feat: dio client interceptor

lib/requests_signature_dart.dart

@@ -16,3 +16,7 @@ export 'src/core/interface/signature_body_source_builder.dart';
 
 // Export default constants
 export 'src/core/default_constants.dart';
+
+// Export client implementation
+///Client: Dio
+export 'src/client/dio_interceptor.dart';

lib/src/client/dio_interceptor.dart

@@ -0,0 +1,89 @@
+import 'dart:math';
+
+import 'package:cryptography/dart.dart';
+import 'package:dio/dio.dart';
+import 'package:requests_signature_dart/requests_signature_dart.dart';
+
+/// Interceptor for signing HTTP requests with HMAC authentication.
+///
+/// This interceptor adds HMAC authentication headers to outgoing HTTP requests
+/// based on the provided client ID and client secret. It calculates the signature
+/// using the specified hash algorithm.
+class HMACDioInterceptor extends Interceptor {
+  /// The client ID used for HMAC authentication.
+  final String clientId;
+
+  /// The client secret used for HMAC authentication.
+  final String clientSecret;
+
+  /// The signer used to calculate the HMAC signature.
+  final HashAlgorithmSignatureBodySigner signer;
+
+  /// Creates a new [HMACInterceptor] instance.
+  ///
+  /// [clientId] is the client ID used for HMAC authentication.
+  ///
+  /// [clientSecret] is the client secret used for HMAC authentication.
+  HMACDioInterceptor(this.clientId, this.clientSecret)
+      : signer =
+            HashAlgorithmSignatureBodySigner(hmacAlgorithm: DartHmac.sha256());
+
+  @override
+  Future onRequest(
+      RequestOptions options, RequestInterceptorHandler handler) async {
+    // Generate timestamp and nonce
+    final timestamp = _epochTime();
+    final nonce = _genGuid();
+
+    // Extract request details
+    final uri = options.uri;
+    final method = options.method;
+    final headers = options.headers;
+
+    // Prepare parameters for signature calculation
+    final signatureBodySourceParameters = SignatureBodySourceParameters(
+      method,
+      uri,
+      headers.map((key, value) => MapEntry(key.toString(), value.toString())),
+      nonce,
+      timestamp,
+      clientId,
+      DefaultConstants.signatureBodySourceComponents,
+    );
+
+    // Build the signature body source
+    final bodySourceBuilder = SignatureBodySourceBuilder();
+    final signatureBodySource =
+        await bodySourceBuilder.build(signatureBodySourceParameters);
+    final signatureBodyParameters =
+        SignatureBodyParameters(signatureBodySource, clientSecret);
+
+    // Calculate HMAC signature
+    final signature = await signer.sign(signatureBodyParameters);
+
+    // Add authentication headers to the request
+    options.headers['X-RequestSignature-ClientId'] = clientId;
+    options.headers['X-RequestSignature-Nonce'] = nonce;
+    options.headers['X-RequestSignature-Timestamp'] = timestamp.toString();
+    options.headers['X-RequestSignature-Signature'] = signature;
+
+    return super.onRequest(options, handler);
+  }
+
+  /// Generates a random nonce.
+  ///
+  /// The nonce is a unique string used for each request to prevent replay attacks.
+  String _genGuid() {
+    const String uuid = 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx';
+    return uuid.replaceAllMapped(RegExp('[xy]'), (match) {
+      final int rand = Random().nextInt(16);
+      final int index = match.group(0) == 'x' ? rand : (rand & 0x3 | 0x8);
+      return index.toRadixString(16);
+    });
+  }
+
+  /// Returns the current epoch time in milliseconds.
+  int _epochTime() {
+    return DateTime.now().millisecondsSinceEpoch;
+  }
+}

test/client/dio_hmac_interceptor_test.dart

@@ -0,0 +1,51 @@
+/// This file contains unit tests for the [HMACDioInterceptor] class.
+///
+/// The [HMACDioInterceptor] class is responsible for adding HMAC authentication headers
+/// to outgoing HTTP requests based on the provided client ID and client secret. It calculates
+/// the signature using the specified hash algorithm.
+///
+/// The tests in this file ensure that the interceptor behaves correctly under different scenarios
+/// and edge cases, verifying that it signs requests with authentication headers correctly.
+/// Suggestions for additional test cases are also provided for further coverage.
+///
+/// To run the tests, use the `dart test` command with the appropriate arguments.
+/// Run test via terminal:
+/// ```
+/// dart test test/client/dio_hmac_interceptor_test.dart
+/// ```
+/// Ensure that the appropriate dependencies are included in the `pubspec.yaml` file
+/// and imported into the test file for the tests to work properly.
+///
+
+import 'package:dio/dio.dart';
+import 'package:test/test.dart';
+import 'package:requests_signature_dart/requests_signature_dart.dart';
+
+void main() {
+  group('HMACDioInterceptor', () {
+    test('Interceptor signs the request with authentication headers', () async {
+      // Test case to ensure that the interceptor signs requests with authentication headers correctly.
+      // Arrange
+      final dio = Dio();
+      final interceptor =
+          HMACDioInterceptor("your_client_id", "your_client_secret");
+      dio.interceptors.add(interceptor);
+
+      final options = RequestOptions(
+        method: 'GET',
+        path: '/api/data',
+        baseUrl: 'https://example.com',
+        headers: {'Content-Type': 'application/json'},
+      );
+
+      // Act
+      await interceptor.onRequest(options, RequestInterceptorHandler());
+
+      // Assert
+      expect(options.headers['X-RequestSignature-ClientId'], "your_client_id");
+      expect(options.headers['X-RequestSignature-Nonce'], isNotEmpty);
+      expect(options.headers['X-RequestSignature-Timestamp'], isNotEmpty);
+      expect(options.headers['X-RequestSignature-Signature'], isNotEmpty);
+    });
+  });
+}