allow fractional feerates (#4324)

gui/qt/amountedit.py

@@ -1,11 +1,12 @@
 # -*- coding: utf-8 -*-
 
+from decimal import Decimal
+
 from PyQt5.QtCore import *
 from PyQt5.QtGui import *
 from PyQt5.QtWidgets import (QLineEdit, QStyle, QStyleOptionFrame)
 
-from decimal import Decimal
-from electrum.util import format_satoshis_plain, decimal_point_to_base_unit_name
+from electrum.util import format_satoshis_plain, decimal_point_to_base_unit_name, FEERATE_PRECISION
 
 
 class MyLineEdit(QLineEdit):
@@ -19,7 +20,7 @@ class MyLineEdit(QLineEdit):
 class AmountEdit(MyLineEdit):
     shortcut = pyqtSignal()
 
-    def __init__(self, base_unit, is_int = False, parent=None):
+    def __init__(self, base_unit, is_int=False, parent=None):
         QLineEdit.__init__(self, parent)
         # This seems sufficient for hundred-BTC amounts with 8 decimals
         self.setFixedWidth(140)
@@ -28,10 +29,14 @@ class AmountEdit(MyLineEdit):
         self.is_int = is_int
         self.is_shortcut = False
         self.help_palette = QPalette()
+        self.extra_precision = 0
 
     def decimal_point(self):
         return 8
 
+    def max_precision(self):
+        return self.decimal_point() + self.extra_precision
+
     def numbify(self):
         text = self.text().strip()
         if text == '!':
@@ -45,7 +50,7 @@ class AmountEdit(MyLineEdit):
             if '.' in s:
                 p = s.find('.')
                 s = s.replace('.','')
-                s = s[:p] + '.' + s[p:p+self.decimal_point()]
+                s = s[:p] + '.' + s[p:p+self.max_precision()]
         self.setText(s)
         # setText sets Modified to False.  Instead we want to remember
         # if updates were because of user modification.
@@ -75,7 +80,7 @@ class AmountEdit(MyLineEdit):
 
 class BTCAmountEdit(AmountEdit):
 
-    def __init__(self, decimal_point, is_int = False, parent=None):
+    def __init__(self, decimal_point, is_int=False, parent=None):
         AmountEdit.__init__(self, self._base_unit, is_int, parent)
         self.decimal_point = decimal_point
 
@@ -87,8 +92,15 @@ class BTCAmountEdit(AmountEdit):
             x = Decimal(str(self.text()))
         except:
             return None
-        p = pow(10, self.decimal_point())
-        return int( p * x )
+        # scale it to max allowed precision, make it an int
+        power = pow(10, self.max_precision())
+        max_prec_amount = int(power * x)
+        # if the max precision is simply what unit conversion allows, just return
+        if self.max_precision() == self.decimal_point():
+            return max_prec_amount
+        # otherwise, scale it back to the expected unit
+        amount = Decimal(max_prec_amount) / pow(10, self.max_precision()-self.decimal_point())
+        return Decimal(amount) if not self.is_int else int(amount)
 
     def setAmount(self, amount):
         if amount is None:
@@ -98,6 +110,11 @@ class BTCAmountEdit(AmountEdit):
 
 
 class FeerateEdit(BTCAmountEdit):
+
+    def __init__(self, decimal_point, is_int=False, parent=None):
+        super().__init__(decimal_point, is_int, parent)
+        self.extra_precision = FEERATE_PRECISION
+
     def _base_unit(self):
         return 'sat/byte'
 

gui/qt/main_window.py

@@ -49,7 +49,7 @@ from electrum.util import (format_time, format_satoshis, format_fee_satoshis,
                            UserCancelled, NoDynamicFeeEstimates, profiler,
                            export_meta, import_meta, bh2u, bfh, InvalidPassword,
                            base_units, base_units_list, base_unit_name_to_decimal_point,
-                           decimal_point_to_base_unit_name)
+                           decimal_point_to_base_unit_name, quantize_feerate)
 from electrum import Transaction
 from electrum import util, bitcoin, commands, coinchooser
 from electrum import paymentrequest
@@ -1102,7 +1102,8 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, PrintError):
                 self.config.set_key('fee_per_kb', fee_rate, False)
 
