qml: when opening channel, validate and show user feedback if amount outside acceptable range

electrum/gui/qml/components/OpenChannelDialog.qml

@@ -201,7 +201,6 @@ ElDialog {
                             if (activeFocus) {
                                 channelopener.amount.isMax = checked
                                 if (checked) {
-                                    maxAmountMessage.text = ''
                                     channelopener.updateMaxAmount()
                                 }
                             }
@@ -232,11 +231,12 @@ ElDialog {
                 Item { visible: Daemon.fx.enabled ; height: 1; width: 1 }
 
                 InfoTextArea {
+                    id: warning
                     Layout.topMargin: constants.paddingMedium
                     Layout.fillWidth: true
                     Layout.columnSpan: 3
-                    id: maxAmountMessage
-                    visible: is_max.checked && text
+                    text: channelopener.warning
+                    visible: text
                     compact: true
                 }
 
@@ -321,9 +321,6 @@ ElDialog {
             // TODO: handle incomplete TX
             root.close()
         }
-        onMaxAmountMessage: (message) => {
-            maxAmountMessage.text = message
-        }
     }
 
     FontMetrics {

electrum/gui/qml/qechannelopener.py

@@ -9,6 +9,7 @@ from PyQt6.QtCore import pyqtProperty, pyqtSignal, pyqtSlot, QObject
 from electrum.i18n import _
 from electrum.gui import messages
 from electrum.util import bfh
+from electrum.lnutil import MIN_FUNDING_SAT
 from electrum.lntransport import extract_nodeid, ConnStringFormatError
 from electrum.bitcoin import DummyAddress
 from electrum.lnworker import hardcoded_trampoline_nodes
@@ -31,7 +32,6 @@ class QEChannelOpener(QObject, AuthMixin):
     channelOpenError = pyqtSignal([str], arguments=['message'])
     channelOpenSuccess = pyqtSignal([str, bool, int, bool],
                                     arguments=['cid', 'has_onchain_backup', 'min_depth', 'tx_complete'])
-    maxAmountMessage = pyqtSignal([str], arguments=['message'])
 
     dataChanged = pyqtSignal()  # generic notify signal
 
@@ -44,6 +44,8 @@ class QEChannelOpener(QObject, AuthMixin):
         self._valid = False
         self._opentx = None
         self._txdetails = None
+        self._warning = ''
+        self._determine_max_message = None
 
         self._finalizer = None
         self._node_pubkey = None
@@ -92,6 +94,21 @@ class QEChannelOpener(QObject, AuthMixin):
     def valid(self):
         return self._valid
 
+    def setValid(self, is_valid):
+        if self._valid != is_valid:
+            self._valid = is_valid
+            self.validChanged.emit()
+
+    warningChanged = pyqtSignal()
+    @pyqtProperty(str, notify=warningChanged)
+    def warning(self):
+        return self._warning
+
+    def setWarning(self, warning):
+        if self._warning != warning:
+            self._warning = warning
+            self.warningChanged.emit()
+
     finalizerChanged = pyqtSignal()
     @pyqtProperty(QETxFinalizer, notify=finalizerChanged)
     def finalizer(self):
@@ -106,10 +123,9 @@ class QEChannelOpener(QObject, AuthMixin):
     def trampolineNodeNames(self):
         return list(hardcoded_trampoline_nodes().keys())
 
-    # FIXME min channel funding amount
     # FIXME have requested funding amount
     def validate(self):
-        """side-effects: sets self._valid, self._node_pubkey, self._connect_str_resolved"""
+        """side-effects: sets self._node_pubkey, self._connect_str_resolved"""
         connect_str_valid = False
         if self._connect_str:
             self._logger.debug(f'checking if {self._connect_str=!r} is valid')
@@ -129,19 +145,36 @@ class QEChannelOpener(QObject, AuthMixin):
                     self._connect_str_resolved = self._connect_str
                     connect_str_valid = True
 
+        self.setWarning('')
+
         if not connect_str_valid:
-            self._valid = False
-            self.validChanged.emit()
+            self.setValid(False)
             return
 
         self._logger.debug(f'amount={self._amount}')
         if not self._amount or not (self._amount.satsInt > 0 or self._amount.isMax):
-            self._valid = False
-            self.validChanged.emit()
+            self.setValid(False)
             return
 
-        self._valid = True
-        self.validChanged.emit()
+        # for MAX, estimate is assumed to be calculated and set in self._amount.satsInt
+        if self._amount.satsInt < MIN_FUNDING_SAT:
+            message = _('Minimum required amount: {}').format(
+                self._wallet.wallet.config.format_amount_and_units(MIN_FUNDING_SAT)
+            )
+            if self._amount.isMax and self._determine_max_message:
+                message += '\n' + self._determine_max_message
+            self.setWarning(message)
+            self.setValid(False)
+            return
+
+        if self._amount.satsInt > self._wallet.wallet.config.LIGHTNING_MAX_FUNDING_SAT:
+            self.setWarning(_('Amount is above maximum channel size: {}').format(
+                self._wallet.wallet.config.format_amount_and_units(self._wallet.wallet.config.LIGHTNING_MAX_FUNDING_SAT)
+            ))
+            self.setValid(False)
+            return
+
+        self.setValid(True)
 
     @pyqtSlot(str, result=bool)
     def validateConnectString(self, connect_str):
@@ -252,13 +285,8 @@ class QEChannelOpener(QObject, AuthMixin):
                     node_id=dummy_nodeid,
                     fee_policy=fee_policy)
 
-                amount, message = self._wallet.determine_max(mktx=make_tx)
-                if amount is None:
-                    self._amount.isMax = False
-                else:
-                    self._amount.satsInt = amount
-                if message:
-                    self.maxAmountMessage.emit(message)
+                amount, self._determine_max_message = self._wallet.determine_max(mktx=make_tx)
+                self._amount.satsInt = amount if amount else 0
             finally:
                 self._updating_max = False
                 self.validate()