dart: add a remote lib to handle http requests

lib/util/remote.dart

@@ -0,0 +1,40 @@
+import 'dart:convert';
+import 'dart:io';
+
+Future<Map<String, dynamic>?> remoteGet(String url) async {
+  HttpClient client = HttpClient();
+  try {
+    final req = await client.getUrl(Uri.parse(url));
+    final response = await req.close();
+    if (response.statusCode / 200 == 2) {
+      final stream = await response.transform(utf8.decoder).toList();
+      final ret = jsonDecode(stream.first) as Map<String, dynamic>;
+      return ret;
+    }
+    throw "request failure";
+  } catch (e) {
+    return null;
+  } finally {
+    client.close();
+  }
+}
+
+Future<Map<String, dynamic>?> remotePost(String url, Map<String, dynamic> data) async {
+  HttpClient client = HttpClient();
+  try {
+    final req = await client.postUrl(Uri.parse(url));
+    req.headers.set("Content-Type", "application/json");
+    req.write(data);
+    final response = await req.close();
+    if (response.statusCode / 200 == 2) {
+      final stream = await response.transform(utf8.decoder).toList();
+      final ret = jsonDecode(stream.first) as Map<String, dynamic>;
+      return ret;
+    }
+    throw "request failure";
+  } catch (e) {
+    return null;
+  } finally {
+    client.close();
+  }
+}