HttpStreaming.md

HTTP: Streaming Requests and Responses

A transport.StreamedRequest accepts a byte stream (Stream<List<int>>) as the request body. When a StreamedRequest is sent, the headers will be sent immediately, but the request body will be sent as items are added to the stream. Once the stream has been closed and has finished, the request will end.

Note: the stream you supply should be a single-subscription stream (not a broadcast stream) to avoid losing data.

List<int> encoded = UTF8.encode('data');
Stream<List<int>> byteStream = new Stream.fromIterable(encoded);

var request = new transport.StreamedRequest()
  ..uri = Uri.parse('/bytes/')
  ..body = byteStream;

Important: in the browser, do not use a transport.StreamedRequest to upload files. The browser restricts access to the filesystem for security reasons and using a transport.StreamedRequest to send a file will result in the entire file being loaded into memory. Instead, use a transport.MultipartRequest. This will allow us to send the dart:html.File instance to the underlying XMLHttpRequest which allows the browser to handle streaming the file contents directly from the filesystem.

Every response is loaded in its entirety into memory by default (more info here). This can be problematic for extremely large responses. The solution is to request the response as a stream of data so that it's loaded asynchronously and - if large enough - in chunks.

To request a streamed response, use the corresponding stream method. For example, instead of get(), use streamGet().

transport.StreamedResponse response = await transport.Http.streamGet(Uri.parse('/file'));
response.body.byteStream.listen((List<int> bytes) { ... });