perf(geodata): Cache metadata object in OGC API Features clients for …

…short periods #181

dart/geodata/CHANGELOG.md

@@ -13,6 +13,7 @@ NOTE: Version 0.12.0 currently [under development](https://github.com/navibyte/g
 * [Add support for API definition (like Open API 3.0) when accessing OGC API Features clients #170](https://github.com/navibyte/geospatial/issues/170)
 * [Map HTTP status codes to feature service exception (OGC API Features) #68](https://github.com/navibyte/geospatial/issues/68)
 * [Add initial support for OGC API - Features - Part 3: Filtering #180](https://github.com/navibyte/geospatial/issues/180)
+* [Cache metadata object in OGC API Features clients for short periods #181](https://github.com/navibyte/geospatial/issues/181)
 
 🛠 Maintenance:
 * Removed extra internal export files and made internal imports more excplicit.

dart/geodata/lib/src/geojson/service/client/geojson_feature_client.dart

@@ -27,8 +27,12 @@ class GeoJSONFeatures {
   /// The required [location] should refer to a web resource containing GeoJSON
   /// compliant data.
   ///
-  /// When given the optional [client] is used for http requests, otherwise the
-  /// default client of the `package:http/http.dart` package is used.
+  /// When given an optional [client] is used for http requests, otherwise the
+  /// default client of the `package:http/http.dart` package is used (a new
+  /// instance of default client for each service request). When [client] is
+  /// given, this allows a client to better maintain persistent connections to a
+  /// service, but it's also responsibility of a caller to close it
+  /// appropriately.
   ///
   /// When given [headers] are injected to http requests (however some can be
   /// overridden by the feature source implementation).

dart/geodata/lib/src/ogcapi_common/service/client/ogc_client.dart

@@ -12,6 +12,7 @@ import '/src/common/service/service_exception.dart';
 import '/src/core/api/open_api_document.dart';
 import '/src/ogcapi_common/model/ogc_service.dart';
 import '/src/ogcapi_common/model/ogc_service_meta.dart';
+import '/src/utils/cached_object.dart';
 import '/src/utils/feature_http_adapter.dart';
 import '/src/utils/resolve_api_call.dart';
 
@@ -33,80 +34,89 @@ const _expectJSONOpenAPI = [
 @internal
 abstract class OGCClientHttp implements OGCService {
   /// Create a http client with HTTP(S) [endpoint] and [adapter].
-  const OGCClientHttp(
+  OGCClientHttp(
     this.endpoint, {
     required this.adapter,
-  });
+    this.metaMaxAge = const Duration(minutes: 15),
+  }) : _cachedMeta = CachedObject(metaMaxAge);
 
   /// The endpoint for this client.
   final Uri endpoint;
 
   /// An adapter used to access HTTP(S) resource.
   final FeatureHttpAdapter adapter;
 
+  /// The max age to cache metadata objects retrieved from a service and that
+  /// are cached internally (in-memory) by this client.
+  final Duration metaMaxAge;
+
+  final CachedObject<OGCServiceMeta> _cachedMeta;
+
   @override
-  Future<OGCServiceMeta> meta() async {
-    // fetch data as JSON Object, and parse meta data
-    return adapter.getEntityFromJsonObject(
-      endpoint,
-      toEntity: (data, _) {
-        final links = Links.fromJson(data['links'] as Iterable<dynamic>);
-        return _OGCServiceMetaImpl(
-          service: this,
-          title: data['title'] as String? ??
-              links.self().first.title ??
-              'An OGC API service',
-          links: links,
-          description: data['description'] as String?,
-          attribution: data['attribution'] as String?,
+  Future<OGCServiceMeta> meta() => _cachedMeta.getAsync(() {
+        // fetch data as JSON Object, and parse meta data
+        return adapter.getEntityFromJsonObject(
+          endpoint,
+          toEntity: (data, _) {
+            final links = Links.fromJson(data['links'] as Iterable<dynamic>);
+            return _OGCServiceMetaImpl(
+              service: this,
+              title: data['title'] as String? ??
+                  links.self().first.title ??
+                  'An OGC API service',
+              links: links,
+              description: data['description'] as String?,
+              attribution: data['attribution'] as String?,
+            );
+          },
         );
-      },
-    );
-  }
+      });
 }
 
 class _OGCServiceMetaImpl extends OGCServiceMeta {
   final OGCClientHttp service;
 
-  const _OGCServiceMetaImpl({
+  final CachedObject<OpenAPIDocument> _cachedAPI;
+
+  _OGCServiceMetaImpl({
     required this.service,
     required super.title,
     super.description,
     super.attribution,
     required super.links,
-  });
+  }) : _cachedAPI = CachedObject(service.metaMaxAge);
 
   @override
-  Future<OpenAPIDocument> openAPI() {
-    // 1. Get a link for the relation "service-desc".
-    // 2. Ensure it's type is "application/vnd.oai.openapi+json".
-    //    (here we are allowing other JSON based content types too)
-    final link = _resolveServiceDescLink();
-    if (link == null) {
-      throw const ServiceException('No valid service-desc link.');
-    }
-    final url = resolveLinkReferenceUri(service.endpoint, link.href);
-
-    // 3. Read JSON content from a HTTP service.
-    // 4. Decode content received as JSON Object using the standard JSON decoder
-    // 5. Wrap such decoded object in an [OpenAPIDefinition] instance.
-    final type = link.type;
-    if (type != null) {
-      return service.adapter.getEntityFromJsonObject(
-        url,
-        headers: {'accept': type},
-        expect: _expectJSONOpenAPI,
-        toEntity: (data, _) => OpenAPIDocument(content: data),
-      );
-    } else {
-      return service.adapter.getEntityFromJsonObject(
-        url,
-        headers: _acceptJSONOpenAPI,
-        expect: _expectJSONOpenAPI,
-        toEntity: (data, _) => OpenAPIDocument(content: data),
-      );
-    }
-  }
+  Future<OpenAPIDocument> openAPI() => _cachedAPI.getAsync(() {
+        // 1. Get a link for the relation "service-desc".
+        // 2. Ensure it's type is "application/vnd.oai.openapi+json".
+        //    (here we are allowing other JSON based content types too)
+        final link = _resolveServiceDescLink();
+        if (link == null) {
+          throw const ServiceException('No valid service-desc link.');
+        }
+        final url = resolveLinkReferenceUri(service.endpoint, link.href);
+
+        // 3. Read JSON content from a HTTP service.
+        // 4. Decode content received as JSON Object using standard JSON decoder
+        // 5. Wrap such decoded object in an [OpenAPIDefinition] instance.
+        final type = link.type;
+        if (type != null) {
+          return service.adapter.getEntityFromJsonObject(
+            url,
+            headers: {'accept': type},
+            expect: _expectJSONOpenAPI,
+            toEntity: (data, _) => OpenAPIDocument(content: data),
+          );
+        } else {
+          return service.adapter.getEntityFromJsonObject(
+            url,
+            headers: _acceptJSONOpenAPI,
+            expect: _expectJSONOpenAPI,
+            toEntity: (data, _) => OpenAPIDocument(content: data),
+          );
+        }
+      });
 
   /// Resolve an url that's providing OpenAPI or JSON service description.
   Link? _resolveServiceDescLink() {