Fix problems on outgoing disconnect

This removes two superfluous erases that occur during connection closing
(the proxy_close_connection just above them already removes the element
from `peers`), and also short-circuits the incoming message loop if our
pollitems becomes stale so that we don't try to use a closed connection.

It also fixes a bug in the outgoing connection index that was
decrementing the wrong connection indices, leading to failures when
trying to send on an existing connection after a disconnect.

Also adds a test case (which fails before the changes in this commit) to
test this.

lokimq/lokimq.cpp

@@ -924,12 +924,15 @@ void update_connection_indices(Container& c, size_t index, AccessIndex get_index
             it = c.erase(it);
             continue;
         }
-        if (index > i)
+        if (i > index)
             --i;
         ++it;
     }
 }
 
+/// Closes outgoing connections and removes all references.  Note that this will invalidate
+/// iterators on the various connection containers - if you don't want that, delete it first so that
+/// the container won't contain the element being deleted.
 void LokiMQ::proxy_close_connection(size_t index, std::chrono::milliseconds linger) {
     connections[index].setsockopt<int>(ZMQ_LINGER, linger > 0ms ? linger.count() : 0);
     pollitems_stale = true;
@@ -959,7 +962,6 @@ void LokiMQ::proxy_expire_idle_peers() {
             }
             LMQ_LOG(info, "Closing outgoing connection to ", it->first, ": idle timeout reached");
             proxy_close_connection(info.conn_index, CLOSE_LINGER);
-            it = peers.erase(it);
         } else {
             ++it;
         }
@@ -1186,6 +1188,14 @@ void LokiMQ::proxy_loop() {
 
             if (!proxy_handle_builtin(i, parts))
                 proxy_to_worker(i, parts);
+
+            if (pollitems_stale) {
+                // If our items became stale then we may have just closed a connection and so our
+                // queue index maybe also be stale, so restart the proxy loop (so that we rebuild
+                // pollitems).
+                LMQ_TRACE("pollitems became stale; short-circuiting incoming message loop");
+                break;
+            }
         }
 
         LMQ_TRACE("done proxy loop");
@@ -1902,7 +1912,6 @@ void LokiMQ::proxy_disconnect(ConnectionID conn, std::chrono::milliseconds linge
         if (peer.outgoing()) {
             LMQ_LOG(info, "Closing outgoing connection to ", conn);
             proxy_close_connection(peer.conn_index, linger);
-            peers.erase(it);
             return;
         }
     }

tests/test_connect.cpp

@@ -1,5 +1,6 @@
 #include "common.h"
 #include <future>
+#include <lokimq/hex.h>
 extern "C" {
 #include <sodium.h>
 }
@@ -121,3 +122,45 @@ TEST_CASE("plain-text connections", "[plaintext][connect]") {
 
 
 }
+
+TEST_CASE("SN disconnections", "[connect][disconnect]") {
+    std::vector<std::unique_ptr<LokiMQ>> lmq;
+    std::vector<std::string> pubkey, privkey;
+    std::unordered_map<std::string, std::string> conn;
+    for (int i = 0; i < 3; i++) {
+        pubkey.emplace_back();
+        privkey.emplace_back();
+        pubkey[i].resize(crypto_box_PUBLICKEYBYTES);
+        privkey[i].resize(crypto_box_SECRETKEYBYTES);
+        crypto_box_keypair(reinterpret_cast<unsigned char*>(&pubkey[i][0]), reinterpret_cast<unsigned char*>(&privkey[i][0]));
+        conn.emplace(pubkey[i], "tcp://127.0.0.1:" + std::to_string(4450 + i));
+    }
+    std::atomic<int> his{0};
+    for (int i = 0; i < pubkey.size(); i++) {
+        lmq.push_back(std::make_unique<LokiMQ>(
+            pubkey[i], privkey[i], true,
+            [conn](auto pk) { auto it = conn.find((std::string) pk); if (it != conn.end()) return it->second; return ""s; },
+            get_logger("S" + std::to_string(i) + "» ")
+        ));
+        auto& server = *lmq.back();
+        server.log_level(LogLevel::debug);
+
+        server.listen_curve(conn[pubkey[i]], [](auto /*ip*/, auto /*pk*/) { return Allow{AuthLevel::none, true}; });
+        server.add_category("sn", Access{AuthLevel::none, true})
+            .add_command("hi", [&](Message& m) { his++; });
+        server.start();
+    }
+    std::this_thread::sleep_for(50ms);
+
+    lmq[0]->send(pubkey[1], "sn.hi");
+    lmq[0]->send(pubkey[2], "sn.hi");
+    std::this_thread::sleep_for(50ms);
+    lmq[2]->send(pubkey[0], "sn.hi");
+    lmq[2]->send(pubkey[1], "sn.hi");
+    lmq[1]->send(pubkey[0], "BYE");
+    std::this_thread::sleep_for(50ms);
+    lmq[0]->send(pubkey[2], "sn.hi");
+    std::this_thread::sleep_for(50ms);
+
+    REQUIRE(his == 5);
+}