public commit

1 files changed, 392 insertions, 0 deletions

diff --git a/relay/btfrv.cpp b/relay/btfrv.cpp
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--- /dev/null
+++ b/relay/btfrv.cpp
@@ -0,0 +1,392 @@
+// Copyright (c) 2026 Bitflash developers
+// Distributed under the MIT/X11 software license.
+//
+// Bitflash rendezvous transport. See btfrv.h.
+// Windows/Winsock implementation (Layer 6 will #ifdef this for Linux/BSD sockets).
+
+#include "btfrv.h"
+
+// Portable sockets: Winsock on Windows, BSD sockets on Linux/POSIX (for the
+// headless relay `bitflashd` that runs on the VPS).
+#ifdef _WIN32
+#include <winsock2.h>
+#include <ws2tcpip.h>
+#define CLOSESOCK closesocket
+#else
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+#include <netdb.h>
+#include <unistd.h>
+#include <csignal>
+typedef int SOCKET;
+#define INVALID_SOCKET (-1)
+#define SOCKET_ERROR (-1)
+#define CLOSESOCK ::close
+#ifndef SD_BOTH
+#define SD_BOTH SHUT_RDWR
+#endif
+#endif
+
+#include <cstring>
+#include <cstdio>
+#include <string>
+#include <deque>
+#include <map>
+#include <thread>
+#include <mutex>
+#include <atomic>
+#include <chrono>
+
+namespace btf
+{
+
+static std::atomic<bool> g_stop(false);
+static SOCKET            g_listen = INVALID_SOCKET;
+
+// Services that have registered and are waiting for a client, keyed by pubkey.
+// More than one registration per node, on purpose.
+//
+// This used to be one socket per pubkey, and a dial *consumed* it: the first
+// caller took the registration and everyone else was told "not found" until the
+// node noticed and registered again. A node re-registers only after its pairing
+// has been handed off, so between the two there is a window where it is
+// unreachable to the whole network. Measured from a node's own counters: half
+// of all outbound dials failed that way -- 15 of 30 in eleven minutes -- while
+// descriptors resolved 53 times out of 54 and the node's own registrations
+// paired 11 times out of 12. The rendezvous was not losing anybody; it was
+// letting one caller in at a time.
+//
+// A queue per key lets a node keep spare registrations parked, so a dial that
+// arrives while another is being paired finds the next one instead of a closed
+// door. Old nodes register exactly as before and simply keep one entry: the
+// wire protocol does not change, so a relay running this serves both.
+static const size_t MAX_WAITING_PER_KEY = 4;
+static std::map<std::string, std::deque<SOCKET> > g_waiting;
+static std::mutex                    g_mtx;
+
+// How often the reaper walks the waiting map.
+static const int REAP_INTERVAL_SECS = 60;
+
+bool RvInit()
+{
+    static bool done = false;
+    if (done) return true;
+#ifdef _WIN32
+    WSADATA wsa;
+    if (WSAStartup(MAKEWORD(2, 2), &wsa) != 0) return false;
+#else
+    signal(SIGPIPE, SIG_IGN); // don't die when writing to a closed peer
+#endif
+    done = true;
+    return true;
+}
+
+// ---- low-level helpers ----
+
+static bool ReadN(SOCKET s, void* buf, int n)
+{
+    char* p = (char*)buf;
+    int off = 0;
+    while (off < n)
+    {
+        int r = recv(s, p + off, n - off, 0);
+        if (r <= 0) return false;
+        off += r;
+    }
+    return true;
+}
+
+static bool WriteN(SOCKET s, const void* buf, int n)
+{
+    const char* p = (const char*)buf;
+    int off = 0;
+    while (off < n)
+    {
+        int r = send(s, p + off, n - off, 0);
+        if (r <= 0) return false;
+        off += r;
+    }
+    return true;
+}
+
+static SOCKET ConnectTo(const char* host, unsigned short port)
+{
+    struct addrinfo hints, *res = NULL;
+    memset(&hints, 0, sizeof(hints));
+    hints.ai_family = AF_INET;
+    hints.ai_socktype = SOCK_STREAM;
+    char portstr[16]; sprintf(portstr, "%u", (unsigned)port);
+    if (getaddrinfo(host, portstr, &hints, &res) != 0 || !res) return INVALID_SOCKET;
+    SOCKET s = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
+    if (s == INVALID_SOCKET) { freeaddrinfo(res); return INVALID_SOCKET; }
+    if (connect(s, res->ai_addr, (int)res->ai_addrlen) != 0)
+    {
+        CLOSESOCK(s); freeaddrinfo(res); return INVALID_SOCKET;
+    }
+    freeaddrinfo(res);
+    return s;
+}
+
+// ---- liveness of a waiting registration ----
+
+// True when the far end of a registration socket is provably gone.
