qt: allow `walletpassphrase` in debug console without -server

Currently it is only possible to use `walletpassphrase` to unlock the
wallet when bitcoin is started in server mode.

Almost everything that manipulates the wallet in the RPC console
needs the wallet to be unlocked and is thus unusable without -server.

This is pretty unintuitive to me, and I'm sure it's even more confusing
to users.

Solve this with a very minimal change: by making the GUI start a
dummy RPC thread just to handle timeouts.

src/qt/bitcoin.cpp

@@ -21,6 +21,7 @@
 
 #include "init.h"
 #include "main.h"
+#include "rpcserver.h"
 #include "ui_interface.h"
 #include "util.h"
 #include "wallet.h"
@@ -227,6 +228,13 @@ void BitcoinCore::initialize()
     {
         LogPrintf("Running AppInit2 in thread\n");
         int rv = AppInit2(threadGroup);
+        if(rv)
+        {
+            /* Start a dummy RPC thread if no RPC thread is active yet
+             * to handle timeouts.
+             */
+            StartDummyRPCThread();
+        }
         emit initializeResult(rv);
     } catch (std::exception& e) {
         handleRunawayException(&e);

src/rpcprotocol.h

@@ -49,7 +49,6 @@ enum RPCErrorCode
     RPC_INVALID_PARAMETER           = -8,  // Invalid, missing or duplicate parameter
     RPC_DATABASE_ERROR              = -20, // Database error
     RPC_DESERIALIZATION_ERROR       = -22, // Error parsing or validating structure in raw format
-    RPC_SERVER_NOT_STARTED          = -18, // RPC server was not started (StartRPCThreads() not called)
 
     // P2P client errors
     RPC_CLIENT_NOT_CONNECTED        = -9,  // Bitcoin is not connected

src/rpcserver.cpp

@@ -38,6 +38,7 @@ static asio::io_service* rpc_io_service = NULL;
 static map<string, boost::shared_ptr<deadline_timer> > deadlineTimers;
 static ssl::context* rpc_ssl_context = NULL;
 static boost::thread_group* rpc_worker_group = NULL;
+static boost::asio::io_service::work *rpc_dummy_work = NULL;
 
 void RPCTypeCheck(const Array& params,
                   const list<Value_type>& typesExpected,
@@ -607,6 +608,19 @@ void StartRPCThreads()
         rpc_worker_group->create_thread(boost::bind(&asio::io_service::run, rpc_io_service));
 }
 
+void StartDummyRPCThread()
+{
+    if(rpc_io_service == NULL)
+    {
+        rpc_io_service = new asio::io_service();
+        /* Create dummy "work" to keep the thread from exiting when no timeouts active,
+         * see http://www.boost.org/doc/libs/1_51_0/doc/html/boost_asio/reference/io_service.html#boost_asio.reference.io_service.stopping_the_io_service_from_running_out_of_work */
+        rpc_dummy_work = new asio::io_service::work(*rpc_io_service);
+        rpc_worker_group = new boost::thread_group();
+        rpc_worker_group->create_thread(boost::bind(&asio::io_service::run, rpc_io_service));
+    }
+}
+
 void StopRPCThreads()
 {
     if (rpc_io_service == NULL) return;
@@ -615,6 +629,7 @@ void StopRPCThreads()
     rpc_io_service->stop();
     if (rpc_worker_group != NULL)
         rpc_worker_group->join_all();
+    delete rpc_dummy_work; rpc_dummy_work = NULL;
     delete rpc_worker_group; rpc_worker_group = NULL;
     delete rpc_ssl_context; rpc_ssl_context = NULL;
     delete rpc_io_service; rpc_io_service = NULL;

src/rpcserver.h

@@ -20,7 +20,14 @@
 
 class CBlockIndex;
 
+/* Start RPC threads */
 void StartRPCThreads();
+/* Alternative to StartRPCThreads for the GUI, when no server is
+ * used. The RPC thread in this case is only used to handle timeouts.
+ * If real RPC threads have already been started this is a no-op.
+ */
+void StartDummyRPCThread();
+/* Stop RPC threads */
 void StopRPCThreads();
 
 /*

src/rpcwallet.cpp

@@ -1562,8 +1562,6 @@ Value walletpassphrase(const Array& params, bool fHelp)
 
     if (fHelp)
         return true;
-    if (!fServer)
-        throw JSONRPCError(RPC_SERVER_NOT_STARTED, "Error: RPC server was not started, use server=1 to change this.");
     if (!pwalletMain->IsCrypted())
         throw JSONRPCError(RPC_WALLET_WRONG_ENC_STATE, "Error: running with an unencrypted wallet, but walletpassphrase was called.");