feat: add initial support for server-sent events

lib/src/binding_http/http_client.dart

@@ -16,6 +16,7 @@ import "../../core.dart";
 import "http_config.dart";
 import "http_request_method.dart";
 import "http_security_exception.dart";
+import "http_subscription.dart";
 
 const _authorizationHeader = "Authorization";
 
@@ -306,13 +307,24 @@ final class HttpClient extends ProtocolClient
 
   @override
   Future<Subscription> subscribeResource(
-    Form form, {
+    AugmentedForm form, {
     required void Function(Content content) next,
     void Function(Exception error)? error,
     required void Function() complete,
   }) async {
-    // TODO(JKRhb): implement subscribeResource
-    throw UnimplementedError();
+    if (form.subprotocol != "sse") {
+      throw const DartWotException(
+        "Only server-sent events are supported at the moment by dart_wot",
+      );
+    }
+
+    return HttpSseSubscription(
+      form,
+      complete,
+      next: next,
+      onError: error,
+      complete: complete,
+    );
   }
 
   Future<DiscoveryContent> _sendDiscoveryRequest(

lib/src/binding_http/http_client_factory.dart

@@ -50,18 +50,7 @@ final class HttpClientFactory implements ProtocolClientFactory {
 
   @override
   bool supportsOperation(OperationType operationType, String? subprotocol) {
-    const unsupportedOperations = [
-      OperationType.observeproperty,
-      OperationType.unobserveproperty,
-      OperationType.subscribeevent,
-      OperationType.unsubscribeevent,
-    ];
-
-    if (unsupportedOperations.contains(operationType)) {
-      return false;
-    }
-
-    if (subprotocol != null) {
+    if (subprotocol != null && !["sse"].contains(subprotocol)) {
       return false;
     }
 

lib/src/binding_http/http_subscription.dart

@@ -0,0 +1,65 @@
+// Copyright 2024 Contributors to the Eclipse Foundation. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+//
+// SPDX-License-Identifier: BSD-3-Clause
+
+import "dart:convert";
+
+import "package:sse_channel/sse_channel.dart";
+
+import "../../core.dart";
+
+/// A [ProtocolSubscription] for supporting server-sent events.
+final class HttpSseSubscription extends ProtocolSubscription {
+  /// Constructor
+  HttpSseSubscription(
+    AugmentedForm form,
+    super._complete, {
+    required void Function(Content content) next,
+    void Function(Exception error)? onError,
+    void Function()? complete,
+  })  : _active = true,
+        _sseChannel = SseChannel.connect(form.resolvedHref) {
+    _sseChannel.stream.listen(
+      (data) {
+        if (data is! String) {
+          return;
+        }
+        next(Content(
+            form.contentType, Stream.fromIterable([utf8.encode(data)])));
+      },
+      onError: (error) {
+        if (error is! Exception) {
+          return;
+        }
+
+        onError?.call(error);
+      },
+      onDone: complete,
+    );
+  }
+
+  final SseChannel _sseChannel;
+
+  bool _active;
+
+  @override
+  bool get active => _active;
+
+  @override
+  Future<void> stop({
+    int? formIndex,
+    Map<String, Object>? uriVariables,
+    Object? data,
+  }) async {
+    if (!_active) {
+      return;
+    }
+    _active = false;
+
+    await _sseChannel.sink.close();
+    await super
+        .stop(formIndex: formIndex, uriVariables: uriVariables, data: data);
+  }
+}