feat(useragent): initial connection impl

useragent/lib/features/connection/arbiter_url.dart

@@ -0,0 +1,56 @@
+import 'dart:convert';
+
+class ArbiterUrl {
+  const ArbiterUrl({
+    required this.host,
+    required this.port,
+    required this.caCert,
+    this.bootstrapToken,
+  });
+
+  final String host;
+  final int port;
+  final List<int> caCert;
+  final String? bootstrapToken;
+
+  static const _scheme = 'arbiter';
+  static const _certQueryKey = 'cert';
+  static const _bootstrapTokenQueryKey = 'bootstrap_token';
+
+  static ArbiterUrl parse(String value) {
+    final uri = Uri.tryParse(value);
+    if (uri == null || uri.scheme != _scheme) {
+      throw const FormatException("Invalid URL scheme, expected 'arbiter://'");
+    }
+
+    if (uri.host.isEmpty) {
+      throw const FormatException('Missing host in URL');
+    }
+
+    if (!uri.hasPort) {
+      throw const FormatException('Missing port in URL');
+    }
+
+    final cert = uri.queryParameters[_certQueryKey];
+    if (cert == null || cert.isEmpty) {
+      throw const FormatException("Missing 'cert' query parameter in URL");
+    }
+
+    final decodedCert = _decodeCert(cert);
+
+    return ArbiterUrl(
+      host: uri.host,
+      port: uri.port,
+      caCert: decodedCert,
+      bootstrapToken: uri.queryParameters[_bootstrapTokenQueryKey],
+    );
+  }
+
+  static List<int> _decodeCert(String cert) {
+    try {
+      return base64Url.decode(base64Url.normalize(cert));
+    } on FormatException catch (error) {
+      throw FormatException("Invalid base64 in 'cert' query parameter: ${error.message}");
+    }
+  }
+}