simplewallet: reject attempts to use too low mixin early

This yields a clear error message rather then some possibly
confusing more technical errors down the line

src/simplewallet/simplewallet.cpp

@@ -2591,6 +2591,12 @@ bool simple_wallet::transfer_main(int transfer_type, const std::vector<std::stri
       local_args.erase(local_args.begin());
     }
   }
+  uint64_t adjusted_fake_outs_count = m_wallet->adjust_mixin(fake_outs_count);
+  if (adjusted_fake_outs_count > fake_outs_count)
+  {
+    fail_msg_writer() << (boost::format(tr("ring size %u is too small, minimum is %u")) % (fake_outs_count+1) % (adjusted_fake_outs_count+1)).str();
+    return true;
+  }
 
   const size_t min_args = (transfer_type == TransferLocked) ? 3 : 2;
   if(local_args.size() < min_args)
@@ -3196,6 +3202,12 @@ bool simple_wallet::sweep_main(uint64_t below, const std::vector<std::string> &a
       local_args.erase(local_args.begin());
     }
   }
+  uint64_t adjusted_fake_outs_count = m_wallet->adjust_mixin(fake_outs_count);
+  if (adjusted_fake_outs_count > fake_outs_count)
+  {
+    fail_msg_writer() << (boost::format(tr("ring size %u is too small, minimum is %u")) % (fake_outs_count+1) % (adjusted_fake_outs_count+1)).str();
+    return true;
+  }
 
   std::vector<uint8_t> extra;
   bool payment_id_seen = false;

src/wallet/wallet2.cpp

@@ -3980,6 +3980,19 @@ int wallet2::get_fee_algorithm()
    return 1;
   return 0;
 }
+//------------------------------------------------------------------------------------------------------------------------------
+uint64_t wallet2::adjust_mixin(uint64_t mixin)
+{
+  if (mixin < 4 && use_fork_rules(6, 10)) {
+    MWARNING("Requested ring size " << (mixin + 1) << " too low for hard fork 6, using 5");
+    mixin = 4;
+  }
+  else if (mixin < 2 && use_fork_rules(2, 10)) {
+    MWARNING("Requested ring size " << (mixin + 1) << " too low for hard fork 2, using 3");
+    mixin = 2;
+  }
+  return mixin;
+}
 //----------------------------------------------------------------------------------------------------
 // separated the call(s) to wallet2::transfer into their own function
 //

src/wallet/wallet2.h

@@ -761,6 +761,7 @@ namespace tools
 
     uint64_t get_fee_multiplier(uint32_t priority, int fee_algorithm = -1);
     uint64_t get_per_kb_fee();
+    uint64_t adjust_mixin(uint64_t mixin);
 
     // Light wallet specific functions
     // fetch unspent outs from lw node and store in m_transfers

src/wallet/wallet_rpc_server.cpp

@@ -227,19 +227,6 @@ namespace tools
       return false;
   }
   //------------------------------------------------------------------------------------------------------------------------------
-  uint64_t wallet_rpc_server::adjust_mixin(uint64_t mixin)
-  {
-    if (mixin < 4 && m_wallet->use_fork_rules(6, 10)) {
-      MWARNING("Requested ring size " << (mixin + 1) << " too low for hard fork 6, using 5");
-      mixin = 4;
-    }
-    else if (mixin < 2 && m_wallet->use_fork_rules(2, 10)) {
-      MWARNING("Requested ring size " << (mixin + 1) << " too low for hard fork 2, using 3");
-      mixin = 2;
-    }
-    return mixin;
-  }
-  //------------------------------------------------------------------------------------------------------------------------------
   void wallet_rpc_server::fill_transfer_entry(tools::wallet_rpc::transfer_entry &entry, const crypto::hash &txid, const crypto::hash &payment_id, const tools::wallet2::payment_details &pd)
   {
     entry.txid = string_tools::pod_to_hex(pd.m_tx_hash);
@@ -607,7 +594,7 @@ namespace tools
 
     try
     {
-      uint64_t mixin = adjust_mixin(req.mixin);
+      uint64_t mixin = m_wallet->adjust_mixin(req.mixin);
       std::vector<wallet2::pending_tx> ptx_vector = m_wallet->create_transactions_2(dsts, mixin, req.unlock_time, req.priority, extra, req.account_index, req.subaddr_indices, m_trusted_daemon);
 
       // reject proposed transactions if there are more than one.  see on_transfer_split below.
@@ -667,7 +654,7 @@ namespace tools
 
     try
     {
-      uint64_t mixin = adjust_mixin(req.mixin);
+      uint64_t mixin = m_wallet->adjust_mixin(req.mixin);
       uint64_t ptx_amount;
       std::vector<wallet2::pending_tx> ptx_vector;
       LOG_PRINT_L2("on_transfer_split calling create_transactions_2");
@@ -784,7 +771,7 @@ namespace tools
 
     try
     {
-      uint64_t mixin = adjust_mixin(req.mixin);
+      uint64_t mixin = m_wallet->adjust_mixin(req.mixin);
       std::vector<wallet2::pending_tx> ptx_vector = m_wallet->create_transactions_all(req.below_amount, dsts[0].addr, dsts[0].is_subaddress, mixin, req.unlock_time, req.priority, extra, req.account_index, req.subaddr_indices, m_trusted_daemon);
 
       if (!req.do_not_relay)