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streaming-roadmap.md

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Overview

This document describes the road-map for gRPC-Web to support different streaming features.

  • Server-streaming
  • Client-streaming and half-duplex streaming
  • Full-duplex streaming over HTTP
  • Full-duplex streaming over Web-transport

Server-streaming

We will keep improving server-streaming in the following areas:

  • Finalizing keep-alive support (via Envoy) - 2020
  • Performance improvements and whatwg Fetch/streams support, including service workers - 2020
  • Addressing runtime behavior gaps between Fetch and XHR - 2020+

Client-streaming and half-duplex streaming

We are actively involved in the Chrome Origin Trial to finalize the fetch/upload stream API spec (whatwg). One of the pending issues that blocks the final spec is to decide whether it is safe to enable upload-streaming over HTTP/1.1. We believe that upload-streaming should be enabled for both HTTP/2 and HTTP/1.1. Specifically for gRPC-Web, the server can't control the client deployment. As a result, if upload-streaming is only enabled over HTTP/2, a gRPC service will have to implement a non-streaming method as a fallback for each client-streaming method.

Once the whatwg spec is finalized and upload-streaming is supported by major browsers (2020), we will add client-streaming support in gRPC-Web (and Envoy) which will also enable half-duplex bidi streaming support.

Full-duplex streaming over HTTP

It is possible to support bidi communication over dual HTTP requests, one for download-streaming and the other for upload-streaming, similar to what's implemented by Google to support the W3C Speech API.

Once client-streaming is supported in gRPC-Web, we will publish a spec to enable bidi streaming over dual HTTP requests and implement the complete support in Envoy (2020+).

Full-duplex streaming over Web-transport

We are working with the Chromium Blink team to evaluate how to leverage this whole new transport and QUIC. Stay tuned.

Issues with WebSockets

We have no plan to support full-duplex streaming over WebSockets (over TCP or HTTP/2). We will not publish any experimental spec for gRPC over WebSockets either.

The main issue with WebSockets is its incompatibility with HTTP, i.e. the ubiquitous Web infrastructure. This means HTTP fallback is always needed. Recent IETF proposal to tunnel WebSockets over HTTP/2 is not widely implemented either.