pool: wait to be paired before wrapping the rendezvous socket

Upstream #30 split rendezvous registration from waiting for a dial, so
RvServiceRegister now returns as soon as the relay lists the service and
no longer consumes the relay's 0x01 pairing byte. It updated its own
caller in net.cpp and left this one behind.

AcceptOneFn went straight from RvServiceRegister to BtfServiceWrap, so
BtfServiceWrap read that 0x01 as the first byte of the miner's 32-byte
ephemeral key and every byte after it was shifted by one. The X25519
handshake has no confirmation step, so it completed against a garbage
shared secret, the tunnel was handed to the Stratum event loop, and
nothing failed loudly: the pool logged a miner arriving and then dropped
it as "never authorized", while the miner logged a pool that closed on it
with gotSubscribeAck=0. Loopback miners were unaffected, which is exactly
what made it look like a relay problem.

Block in RvServiceWaitPaired before wrapping, and close and re-register if
the relay drops us first.

test_rvaccept.cpp covers both shapes against a real bitflashd on loopback:
the pre-fix order establishes a tunnel that carries no bytes, the fixed
order round-trips. Also corrects the btftunnel.h contract comment, which
still described the pre-#30 behaviour and is what the old code was written
against -- upstream's own test_relayproc.cpp, test_btftunnel.cpp and
test_btfrv.cpp are still on that stale contract and fail the same way.

(cherry picked from commit 3e3a36b2bf1e6ffb4861507089b743688619377f)

3 files changed, 211 insertions, 10 deletions

diff --git a/src/btftunnel.h b/src/btftunnel.h
index 1fa4f01..24a7509 100644
--- a/src/btftunnel.h
+++ b/src/btftunnel.h
@@ -10,8 +10,12 @@
 // caller), then BtfClientTunnel connects through the relay, runs the echan
 // handshake, and returns a local SOCKET to hand a new outbound CNode.
 //
-// Service side: after RvServiceRegister pairs us with a client, BtfServiceWrap
-// completes the echan handshake and returns a local SOCKET for an inbound CNode.
+// Service side: RvServiceRegister only registers -- callers must then block in
+// RvServiceWaitPaired until a client is actually paired to them. BtfServiceWrap
+// completes the echan handshake on that paired socket and returns a local
+// SOCKET for an inbound CNode. Wrapping a registered-but-unpaired socket reads
+// the relay's 0x01 pairing byte as the first byte of the client's ephemeral
+// key, which silently corrupts the tunnel instead of failing.
 
 #ifndef BITFLASH_BTFTUNNEL_H
 #define BITFLASH_BTFTUNNEL_H
@@ -39,8 +43,9 @@ btf_socket_t BtfClientTunnel(const char* meeting_host, unsigned short port,
                              const unsigned char target_pubkey[32],
                              const unsigned char service_enc_pub[32]);
 
-// Service: wrap an already-paired rendezvous socket (from RvServiceRegister)
-// with echan using my static x25519 secret, returning a local plaintext SOCKET
+// Service: wrap an already-paired rendezvous socket (RvServiceRegister followed
+// by RvServiceWaitPaired -- the pairing byte MUST already be consumed) with
+// echan using my static x25519 secret, returning a local plaintext SOCKET
 // for an inbound CNode. Consumes `rv` (closed when the tunnel tears down).
 btf_socket_t BtfServiceWrap(RvSocket rv, const unsigned char my_enc_sk[32]);
 
diff --git a/src/rpc.cpp b/src/rpc.cpp
index 3dd05bb..21a8d77 100644
--- a/src/rpc.cpp
+++ b/src/rpc.cpp
@@ -6,8 +6,8 @@
 // Architecture:
 //   PoolEventLoop  -- single thread, owns all miner fds, all job/share/payout
 //                     state. No locks needed on any of that data.
-//   AcceptOneFn    -- one thread per relay. Blocks on RvServiceRegister +
-//                     BtfServiceWrap, pushes finished socket to gReadyQueue.
+//   AcceptOneFn    -- one thread per relay. Registers, waits to be paired,
+//                     wraps the tunnel, pushes finished socket to gReadyQueue.
 //   AcceptLoopFn   -- spawns AcceptOneFn threads, re-polls relay list every
 //                     60s so dynamically discovered relays get picked up.
 //
@@ -1388,12 +1388,11 @@ static void AcceptOneFn(void* arg)
     LogPrint("pool", "[pool] accept thread started for relay %s\n", relay.c_str());
 
