fixup

bip-0078.mediawiki

@@ -556,7 +556,7 @@ public async Task<PSBT> RequestPayjoin(
         if (isOriginalOutput || substitutedOutput)
         {
             originalOutputs.Dequeue();
-            if (output.OriginalTxOut == feeOutput)
+            if (originalOutput.OriginalTxOut == feeOutput)
             {
                 var actualContribution = feeOutput.Value - proposedPSBTOutput.Value;
                 // The amount that was subtracted from the output's value is less than or equal to maxadditionalfeecontribution
@@ -566,9 +566,10 @@ public async Task<PSBT> RequestPayjoin(
                 if (actualContribution > additionalFee)
                     throw new PayjoinSenderException("The actual contribution is not only paying fee");
                 // Make sure the actual contribution is only paying for fee incurred by additional inputs
+                // This assumes an additional input can be up to 110 bytes.
                 int additionalInputsCount = proposalGlobalTx.Inputs.Count - originalGlobalTx.Inputs.Count;
-                if (additionalInputsCount <= 0)
-                    throw new PayjoinSenderException("Our additional contribution is not paying for additional inputs");
+                if (actualContribution > originalFeeRate * 110 * additionalInputsCount)
+                    throw new PayjoinSenderException("The actual contribution is not only paying for additional inputs");
             }
             else if (allowOutputSubstitution && output.OriginalTxOut.ScriptPubKey == paymentScriptPubKey)
             {
@@ -602,21 +603,6 @@ public async Task<PSBT> RequestPayjoin(
     return proposal;
 }
 
-int GetVirtualSize(ScriptPubKeyType? scriptPubKeyType)
-{
-    switch (scriptPubKeyType)
-    {
-        case ScriptPubKeyType.Legacy:
-            return 148;
-        case ScriptPubKeyType.Segwit:
-            return 68;
-        case ScriptPubKeyType.SegwitP2SH:
-            return 91;
-        default:
-            return 110;
-    }
-}
-
 // Finalize the signedPSBT and remove confidential information
 PSBT CreateOriginalPSBT(PSBT signedPSBT)
 {