validate and deduplicate relay config input in qt gui

Adds validation and deduplication of the relay urls entered in the QT
settings dialog. This is supposed to prevent malformed or duplicated
relay entries.
Also resets the relays to the default value if no (valid) url
is entered. This prevents the user from getting stuck without relays
(otherwise the user would have to research for relay urls manually if
they don't know any).

electrum/util.py

@@ -31,14 +31,13 @@ from typing import (NamedTuple, Union, TYPE_CHECKING, Tuple, Optional, Callable,
 from datetime import datetime, timezone, timedelta
 import decimal
 from decimal import Decimal
-import urllib
+from urllib.parse import urlparse
 import threading
 import hmac
 import hashlib
 import stat
 import locale
 import asyncio
-import urllib.request, urllib.parse, urllib.error
 import builtins
 import json
 import time
@@ -699,6 +698,27 @@ def is_valid_email(s):
     regexp = r"[^@]+@[^@]+\.[^@]+"
     return re.match(regexp, s) is not None
 
+def is_valid_websocket_url(url: str) -> bool:
+    """
+    uses this django url validation regex:
+    https://github.com/django/django/blob/2c6906a0c4673a7685817156576724aba13ad893/django/core/validators.py#L45C1-L52C43
+    Note: this is not perfect, urls and their parsing can get very complex (see recent django code).
+    however its sufficient for catching weird user input in the gui dialog
+    """
+    # stores the compiled regex in the function object itself to avoid recompiling it every call
+    if not hasattr(is_valid_websocket_url, "regex"):
+        is_valid_websocket_url.regex = re.compile(
+            r'^(?:ws|wss)://'  # ws:// or wss://
+            r'(?:(?:[A-Z0-9](?:[A-Z0-9-]{0,61}[A-Z0-9])?\.)+(?:[A-Z]{2,6}\.?|[A-Z0-9-]{2,}\.?)|'  # domain...
+            r'localhost|'  # localhost...
+            r'\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}|'  # ...or ipv4
+            r'\[?[A-F0-9]*:[A-F0-9:]+\]?)'  # ...or ipv6
+            r'(?::\d+)?'  # optional port
+            r'(?:/?|[/?]\S+)$', re.IGNORECASE)
+    try:
+        return re.match(is_valid_websocket_url.regex, url) is not None
+    except Exception:
+        return False
 
 def is_hash256_str(text: Any) -> bool:
     if not isinstance(text, str): return False