+//
+// A registered service sends nothing while it waits, so the socket should never
+// be readable. Readable therefore means one of two things, and recv tells them
+// apart: 0 is a clean close, negative is an error, and either way the
+// registration is worthless. Anything else -- including a service that somehow
+// has data pending -- is left alone, because guessing wrong here unregisters a
+// node that is perfectly fine.
+//
+// select() rather than MSG_DONTWAIT so the same code compiles on Windows, and
+// so the socket's blocking mode is never touched.
+static bool RegistrationDead(SOCKET s)
+{
+    fd_set rd;
+    FD_ZERO(&rd);
+    FD_SET(s, &rd);
+    struct timeval tv;
+    tv.tv_sec = 0;
+    tv.tv_usec = 0;
+    int r = select((int)(s + 1), &rd, NULL, NULL, &tv);
+    if (r <= 0)
+        return false;               // not readable: still waiting, healthy
+    char c;
+    int n = recv(s, &c, 1, MSG_PEEK);
+    return (n <= 0);
+}
+
+// Drop registrations whose far end has gone away.
+//
+// Deliberately no expiry by age. Nodes older than v1.2.7 register once and then
+// block forever waiting to be dialled -- they never re-register, so a clock
+// based rule would quietly make every one of them unreachable, and being
+// blocked in recv they would never find out. Only provable death counts.
+static void ReapDeadRegistrations()
+{
+    int nBefore = 0, nReaped = 0;
+    {
+        std::lock_guard<std::mutex> lk(g_mtx);
+        std::map<std::string, std::deque<SOCKET> >::iterator it = g_waiting.begin();
+        while (it != g_waiting.end())
+        {
+            std::deque<SOCKET>& q = it->second;
+            nBefore += (int)q.size();
+            for (std::deque<SOCKET>::iterator jt = q.begin(); jt != q.end();)
+            {
+                if (RegistrationDead(*jt))
+                {
+                    CLOSESOCK(*jt);
+                    jt = q.erase(jt);
+                    nReaped++;
+                }
+                else
+                    ++jt;
+            }
+            if (q.empty())
+                g_waiting.erase(it++);
+            else
+                ++it;
+        }
+    }
+    if (nReaped > 0)
+        printf("reaper: dropped %d dead registration(s), %d waiting\n",
+               nReaped, nBefore - nReaped);
+    fflush(stdout);
+}
+
+static void ReaperThread()
+{
+    while (!g_stop)
+    {
+        for (int i = 0; i < REAP_INTERVAL_SECS && !g_stop; i++)
+            std::this_thread::sleep_for(std::chrono::seconds(1));
+        if (g_stop) break;
+        ReapDeadRegistrations();
+    }
+}
+
+// ---- relay side ----
+
+// Pump bytes from `from` to `to`. Owns closing `from`; shuts down `to` on exit
+// so the peer-direction thread unblocks and closes its own socket exactly once.
+static void Forward(SOCKET from, SOCKET to)
+{
+    char buf[32 * 1024];
+    for (;;)
+    {
+        int r = recv(from, buf, sizeof(buf), 0);
+        if (r <= 0) break;
+        if (!WriteN(to, buf, r)) break;
+    }
+    shutdown(to, SD_BOTH);
+    CLOSESOCK(from);
+}
+
+static void HandleIncoming(SOCKET s)
+{
+    unsigned char hdr[33];
+    if (!ReadN(s, hdr, 33)) { CLOSESOCK(s); return; }
+    char role = (char)hdr[0];
+    std::string pubkey((char*)hdr + 1, 32);
+
+    if (role == 'S')
+    {
+        // Register and wait; a future client will pair us.
+        std::lock_guard<std::mutex> lk(g_mtx);
+        std::deque<SOCKET>& q = g_waiting[pubkey];
+
+        // Drop registrations this node has already lost the far end of, rather
+        // than dropping the previous one on principle. The old code closed the
+        // prior registration on every new one, which is why a node could never
+        // hold a spare.
+        for (std::deque<SOCKET>::iterator it = q.begin(); it != q.end();)
+        {
+            if (RegistrationDead(*it)) { CLOSESOCK(*it); it = q.erase(it); }
+            else ++it;
+        }
+
+        // A ceiling, because a stranger can open these. Oldest goes first: it
+        // is the one most likely to be stale.
+        while (q.size() >= MAX_WAITING_PER_KEY)
+        {
+            CLOSESOCK(q.front());
+            q.pop_front();
+        }
+        q.push_back(s);
+        // leave the socket open in the queue; do not close here.
+    }
+    else if (role == 'C')
+    {
+        SOCKET svc = INVALID_SOCKET;
+        {
+            std::lock_guard<std::mutex> lk(g_mtx);
+            std::map<std::string, std::deque<SOCKET> >::iterator it = g_waiting.find(pubkey);
+            if (it != g_waiting.end())
+            {
+                std::deque<SOCKET>& q = it->second;
+                // Take the oldest one that is still alive, discarding the dead
+                // as we go. Checking before handing it over matters: pairing a
+                // client with a dead registration produces a tunnel that fails
+                // after both sides think they succeeded, which is the failure
+                // the dialling node reports as "tunnel to X failed" with
+                // nothing to explain it.