     while (!fShutdown && gPoolRunning) {
-        // Advertise this relay as the pool's meeting node BEFORE registering:
-        // RvServiceRegister blocks until a miner pairs, and miners can only
-        // find us if the published descriptor already names a relay where the
+        // Advertise this relay as the pool's meeting node BEFORE registering,
+        // so that miners which resolve our descriptor find a relay where the
         // pool (not the node's peer-accept) holds the registration.
         BtfSetActiveRelay(relay);
-        // Blocks until a miner connects to us at this relay
+        // Returns as soon as the relay lists us -- registered, not yet paired.
         btf::RvSocket rv = btf::RvServiceRegister(host.c_str(), (unsigned short)port, pk);
 
         if (fShutdown || !gPoolRunning) {
@@ -1407,6 +1406,23 @@ static void AcceptOneFn(void* arg)
             continue;
         }
 
+        // Block for a miner to actually arrive. RvServiceRegister used to do
+        // this itself and returned with the relay's 0x01 pairing byte already
+        // consumed; it no longer does. Without waiting here, BtfServiceWrap
+        // reads that 0x01 as the first byte of the miner's 32-byte ephemeral
+        // key -- every subsequent byte is shifted by one, so the X25519
+        // handshake completes against a garbage shared secret (it has no
+        // confirmation step to catch it), the tunnel is handed to the event
+        // loop, and the miner's mining.subscribe never decrypts into a valid
+        // line. The miner sees the pool close on it; the pool sees a peer that
+        // never authorized.
+        if (!btf::RvServiceWaitPaired(rv)) {
+            btf::RvClose(rv);
+            LogPrint("pool", "[pool] relay %s: dropped us before any miner dialed"
+                     " -- re-registering\n", relay.c_str());
+            continue;
+        }
+
         // Echan handshake -- blocking but fast (local + relay round-trip)
         btf_socket_t fd = btf::BtfServiceWrap(rv, sk);
         if (fd == INVALID_SOCKET) {
diff --git a/src/test_rvaccept.cpp b/src/test_rvaccept.cpp
new file mode 100644
index 0000000..afa9046
--- /dev/null
+++ b/src/test_rvaccept.cpp
@@ -0,0 +1,180 @@
+// Local regression test for the pool's rendezvous accept path.
+//
+// Reproduces the exact failure that took remote miners off the pool: since
+// upstream #30, RvServiceRegister returns as soon as the relay lists the
+// service and no longer consumes the relay's 0x01 pairing byte. A service that
+// goes straight from RvServiceRegister to BtfServiceWrap therefore reads that
+// 0x01 as the first byte of the client's 32-byte ephemeral key, shifting the
+// whole stream by one. X25519 has no confirmation step, so the handshake
+// "succeeds" against a garbage shared secret and the corruption only shows up
+// as a tunnel that never carries a valid byte.
+//
+// Build: g++ -std=gnu++14 -O2 -pthread test_rvaccept.cpp btftunnel.cpp btfrv.cpp \
+//        btfchan.cpp -lsodium -o test_rvaccept
+//
+// Build: g++ -std=gnu++14 -O2 -pthread test_rvaccept.cpp btftunnel.cpp \
+//        btfrv.cpp btfchan.cpp -lsodium -o test_rvaccept
+//
+// Run against a bitflashd relay already listening on 127.0.0.1:<port>.
+//   test_rvaccept broken <port>  -- the pre-fix pool code path, expected to FAIL
+//   test_rvaccept fixed  <port>  -- with RvServiceWaitPaired, expected to PASS
+
+#include "btftunnel.h"
+#include "btfrv.h"
+#include "btfchan.h"
+
+#include <sys/socket.h>
+#include <sys/time.h>
+#include <unistd.h>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+#include <string>
+#include <vector>
+#include <thread>
+#include <chrono>
+
+using namespace btf;
+
+static const char*    HOST = "127.0.0.1";
+static unsigned short PORT = 18446;
+static const char*    MSG  = "mining.subscribe stand-in payload";
+
+static void SetTimeout(int fd, int secs)
+{
+    struct timeval tv;
+    tv.tv_sec  = secs;
+    tv.tv_usec = 0;
+    setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));
+    setsockopt(fd, SOL_SOCKET, SO_SNDTIMEO, &tv, sizeof(tv));
+}
+
+static bool RecvN(int fd, void* buf, int n)
+{
+    char* p = (char*)buf;
+    int off = 0;
+    while (off < n) {
+        int r = recv(fd, p + off, n - off, 0);
