed and read only on
+    // the UI thread (the consumer thread never touches it), so unlike
+    // `rows`/`packet_count` it doesn't need state_mutex.
+    bool searching = false;
+    std::string search_term;
+    bool replay_finished = false;  // guarded by state_mutex, like rows/packet_count
+
+    auto screen = ScreenInteractive::Fullscreen();
+
+    std::thread consumer_thread([&] {
+        while (auto packet = queue.pop()) {
+            std::span<const unsigned char> bytes{packet->data};
+            std::string line = wireframe::summarize_packet(bytes, opts.datalink);
+
+            if (opts.pcapng_writer) {
+                opts.pcapng_writer->write_packet(/*interface_id=*/0, packet->ts_sec,
+                                                  packet->ts_usec, bytes, packet->original_len);
+            }
+
+            {
+                std::lock_guard<std::mutex> lock(state_mutex);
+                rows.push_back(std::move(line));
+                if (rows.size() > kMaxRows) rows.pop_front();
+                ++packet_count;
+            }
+            screen.PostEvent(Event::Custom);
+        }
+        // Replay reaching end-of-file on its own (stop_requested() still
+        // false) shouldn't close the window - the point of replaying a
+        // file is browsing/searching it afterward, not watching it flash
+        // by. An explicit stop (q/Esc below, or an external signal, both
+        // of which set stop_requested()) always closes, live capture
+        // included - that's still the same behavior as before.
+        if (session.is_replay() && !session.stop_requested()) {
+            {
+                std::lock_guard<std::mutex> lock(state_mutex);
+                replay_finished = true;
+            }
+            screen.PostEvent(Event::Custom);  // one more redraw for the final state
+        } else {
+            screen.Exit();
+        }
+    });
+
+    auto renderer = Renderer([&] {
+        std::lock_guard<std::mutex> lock(state_mutex);
+        Elements lines;
+        std::size_t shown = 0;
+        for (const auto& row : rows) {
+            if (!wireframe::matches_search(row, search_term)) continue;
+            lines.push_back(text(row));
+            ++shown;
+        }
+
+        std::string status = "packets: " + std::to_string(packet_count);
+        if (!search_term.empty()) status += " (" + std::to_string(shown) + " shown)";
+        if (replay_finished) status += "  [replay finished]";
+        status += "  dropped: " + std::to_string(queue.dropped()) +
+                  (searching ? "  (Enter to apply, Esc to clear)" : "  (/ to search, q to quit)");
+        // 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.
+        Elements footer = {text(status) | dim};
+        if (auto stats = session.stats()) {
+            if (stats->dropped > 0 || stats->if_dropped > 0) {
+                std::string kernel_status = "kernel/interface dropped " +
+                                             std::to_string(stats->dropped) + "/" +
+                                             std::to_string(stats->if_dropped) + " (received " +
+                                             std::to_string(stats->received) + ")";
+                footer.push_back(text(kernel_status) | color(Color::Yellow));
+            }
+        }
+        if (searching || !search_term.empty()) {
+            footer.push_back(text("search: " + search_term + (searching ? "_" : "")) |
+                              color(Color::Green));
+        }
+        std::string title = session.is_replay() ? ("wireframe - replaying " + session.device())
+                                                 : "wireframe - live capture";
+        return vbox({
+                   text(title) | bold | color(Color::Cyan),
+                   separator(),
+                   vbox(std::move(lines)) | yframe | flex,
+                   separator(),
+                   vbox(std::move(footer)),
+               }) |
+               border;
+    });
+
+    auto component = CatchEvent(renderer, [&](const Event& event) {
+        if (searching) {
+            if (event == Event::Return) {
+                searching = false;
+                return true;
+            }
+            if (event == Event::Escape) {
+                searching = false;
+                search_term.clear();
+                return true;
+            }
+            if (event == Event::Backspace) {
+                if (!search_term.empty()) search_term.pop_back();
+                return true;
+            }
+            if (event.is_character()) {
+                search_term += event.character();
+                return true;
+            }
+            return true;  // swallow anything else while typing (don't let it fall through to quit)
+        }
+        if (event == Event::Character('/')) {
+            searching = true;
+            return true;
+        }
+        if (event == Event::Character('q') || event == Event::Escape) {
+            session.request_stop();
+            // Closes immediately rather than waiting for the capture/
+            // replay thread to actually finish and drain the queue --
+            // necessary for replay mode specifically (that thread may
+            // already be long gone once the user quits after browsing a
+            // finished replay, so nothing else would ever call this).
+            // main() still joins the thread properly afterward either way.
+            screen.Exit();
+            return true;
+        }
+        return false;
+    });
+
+    screen.Loop(component);
+    consumer_thread.join();
+}
+
+}  // namespace
+
+int main(int argc, char** argv) {
+    wireframe::CaptureSessionOptions options;
+    bool tui_mode = false;
+    RenderOptions opts{
+        .verbose_hex = false, .datalink = 0, .pcapng_writer = nullptr, .search_term = ""};
+
+    for (int i = 1; i < argc; ++i) {
+        if (std::strcmp(argv[i], "-x") == 0) {
+            opts.verbose_hex = true;
+        } else if (std::strcmp(argv[i], "-t") == 0 || std::strcmp(argv[i], "--tui") == 0) {
+            tui_mode = true;
+        } else 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 (std::strcmp(argv[i], "-g") == 0 && i + 1 < argc) {
+            opts.search_term = 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;
+    }
+    opts.datalink = session.datalink();
+    opts.pcapng_writer = session.pcapng_writer();
+    session.install_signal_handlers();
+
+    if (!tui_mode) {
+        if (session.is_replay()) {
+            std::printf("replaying %s (%s)\n", session.device().c_str(),
+                         pcap_datalink_val_to_name(session.datalink()));
+        } else {
+            std::printf("capturing on %s (%s, ctrl-c to stop)\n", session.device().c_str(),
+                         pcap_datalink_val_to_name(session.datalink()));
+        }
+    }
+
+    wireframe::CaptureQueue queue(kQueueCapacity);
+    std::thread capture_thread = session.start_capture_thread(queue);
+
+    if (tui_mode) {
+        run_tui(session, queue, opts);
+    } else {
+        while (auto packet = queue.pop()) {
+            render_packet(*packet, opts);
+        }
+    }
+
+    capture_thread.join();
+
+    if (queue.dropped() > 0) {
+        std::fprintf(stderr, "dropped %llu packets (render side fell behind)\n",
+                     static_cast<unsigned long long>(queue.dropped()));
+    }
+    // Kernel-level counters, queried before the session closes its
+    // handle: a traffic spike can drop packets before libpcap ever
+    // hands them to our callback, which queue.dropped() can't see.
+    if (auto stats = session.stats()) {
+        if (stats->dropped > 0 || stats->if_dropped > 0) {
+            std::fprintf(stderr, "kernel/interface dropped %u/%u packets (received %u)\n",
+                         stats->dropped, stats->if_dropped, stats->received);
+        }
+    }
+
+    return 0;
+}