+                while (!q.empty())
+                {
+                    SOCKET candidate = q.front();
+                    q.pop_front();
+                    if (RegistrationDead(candidate))
+                    {
+                        CLOSESOCK(candidate);
+                        continue;
+                    }
+                    svc = candidate;
+                    break;
+                }
+                if (q.empty())
+                    g_waiting.erase(it);
+            }
+        }
+        if (svc == INVALID_SOCKET)
+        {
+            unsigned char no = 0x00;
+            WriteN(s, &no, 1);
+            CLOSESOCK(s);
+            return;
+        }
+        // Pair: tell both sides, then forward raw bytes bidirectionally.
+        unsigned char ok = 0x01;
+        bool a = WriteN(svc, &ok, 1);
+        bool b = WriteN(s, &ok, 1);
+        if (!a || !b) { CLOSESOCK(svc); CLOSESOCK(s); return; }
+        std::thread(Forward, s, svc).detach();
+        std::thread(Forward, svc, s).detach();
+    }
+    else
+    {
+        CLOSESOCK(s);
+    }
+}
+
+bool RvRelayRun(unsigned short port)
+{
+    if (!RvInit()) return false;
+    g_stop = false;
+
+    g_listen = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
+    if (g_listen == INVALID_SOCKET) return false;
+    int yes = 1;
+    setsockopt(g_listen, SOL_SOCKET, SO_REUSEADDR, (char*)&yes, sizeof(yes));
+
+    struct sockaddr_in addr;
+    memset(&addr, 0, sizeof(addr));
+    addr.sin_family = AF_INET;
+    addr.sin_addr.s_addr = INADDR_ANY;
+    addr.sin_port = htons(port);
+    if (bind(g_listen, (struct sockaddr*)&addr, sizeof(addr)) != 0) { CLOSESOCK(g_listen); return false; }
+    if (listen(g_listen, 16) != 0) { CLOSESOCK(g_listen); return false; }
+
+    std::thread(ReaperThread).detach();
+
+    while (!g_stop)
+    {
+        struct sockaddr_in cli;
+        socklen_t len = sizeof(cli);
+        SOCKET s = accept(g_listen, (struct sockaddr*)&cli, &len);
+        if (s == INVALID_SOCKET)
+        {
+            if (g_stop) break;
+            continue;
+        }
+        std::thread(HandleIncoming, s).detach();
+    }
+    CLOSESOCK(g_listen);
+    g_listen = INVALID_SOCKET;
+    return true;
+}
+
+void RvRelayStop()
+{
+    g_stop = true;
+    if (g_listen != INVALID_SOCKET)
+        CLOSESOCK(g_listen); // unblock accept()
+}
+
+// ---- service / client helpers ----
+
+RvSocket RvServiceRegister(const char* relay_host, unsigned short port,
+                           const unsigned char my_pubkey[32])
+{
+    if (!RvInit()) return RV_INVALID;
+    SOCKET s = ConnectTo(relay_host, port);
+    if (s == INVALID_SOCKET) return RV_INVALID;
+    unsigned char hdr[33];
+    hdr[0] = (unsigned char)'S';
+    memcpy(hdr + 1, my_pubkey, 32);
+    if (!WriteN(s, hdr, 33)) { CLOSESOCK(s); return RV_INVALID; }
+    unsigned char paired = 0;
+    if (!ReadN(s, &paired, 1) || paired != 0x01) { CLOSESOCK(s); return RV_INVALID; }
+    return (RvSocket)s;
+}
+
+RvSocket RvClientConnect(const char* relay_host, unsigned short port,
+                         const unsigned char target_pubkey[32])
+{
+    if (!RvInit()) return RV_INVALID;
+    SOCKET s = ConnectTo(relay_host, port);
+    if (s == INVALID_SOCKET) return RV_INVALID;
+    unsigned char hdr[33];
+    hdr[0] = (unsigned char)'C';
+    memcpy(hdr + 1, target_pubkey, 32);
+    if (!WriteN(s, hdr, 33)) { CLOSESOCK(s); return RV_INVALID; }
+    unsigned char paired = 0;
+    if (!ReadN(s, &paired, 1) || paired != 0x01) { CLOSESOCK(s); return RV_INVALID; }
+    return (RvSocket)s;
+}
+
+bool RvReadN(RvSocket s, void* buf, int n)  { return ReadN((SOCKET)s, buf, n); }
+bool RvWriteN(RvSocket s, const void* buf, int n) { return WriteN((SOCKET)s, buf, n); }
+void RvClose(RvSocket s) { if (s != RV_INVALID) CLOSESOCK((SOCKET)s); }
+
+} // namespace btf