wallet: make it possible to disable transaction broadcast

This is an advanced feature which will disable any kind of automatic
transaction broadcasting in the wallet. This gives the user full control
of how the transaction is sent.

For example they can broadcast new transactions through some other
mechanism themselves, after getting the transaction hex through `gettransaction`.

This just adds the option `-walletbroadcast=<0,1>`. Right now these
transactions will get the status

    Status: conflicted, has not been successfully broadcast yet

They shouldn't be shown as conflicted at all (`walletconflicts` is empty). This status
will go away when the transaction is received through the network.

src/init.cpp

@@ -337,6 +337,7 @@ std::string HelpMessage(HelpMessageMode mode)
         FormatMoney(maxTxFee)));
     strUsage += HelpMessageOpt("-upgradewallet", _("Upgrade wallet to latest format") + " " + _("on startup"));
     strUsage += HelpMessageOpt("-wallet=<file>", _("Specify wallet file (within data directory)") + " " + strprintf(_("(default: %s)"), "wallet.dat"));
+    strUsage += HelpMessageOpt("-walletbroadcast", _("Make the wallet broadcast transactions") + " " + strprintf(_("(default: %u)"), true));
     strUsage += HelpMessageOpt("-walletnotify=<cmd>", _("Execute command when a wallet transaction changes (%s in cmd is replaced by TxID)"));
     strUsage += HelpMessageOpt("-zapwallettxes=<mode>", _("Delete all wallet transactions and only recover those parts of the blockchain through -rescan on startup") +
         " " + _("(1 = keep tx meta data e.g. account owner and payment request information, 2 = drop tx meta data)"));
@@ -1242,6 +1243,7 @@ bool AppInit2(boost::thread_group& threadGroup)
                 }
             }
         }
+        pwalletMain->SetBroadcastTransactions(GetBoolArg("-walletbroadcast", true));
     } // (!fDisableWallet)
 #else // ENABLE_WALLET
     LogPrintf("No wallet compiled in!\n");

src/wallet/wallet.cpp

@@ -1096,6 +1096,9 @@ int CWallet::ScanForWalletTransactions(CBlockIndex* pindexStart, bool fUpdate)
 
 void CWallet::ReacceptWalletTransactions()
 {
+    // If transcations aren't broadcasted, don't let them into local mempool either
+    if (!fBroadcastTransactions)
+        return;
     LOCK2(cs_main, cs_wallet);
     BOOST_FOREACH(PAIRTYPE(const uint256, CWalletTx)& item, mapWallet)
     {
@@ -1116,6 +1119,7 @@ void CWallet::ReacceptWalletTransactions()
 
 bool CWalletTx::RelayWalletTransaction()
 {
+    assert(pwallet->GetBroadcastTransactions());
     if (!IsCoinBase())
     {
         if (GetDepthInMainChain() == 0) {
@@ -1354,7 +1358,7 @@ void CWallet::ResendWalletTransactions(int64_t nBestBlockTime)
 {
     // Do this infrequently and randomly to avoid giving away
     // that these are our transactions.
-    if (GetTime() < nNextResend)
+    if (GetTime() < nNextResend || !fBroadcastTransactions)
         return;
     bool fFirst = (nNextResend == 0);
     nNextResend = GetTime() + GetRand(30 * 60);
@@ -1979,14 +1983,17 @@ bool CWallet::CommitTransaction(CWalletTx& wtxNew, CReserveKey& reservekey)
         // Track how many getdata requests our transaction gets
         mapRequestCount[wtxNew.GetHash()] = 0;
 
-        // Broadcast
-        if (!wtxNew.AcceptToMemoryPool(false))
+        if (fBroadcastTransactions)
         {
-            // This must not fail. The transaction has already been signed and recorded.
-            LogPrintf("CommitTransaction(): Error: Transaction not valid");
-            return false;
+            // Broadcast
+            if (!wtxNew.AcceptToMemoryPool(false))
+            {
+                // This must not fail. The transaction has already been signed and recorded.
+                LogPrintf("CommitTransaction(): Error: Transaction not valid");
+                return false;
+            }
+            wtxNew.RelayWalletTransaction();
         }
-        wtxNew.RelayWalletTransaction();
     }
     return true;
 }

src/wallet/wallet.h

@@ -455,6 +455,7 @@ private:
 
     int64_t nNextResend;
     int64_t nLastResend;
+    bool fBroadcastTransactions;
 
     /**
      * Used to keep track of spent outpoints, and
@@ -518,6 +519,7 @@ public:
         nNextResend = 0;
         nLastResend = 0;
         nTimeFirstKey = 0;
+        fBroadcastTransactions = false;
     }
 
     std::map<uint256, CWalletTx> mapWallet;
@@ -723,6 +725,11 @@ public:
 
     /** Watch-only address added */
     boost::signals2::signal<void (bool fHaveWatchOnly)> NotifyWatchonlyChanged;
+
+    /** Inquire whether this wallet broadcasts transactions. */
+    bool GetBroadcastTransactions() const { return fBroadcastTransactions; }
+    /** Set whether this wallet broadcasts transactions. */
+    void SetBroadcastTransactions(bool broadcast) { fBroadcastTransactions = broadcast; }
 };
 
 /** A key allocated from the key pool. */