1 files changed, 161 insertions, 0 deletions

diff --git a/src/btftunnel.cpp b/src/btftunnel.cpp
new file mode 100644
index 0000000..65c4b89
--- /dev/null
+++ b/src/btftunnel.cpp
@@ -0,0 +1,161 @@
+// Copyright (c) 2026 Bitflash developers
+// Distributed under the MIT/X11 software license.
+//
+// Transparent anonymous tunnel. See btftunnel.h.
+
+#include "btftunnel.h"
+#include "btfchan.h"
+
+#ifdef _WIN32
+#include <winsock2.h>
+#include <ws2tcpip.h>
+#else
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+#include <unistd.h>
+typedef int SOCKET;
+#ifndef INVALID_SOCKET
+#define INVALID_SOCKET (-1)
+#endif
+#define closesocket(s) ::close(s)
+#ifndef SD_BOTH
+#define SD_BOTH SHUT_RDWR
+#endif
+#endif
+#include <cstring>
+#include <vector>
+#include <thread>
+
+namespace btf
+{
+
+bool TunnelInit()
+{
+    return RvInit() && ChanInit();
+}
+
+// Create a connected loopback socket pair (no socketpair() on Windows).
+// Returns app end and pump end; both are ordinary full-duplex TCP sockets.
+static bool MakeLocalPair(btf_socket_t& appEnd, btf_socket_t& pumpEnd)
+{
+    SOCKET listener = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
+    if (listener == INVALID_SOCKET) return false;
+
+    struct sockaddr_in addr;
+    memset(&addr, 0, sizeof(addr));
+    addr.sin_family = AF_INET;
+    addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
+    addr.sin_port = 0; // ephemeral
+    if (bind(listener, (struct sockaddr*)&addr, sizeof(addr)) != 0) { closesocket(listener); return false; }
+    if (listen(listener, 1) != 0) { closesocket(listener); return false; }
+
+#ifdef _WIN32
+    int len = sizeof(addr);
+#else
+    socklen_t len = sizeof(addr);
+#endif
+    if (getsockname(listener, (struct sockaddr*)&addr, &len) != 0) { closesocket(listener); return false; }
+
+    SOCKET a = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
+    if (a == INVALID_SOCKET) { closesocket(listener); return false; }
+    if (connect(a, (struct sockaddr*)&addr, sizeof(addr)) != 0) { closesocket(a); closesocket(listener); return false; }
+
+    SOCKET b = accept(listener, NULL, NULL);
+    closesocket(listener);
+    if (b == INVALID_SOCKET) { closesocket(a); return false; }
+
+    appEnd = a;
+    pumpEnd = b;
+    return true;
+}
+
+static bool SockReadN(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 SockWriteN(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;
+}
+
+// Outbound pump: plaintext from the app -> echan frame -> rendezvous socket.
+static void PumpOut(SOCKET pumpEnd, RvSocket rv, std::vector<unsigned char> key)
+{
+    char buf[16 * 1024];
+    for (;;)
+    {
+        int r = recv(pumpEnd, buf, sizeof(buf), 0);
+        if (r <= 0) break;
+        std::vector<unsigned char> frame = ChanEncryptFrame(key.data(), (const unsigned char*)buf, r);
+        if (!RvWriteN(rv, frame.data(), (int)frame.size())) break;
+    }
+    // Tear down: unblock the inbound pump and the app.
+    shutdown((SOCKET)rv, SD_BOTH);
+    shutdown(pumpEnd, SD_BOTH);
+}
+
+// Inbound pump: echan frames from the rendezvous socket -> plaintext to the app.
+static void PumpIn(SOCKET pumpEnd, RvSocket rv, std::vector<unsigned char> key)
+{
+    for (;;)
+    {
+        unsigned char len[4];
+        if (!RvReadN(rv, len, 4)) break;
+        size_t n = ((size_t)len[0]<<24)|((size_t)len[1]<<16)|((size_t)len[2]<<8)|len[3];
+        if (n < (size_t)(CHAN_NONCEBYTES + CHAN_MACBYTES) || n > (1u<<20)) break;
+        std::vector<unsigned char> body(n);
+        if (!RvReadN(rv, body.data(), (int)n)) break;
+        std::vector<unsigned char> pt;
+        if (!ChanDecryptBody(key.data(), body.data(), (int)n, pt)) break; // auth fail -> drop
+        if (!pt.empty() && !SockWriteN(pumpEnd, pt.data(), (int)pt.size())) break;
+    }
+    shutdown(pumpEnd, SD_BOTH);
+    shutdown((SOCKET)rv, SD_BOTH);
+}
+
+// Start the two pumps and hand back the app-facing socket. When both pumps
+// finish, close the pump end and the rendezvous socket.
+static btf_socket_t StartTunnel(RvSocket rv, const unsigned char shared[32])
+{
+    btf_socket_t appEnd, pumpEnd;
+    if (!MakeLocalPair(appEnd, pumpEnd)) { RvClose(rv); return INVALID_SOCKET; }
+
+    std::vector<unsigned char> key(shared, shared + 32);
+    std::thread(PumpOut, pumpEnd, rv, key).detach();
+    std::thread([pumpEnd, rv, key]() {
+        PumpIn(pumpEnd, rv, key);
+        closesocket(pumpEnd);
+        RvClose(rv);
+    }).detach();
+    return appEnd;
+}
+
+btf_socket_t BtfClientTunnel(const char* meeting_host, unsigned short port,
+                             const unsigned char target_pubkey[32],
+                             const unsigned char service_enc_pub[32])
+{
+    if (!TunnelInit()) return INVALID_SOCKET;
+    RvSocket rv = RvClientConnect(meeting_host, port, target_pubkey);
+    if (rv == RV_INVALID) return INVALID_SOCKET;
+
+    unsigned char eph_pub[32], shared[32];
+    if (!ChanClientHandshake(service_enc_pub, eph_pub, shared)) { RvClose(rv); return INVALID_SOCKET; }
+    if (!RvWriteN(rv, eph_pub, 32)) { RvClose(rv); return INVALID_SOCKET; }
+    return StartTunnel(rv, shared);
+}
+
+btf_socket_t BtfServiceWrap(RvSocket rv, const unsigned char my_enc_sk[32])
+{
+    if (!TunnelInit()) { RvClose(rv); return INVALID_SOCKET; }
+    unsigned char eph_pub[32], shared[32];
+    if (!RvReadN(rv, eph_pub, 32)) { RvClose(rv); return INVALID_SOCKET; }
+    if (!ChanEndpointHandshake(eph_pub, my_enc_sk, shared)) { RvClose(rv); return INVALID_SOCKET; }
+    return StartTunnel(rv, shared);
+}
+
+} // namespace btf