+        if (r <= 0) return false;
+        off += r;
+    }
+    return true;
+}
+
+static bool SendN(int fd, const void* buf, int n)
+{
+    const char* p = (const char*)buf;
+    int off = 0;
+    while (off < n) {
+        int r = send(fd, p + off, n - off, 0);
+        if (r <= 0) return false;
+        off += r;
+    }
+    return true;
+}
+
+static bool  g_serviceEcho = false;
+static std::string g_serviceSaw;
+
+// The pool's AcceptOneFn, in both shapes.
+static void ServiceThread(bool fWaitPaired,
+                          std::vector<unsigned char> id,
+                          std::vector<unsigned char> enc_sk,
+                          int len)
+{
+    RvSocket rv = RvServiceRegister(HOST, PORT, id.data());
+    if (rv == RV_INVALID) { printf("    service: RvServiceRegister failed\n"); return; }
+
+    if (fWaitPaired) {
+        if (!RvServiceWaitPaired(rv)) {
+            printf("    service: RvServiceWaitPaired failed\n");
+            RvClose(rv);
+            return;
+        }
+        printf("    service: paired (0x01 consumed by RvServiceWaitPaired)\n");
+    } else {
+        printf("    service: skipped RvServiceWaitPaired (pre-fix behaviour)\n");
+    }
+
+    btf_socket_t app = BtfServiceWrap(rv, enc_sk.data());
+    if (app == INVALID_SOCKET) { printf("    service: BtfServiceWrap failed\n"); return; }
+    printf("    service: BtfServiceWrap returned a tunnel\n");
+
+    SetTimeout(app, 5);
+    std::vector<char> buf(len);
+    if (!RecvN(app, buf.data(), len)) {
+        printf("    service: never received the client's plaintext\n");
+        close(app);
+        return;
+    }
+    g_serviceSaw.assign(buf.data(), len);
+    g_serviceEcho = SendN(app, buf.data(), len);
+    close(app);
+}
+
+int main(int argc, char* argv[])
+{
+    bool fWaitPaired = (argc >= 2 && strcmp(argv[1], "fixed") == 0);
+    if (argc >= 3) PORT = (unsigned short)atoi(argv[2]);
+
+    if (!TunnelInit()) { printf("TunnelInit failed\n"); return 2; }
+
+    unsigned char enc_pk[32], enc_sk[32];
+    ChanKeypair(enc_pk, enc_sk);
+
+    std::vector<unsigned char> id(32);
+    for (int i = 0; i < 32; i++) id[i] = (unsigned char)(i * 7 + 13);
+
+    const std::string msg(MSG);
+    const int len = (int)msg.size();
+
+    printf("  mode: %s   relay: %s:%u\n", fWaitPaired ? "fixed" : "broken", HOST, PORT);
+
+    std::thread svc(ServiceThread, fWaitPaired, id,
+                    std::vector<unsigned char>(enc_sk, enc_sk + 32), len);
+    std::this_thread::sleep_for(std::chrono::milliseconds(500));
+
+    int nFail = 0;
+
+    btf_socket_t app = BtfClientTunnel(HOST, PORT, id.data(), enc_pk);
+    if (app == INVALID_SOCKET) {
+        printf("    client: BtfClientTunnel failed\n");
+        nFail++;
+    } else {
+        printf("    client: tunnel established\n");
+        SetTimeout(app, 5);
+        if (!SendN(app, msg.data(), len)) { printf("    client: send failed\n"); nFail++; }
+        std::vector<char> echo(len);
+        if (!RecvN(app, echo.data(), len)) {
+            printf("    client: no echo came back\n");
+            nFail++;
+        } else if (std::string(echo.data(), len) != msg) {
+            printf("    client: echo did not match what was sent\n");
+            nFail++;
+        } else {
+            printf("    client: round-tripped the payload intact\n");
+        }
+        close(app);
+    }
+
+    svc.join();
+
+    if (g_serviceSaw != msg) {
+        printf("    service did not see the correct plaintext (saw %d bytes)\n",
+               (int)g_serviceSaw.size());
+        nFail++;
+    }
+    if (!g_serviceEcho) { printf("    service could not echo\n"); nFail++; }
+
+    bool fPassed = (nFail == 0);
+    printf("  RESULT: %s\n", fPassed ? "PASS -- tunnel carries plaintext end to end"
+                                     : "FAIL -- tunnel never carried a valid byte");
+
+    // A broken run is the expected outcome pre-fix, so exit 0 when the
+    // observed behaviour matches the expectation for the mode under test.
+    bool fAsExpected = (fWaitPaired ? fPassed : !fPassed);
+    printf("  EXPECTED %s -> %s\n",
+           fWaitPaired ? "PASS" : "FAIL",
+           fAsExpected ? "as expected" : "UNEXPECTED");
+    return fAsExpected ? 0 : 1;
+}