lnurl: implement LNURL-withdraw

adds handling of lnurl-withdraw payment identifiers which allow users to
withdraw bitcoin from a service by scanning a qr code or pasting the
lnurl-w code as "sending" address.

tests/test_lnurl.py

@@ -20,3 +20,85 @@ class TestLnurl(TestCase):
     def test_lightning_address_to_url(self):
         url = lnurl.lightning_address_to_url("mempool@jhoenicke.de")
         self.assertEqual("https://jhoenicke.de/.well-known/lnurlp/mempool", url)
+
+    def test_parse_lnurl3_response(self):
+        # Test successful parsing with all fields
+        sample_response = {
+            'callback': 'https://service.io/withdraw?sessionid=123',
+            'k1': 'abcdef1234567890',
+            'defaultDescription': 'Withdraw from service',
+            'minWithdrawable': 10_000_000,
+            'maxWithdrawable': 100_000_000,
+        }
+
+        result = lnurl._parse_lnurl3_response(sample_response)
+
+        self.assertEqual('https://service.io/withdraw?sessionid=123', result.callback_url)
+        self.assertEqual('abcdef1234567890', result.k1)
+        self.assertEqual('Withdraw from service', result.default_description)
+        self.assertEqual(10_000, result.min_withdrawable_sat)
+        self.assertEqual(100_000, result.max_withdrawable_sat)
+
+        # Test with .onion URL
+        onion_response = {
+            'callback': 'http://robosatsy56bwqn56qyadmcxkx767hnabg4mihxlmgyt6if5gnuxvzad.onion/withdraw?sessionid=123',
+            'k1': 'abcdef1234567890',
+            'minWithdrawable': 10_000_000,
+            'maxWithdrawable': 100_000_000
+        }
+
+        result = lnurl._parse_lnurl3_response(onion_response)
+        self.assertEqual('http://robosatsy56bwqn56qyadmcxkx767hnabg4mihxlmgyt6if5gnuxvzad.onion/withdraw?sessionid=123',
+                         result.callback_url)
+        self.assertEqual('', result.default_description)  # Missing defaultDescription uses empty string
+
+        # Test missing callback (should raise error)
+        no_callback_response = {
+            'k1': 'abcdef1234567890',
+            'minWithdrawable': 10_000_000,
+            'maxWithdrawable': 100_000_000
+        }
+
+        with self.assertRaises(lnurl.LNURLError):
+            lnurl._parse_lnurl3_response(no_callback_response)
+
+        # Test unsafe callback URL
+        unsafe_response = {
+            'callback': 'http://service.io/withdraw?sessionid=123',  # HTTP URL
+            'k1': 'abcdef1234567890',
+            'minWithdrawable': 10_000_000,
+            'maxWithdrawable': 100_000_000
+        }
+
+        with self.assertRaises(lnurl.LNURLError):
+            lnurl._parse_lnurl3_response(unsafe_response)
+
+        # Test missing k1 (should raise error)
+        no_k1_response = {
+            'callback': 'https://service.io/withdraw?sessionid=123',
+            'minWithdrawable': 10_000_000,
+            'maxWithdrawable': 100_000_000
+        }
+
+        with self.assertRaises(lnurl.LNURLError):
+            lnurl._parse_lnurl3_response(no_k1_response)
+
+        # Test missing withdrawable amounts (should raise error)
+        no_amounts_response = {
+            'callback': 'https://service.io/withdraw?sessionid=123',
+            'k1': 'abcdef1234567890',
+        }
+
+        with self.assertRaises(lnurl.LNURLError):
+            lnurl._parse_lnurl3_response(no_amounts_response)
+
+        # Test malformed withdrawable amounts (should raise error)
+        bad_amounts_response = {
+            'callback': 'https://service.io/withdraw?sessionid=123',
+            'k1': 'abcdef1234567890',
+            'minWithdrawable': 'this is not a number',
+            'maxWithdrawable': 100_000_000
+        }
+
+        with self.assertRaises(lnurl.LNURLError):
+            lnurl._parse_lnurl3_response(bad_amounts_response)