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electrum-bitcoinprivate
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Track tx size directly; calculate fees from that 

This has several advantages.  Fee calculation is now very fast,
as we don't need to keep reserializing the tx.  Another is that
we can reason about the fees after adding a change output without
having to add it, recalculate the tx fee, and remove it again.
This commit is contained in:
Neil Booth 2015-11-29 13:29:33 +09:00
parent a4dd5acc48
commit 93bb09230c
3 changed files with 48 additions and 52 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

56
lib/coinchooser.py
View File

@ -33,60 +33,42 @@ class CoinChooser(PrintError):
amount = sum(map(lambda x: x[2], outputs))
total = 0
tx = Transaction.from_io([], outputs)
fee = fee_estimator(tx)
# Size of the transaction with no inputs and no change
base_size = tx.estimated_size()
# Pay to bitcoin address serializes as 34 bytes
change_size = 34
# Size of each serialized coin
for coin in coins:
coin['size'] = Transaction.estimated_input_size(coin)
size = base_size
# add inputs, sorted by age
for item in coins:
v = item.get('value')
total += v
size += item['size']
tx.add_input(item)
# no need to estimate fee until we have reached desired amount
if total < amount + fee:
continue
fee = fee_estimator(tx)
if total >= amount + fee:
if total >= amount + fee_estimator(size):
break
else:
raise NotEnoughFunds()
# remove unneeded inputs.
removed = False
for item in sorted(tx.inputs, key=itemgetter('value')):
v = item.get('value')
if total - v >= amount + fee:
if total - v >= amount + fee_estimator(size - item['size']):
tx.inputs.remove(item)
total -= v
removed = True
continue
else:
break
if removed:
fee = fee_estimator(tx)
for item in sorted(tx.inputs, key=itemgetter('value')):
v = item.get('value')
if total - v >= amount + fee:
tx.inputs.remove(item)
total -= v
fee = fee_estimator(tx)
continue
break
size -= item['size']
self.print_error("using %d inputs" % len(tx.inputs))
# if change is above dust threshold, add a change output.
change_addr = change_addrs[0]
change_amount = total - (amount + fee)
# See if change would still be greater than dust after adding
# the change to the transaction
# If change is above dust threshold after accounting for the
# size of the change output, add it to the transaction.
change_amount = total - (amount + fee_estimator(size + change_size))
if change_amount > dust_threshold:
tx.outputs.append(('address', change_addr, change_amount))
fee = fee_estimator(tx)
# remove change output
tx.outputs.pop()
change_amount = total - (amount + fee)
# If change is still above dust threshold, keep the change.
if change_amount > dust_threshold:
tx.outputs.append(('address', change_addr, change_amount))
tx.outputs.append(('address', change_addrs[0], change_amount))
size += change_size
self.print_error('change', change_amount)
elif change_amount:
self.print_error('not keeping dust', change_amount)

35
lib/transaction.py
View File

@ -595,6 +595,7 @@ class Transaction:
raise
return script
@classmethod
def input_script(self, txin, i, for_sig):
# for_sig:
# -1 : do not sign, estimate length
@ -641,6 +642,18 @@ class Transaction:
return script
@classmethod
def serialize_input(self, txin, i, for_sig):
# Prev hash and index
s = txin['prevout_hash'].decode('hex')[::-1].encode('hex')
s = int_to_hex(txin['prevout_n'], 4)
# Script length, script, sequence
script = self.input_script(txin, i, for_sig)
s += var_int(len(script) / 2)
s += script
s += "ffffffff"
return s
def BIP_LI01_sort(self):
# See https://github.com/kristovatlas/rfc/blob/master/bips/bip-li01.mediawiki
self.inputs.sort(key = lambda i: (i['prevout_hash'], i['prevout_n']))
@ -652,12 +665,7 @@ class Transaction:
s = int_to_hex(1,4) # version
s += var_int( len(inputs) ) # number of inputs
for i, txin in enumerate(inputs):
s += txin['prevout_hash'].decode('hex')[::-1].encode('hex') # prev hash
s += int_to_hex(txin['prevout_n'], 4) # prev index
script = self.input_script(txin, i, for_sig)
s += var_int( len(script)/2 ) # script length
s += script
s += "ffffffff" # sequence
s += self.serialize_input(txin, i, for_sig)
s += var_int( len(outputs) ) # number of outputs
for output in outputs:
output_type, addr, amount = output
@ -690,7 +698,7 @@ class Transaction:
return self.input_value() - self.output_value()
@classmethod
def estimated_fee_for_size(self, fee_per_kb, size):
def fee_for_size(self, fee_per_kb, size):
'''Given a fee per kB in satoshis, and a tx size in bytes,
returns the transaction fee.'''
fee = int(fee_per_kb * size / 1000.)
@ -699,11 +707,18 @@ class Transaction:
return fee
@profiler
def estimated_size(self):
'''Return an estimated tx size in bytes.'''
return len(self.serialize(-1)) / 2 # ASCII hex string
@classmethod
def estimated_input_size(self, txin):
'''Return an estimated of serialized input size in bytes.'''
return len(self.serialize_input(txin, -1, -1)) / 2
def estimated_fee(self, fee_per_kb):
'''Return an estimated fee given a fee per kB in satoshis.'''
# Remember self.serialize returns an ASCII hex string
size = len(self.serialize(-1)) / 2
return self.estimated_fee_for_size(fee_per_kb, size)
return self.fee_for_size(fee_per_kb, self.estimated_size())
def signature_count(self):
r = 0

9
lib/wallet.py
View File

@ -24,6 +24,7 @@ import random
import time
import json
import copy
from functools import partial
from util import PrintError, profiler
@ -929,12 +930,10 @@ class Abstract_Wallet(PrintError):
# Fee estimator
if fixed_fee is None:
fee_per_kb = self.fee_per_kb(config)
def fee_estimator(tx):
return tx.estimated_fee(fee_per_kb)
fee_estimator = partial(Transaction.fee_for_size,
self.fee_per_kb(config))
else:
def fee_estimator(tx):
return fixed_fee
fee_estimator = lambda size: fixed_fee
# Change <= dust threshold is added to the tx fee
dust_threshold = 182 * 3 * MIN_RELAY_TX_FEE / 1000