Test persistentConnection with large request bodies (#984)

pkgs/http_client_conformance_tests/lib/src/request_body_tests.dart

@@ -260,6 +260,47 @@ void testRequestBody(Client client) {
       expect(serverReceivedBody.codeUnits, <int>[]);
     });
 
+    test('client.send() with persistentConnection', () async {
+      // Do five requests to verify that the connection persistance logic is
+      // correct.
+      for (var i = 0; i < 5; ++i) {
+        final request = Request('POST', Uri.http(host, ''))
+          ..headers['Content-Type'] = 'text/plain; charset=utf-8'
+          ..persistentConnection = true
+          ..body = 'Hello World $i';
+
+        final response = await client.send(request);
+        expect(response.statusCode, 200);
+
+        final serverReceivedContentType = await httpServerQueue.next;
+        final serverReceivedBody = await httpServerQueue.next as String;
+
+        expect(serverReceivedContentType, ['text/plain; charset=utf-8']);
+        expect(serverReceivedBody, 'Hello World $i');
+      }
+    });
+
+    test('client.send() with persistentConnection and body >64K', () async {
+      // 64KiB is special for the HTTP network API:
+      // https://fetch.spec.whatwg.org/#http-network-or-cache-fetch
+      // See https://github.com/dart-lang/http/issues/977
+      final body = ''.padLeft(64 * 1024, 'XYZ');
+
+      final request = Request('POST', Uri.http(host, ''))
+        ..headers['Content-Type'] = 'text/plain; charset=utf-8'
+        ..persistentConnection = true
+        ..body = body;
+
+      final response = await client.send(request);
+      expect(response.statusCode, 200);
+
+      final serverReceivedContentType = await httpServerQueue.next;
+      final serverReceivedBody = await httpServerQueue.next as String;
+
+      expect(serverReceivedContentType, ['text/plain; charset=utf-8']);
+      expect(serverReceivedBody, body);
+    });
+
     test('client.send() GET with non-empty stream', () async {
       final request = StreamedRequest('GET', Uri.http(host, ''));
       request.headers['Content-Type'] = 'image/png';