[N4] Unify RPC logic and fix size check (#937)

* unify logic and fix length

* fix usings

Author: shargon

plugins/RpcServer/RpcServer.Wallet.cs

@@ -373,13 +373,7 @@ protected internal virtual JToken SendFrom(UInt160 assetId, Address from, Addres
         if (!transContext.Completed) return transContext.ToJson();
 
         tx.Witnesses = transContext.GetWitnesses();
-        if (tx.Size > 1024)
-        {
-            long calFee = tx.Size * NativeContract.Policy.GetFeePerByte(snapshot) + 100000;
-            if (tx.NetworkFee < calFee)
-                tx.NetworkFee = calFee;
-        }
-        (tx.NetworkFee <= settings.MaxFee).True_Or(RpcError.WalletFeeLimit);
+        EnsureNetworkFee(snapshot, tx);
         return SignAndRelay(snapshot, tx);
     }
 
@@ -490,13 +484,7 @@ protected internal virtual JToken SendMany(JArray _params)
         if (!transContext.Completed) return transContext.ToJson();
 
         tx.Witnesses = transContext.GetWitnesses();
-        if (tx.Size > 1024)
-        {
-            long calFee = tx.Size * NativeContract.Policy.GetFeePerByte(snapshot) + 100000;
-            if (tx.NetworkFee < calFee)
-                tx.NetworkFee = calFee;
-        }
-        (tx.NetworkFee <= settings.MaxFee).True_Or(RpcError.WalletFeeLimit);
+        EnsureNetworkFee(snapshot, tx);
         return SignAndRelay(snapshot, tx);
     }
 
@@ -553,16 +541,18 @@ protected internal virtual JToken SendToAddress(UInt160 assetId, Address to, str
             return transContext.ToJson();
 
         tx.Witnesses = transContext.GetWitnesses();
-        if (tx.Size > 1024)
-        {
-            long calFee = tx.Size * NativeContract.Policy.GetFeePerByte(snapshot) + 100000;
-            if (tx.NetworkFee < calFee)
-                tx.NetworkFee = calFee;
-        }
-        (tx.NetworkFee <= settings.MaxFee).True_Or(RpcError.WalletFeeLimit);
+        EnsureNetworkFee(snapshot, tx);
         return SignAndRelay(snapshot, tx);
     }
 
+    private void EnsureNetworkFee(StoreCache snapshot, Transaction tx)
+    {
+        long calFee = tx.Size * NativeContract.Policy.GetFeePerByte(snapshot) + 100000;
+        if (tx.NetworkFee < calFee)
+            tx.NetworkFee = calFee;
+        (tx.NetworkFee <= settings.MaxFee).True_Or(RpcError.WalletFeeLimit);
+    }
+
     /// <summary>
     /// Cancels an unconfirmed transaction.
     /// <para>Request format:</para>