add dart client to packages

packages/dart_client/lib/src/exceptions.dart

@@ -0,0 +1,54 @@
+import 'dart:convert';
+
+/// Exception related to api calls
+class ApiError extends Error {
+  /// Raw body of the response
+  final String body;
+
+  /// Json parsed body
+  final Map<String, dynamic> jsonData;
+
+  /// Http status code of the response
+  final int status;
+
+  /// Stream specific error code
+  int get code => _code;
+  int _code;
+
+  static Map<String, dynamic> _decode(String body) {
+    try {
+      if (body == null) {
+        return null;
+      }
+      return json.decode(body);
+    } on FormatException {
+      return null;
+    }
+  }
+
+  /// Creates a new ApiError instance using the response body and status code
+  ApiError(this.body, this.status) : jsonData = _decode(body) {
+    if (jsonData != null && jsonData.containsKey('code')) {
+      _code = jsonData['code'];
+    }
+  }
+
+  @override
+  bool operator ==(Object other) =>
+      identical(this, other) ||
+      other is ApiError &&
+          runtimeType == other.runtimeType &&
+          body == other.body &&
+          jsonData == other.jsonData &&
+          status == other.status &&
+          _code == other._code;
+
+  @override
+  int get hashCode =>
+      body.hashCode ^ jsonData.hashCode ^ status.hashCode ^ _code.hashCode;
+
+  @override
+  String toString() {
+    return 'ApiError{body: $body, jsonData: $jsonData, status: $status, code: $_code}';
+  }
+}