add lnurl-pay and lightning address support

* bundles all payment identifiers into handle_payment_identifier
* adds lnurl decoding
* adds lightning address decoding

electrum/lnurl.py

@@ -0,0 +1,75 @@
+"""Module for lnurl-related functionality."""
+# https://github.com/sipa/bech32/tree/master/ref/python
+# https://github.com/lnbits/lnurl
+
+import asyncio
+import json
+from typing import Callable, Optional
+import re
+
+import aiohttp.client_exceptions
+from aiohttp import ClientResponse
+
+from electrum.segwit_addr import bech32_decode, Encoding, convertbits
+from electrum.lnaddr import LnDecodeException
+
+
+class LNURLError(Exception):
+    pass
+
+
+def decode_lnurl(lnurl: str) -> str:
+    """Converts bech32 encoded lnurl to url."""
+    decoded_bech32 = bech32_decode(
+        lnurl, ignore_long_length=True
+    )
+    hrp = decoded_bech32.hrp
+    data = decoded_bech32.data
+    if decoded_bech32.encoding is None:
+        raise LnDecodeException("Bad bech32 checksum")
+    if decoded_bech32.encoding != Encoding.BECH32:
+        raise LnDecodeException("Bad bech32 encoding: must be using vanilla BECH32")
+    if not hrp.startswith("lnurl"):
+        raise LnDecodeException("Does not start with lnurl")
+    data = convertbits(data, 5, 8, False)
+    url = bytes(data).decode("utf-8")
+    return url
+
+
+def request_lnurl(url: str, request_over_proxy: Callable) -> dict:
+    """Requests payment data from a lnurl."""
+    try:
+        response = request_over_proxy("get", url, timeout=2)
+    except asyncio.TimeoutError as e:
+        raise LNURLError("Server did not reply in time.") from e
+    except aiohttp.client_exceptions.ClientError as e:
+        raise LNURLError(f"Client error: {e}") from e
+    # TODO: handling of specific client errors
+    response = json.loads(response)
+    if "metadata" in response:
+        response["metadata"] = json.loads(response["metadata"])
+    status = response.get("status")
+    if status and status == "ERROR":
+        raise LNURLError(f"LNURL request encountered an error: {response['reason']}")
+    return response
+
+
+def callback_lnurl(url: str, params: dict, request_over_proxy: Callable) -> dict:
+    """Requests an invoice from a lnurl supporting server."""
+    try:
+        response = request_over_proxy("get", url, params=params)
+    except aiohttp.client_exceptions.ClientError as e:
+        raise LNURLError(f"Client error: {e}") from e
+    # TODO: handling of specific errors
+    response = json.loads(response)
+    status = response.get("status")
+    if status and status == "ERROR":
+        raise LNURLError(f"LNURL request encountered an error: {response['reason']}")
+    return response
+
+
+def lightning_address_to_url(address: str) -> Optional[str]:
+    """Converts an email-type lightning address to a decoded lnurl."""
+    if re.match(r"[^@]+@[^@]+\.[^@]+", address):
+        username, domain = address.split("@")
+        return f"https://{domain}/.well-known/lnurlp/{username}"