             if fee_rate:
-                self.feerate_e.setAmount(fee_rate // 1000)
+                fee_rate = Decimal(fee_rate)
+                self.feerate_e.setAmount(quantize_feerate(fee_rate / 1000))
             else:
                 self.feerate_e.setAmount(None)
             self.fee_e.setModified(False)
@@ -1334,12 +1335,12 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, PrintError):
             if freeze_feerate or self.fee_slider.is_active():
                 displayed_feerate = self.feerate_e.get_amount()
                 if displayed_feerate:
-                    displayed_feerate = displayed_feerate // 1000
+                    displayed_feerate = quantize_feerate(displayed_feerate / 1000)
                 else:
                     # fallback to actual fee
-                    displayed_feerate = fee // size if fee is not None else None
+                    displayed_feerate = quantize_feerate(fee / size) if fee is not None else None
                     self.feerate_e.setAmount(displayed_feerate)
-                displayed_fee = displayed_feerate * size if displayed_feerate is not None else None
+                displayed_fee = round(displayed_feerate * size) if displayed_feerate is not None else None
                 self.fee_e.setAmount(displayed_fee)
             else:
                 if freeze_fee:
@@ -1349,14 +1350,14 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, PrintError):
                     displayed_fee = fee
                     self.fee_e.setAmount(displayed_fee)
                 displayed_fee = displayed_fee if displayed_fee else 0
-                displayed_feerate = displayed_fee // size if displayed_fee is not None else None
+                displayed_feerate = quantize_feerate(displayed_fee / size) if displayed_fee is not None else None
                 self.feerate_e.setAmount(displayed_feerate)
 
             # show/hide fee rounding icon
             feerounding = (fee - displayed_fee) if fee else 0
-            self.set_feerounding_text(feerounding)
+            self.set_feerounding_text(int(feerounding))
             self.feerounding_icon.setToolTip(self.feerounding_text)
-            self.feerounding_icon.setVisible(bool(feerounding))
+            self.feerounding_icon.setVisible(abs(feerounding) >= 1)
 
             if self.is_max:
                 amount = tx.output_value()

lib/simple_config.py

@@ -3,6 +3,7 @@ import threading
 import time
 import os
 import stat
+from decimal import Decimal
 
 from copy import deepcopy
 
@@ -473,12 +474,9 @@ class SimpleConfig(PrintError):
 
     @classmethod
     def estimate_fee_for_feerate(cls, fee_per_kb, size):
-        # note: We only allow integer sat/byte values atm.
-        # The GUI for simplicity reasons only displays integer sat/byte,
-        # and for the sake of consistency, we thus only use integer sat/byte in
-        # the backend too.
-        fee_per_byte = int(fee_per_kb / 1000)
-        return int(fee_per_byte * size)
+        fee_per_kb = Decimal(fee_per_kb)
+        fee_per_byte = fee_per_kb / 1000
+        return round(fee_per_byte * size)
 
     def update_fee_estimates(self, key, value):
         self.fee_estimates[key] = value

lib/util.py

@@ -24,6 +24,7 @@ import binascii
 import os, sys, re, json
 from collections import defaultdict
 from datetime import datetime
+import decimal
 from decimal import Decimal
 import traceback
 import urllib
@@ -472,8 +473,21 @@ def format_satoshis(x, num_zeros=0, decimal_point=8, precision=None, is_diff=Fal
         result = " " * (15 - len(result)) + result
     return result
 
+
+FEERATE_PRECISION = 1  # num fractional decimal places for sat/byte fee rates
+_feerate_quanta = Decimal(10) ** (-FEERATE_PRECISION)
+
+
 def format_fee_satoshis(fee, num_zeros=0):
-    return format_satoshis(fee, num_zeros, 0, precision=1)
+    return format_satoshis(fee, num_zeros, 0, precision=FEERATE_PRECISION)
+
+
+def quantize_feerate(fee):
+    """Strip sat/byte fee rate of excess precision."""
+    if fee is None:
+        return None
+    return Decimal(fee).quantize(_feerate_quanta, rounding=decimal.ROUND_HALF_DOWN)
+
 
 def timestamp_to_datetime(timestamp):
     if timestamp is None: