Corrected fee estimation for general transactions

The byte size of inputs and outputs was changed to reflect the current
serialization sizes of Decred transactions. The size of the transaction
is also now more generously estimated in case a large amount of inputs
are required.

wallet/createtx.go

@@ -42,9 +42,9 @@ import (
 
 const (
 	// All transactions have 4 bytes for version, 4 bytes of locktime,
-	// and 2 varints for the number of inputs and outputs, and 1 varint
-	// for the witnesses.
-	txOverheadEstimate = 4 + 4 + 1 + 1 + 1
+	// 4 bytes of expiry, and 2 varints for the number of inputs and
+	// outputs, and 1 varint for the witnesses.
+	txOverheadEstimate = 4 + 4 + 4 + 1 + 1 + 1
 
 	// A worst case signature script to redeem a P2PKH output for a
 	// compressed pubkey has 73 bytes of the possible DER signature
@@ -54,9 +54,9 @@ const (
 	sigScriptEstimate = 1 + 73 + 1 + 65 + 1
 
 	// A best case tx input serialization cost is 32 bytes of sha, 4 bytes
-	// of output index, 1 byte for tree, 4 bytes of sequence, and the
-	// estimated signature script size.
-	txInEstimate = 32 + 4 + 1 + 4 + sigScriptEstimate
+	// of output index, 1 byte for tree, 4 bytes of sequence, 12 bytes for
+	// fraud proof, and the estimated signature script size.
+	txInEstimate = 32 + 4 + 1 + 12 + 4 + sigScriptEstimate
 
 	// A P2PKH pkScript contains the following bytes:
 	//  - OP_DUP
@@ -69,12 +69,13 @@ const (
 	// pkScriptEstimateSS
 	pkScriptEstimateSS = 1 + 1 + 1 + 1 + 20 + 1 + 1
 
-	// txOutEstimate is a best case tx output serialization cost is 8 bytes of value, one
-	// byte of varint, and the pkScript size.
-	txOutEstimate = 8 + 1 + pkScriptEstimate
+	// txOutEstimate is a best case tx output serialization cost is 8 bytes
+	// of value, two bytes of version, one byte of varint, and the pkScript
+	// size.
+	txOutEstimate = 8 + 2 + 1 + pkScriptEstimate
 
 	// ssTxOutEsimate
-	ssTxOutEsimate = 8 + 1 + pkScriptEstimateSS
+	ssTxOutEsimate = 8 + 2 + 1 + pkScriptEstimateSS
 )
 
 var (
@@ -352,7 +353,9 @@ func (w *Wallet) txToPairs(pairs map[string]dcrutil.Amount, account uint32,
 		needed += amt
 	}
 
-	// Simple fee guesstimate.
+	// Simple fee guesstimate. Assume that there are double
+	// the amount of inputs as compared to the amount of
+	// outputs.
 	var feeIncrement dcrutil.Amount
 	switch {
 	case w.chainParams == &chaincfg.MainNetParams:
@@ -363,7 +366,7 @@ func (w *Wallet) txToPairs(pairs map[string]dcrutil.Amount, account uint32,
 		feeIncrement = FeeIncrementTestnet
 	}
 	needed += feeForSize(feeIncrement,
-		estimateTxSize(len(pairs), len(pairs)))
+		estimateTxSize(len(pairs)*2, len(pairs)))
 
 	eligible, err := w.findEligibleOutputsAmount(account, minconf, needed, bs)
 	if err != nil {