Do not abort if RPC listening for IPv6 fails

Instead, fall back to IPv4 listening.

src/bitcoinrpc.cpp

@@ -761,17 +761,19 @@ void ThreadRPCServer2(void* parg)
     const bool loopback = !mapArgs.count("-rpcallowip");
     asio::ip::address bindAddress = loopback ? asio::ip::address_v6::loopback() : asio::ip::address_v6::any();
     ip::tcp::endpoint endpoint(bindAddress, GetArg("-rpcport", 8332));
+    boost::system::error_code v6_only_error;
+    boost::shared_ptr<ip::tcp::acceptor> acceptor(new ip::tcp::acceptor(io_service));
 
     boost::signals2::signal<void ()> StopRequests;
 
+    bool fListening = false;
+    std::string strerr;
     try
     {
-        boost::shared_ptr<ip::tcp::acceptor> acceptor(new ip::tcp::acceptor(io_service));
         acceptor->open(endpoint.protocol());
         acceptor->set_option(boost::asio::ip::tcp::acceptor::reuse_address(true));
 
         // Try making the socket dual IPv6/IPv4 (if listening on the "any" address)
-        boost::system::error_code v6_only_error;
         acceptor->set_option(boost::asio::ip::v6_only(loopback), v6_only_error);
 
         acceptor->bind(endpoint);
@@ -783,8 +785,16 @@ void ThreadRPCServer2(void* parg)
                     static_cast<void (ip::tcp::acceptor::*)()>(&ip::tcp::acceptor::close), acceptor.get())
                 .track(acceptor));
 
+        fListening = true;
+    }
+    catch(boost::system::system_error &e)
+    {
+        strerr = strprintf(_("An error occurred while setting up the RPC port %i for listening on IPv6, falling back to IPv4: %s"), endpoint.port(), e.what());
+    }
+
+    try {
         // If dual IPv6/IPv4 failed (or we're opening loopback interfaces only), open IPv4 separately
-        if (loopback || v6_only_error)
+        if (!fListening || loopback || v6_only_error)
         {
             bindAddress = loopback ? asio::ip::address_v4::loopback() : asio::ip::address_v4::any();
             endpoint.address(bindAddress);
@@ -800,12 +810,17 @@ void ThreadRPCServer2(void* parg)
             StopRequests.connect(signals2::slot<void ()>(
                         static_cast<void (ip::tcp::acceptor::*)()>(&ip::tcp::acceptor::close), acceptor.get())
                     .track(acceptor));
+
+            fListening = true;
         }
     }
     catch(boost::system::system_error &e)
     {
-        uiInterface.ThreadSafeMessageBox(strprintf(_("An error occurred while setting up the RPC port %i for listening: %s"), endpoint.port(), e.what()),
+        strerr = strprintf(_("An error occurred while setting up the RPC port %i for listening on IPv4: %s"), endpoint.port(), e.what());
-                             _("Error"), CClientUIInterface::OK | CClientUIInterface::MODAL);
+    }
+
+    if (!fListening) {
+        uiInterface.ThreadSafeMessageBox(strerr, _("Error"), CClientUIInterface::OK | CClientUIInterface::MODAL);
         StartShutdown();
         return;
     }